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1
Svensson, Niklas. "Fatigue Analysis with Loads from MBS." Thesis, KTH, Maskinkonstruktion (Inst.), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-168720.
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Detta examensarbete har utförts i samarbete med Scania CV AB, en lastbils- och busstillverkare. Scania tror att en stor del i att behålla en ledande position är att erbjuda sina kunder pålitlighet, bland annat i form av livslängd. På grund av detta så är utbyggnad av kompetens och kunskap kring utmattningsanalys alltid aktuellt. Simuleringsdriven produktutveckling har dessutom ökat intresset för simuleringar tidigare i produktutvecklingen. Detta skapar nya utmaningar då det kräver att utmattningsanalyser utförs innan en fysisk prototyp finns. Då laster krävs för utmattningsanalyser är en tänkbar lösning att skapa lastfall med multibody simulations (MBS) med virtuella prototypfordon körandes en virtuell provbana.Huvudsyftet med detta arbete är att undersöka potentialen för att utföra analyser med laster från MBS. Fyra olika analysmetoder, som används inom Scania, har utförts med laster från MBS istället för från provbana. En utvärdering av metodernas robusthet och deras resultat jämfört med resultat från testrigg var tänkt att ge en indikation för vilken virtuell metod som har störst potential. Ett rammonterat inverterfäste som gått sönder i testrigg analyserades under arbetet. En modell av komponenten genererades i Abaqus och importerades i Adams för MBS. Laster som uppmättes i Adams användes för att utföra de olika utmattningsanalyserna.Det visade sig att två metoder var mer lovande än övriga: Dynamisk simulering med PSD och Superposition av modala spänningar. Men, utmattningsuppskattningarna från de genererade lasterna överensstämde inte med utfallet från det fysiska testet. I testrigg gick komponenten sönder medan analyserna indikerade att den inte skulle komma nära utmattningsbrott. Genom att jämföra lastsignalerna från testrigg och MBS uppdagades det att signalerna avvek kraftigt från varandra. Analys med testriggsignal indikerade att komponenten skulle gå sönder, vilket den också gjorde. Användande av lastsignalen från provbanan ledde däremot till ungefär samma skada som analyserna med MBS gav.Dessa resultat indikerar att det finns potential för utmattningsanalyser med virtuellt anhållna laster. Vidare undersökningar med ytterligare komponenter behöver dock genomföras innan definitiva slutsatser kan dras. Att utröna anledningen till att provet i testrigg varit tuffare än verkligheten är också av intresse.Scania is a truck and bus developer. They believe that reliability, which is strongly associated with life length, has been critical in achieving a leading position and is key to retaining it. Therefore, there is a continuous drive to increase their capability to simulate life length, specifically fatigue. Additionally, the recent popularity of simulation driven product development has created an additional interest in performing simulations earlier in the product development process. This creates a challenge since it requires fatigue analyses to be performed before prototype vehicles are available. Since loads are required for fatigue analyses, one solution is to perform a multibody simulation (MBS) of a virtual prototype vehicle on a virtual test track and derive load cases.This thesis investigated the possibility of using loads derived from MBS simulations to perform fatigue analyses. Four different simulation methods which are currently used by Scania were evaluated with MBS loads instead of physically measured loads. By comparing the methods’ results to those of physical tests, the virtual methods with the greatest potential were identified. A chassis mounted inverter bracket was analyzed in this work. The component was modeled in Abaqus, a model which then was merged into a complete bus model in Adams. Next, this model was run as an MBS over the virtual test track and load data was extracted. The component was then analyzed with different fatigue analysis methods, with the data from the MBS used as input. The fatigue results were then compared with the results of a physical shake rig test of the same component.Two methods were found to be most promising: Dynamic simulation with PSD and Superposition of modal stresses. Interestingly, the fatigue estimation for these methods substantially differed from the outcome of the physical test. The component failed in the physical test but according to the simulation it should have survived. Upon further investigation, it was found that the component was subjected to higher loads in the shake rig than on the shake track. A fatigue simulation using the signal from the shake rig agreed with the outcome of the physical test, namely failure. Analysis using the figures from the test track gave values similar to the results for analyses with MBS loads.These results suggest that this type of virtual analysis has potential. But before more definite conclusions can be drawn further investigations with more than one component need to be performed. Another path of investigation is to look at why the shake rig test is more severe than the virtual shake track.
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Hajigholi, Pedram. "Optimal block loads of dynamic load history for fatigue durability testing." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-67746.
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During a vehicle’s life it is experiencing complex loading from both driving and road conditions. This accumulating of loading might be damaging to the vehicle, leading to possible material fatigue cracking, hence it is a major importance to take it into account. During the design phase the vehicle will be tested on a rig to check the durability and fatigue life. This is done on the system as a whole or at component level. But as it is difficult to reproduce the actual complex loading, a much simpler loading sequence is applied on the component(s) during these tests. The purpose of this master thesis is to use an optimization software called HEEDS, which is based on a mathematical model that is applied in the software, to identify a possible multi-level block sequence which would generate the same fatigue damage as the reference complex loading sequence. This work is fully performed in calculation software, without using actual physical testing. The selected component is a front suspension low control arm (LCA) for which life is checked at various locations. The objective is to have the relative error identified as a relative ratio.
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Perng, Horng-Linn. "Damage accumulation in random loads." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184822.
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An equivalent constant amplitude fatigue loading (Miner's stress) is developed for stationary random amplitude loadings. The effects of rainflow cycle counting and fatigue crack closure are included. A method for determining the opening stress in a random loading is also proposed. This research takes a fatigue damage factor approach. The damage factor is defined as the ratio of the wide band rainflow fatigue damage to the equivalent narrow band fatigue damage. The mathematical form of the damage factor equations is derived from theoretical derivations using the analytically tractable local range cycle counting method. Simulations of stationary Gaussian random processes are used to empirically derive the values of certain parameters dependent on the spectral shape for the rainflow cycle counting equations. There are five tasks in this research. (1) A simulation program for generating a Gaussian process has been written and is used to generate random loading histories for this study. (2) A previously proposed rainflow damage factor has been verified and refined with these simulations, without considering crack closure. (3) Using a sinusoidal approximation, the joint probability density functions between peaks, valleys and rises counted by the local range method are derived. (4) The resulting joint probability distributions are used to determine the theoretical damage with crack closure; simulations are again used to calibrate the parameters for rainflow stress cycles. (5) A procedure for finding an equivalent constant fatigue crack opening stress for stationary random loadings is described. An example application of the procedures and equations is given.
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Reytier, Thomas. "Modelling fatigue spectra of aircraft structure under gust loads." Toulouse 3, 2012. http://thesesups.ups-tlse.fr/1614/.
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Cette thèse est consacrée à l'analyse de fatigue et de tolérance aux dommages des structures d'avions soumis aux rafales de vent. L'analyse de fatigue et de tolérance aux dommages est un enjeu essentiel dans la conception des structures d'avions. Elle permet de définir un programme d'inspection de la structure afin d'assurer sa sécurité tout au long de la vie de l'avion. La première partie passe en revue l'état de l'art dans les différents domaines impliqués dans le processus global d'analyse de fatigue des structures d'avions soumis aux rafales de vent: la modélisation de la turbulence atmosphérique, le calcul des charges et des contraintes à l'aide d'analyses par éléments finis, la construction du spectre de fatigue et enfin, l'analyse de fatigue et de tolérance aux dommages. La deuxième partie présente le processus complet actuellement implémenté au sein d'Airbus. Les points forts et les points faibles de ce processus sont d'identifiés et permettent de dégager des axes d'amélioration. A partir du modèle de turbulence continue basé sur la densité spectrale de puissance (DSP) de Von Karman, les contraintes calculées sont insérées selon des statistiques établies par des mesures envol dans le spectre de fatigue pour former une séquence de cycles de contraintes. Les données d'entrée pour l'analyse de fatigue et tolérance aux dommages sont obtenues à partir de la définition des différents profils de mission, des valeurs de contraintes unitaires, de la réponse dynamique de la structure et des statistiques de turbulence. Dans la troisième partie, une nouvelle méthodologie est présentée afin d'obtenir des séquences temporelles des contraintes dues à la turbulence de manière précise et efficace. Cette méthode s'appuie sur de nouveaux résultats permettant de générer des signaux temporels corrélés à partir des DSP. Tout d'abord, les DSP des différentes composantes des contraintes sont directement obtenues à l'aide d'une analyse par éléments finis à partir de la DSP de Von Karman. Puis, les séquences temporelles corrélées de ces contraintes sont générées et sont ensuite distribuées dans le spectre de fatigue selon la loi statistique de l'intensité de la turbulence atmosphérique. Ce nouveau processus permet d'améliorer le calcul des contraintes et la génération du spectre de fatigue. Il remplace les statistiques de turbulence par des statistiques de franchissement de niveaux de contraintes raisonnablement conservatives définies par une formule analytique. De plus, le temps de livraison des données d'entrée pour l'analyse de fatigue et tolérance aux dommages est significativement réduit. Les résultats présentés, issus de l'analyse de fatigue et de tolérance aux dommages, permettent de souligner la qualité des améliorations apportées à la fois en termes de précision et de durée du processusThis thesis is dedicated to the fatigue and damage tolerance analysis of the aircraft structures under gust loads. The fatigue and damage tolerance analysis is a significant issue in the aircraft structure design. It aims at defining the inspection program of the aircraft structure in order to ensure its safety through its entire life. The first part reviews the state-of-the-art in the various involved topics for the global process for fatigue analysis of aircraft structure under gust loads: the atmospheric turbulence modelling, the load and stress computation by a finite element analysis, the generation of the fatigue spectrum and at the end, the fatigue and damage tolerance analysis. The second part presents the whole process currently implemented at Airbus. The main strengths and weaknesses are pointed out and this en-ables the identification of several improvement axes. From the continuous turbulence model based on the Von Karman Power Spectral Density(PSD), the computed stresses are included according to statistics established from in-flight measurements in the fatigue spectrum in order to build a stress cycle sequence. The input data for the fatigue and damage tolerance analysis are obtained from the definition of the various fatigue mission profiles, the unitary stress values, the dynamic response of the structure and the turbulence statistics. In the third part,a new methodology is presented in order to obtaine efficiently and accurately the temporal stress sequences due to the atmospheric turbulence. This method relies on new results enabling the generation of correlated time signals from the PSD functions. First, the PSD of the various stress components are directly obtained from the Von Karman PSD via a finite element analysis. Then, the correlated temporal stress sequences are generated and distributed in the fatigue spectrum according to the turbulence intensity statistical law. This new process enables the improvement of the stress computation and the fatigue spectrum generation. It replaces the turbulence statistics by stress exceedance statistics which are defined by an analytical formula in a reasonably conservative way. In addition, the lead time to build the input data for the fatigue and damage tolerance analysis is significantly reduced. Results from the fatigue and damage tolerance analysis are presented in order to highlight the quality of the improved processes both in terms of accuracy and lead time
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Bulusu, Prashant. "Rolling contact fatigue predictions based on elastic-plastic finite element stress analysis and multiaxial fatigue /." abstract and full text PDF (free order & download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1437664.
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Thesis (M.S.)--University of Nevada, Reno, 2006."August, 2006." Includes bibliographical references (leaves 38-45). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2006]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.
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Ek, Therese. "Fatigue analysis of engine brackets subjected to road induced loads." Thesis, KTH, Hållfasthetslära (Inst.), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193564.
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In this master thesis, methods for fatigue analysis of front engine brackets subjected to road induced gravity loads (g-loads) are studied. The objective of the thesis is to investigate the possibility to improve simulation and test analysis for the components. The powertrain is modeled with varying degrees of complexity and the different models are compared to each other and to Scania's models for analysis of the engine suspension. The analysis begins with g-loads and proceeds with time-dependent loads. It is investigated how simulated strains in the cylinder block correspond to measured strains from the test track at Scania. Finally, it is investigated how component tests corresponds to actual loads by comparing the results. The results from the first part of the thesis indicate that worst load case is loading in the negative z -direction and the model of the powertrain with isolators modelled as spring elements is the best for g-loads lower than -3g and the model is sufficient for loads lower than -8g. The results from the second part of the thesis indicate that the simulated strains generally correspond to the measured strains, but with a slight difference in strain amplitude.
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Juneja, Lokesh Kumar. "Multiaxial fatigue damage model for random amplitude loading histories." Thesis, Virginia Tech, 1992. http://hdl.handle.net/10919/41522.
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In spite of many multiaxial fatigue life prediction methods proposed over decades of
research, no universally accepted approach yet exists. A multiaxial fatigue damage
model developed for approximately proportional random amplitude loading is proposed
in this study. A normal strain based analysis incorporating the multiaxial state
of stress is conducted along a critical orientation assuming a constant strain ratio.
The dominant deformation direction is chosen to be the critical orientation which
is selected with the help of a principal strain histogram generated from the given
multiaxial loading history. The uniaxial cyclic stress-strain curve is modified for the
biaxial state of stress present along the critical orientation for the plane stress conditions.
Modified versions of Morrow's and of Smith, Watson, and Topper's (SWT)
mean-stress models are used to incorporate mean stresses. A maximum shear strain
based analysis is, in addition, conducted to check for the shear dominant fatigue
crack growth possibility along the critical direction. The most damaging maximum
shear strain is chosen after analyzing the in-plane and the two out-of-plane shear
strains.
The minimum of the two life values obtained from SWT model and the shear
strain model is compared with the life estimated by the proposed model with the
modified Morrow's mean stress model. The former is essentially the life predicted by
Socie. The results of the proposed model, as reduced to the uniaxial case, are also
compared with the experimental data obtained by conducting one-channel random
amplitude loading history experiments.
Master of Science
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Bakis, Charles E. "Fatigue behavior of notched carbon epoxy laminates during reversed cyclic loads." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53903.
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The relationships between fatigue damage, stress redistribution, and residual stiffness and strength were investigated for notched graphite epoxy laminates during fulIy-reversed cyclic loads. Two material systems, AS4/3501-6 and AS4/1808, two lamination arrangements, (0,45,90,-45)s₄ and (0,45,0,-45)s₄, and two notch configurations, central hole and opposing semi-circular edge notches, were used to obtain a fundamental understanding of the fatigue effect in specimens under low and high cycle lifetimes. Damage was evaluated with penetrant-enhanced X-ray radiography and Iaminate deply. Tensile and compressive residual strengths were measured at three stages of damage development. A recently developed nondestructive testing technique, Stress Pattern Analysis by Thermal Emission, was implemented to obtain full-field measurements of surface stresses during damage initiation and growth. A new micromechanical theory of the adiabatic thermoelastic effect in Iaminated fiber composites was conceived to assist the interpretation of SPATE measurements.Ph. D.
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Mohammadi, Mohammad Mehdi. "PREDICTION OF WIND TURBINE BLADE FATIGUE LOADS USING FEED-FORWARD NEURAL NETWORKS." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-444115.
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In recent years, machine learning applications have gained great attention in the wind power industry. Among these, artificial neural networks have been utilized to predict the fatigue loads of wind turbine components such as rotor blades. However, the limited number of contributions and differences in the used databases give rise to several questions which this study has aimed to answer. Therefore, in this study, 5-min SCADA data from the Lillgrund wind farm has been used to train two feed-forward neural networks to predict the fatigue loads at the blade root in flapwise and edgewise directions in the shape of damage equivalent loads.The contribution of different features to the model’s performance is evaluated. In the absence of met mast measurements, mesoscale NEWA data are utilized to present the free flow condition. Also, the effect of wake condition on the model’s accuracy is examined. Besides, the generalization ability of the model trained on data points from one or multiple turbines on other turbines within the farm is investigated. The results show that the best accuracy was achieved for a model with 34 features, 5 hidden layers with 100 neurons in each hidden layer for the flapwise direction. For the edgewise direction, the best model has 54 features, 6 hidden layers, and 125 neurons in each hidden layer.For a model trained and tested on the same turbine, mean absolute percentage errors (MAPE) of 0.78% and 9.31% are achieved for the flapwise and edgewise directions, respectively. The seen difference is argued to be a result of not having enough data points throughout the range of edgewise moments. The use of NEWA data has been shown to improve the model’s accuracy by 10% for MAPE values, relatively. Training the model under different wake conditions did not improve the model showing that the wake effects are captured through the input features to some extent. Generalization of the model trained on data points from one turbine resulted in poor results in the flapwise direction. It was shown that using data points from multiple turbines can improve the model’s accuracy to predict loading on other turbines.
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Jonk, Eric Frederick. "A comparison between two methods of fatigue lifetime predictions for random loads." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26302.
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The purpose of this thesis is to compare the results obtained from two different methods to account for fatigue, the Root Mean Square (RMS) and the Histogram, to determine which method better represents reality.
The test procedure used subjected compact tension specimens to randomly selected block loads, then compared the actual lifetimes obtained by experiment to the lifetimes predicted by the methods. A statistical analysis was attempted to determine which method was superior.
The results of the analysis suggest that the RMS model is superior. However, no firm conclusions can be drawn, since the data obtained suggest that the Paris Law parameters used in the analysis are possibly biased.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
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Dakin, John D. "Using experimental loads with finite element analysis for durability predictions." Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/10407.
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This research work involved the prediction of the fatigue life of an automotive rear suspension twistbeam assembly fitted to a vehicle travelling over a customer correlated durability route. This was achieved by making use of the integrated concepts of scaling and superposition of linear static finite element analysis being driven by experimental load data - the so called 'quasi-static time domain' approach. A study of the free body diagram of the twistbeam resulted in an indeterminate load set of some 24 components, with experimental data indicating that a state of static unbalance existed. Subsequent to developing a matrix-based generalised method ofload cell calibration to confum the foregoing, a modal technique was developed to partition the experimental data into a static load set, causing elastic deformations, and a rigid load set, imparting rigid body accelerations. The semi-independent characteristics of the twistbeam necessitated the coupling of large structural displacements with inertia relief. This required extensive modifications to the current techniques and led to the development and use of a three dimensional functional response matrix in place of the conventional two dimensional one. Recommendations concerning appropriate finite element boundary conditions were also formulated to handle these effects. Finally, the limitations of the uniaxial fatigue model were revealed under the application of a set of tools for analysing the biaxiality and mobility of the maximum absolute principal stress.
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Ilic, Slobodan Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Methodology of evaluation of in-service loads applied to the output shafts of automatic transmissions." Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2006. http://handle.unsw.edu.au/1959.4/30172.
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This work presents a novel methodology for evaluation of in service loads applied to the output shafts of automatic transmissions. It also presents a novel methodology of data reduction for shaft load signals as an alternative to the cycle counting methods. Current durability testing of automatic transmission output shafts uses 50 000 stall torque cycles from zero to wide open throttle. In the majority of cases, these requirements lead to an over design that can result in an unnecessarily bulky transmission system. As a solution to this problem a novel methodology for evaluation of loads applied to the output shafts of automatic transmissions was developed. The methodology is based on real world loading conditions and therefore leads to a more realistic estimation of the fatigue life of shafts. The methodology can be used as a tool for shaft optimisation in different drive conditions. Using the developed methodology the effects of different road conditions on the fatigue life of a transmission output shaft were compared. Four routes having differing driving conditions were investigated and of those routes, the route with most stop-start events resulted in the greatest reduction in fatigue life. A novel methodology of data reduction for shaft load signals was also developed. The methodology is based on knowledge of the bandwidth and dynamic range of the expected in-service load signal. This novel methodology allows significant reduction of the volume of data to be acquired. It preserves the time sequence of peaks and valleys of the signal, which is vital in the case of fatigue analysis. This is in contrast to current methods based on cycle counting. Cycle counting methods achieve high data reduction but do not preserve the time sequence of the signal. The developed novel methodology has been validated on the newly developed data acquisition system capable of real time data acquisition and compression of shaft torque signal. The performed tests show that the proposed one-channel low cost system equipped with 1 GB compact flash card can store well over 10 000 hrs of load history.
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Kinawy, Moustafa. "Static and fatigue propagation of buckle-driven delaminations under bending and compressive loads." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545324.
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Williams, Joseph Louis. "Fatigue of Masonry Walls with CFRP Applied Externally for Out-of-Plane Loads." DigitalCommons@CalPoly, 2009. https://digitalcommons.calpoly.edu/theses/153.
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This master’s thesis presents an investigation on the effects of fatigue on fiber- reinforced polymers (FRP) when applied to masonry walls subjected to out-of-plane loading. The project aims to provide further research and add to the general testing database of FRP enhanced masonry. An introduction to the problems and solutions associated with unreinforced masonry is discussed along with a literature review on previous testing done in the field of FRP enhanced masonry. The investigation on the effects of fatigue on FRP when applied to masonry walls subjected to out-of-plane loading is performed through experimental testing. A total of four wall specimens (6 ft x 4 ft x 8 in) were constructed. One of the specimens was left unreinforced and used as a baseline for testing while the remaining three specimens were reinforced with carbon fiber reinforced polymer (CFRP) strips designed to take the out-of-plane loads capable of creating the cracking moment in the unreinforced wall. The material testing, construction of the test specimens, and CFRP application are all presented in this thesis.
With the use of an oscillating shake table to generate the out-of-plane loading, the walls were fixed at the base and cantilevered from the shake table. By determining the frequency and amplitude that generated the cracking moment in the baseline unreinforced wall, the remaining three CFRP reinforced walls were tested at the same frequency and amplitude. The results from the testing of the three CFRP reinforced walls are presented along with time histories showing the shake table displacement and wall’s tip displacement versus time. In general, fatigue of masonry walls reinforced with CFRP strips can be managed as long as the out-of-plane reinforcement has sufficient strength and development length. Additional findings were made as a result from the testing. The development length of a vertical CFRP strip can be increased by adding a horizontal CFRP strips near the critical section and surface damage to CFRP may have severe consequences.
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Dahlvik, Mathias, and Johan Eriksson. "Load Effect Modelling in Fatigue Design of Composite Bridges : An assessment of Fatigue Load Models 3, 4 and 5 according to SS-EN-1991-2 Actions on Structures – Part 2: Traffic loads on Bridges." Thesis, KTH, Stålbyggnad, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-147820.
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At the turn of 2010/2011, Sweden went from designing structures according to nationaldesign codes to the new European standards Eurocode. For bridge engineers, this implieda change from a combination of BRO 2004 and BSK 07 to the Eurocode as the maindocuments, complemented by national documents such as TRVK Bro 11. The normtransition did not only change the calculation methods, but also turned a phenomenonthat never was of great importance for road bridges before into something that could limitthe carrying capacity of the structure. This phenomenon is called fatigue, i.e. repeatedload cycles, where each load is much lower than the ultimate limit state capacity, thatfinally results in collapse. This master thesis investigates why fatigue is significant in the design today. This is donethrough a comparison of how the new and old regulations assesses fatigue. A bridge builtin 2011, designed by ELU Konsult AB according to the old regulations, was modelledin the finite element program LUSAS. Several lorry crossings from different fatigue loadmodels were then simulated. The output from LUSAS was then used to calculate theutilization ratios for three critical points along the bridge. The result indicates that both regulations give rise to similar stress ranges, i.e. thedifference between the maximum and minimum stress obtained during a crossing. Thedifferences between the regulations are instead within the fatigue calculations, where themajor difference is the number of lorries crossing the bridge during its lifetime. Theutilization ratio according to the old regulations for the worst exposed point is 27.0 %,corresponding to 9.13 daily crossings by heavy lorries, which is the maximum numberof daily crossings provided by BRO 2004. The lowest utilization ratio according tothe Eurocode is 70.0 %, calculated for 137 daily crossings which is the lowest amountof crossings allowed. An interpretation of the Eurocode, which allows usage of fatigue loadmodel 5 even for smaller bridges, results in a utilization ratio of 56.0% which correspondsto 90.0 daily crossings, i.e. lower than the other fatigue load models provided by theEurocode but clearly above the old regulations. The conclusion is that an alternative way of deciding the number of crossings shouldbe provided by the Eurocode. Today, the classification consists of four steps, which arevery rough. Instead, a proposal is given in this thesis which advocates usage of a linearfunction for deciding the number of design crossings based on the number of daily crossingsby lorries. The proposed alternative design method is between the two regulations withrespect to daily crossings and utilization ratio.Vid årsskiftet 2010/2011 övergick Sverige från att dimensionera byggnadsverk enligt nationellastandarder till den nya europastandarden Eurokod. För brokonstruktörer innebar dettaen övergång från en kombination av BRO 2004 och BSK 07, till att Eurokod blev dethuvudsakligt styrande dokumentet, med bland annat TRVK Bro 11 som ett dokumentmed tillhörande nationella val. Övergången medförde inte bara att verksamma konstruktörertvingades lära sig förändrade beräkningsmetoder, utan också att ett fenomen som tidigaresällan var dimensionerande för vägbroar nu kunde vara det som ställde högst krav påbärförmågan. Detta fenomen kallas utmattning, dvs. upprepade av- och pålastningar, varoch en betydligt lägre än brons maximala bärförmåga, som i slutändan resulterar i brott. I detta examensarbete utreds det varför utmattning numera är en betydande del avdimensioneringen. Detta sker genom en jämförelse av hur de gamla och nya normernautvärderar utmattning. Som modell har en befintlig bro invigd 2011, dimensioneradav ELU Konsult AB enligt de gamla normerna, använts. Denna bro har modellerats ifinita element programmet LUSAS, varpå en mängd olika lastbilsöverfarter simulerats ochutmattningsutnyttjandet för tre utvalda kritska punkter beräknats. Resultatet indikerar att båda normerna har liknande storlekar på spänningsvidderna,dvs. skillnaden på största och minsta spänningen som uppstår vid en överfart. Däremotråder det skillnader vid utmattningsberäkningarna, där den stora skillnaden är antalettunga fordon som passerar bron under dess livslängd. Enligt de gamla normerna ärutnyttjandegraden för den värst utsatta studerade punkten 27.0 %, vilket är beräknatpå det högsta antalet dagliga passager från tunga fordon som BRO 2004 tillåter, d.v.s.9.13 dagliga passager. Enligt Eurokod uppgår den lägsta utnyttjandegraden till 70.0 %,vilket motsvarar 137 dagliga överfarter vilket är det lägsta Eurokod tillåter. Vid ettalternativt sätt att tolka Eurokod, som tillåter användandet av utmattningslastmodell5 även för mindre broar, fås en utnyttjandegrad på 56.0% vilket motsvarar 90.0 dagligaöverfarter. Detta är något lägre än de andra utmattningslastmodellerna enligt Eurokodmen fortfarande högre än det gamla regelverket. Slutsatsen av uppsatsen är att ett alternativt sätt att bestämma antalet överfarter bordeerbjudas i Eurokod, då indelningen idag består av fyra stora trappsteg vilket ger en väldigtsnäv indelning. I detta examensarbete presenteras ett förslag som innebär att antaletdimensionerande överfarter istället bör bestämmas som en rätlinjig funktion av antaletdagliga överfarter från tung trafik. Det föreslagna sättet ligger mellan de båda normernamed hänsyn till passager och utnyttjandegrad.
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Nesterova, Mariia. "Reliability of structures exposed to traffic and environmental loads." Thesis, Paris Est, 2019. http://www.theses.fr/2019PESC2056.
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Cette thèse est consacrée à l’analyse de la fiabilité du tablier du viaduc de Millau, un pont à haubans situé dans le sud de la France. Le but principal est d’extrapoler dans le temps les charges et les effets de charges sur le pont afin d’observer la fiabilité de différentes parties de la structure pendant sa durée de vie. Le viaduc de Millau est une infrastructure routière française, complexe et unique, qui est en début de vie. Il est important de pouvoir prévoir les charges extrêmes possibles sur le tablier du pont en raison de l’augmentation du volume ou du poids des véhicules. De telles prévisions nécessitent des données mesurées sur l’ouvrage, soit les charges ou actions, soit les effets de celles-ci. Les structures à grande échelle ont besoin d’une grande quantité de données, qu’il est difficile d’obtenir, de stocker et d’analyser. Cela pose un autre défi : les prévisions basées sur un temps limité et des données de surveillance accessibles. Les prévisions de charges de trafic dans ce travail sont effectuées à l’aide des données fournies par la surveillance du trafic du système BWIM pour le cas d’état limite ultime. Pour l’extrapolation de charge dans le temps, plusieurs méthodes de la théorie des valeurs extrêmes (EVT) sont comparées, une attention particulière étant accordée à l’approche POT. De plus, une contribution aux méthodes existantes pour le choix du seuil, en tant que principal défi de l’approche de POT, est apportée. Dans les grands ponts à haubans, le trafic n’est pas nécessairement l’action principale, mais les charges climatiques peuvent avoir un effet similaire ou supérieur. Le centre de ce travail est le tablier du viaduc de Millau. Par conséquent, la charge de vent statique obtenue à partir du système de surveillance de la santé structurelle du viaduc est considérée en combinaison avec les files de camions de circulation. Un modèle probabiliste est créé pour observer les probabilités de cas extrêmes pour les actions et leur combinaison. De même, l’influence de la durée de surveillance sur les intervalles de confiance pour les niveaux de retour de charges est étudiée. Dans le détail du tablier orthotrope en acier, les effets locaux causés par le passage de véhicules et les effets globaux contribuent à la valeur des contraintes. Les effets globaux proviennent des files des véhicules sur les deux voies de tablier et du vent statique dans une direction perpendiculaire. Dans cette thèse, un modèle d’éléments finis du pont est créé afin d’évaluer les contraintes dans le pont. Cela offre également la possibilité de prévoir l’état limite de fatigue. Habituellement, les dommages de fatigue accumulées dans un détail pendant la période de surveillance sont extrapolées linéairement. Le travail actuel propose une méthodologie pour extrapoler le nombre de cycles de fatigue dans le temps avec l’approche POT, qui prend en compte une variation du trafic en volume et en poids avec le temps. Une comparaison de l’approche proposée avec la méthode classique est effectuée et utilisée dans l’analyse de fiabilité en raison de fatigue. Une analyse de fiabilité est également effectuée pour l’état limite ultime afin de comparer les résultats obtenus avec plusieurs approches de EVT, d’observer l’importance des actions du vent sur la fiabilité du tablier et de comparer les prévisions basées sur EVT avec les modèles de charge de calcul des normes Européennes pour le trafic et le ventThe Thesis is dedicated to reliability analysis of the deck of Millau viaduct, a cable-stayed bridge located in Southern France. The main interest is the extrapolation in time of loads and load effects affecting the bridge in order to observe the reliability of chosen elements during the operational life of the structure. Millau viaduct is a complex unique bridge of French road infrastructure in the early stage of its life. It is important to be able to predict possible extreme loads on the deck of the bridge due to traffic growing in volume or weight. Such predictions require data from monitored actions or load effects in elements of the bridge. Large-scale structures need an enormous amount of data, that is not easy to obtain, to store and to analyze. It leads to another challenge - predictions based on limited time and accessible monitoring data.In the current work, predictions for traffic loads are done using provided data from bridge Weigh-in-Motion (BWIM) traffic monitoring for the case of the the ultimate limit state (ULS). For load extrapolation in time, several methods of Extreme Value Theory (EVT) are compared, with the most attention to the Peaks Over Threshold (POT) approach. Moreover, a contribution to existing methods for threshold choice, as the main challenge of POT approach, is made.In large cable-stayed bridges, not necessarily traffic is the leading action, but environment loads can have similar or superior effect. The focus of this work is on the deck of Millau viaduct, therefore, static wind loads obtained from structural health monitoring (SHM) of the viaduct are considered in combination with queues of traffic lorries. A probabilistic model is made to observe probabilities of extreme cases for both actions and their combination. As well, the influence of monitoring duration on confidence intervals for return levels of loads is studied.For the steel orthotropic deck of the bridge, both, local effects caused by passing vehicles and global effects, contribute to values of stresses. Global effects are coming from traffic queues on both lanes and static wind in a perpendicular direction. In this Thesis, finite element model (FEM) of the deck is performed in order to assess stresses in the deck. That brings a possibility to make predictions for the fatigue limit state too. Usually, fatigue damage accumulated in a chosen part of the deck during a monitoring period is extrapolated in time linearly. The current work proposes a methodology to extrapolate numbers of fatigue cycles in time with the POT approach, which accounts for a change in traffic in volume and weight with time. Comparison of the proposed approach with the classical method is made and used in the fatigue reliability analysis. Reliability analysis is made as well for the ULS in order to compare the results obtained from several EVT approaches, to observe the importance of wind actions on the reliability of the deck, and to compare EVT-based predictions with design load models of European Norms (EN) for traffic and wind
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Pesmajoglou, Stelianos. "Three-dimensional wake computations applied to horizontal axis wind turbines." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367829.
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Chang, Byungik. "A time-domain model for predicting aerodynamic loads on a slender support structure for fatigue design." [Ames, Iowa : Iowa State University], 2007.
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Schwarz, Brandon A. (Brandon Alexander). "Evaluation of a methodology for detecting railroad track geometry anomalies and determining rail vehicle fatigue loads." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12401.
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Wannenburg, Johann. "A study of fatigue loading on automotive and transport structures." Thesis, University of Pretoria, 2007. http://upetd.up.ac.za/thesis/available/etd-04032008-100638/.
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Wang, Xiaohua. "Stress and reliability analysis of multilayered composite cylinder under thermal and mechanical loads." Diss., Virginia Polytechnic Institute and State University, 1992. http://hdl.handle.net/10919/49934.
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The coupling resulting from the mutual influence of material thermal and mechanical parameters is examined in the thermal stress analysis of a long, hollow, multilayered, isotropic composite cylinder subjected to sudden axisymmetric external and internal temperature. The method of complex frequency response functions together with the Fourier transform technique is utilized.
Because coupling parameters for some composite materials, such as carbon-carbon, are very small, the effect of coupling is neglected in the orthotropic thermal stress analysis. The stress distributions in long, hollow, multilayered orthotropic cylinders subjected to sudden axisymmetric temperature loading combined with dynamic pressure as well as asymmetric temperature loading are also obtained. The method of Fourier series together with Laplace transform is utilized in solving the heat conduction equation and thermal stress analysis. The inertial term is considered and the perturbation technique is applied to cylinders subjected to dynamic pressure loading.
For brittle materials, like carbon-carbon composite, the strength variability is represented by two or three parameter Weibull distributions. The “weakest link" principle which takes into consideration both the applied stresses and the effected volume of material is used in the reliability analyses for both the isotropic and orthotropic carbon-carbon composite cylinders.
The complex frequency response analysis is performed on a long hollow multilayed orthotropic cylinder under asymmetrical thermal load. Both deterministic and random thermal stress and reliability analyses can be based on the results of this frequency response analysis.
The stress and displacement distributions and reliability of rocket motors under static or dynamic line loads are analyzed by an elasticity approach. Rocket motors are modeled as long hollow multilayered cylinders with an air core, a thick isotropic propellant inner layer and a thin orthotropic kevlar-epoxy case. The case is treated as a single orthotropic layer or a ten layered orthotropic structure. Five material properties and the load are treated as random variables with normal distributions when the reliability of the rocket motor is analyzed by the first-order, second-moment method (FOSM).Ph. D.
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Teeling-Smith, R. Graeme. "An investigation into the deformation and tearing of thin circular plates subjected to impulsive loads." Master's thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/14564.
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Includes bibliographical references.This investigation, primarily experimental, examines the failure of circular plates subjected to impulsive velocities. The experiments are conducted on fully clamped circular steel plates subjected to a uniformly distributed impulse. The strain-rate-sensitive mild steel plates fail with mode I (large ductile deformation), mode II (tensile-tearing and deformation) and mode III (transverse-shear) failure modes. The impulse is measured by means of a ballistic pendulum upon which the test plates are attached. During mode II and mode III failure the complete circumferential tearing of the test plate produces a circular disc. The velocity of this disc is recorded. An energy analysis is performed on the test results and an energy balance equation is formulated. Einput = Edeformation + Etearing + Edisc. The input and disc energies are obtained from the experimental measurements and the deformation energy is predicted by using the final deformed height and a shape function together with a rigid-plastic energy analysis adopted by Duffey. Etearing refers to the energy for tensile-tearing in mode II failure or the energy for transverse-shear in mode III failure. Good correlation is found and the experiments show good repeatability. The threshold velocities for the onset of failure modes II and III are given.
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Carn, Cheril, and cheril Carn@dsto defence gov au. "The inverse determination of aircraft loading using artificial neural network analysis of structural response data with statistical methods." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080109.090600.
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An artificial Neural Network (ANN) system has been developed that can analyse aircraft flight data to provide a reconstruction of the aerodynamic loads experienced by the aircraft during flight, including manoeuvre, buffet and distributed loading. For this research data was taken from the International Follow-On Structural Test Project (IFOSTP) F/A-18 fatigue test conducted by the Royal Australian Air Force and Canadian Forces. This fatigue test involved the simultaneous application of both manouevre and buffet loads using airbag actuators and shakers. The applied loads were representative of the actual loads experienced by an FA/18 during flight tests. Following an evaluation of different ANN types an Ellman network with three linear layers was selected. The Elman back-propagation network was tested with various parameters and structures. The network was trained using the MATLAB 'traingdx' function with is a gradient descent with momentum and adaptive learning rate back-propagation algorithm. The ANN was able to provide a good approximation of the actual manoeuvre or buffet loads at the location where the training loads data were recorded even for input values which differ from the training input values. In further tests the ability to estimate distributed loading at locations not included in the training data was also demonstrated. The ANN was then modified to incorporate various methods for the calculation and prediction of output error and reliability Used in combination and in appropriate circumstances, the addition of these capabilities significantly increase the reliability, accuracy and therefore usefulness of the ANN system's ability to estimate aircraft loading.To demonstrate the ANN system's usefulness as a fatigue monitoring tool it was combined with a formulae for crack growth analysis. Results inficate the ANN system may be a useful fatigue monitoring tool enabling real time monitoring of aircraft critical components using existing strain gauge sensors.
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Lin, Dingding. "Effects of Localized Muscle Fatigue on Postural Control: Interactive Effects with Inclined Surfaces and Unexpected Loads, and Intervention Efficacy." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/37218.
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Falls in the workplace are a major cause of injuries and fatalities. Muscle fatigue is one important factor that has been linked to a decrement in postural control and a potential increased falling risk. However, potential interactive effects of muscle fatigue with other risk factors remain unclear, and practical interventions are needed to mitigate the adverse effects of muscle fatigue. The current work was conducted to address these research needs through three experimental studies.
The first study investigated how muscle fatigue affects postural control during quiet standing on inclined surfaces. Inclined surfaces compromised postural control, with the most deleterious effects found while standing in a lateral direction. Fatigue did not result in further decrements in postural control during standing on inclined surfaces.
The second study investigated the effects of muscle fatigue on postural control while lifting unexpected loads. Lifting an object with unexpected mass compromised postural control, with a more substantial effect found in the unexpectedly light load condition. Fatigue-related effects were not consistent, though there was evidence that lumbar muscle fatigue did not compound the adverse effects of lifting an object in unexpected mass conditions.
The last study evaluated the efficacy of three interventions (two auditory stimulations and periodic rest breaks) at mitigating the adverse effects of muscle fatigue on postural control. Allowance of rest breaks did not improve postural control during the fatiguing work, though it was indicated that benefits may be present for some individuals. Both a static pure tone and moving conversation appeared to offset fatigue-induced postural instability.
The current research provides a more comprehensive understanding of the contribution of muscle fatigue to fall risks during occupationally relevant tasks and assessed the efficacy of practical interventions to reduce the risk of falls. These findings may facilitate the development of strategies to prevent occupational falls related to muscle fatigue, inclined surfaces, and manual material handling tasks.Ph. D.
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Nosek, Michael. "Modeling helicopter dynamic loads using artificial neural networks." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-08182009-040457/.
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Giaccio, Craig 1974. "Flange effectiveness in the resistance of shear on RC T-beams subjected to point loads." Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/5708.
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Puigvert, Cobos Francesc. "Analysis of circular bond-type anchorages for prestressing composite rods under quasi-static, fatigue and time-dependent loads." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/284216.
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En estructures pretesades sotmeses a ambients corrosius, s'està estudiant la possibilitat de substituir els tendons d’acer per tendons que no pateixin els efectes de la corrosió. En aquest sentit, els materials compostos Fibre Reinforced Polymer (FRP) són una opció duradora en el disseny d'estructures de formigó pretesat degut a les seves altes propietats mecàniques, pes lleuger i alta resistència a la corrosió. No obstant,
un dels reptes associats amb aquesta opció es troba en el desenvolupament d'un sistema d'ancoratge adequat
per als tendons de FRP .
Per això aquesta investigació ha estudiat la resposta mecànica d’ancoratges d’unió adhesiva per a tendons de FRP sota càrregues quasi-estàtiques, de fatiga i en funció del temps. Aquest objectiu s'ha aconseguit mitjançant la combinació d'una campanya experimental i un treball de modelatge amb el mètode dels elements finits.
En aquest sentit s’han dut a terme assaigs experimentals quasi-estàtics en els ancoratges d’unió adhesiva, observant que la ruptura del sistema es produïa en la unió adhesiva entre l’adhesiu i el tendó. En conseqüència, les principals variables estudiades van ser l’espessor de l'adhesiu i la longitud d’adhesió. A través d’una campanya de modelatge numèric amb diferents models, de complexitat creixent, del material adhesiu, es va investigar la resposta quasi-estàtica de l'ancoratge i el seu mecanisme de fallada. El model numèric va ser capaç de predir les dades enregistrades experimentalment quan el modelatge de l’adhesiu es va realitzar amb elements cohesius amb dany progressiu.
A més, s’ha desenvolupat una formulació analítica (i validat amb èxit) amb l'objectiu de proporcionar una distribució aproximada de les tensions de tall que es produeixen en la capa adhesiva per ancoratges amb adhesius que es comporten principalment elàstic lineal fins a ruptura. D’altra banda l'ancoratge d’unió adhesiva també es va investigar sota els fenòmens dependents del temps.
Per això es van dur a terme assaigs de fluència en unions simples Single Lap Joints ( SLJs ), per tal d'obtenir una llei experimental de fluència, i es van realitzar assaigs de relaxació de la tensió en els ancoratges per estudiar la pèrdua de càrrega en funció del temps. Durant aquests assaigs de relaxació es va estudiar la tècnica del retesat amb l’objectiu d’estudiar l’evolució de les pèrdues de tensió. Es va observar que la tècnica del retesat permet assolir càrregues de treball superiors amb una pèrdua de càrrega mínima.
A més a través d’un model visco-plàstic es va predir el temps de fallada a fluència de les SLJs i els ancoratges, basat en la llei de Bailey-Norton i calibrat amb les dades experimentals obtingudes en els assaigs de fluència de les SLJs. El dany de fluència es va modelar mitjançant la degradació de la tensió de fluència plàstica de l'adhesiu i el model numèric es va utilitzar per predir la pèrdua de càrrega dels ancoratges sota el fenomen de relaxació de la tensió. Els resultats enregistrats experimentalment van ser predits adequadament amb el model numèric proposat.
Finalment, es va investigar la resposta a la fatiga dels ancoratges d’unió adhesiva. Es van avaluar quatre configuracions d’ancoratge sota tres càrregues de fatiga d'amplitud constant. Els resultats experimentals van permetre l’obtenció d’una corba de vida a fatiga dels ancoratges en funció del nombre de cicles.
Mitjançant el mètode d’elements finits, també es va investigar el comportament a fatiga. La llei cohesiva obtinguda en l'anàlisi quasi-estàtic es va utilitzar en el model de la fatiga, on el dany per fatiga s’ha basat en la degradació de les propietats dels elements cohesius. El model numèric va predir amb èxit l'evolució dany per fatiga i la vida per fatiga observada experimentalment .
A partir del treball experimental i numèric realitzat en aquesta recerca, es proposen les recomanacions més pertinents per a un possible ús dels ancoratges d’unió adhesiva per tendons FRP en aplicacions de pretensat.In prestressed structures subjected to corrosive environments, consideration is being given to replacing the steels tendons with non-corrosive tendons. In this respect, Fibre Reinforced Polymer (FRP) materials are a durable option in the design of prestressed concrete structures for use in corrosive environments due to their high mechanical properties, light weight and high resistance to corrosion. However, one of the challenges associated with this option lies in developing a suitable anchorage system for FRP tendons. In the present work, the mechanical response of circular adhesively bonded anchorages for FRP tendons has been investigated under quasi-static, time-dependent and fatigue loading. This has been achieved through a combination of an experimental campaign and finite element modelling work. Experimental quasi-static tests of adhesively bonded anchorages were undertaken with failure occurring in the adhesive-tendon interface. The main variables assessed were the adhesive thickness and the bonded length. In order to investigate the quasi-static response of the bonded anchorage and its failure mechanism, a campaign of numerical modelling was carried out with different material models of increasing complexity for the adhesive layer. A cohesive zone model with progressive damage in the bonded joint was found to be in reasonable agreement with the experimentally recorded data. Additionally, an analytical formulation was developed (and validated against experimental data) with the aim to provide an approximate shear stress distribution in the bonded joint for circular anchors with adhesives which mainly behave linearly elastic up to failure. The adhesively bonded anchor for FRP tendons was also investigated under the time-dependent phenomena. Creep tests on Single Lap Joints (SLJs) were conducted in order to obtain an experimental creep law whereas stress relaxation tests were conducted on adhesively bonded anchorages to study the load loss in time. Furthermore, the restressing technique was assessed during the stress relaxation tests by restressing the specimens, to the original tensioning load, when the load loss was stabilised and constant. It was found that the restressing technique allows for the working load of the composite tendon to be reached with a minimum load loss. A visco-plastic material model, based on the Bailey-Norton law, was calibrated with the experimental data obtained from the creep tests and utilised to predict the creep time to failure of SLJs and anchorages. The creep damage was modelled by degrading the plastic yield stress of the adhesive. The viscoelastic model was also used to predict the load loss of the anchors under the stress relaxation phenomenon. The predicted load loss results were found to be in good agreement with the experimental results recorded. Finally, the fatigue response of the bonded anchorages was investigated. Anchorages with four different adhesive thicknesses were evaluated under three constant amplitude fatigue loadings. The experimental fatigue response of adhesively bonded anchorages was discussed and an experimental load-life average curve was obtained for all the anchorages. The fatigue behaviour was also predicted using Finite Element Analysis. A multi-linear traction-separation cohesive zone model was implemented at the adhesive-tendon interface. The cohesive law obtained in the quasi-static analysis was utilised in the fatigue model. The fatigue damage model utilised in this research was based on the degradation of the cohesive elements taking into account the fatigue damage evolution. The damage model was able to successfully predict the fatigue damage evolution and failure life experimentally observed. From the experimental and numerical work conducted in this investigation, the most relevant recommendations are proposed for a potential use of adhesively bonded anchorages for CFRP tendons in prestressing applications.
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Fauriat, William. "Stochastic modeling of road-induced loads for reliability assessment of chassis and vehicle components through simulation." Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22689/document.
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Concevoir un composant automobile et s’assurer que celui-ci atteindra un niveau de fiabilité cible requière une connaissance précise de la variabilité des chargements que ce composant est susceptible de rencontrer dans son environnement d’utilisation. La grande diversité des chargements appliqués à différents véhicules par différents clients, ou à un même véhicule tout au long de son historique d’utilisation, représente un défi statistique majeur. Généralement, l’acquisition d’information relative à la variabilité des chargements imposés aux composants des véhicules, repose sur la réalisation de campagnes de mesures. La complexité, la durée et le coût de telles campagnes limite naturellement la taille des échantillons statistiques constitués et les chargements enregistrés sont inévitablement dépendants du véhicule utilisé pour la mesure.Le travail présenté dans ce manuscrit explore la possibilité de changer fondamentalement d’approche, en se basant sur la simulation plutôt que sur la mesure et en concentrant l’effort d’analyse statistique non pas directement sur la variabilité des chargements mais sur la variabilité des facteurs qui les déterminent. Dans ce but, des modèles stochastiques sont proposés pour décrire l’évolution de la géométrie des surfaces de routes rencontrées par les véhicules ainsi que l’évolution de la vitesse à laquelle les conducteurs les parcourent. La caractérisation de la variabilité de ces facteurs est couplée à la notion de situations de vie. Ces dernières permettent de segmenter l’historique d’utilisation des véhicules, afin de faciliter l’analyse statistique de leur évolution au sein d’une population de clients. Pour finir, la réponse dynamique du véhicule à l’excitation générée par la route est déduite par la simulation.Des données statistiques relatives à la variabilité des facteurs de route et de vitesse sont évidemment nécessaires. L’information sur les routes parcourues peut par exemple être acquise à moindre coût au moyen d’une méthode d’estimation des profils de route proposée dans ce manuscrit. Cette information peut ensuite être exploitée afin de constituer, par la simulation, à un coût très faible et pour n’importe quel véhicule dont les caractéristiques sont connues, un échantillon d’historiques de chargements aussi important que souhaité. Cette méthodologie basée sur la simulation offre la possibilité d’analyser plus largement la variabilité des chargements de fatigue provenant de la route, l’influence des différents facteurs qui les déterminent ainsi que l’effet sur la fiabilité des composants du véhicule étudiéIn order to design vehicle components that will achieve a prescribed reliability target, it is imperative to possess a precise description of the variability of the loads to which such components may be subjected within the environment in which they are used. The strong diversity of the loads imposed on different vehicles by different customers, or on a particular vehicle throughout its life, constitutes a formidable statistical challenge. Generally, the acquisition of information about the load variability experienced by vehicle components is based on the use of load measurement campaigns. The complexity, duration and cost of such campaigns naturally limit the size of the statistical samples that may be collected. Moreover, the recorded load histories are inevitably dependent on the vehicle used for the measurements.The work presented within this manuscript explores the possibility of a fundamental change in the approach to load characterisation. The objective is to make use of simulation rather than measurements and focus statistical analysis efforts not directly on load variability itself but on the variability of the factors that determine such loads. Stochastic models are proposed to describe the evolution of the geometry of road surfaces covered by vehicles, as well as the evolution of vehicles’ speed on those road surfaces. The characterisation of the variability of such factors is performed in combination with the use of life situations. The latter may be employed to divide the load histories associated to different vehicles, within a population of customers, and analyse their variation more easily. Eventually, the dynamic response of the vehicle to the excitation imposed by the road can bederived through simulation.Statistical data on the variation of the road and speed factors obviously have to be acquired in order to apply the methodology. For example, road-related information may be obtained through the use of a road profile estimation algorithm proposed within the framework of this manuscript. Such information may then be exploited to constitute, through simulation, an arbitrarily large set of load histories at a very low cost and for any vehicle whose mechanical characteristics are known.The proposed methodology based on simulation enables us to study more extensively the variability of road-induced fatigue loads, the influence of the different factors that determine such loads, as well as the effect they have on the reliability of any considered vehicle component
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Cook, Byron Lloyd. "An investigation of an existing aluminum lattice dome under snow loads." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08042009-040245/.
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McKnight, Dustin Henry. "The use of compression precracking constant amplitude (CPCA) test method to obtain near-threshold fatigue crack growth behavior in AA7075-T7351." MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11102005-065337/.
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Traditionally, pre-cracking has been performed under tension-tension loading, followed by a load reduction scheme to obtain fatigue crack growth rate data in the near threshold regime. These data have been shown to exhibit load history effects due to remote crack closure. An alternative test method has been developed to minimize these load history effects. This test procedure uses compression pre-cracking to initiate a crack, followed by constant amplitude loading to grow the crack to failure. Compression-compression (C-C) loading as a means of forming a starter crack for fatigue crack growth is a relatively new concept. Cracks grown under C-C loading emanate from the notch tip due to a tensile residual stress field formed during the unloading cycle. The subsequent constant amplitude steady-state crack growth is free of load history effects, after crack growth beyond several compressive plastic zone sizes, and therefore will give a better steady-state representation of the near-threshold regime. A more in-depth examination at this phenomenon is performed herein.
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Al-Mukhtar, Ahmed. "The safety analysis concept of welded components under cyclic loads using fracture mechanics method." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2010. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-39477.
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Fracture Mechanics process of Welded Joint is a very vast research area and has many possibilities for solution and prediction. Although the fatigue strength (FAT) and stress intensity factor (SIF) solutions are reported in several handbooks and recommendations, these values are available only for a small number of specimens, components, loading and welding geometries. The available solutions are not always adequate for particular engineering applications. Moreover, the reliable solutions of SIF are still difficult to find in spite of several SIF handbooks have been published regarding the nominal applied SIF. The effect of residual stresses is still the most challenge in fatigue life estimation. The reason is that the stress distributions and SIF modified by the residual stresses have to be estimated. The stress distribution is governed by many parameters such as the materials type, joint geometry and welding processes. In this work, the linear elastic fracture mechanics (LEFM), which used crack tip SIFs for cases involving the effect of weld geometry, is used to calculate the crack growth life for some different notch cases. The variety of crack configurations and the complexity of stress fields occurring in engineering components require more versatile tools for calculating SIFs than available in handbook’s solutions that were obtained for a range of specific geometries and load combinations. Therefore, the finite element method (FEM) has been used to calculate SIFs of cracks subjected to stress fields. LEFM is encoded in the FEM software, FRANC, which stands for fracture analysis code. The SIFs due to residual stress are calculated in this work using the weight function method. The fatigue strength (FAT) of load-carrying and non-load carrying welded joints with lack of penetration (LOP) and toe crack, respectively, are determined using the LEFM. In some studied cases, the geometry, material properties and loading conditions of the joints are identical to those of specimens for which experimental results of fatigue life and SIF were available in literature so that the FEM model could be validated. For a given welded material and set of test conditions, the crack growth behavior is described by the relationship between cyclic crack growth rate, da/dN, and range of the stress intensity factor ( K) , i.e., by Paris’ law. Numerical integration of the Paris’ equation is carried out by a FORTRAN computer routine. The obtained results can be used for calculating FAT values. The computed SIFs along with the Paris’ law are used to predict the crack propagation. The typical crack lengths for each joint geometry are determined using the built language program by backward calculations. To incorporate the effect of residual stresses, the fatigue crack growth equations which are sensitive to stress ratio R are recommended to be used. The Forman, Newman and de Konig (FNK) solution is considered to be the most suitable one for the present purpose. In spite of the recent considerable progress in fracture mechanics theories and applications, there seems to be no, at least to the author’s knowledge, systematic study of the effect of welding geometries and residual stresses upon fatigue crack propagation based completely on an analytical approach where the SIF due to external applied load (Kapp) is calculated using FEM. In contrast, the SIF due to residual stresses (Kres) is calculated using the analytical weight function method and residual stress distribution. To assess the influence of the residual stresses on the failure of a weldment, their distribution must be known. Although residual stresses in welded structures and components have long been known to have an effect on the components fatigue performance, access to reliable, spatially accurate residual stress field data are limited. This work constitutes a systematic research program regarding the concept for the safety analysis of welded components with fracture mechanics methods, to clarify the effect of welding residual stresses upon fatigue crack propagationDie Bewertung einer Schweißnaht ist ein großes Forschungsgebiet und hat viele Möglichkeiten für Lösungskonzepte und Vorhersagen. Obwohl für die Schwingfestigkeit und die Spannungsintensitätsfaktor (SIF)-Lösungen in verschiedenen Handbüchern Empfehlungen ausgewiesen sind, sind diese Werte nur für eine geringe Anzahl von Proben, Komponenten, Belastungsfälle und Schweißgeometrien verfügbar. Die vorhandenen Lösungsansätze sind nicht immer für spezielle technische Anwendungen geeignet. Darüber hinaus sind zuverlässige bewährte Lösungen von Spannungsintensitätsfaktoren immer noch schwierig zu finden, obwohl verschiedene SIF-Handbücher mit Hinweis auf den anliegenden nominalen SIF veröffentlicht sind. Der Einfluss von Eigenspannungen ist eine der größten Herausforderungen bei der Lebensdauerabschätzung. Aufgrund der Tatsache, dass infolge der Eigenspannungen sowohl die Spannungsverteilung als auch der SIF verändert werden, muss eine Abschätzung erfolgen. Die Spannungsverteilung wird durch viele Parameter beeinflusst, wie zum Beispiel den Werkstoff, die Nahtgeometrie und den Schweißprozess. In der vorliegenden Arbeit wurde für die Berechnung des Ermüdungsrisswachstums unter verschiedenen Kerbfällen das Konzept der linear-elastischen Bruchmechanik (LEBM) verwendet, welches K-Lösungen für die Rissspitze bei unterschiedlichen Fällen der Schweißgeometrie berücksichtigt. Aufgrund der Komplexität der Risskonfigurationen und der Spannungsfelder in praxisrelevanten Komponenten werden weitere Hilfsmittel zur Berechnung von Spannungsintensitätsfaktoren benötigt, welche die herkömmlichen Lösungen in Handbüchern erweitern. Deshalb wurde die Finite Elemente Methode (FEM) zur Berechnung von Spannungsintensitätsfaktoren an Rissen verwendet. Die LEBM wird in der FEMSoftware FRANC berücksichtigt. Die aus Eigenspannungen resultierenden Spannungsintensitätsfaktoren wurden mit Hilfe der Gewichtsfunktionsmethode berechnet. Die Ermüdungslebensdauer (Schwingfestigkeit) von tragenden und nichttragenden Schweißnähten mit ungenügender Durchschweißung beziehungsweise Kerbriss wurden mit Hilfe der LEBM durch Integration der Zyklischen Risswachstumskurve ermittelt. Zur Validierung des FEM-Modells konnte in einigen untersuchten Fällen auf experimentelle Ergebnisse zur Lebensdauer und zum SIF aus der Literatur zurückgegriffen werden, wo identische Geometrien, Materialeigenschaften und Belastungsverhältnisse der Naht vorlagen. Unter Vorgabe des Werkstoffes und der Prüfbedingungen wurde das Risswachstumsverhalten mit dem Zusammenhang von Risswachstumsgeschwindigkeit da/dN und zyklischem Spannungsintensitätsfaktor K mit dem Paris-Gesetz beschrieben. Eine numerische Integration der Paris-Gleichung erfolgte über ein FORTRAN-Programm. Die damit erhaltenen Ergebnisse sind als Ermüdungslebensdauer (Schwingfestigkeit) verwendbar. Die berechneten SIF‘en entlang der Paris-Geraden werden zur Vorhersage des Risswachstums benutzt. Die typischen Risslängen für jede Nahtgeometrie wurden mit Hilfe des eigens integrierten Programmes ermittelt. Zur Berücksichtigung des Einflusses von Eigenspannungen wird empfohlen, Risswachstumsgleichungen zu nutzen, die empfindlich auf das Spannungsverhältnis R reagieren. Für die vorliegende Zielsetzung gilt der Lösungsansatz nach Forman, Newman und de Konig (FNK) als der am besten geeignete. Trotz der jüngsten, beträchtlichen Fortschritte in den bruchmechanischen Theorien und Anwendungen sind systematische Studien zum Einfluss der Schweißgeometrie und der Eigenspannungen auf das Ermüdungsrisswachstum, in welchen der SIF aufgrund extern anliegender Beanspruchungen (Kapp) mit der FEM berechnet wurde, in der Literatur kaum vorhanden. Im Gegensatz dazu wurde der SIF infolge von Eigenspannungen (Kres) mit Hilfe der analytischen Gewichtsfunktionsmethode und der Eigenspannungsverteilung berechnet. Um den Einfluss von Eigenspannungen auf das Versagen einer Schweißverbindung abzuschätzen, muss deren Verteilung bekannt sein. Obwohl die Wirkung von Eigenspannungen auf das Ermüdungsverhalten in geschweißten Strukturen und Komponenten schon lange bekannt ist, ist der Zugriff auf verlässliche und präzise Daten von räumlichen Eigenspannungsfeldern begrenzt. Bezüglich einer konzeptionellen Sicherheitsanalyse von geschweißten Komponenten mit bruchmechanischen Methoden begründet diese Arbeit einen systematischen Ansatz, um den Einfluss von Schweißeigenspannungen auf das Ermüdungsrisswachstum zu verdeutlichen
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Darestani, Mostafa Yousefi. "Response of concrete pavements under moving vehicular loads and environmental effects." Queensland University of Technology, 2007. http://eprints.qut.edu.au/16662/.
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The need for modern transportation systems together with the high demand for sustainable pavements under applied loads have led to a great deal of research on concrete pavements worldwide. Development of finite element techniques enabled researchers to analyse the concrete pavement under a combination of axle group loadings and environmental effects. Consequently, mechanistic approaches for designing of concrete pavements were developed based on results of finite element analyses. However, unpredictable failure modes of concrete pavements associated with expensive maintenance and rehabilitation costs have led to the use of empiricalmechanistic approach in concrete pavement design. Despite progressive knowledge of concrete pavement behaviour under applied loads, concrete pavements still suffer from deterioration due to crack initiation and propagation, indicating the need for further research. Cracks can be related to fatigue of the concrete and/or erosion of materials in sub-layers. Although longitudinal, midedge and corner cracks are the most common damage modes in concrete pavements, Austroads method for concrete pavement design was developed based on traditional mid-edge bottom-up transverse cracking introduced by Packard and Tayabji (1985). Research presented in this thesis aims to address the most common fatigue related distresses in concrete pavements. It uses comprehensive finite element models and analyses to determine the structural behaviour of concrete pavements under vehicular loads and environmental effects. Results of this research are supported by laboratory tests and an experimental field test. Results of this research indicate that the induced tensile stresses within the concrete pavement are significantly affected by vehicle speed, differential temperature gradient and loss of moisture content. Subsequently, the interaction between the above mentioned factors and concrete damage modes are discussed. Typical dynamic amplifications of different axle groups are presented. A new fatigue test setup is also developed to take into consideration effects of pavement curvature on fatigue life of the concrete. Ultimately, results of the research presented in this thesis are employed to develop a new guide for designing concrete pavements with zero maintenance of fatigue damage.
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MANESCHY, JOSE E. "Integral-J para carregamentos ciclicos." reponame:Repositório Institucional do IPEN, 1998. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10703.
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Made available in DSpace on 2014-10-09T12:43:11Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T13:56:42Z (GMT). No. of bitstreams: 1 06170.pdf: 3620725 bytes, checksum: 20c306e1c39ebb9a11fa8090fb30a119 (MD5)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Truant, Xavier. "Etude et modélisation du comportement mécanique de panneaux de structure soudés par friction-malaxage (FSW)." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEM043/document.
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Le procédé de soudage par friction malaxage (FSW) entraîne, d’une manière générale, une importante chute de dureté à travers le joint soudé. Dans le but de concevoir des structures aéronautiques soudées par FSW en fatigue, il est nécessaire de connaître l’impact de cette chute de dureté dans le comportement mécanique global de la soudure. Dans ces travaux, l’alliage d’aluminium à durcissement structural 2198-T8 est considéré. Une chaîne de calcul de durée de vie en fatigue d’une structure soudée par FSW est mise en place. Elle intègre un couplage de calculs et d’expériences grâce auxquels le comportement mécanique de la structure est modélisé. Dans un premier temps, le gradient de comportement mécanique de la soudure est étudié. Des essais mécaniques de traction et cycliques sont réalisés à température ambiante. La méthode de corrélation d’images numériques (DIC) est utilisée dans le but de mesurer les champs de déplacements localement dans et au voisinage du joint soudé. À partir des résultats expérimentaux, les paramètres mécaniques d’un modèle de comportement sont identifiés à partir d’un élément de volume, zone par zone à travers le joint soudé. En parallèle, une quantification des précipités durcissants T1 (Al2CuLi) est menée dans différentes zones du joint soudé à l’aide d’un Microscope Electronique en Transmission (MET). Un lien entre l’évolution de la microstructure à travers la soudure et l’évolution des paramètres mécaniques est recherché. Le modèle de comportement mécanique est utilisé sur des calculs de structure utilisant la méthode des éléments finis pour simuler le joint soudé. En parallèle, des essais de fatigue sont réalisés sur des éprouvettes uniaxiales et cruciformes soumises à des chargements uniaxiaux et multiaxiaux. À l’aide des simulations du gradient de comportement mécanique du joint soudé ainsi que des résultats mesurés en fatigue, les paramètres d’un modèle d’endommagement sont identifiés. Ce modèle est utilisé pour prédire les durées de vie en fatigue et les zones d’amorçages de fissure pour une structure soudée soumise à des chargements multiaxiauxThe Friction Stir Welding (FSW) process generally induces a critical hardness decrease inside the welded joint. To design aeronautical structure welded by FSW in fatigue, it is then necessary to know the impact of this hardness drop on the constitutive behaviour of the junction. In this study, the hardening structural aluminium alloy 2198-T8 is considered.A fatigue lifetime assessment loop of a welded structure is implemented. It integrates a calculations and experiments coupling which is used to model the structure’s mechanical behaviour. The gradient mechanical behaviour of the weldment is initially studied.Monotonic and cyclic mechanical tests are carried out to room temperature. Digital Image Correlation (DIC) is used to measure local displacement fields around the junction. Based on this experimental data, mechanical parameters for a constitutive model are identified on a volume element, zone by zone across the welded joint. In parallel, a quantification of the T1 (Al2CuLi) strengthening precipitates is realized in different region of the joint with a Transmission Electron Microscope. A connection between the microstructure evolution and the mechanical parameters is researched. The gradient mechanical behaviour of the joint is assessed on a 3D structure by Finite Element Analysis. Furthermore, fatigue tests are carried out on uniaxial and multiaxial loadings welded specimen. Thanks to the mechanical behaviour model and the fatigue lifetime measured, a damage model is used to predict the fatigue lifetime and the crack initiation zone for a welded structure which is subjected to higher multiaxial loads
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Mseddi, Amina. "Modélisation et commande d’un générateur éolien à double excitation isolé en vue de l’amélioration de son rendement et de la diminution de la fatigue mécanique." Thesis, Cergy-Pontoise, 2019. http://www.theses.fr/2019CERG1032.
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Le présent sujet contribue à la modélisation et à la commande de systèmes de conversion éoliens basés sur un Générateur Synchrone à Double Excitation (GSDE). Le degré de liberté apporté par l’excitation bobinée offre la possibilité de travailler sur l’amélioration de l’efficacité énergétique sur les cycles de fonctionnement avec sollicitations aléatoires, comme dans le cas de l’éolien.On vise, à travers cette recherche, la mise en place de techniques de commande robuste d’un GSDE en vue de l’optimisation de son rendement aérodynamique et de la réduction de la fatigue mécanique. Dans ce contexte, un générateur hybride relié à une charge isolée pour des applications éoliennes est présenté. Des modèles linéaires sont tout d’abord établis. Ces modèles sont ensuite utilisés pour mettre en place les structures de contrôle appropriées tant du point de vue électrique que mécanique. Parallèlement, des modèles non linéaires très complets sont développés permettant une validation en simulation très poussée prenant en compte les harmoniques d’espace du générateur, les effets de commutation des convertisseurs et les effets de torsion sur l’arbre. En outre, un émulateur éolien de 3 kW est construit, en vue d'évaluer expérimentalement l’apport de notre générateur hybride dans le domaine éolien puis d'améliorer les contrôleurs synthétisés. Dans ce travail, deux stratégies de contrôle robuste pour une machine hybride sont implémentées et une comparaison entre un contrôleur CRONE et un contrôleur H∞ est établie. Des résultats très satisfaisants sont obtenus avec une meilleure performance du CRONE par rapport au H∞. Outre la problématique de l’optimisation de la production du système de conversion éolien, on a aussi cherché à réduire le taux d’harmonique en recourant à deux solutions : le filtrage passif et la réduction des ondulations du couple électromagnétique par action sur le courant d’excitation. Bien qu’on ait apporté des améliorations pour de grandes vitesses de rotation de la génératrice, ces solutions restent insuffisantes pour une connexion de l’architecture proposée au réseau électrique...Une fois l’applicabilité de la GSDE dans le domaine éolien prouvée pour le cas d’un système éolien de 3 kW, nous sommes passé à une puissance plus réaliste en interfaçant notre modèle électrique avancé avec un modèle aéroélastique, disponible sur le logiciel FAST. Ce dernier permet de prendre en compte les éléments mécaniques, les couplages et les éventuelles flexibilités. La turbine choisie pour l’étude est la turbine WindPACT de puissance 1.5MW. Dans cette partie, des commandes robustes traitant la réduction de la fatigue mécanique sont élaborées.Le modèle de la turbine WindPACT basé sur le générateur hybride est finalement connecté au réseau, les lois de commande nécessaires pour cette connexion sont implémentées puis validées sous la plateforme Matlab SimulinkThis subject contributes to the modeling and control of a wind conversion system based on a Double Excitation Synchronous Generator (DESG). The degree of freedom provided by the wound excitation allows the improvement of the energy efficiency on the operation’s cycles with random solicitations, as it is the case for wind turbines.The aim of this research is to implement robust control techniques for the DESG in order to optimize its aerodynamic efficiency and to reduce its mechanical loads. In this context, a hybrid generator connected to an isolated load for wind applications is presented. First, linear models are established. These models are used to set up the appropriate control structures from both an electrical and mechanical point of view. At the same time, very complete nonlinear models are developed allowing a validation in an advanced simulation platform taking into account the space harmonics of the generator, the switching effects of the converters and the torsional effects on the shaft. Moreover, a 3 kW wind emulator is built to evaluate the contribution of the hybrid generator in the wind conversion systems field and then improve the synthesized controllers. Two robust control strategies for a hybrid machine are implemented and a comparison between a CRONE controller and a H∞ controller is presented. Satisfying results are obtained with a better performance for the CRONE regulator compared to H∞ one. In addition to the problem of optimizing the production of the wind energy conversion system, attempts have also been made to reduce the generator harmonic distortion ratios by using two solutions: passive filtering and reduction of the electromagnetic torque ripple by acting on the excitation current. Although there are improvements at high rotation speeds, these solutions are not sufficient for a connection of the proposed architecture to the grid.Once the applicability of the DESG in the wind energy field has been proven in the case of a 3 kW wind conversion system, we have considered a more realistic case. To this end, we have interfaced the developed advanced electric model with an aeroelastic model available on the FAST software, to take into account the mechanical couplings and the flexibilities. The turbine chosen for the study is the WindPACT 1.5MW turbine. In this part, robust controllers dealing with the reduction of mechanical fatigue are developed.The model of WindPACT turbine based on the hybrid generator is finally connected to the grid and the control laws necessary for this connection are implemented and validated under the Matlab Simulink platform
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Albaldawi, Hisham, and Diana Kobbah. "Dimensionering av Traverskranbana." Thesis, Örebro universitet, Institutionen för naturvetenskap och teknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-44910.
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Kranlaster som verkar på kranbanor varierar med tiden och kan inte behandlas som statiska laster, detta gör att en statisk beräkning inte är tillräckligt säker, därför bör kranbalkar utformas på så sett att den klarar av statiska såväl som dynamiska kranlaster. Arbetet valdes efter förstudier som gjordes på internet för att få grundläggande kunskap om ämnet. Informationen söktes på svenska, engelska och tyska för att kunna hitta relevanta och pålitliga källor som behandlar traverskranbanor enligt eurokod. Tack vare råd från Björn Åsted från Stålbyggnadsinstitutet (SBI), kunde en bok på tyska hittas. För att kunna jämföra resultaten används ett svenskt program CraneGirder EC3 under arbetet. Rapporten innehåller en beräkningsmodell för en valsad profil balk, beräkningar baserades på eurokod ekvationer och föreskrifter vilket var som dimensionerings underlag för arbetet. I denna rapport hänvisas hur en kranbana skall dimensioneras med hög utnyttjandegrad, ett antal kontroller gjordes för att säkerställa att balken och dess detaljer, såsom räl och svets är säkert utformade mot utmattning och deformation. Dimensioneringen utgick ifrån lastberäkningar för traverskranen. Handberäkningar visade hur olika kranlaster kan kombineras i lastgrupper för att åstadkomma högsta inverkan på balken, handberäknings resultat visade att HEB 280 och dimensioneringen dominerades enbart av lastgrupp 1 och 5. Med hjälp av beräkningsprogram stämde resultaten i hög grad överens med programmet men med några avvikelser. För den avgränsningen som antogs i arbetet verkade utmattningen inte ha en dominerande inverkan.Crane Loads acts on runways which varies with time and cannot be treated as static loads, this allows that the static estimation is not secure enough, therefore the crane runways should be designed in such terms that it can handle static as well as dynamic crane loads. The work was chosen after feasibility studies which were made on the internet to get basic knowledge on the subject. The information was sought in Swedish, English and German in order to find relevant and reliable sources which deal with overhead crane runway according to Eurocode. Thanks to advice from Björn Åsted from the Steel Construction Institute (SBI), a book in German was found. In order to compare the results, a Swedish software CraneGirder EC3 was used during the project. The report contains a calculation method for a rolled section girder, calculations were based on Eurocode equations and regulations which were the design basis for the project. The report refer to how a crane runway must be designed with a high utilization level, a number of controls were made to ensure that the beam and its details, such as rail and welding are surely designed to fatigue and deformation. The design was based on load calculations for the overhead crane. Traditional calculations showed how different crane loads can be combined in load groups to achieve the highest impact on the beam, calculations showed that HEB 280 and dimensioning dominated only by load group 1 and 5. With the help of calculation software the results were largely consistent with the program but with some differences. For the delimitation that was assumed in the project the fatigue seemed to have an effect especially on some small details like weld.
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Güngör, Güven. "Biaxial Load Effects on Fatigue Properties." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/19079/.
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This study aims to aid many issues related to fatigue, namely biaxial loading, the definition of the finite geometry correction factor of the stress intensity factor and the understanding of the energy dissipation per fatigue crack growth. In our work, we are using the geometry correction factor definition that uses the ratio
of external work introduced to the material. Using different biaxiality ratios varies the external work done, thus makes it possible for us to observe how the geometry correction factor handles this variation. The trend of strain energy release rate per crack growth is also investigated through biaxiality. Moreover,
the common discussion of the effects of biaxiality on fatigue properties is aided with yet another study. For this purpose, cruciform shaped plate specimen from an aluminum alloy are manufactured and biaxially loaded. Crack growth is observed while load-to-displacement data is recorded to evaluate the external work done on the specimen. As a result, it is seen that biaxiality delays the fatigue failure. Crack growth rates decreases as the biaxiality increases for a given effective stress intensity factor. Making use of the work values for the calculation of the finite geometry correction factor handles the effects of
biaxiality well. Strain energy release rate increases as the crack propagates, but there is no trend between strain energy release rate and biaxiality of the loading. In the future works, observing also the crack tip plasticity and trying out a wider range of biaxiality ratios with different types of material would result in more generalizable conclusions. Moreover, more repetitions of the fatigue tests would give more accurate values for the amount work introduced to the material with changing biaxiality.
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Khosrovaneh, Abolhassan K. "Fatigue analysis and reconstruction of helicopter load spectra." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54213.
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Helicopter load histories applied to notched metal samples are taken as examples, and their fatigue lives are predicted by using a simplified version of the local strain approach. This simplified method requires an input load history in the form of the rain-flow matrix and places bounds on the fatigue life. A peak-valley reconstructed history is generated based on the standard spectrum Helix. A second history studied is a more irregular one based on actual flight data. lt is used to generate three reconstructed histories based on three principles: peak-valley, to-from, and rain-flow. Emphasis is given to the rain-flow reconstruction method, and different reconstruction methods based on rain-flow cycle counting are presented. Life predictions are presented for all of the above cases, and the comparison with test data and other considerations suggest that the most promising reconstruction approach is one based on rain-flow cycle counting. Finally, a method is presented which reconstructs a history with the same rain-flow cycles and also the same distribution of relative time increments between adjacent peaks and valleys. This reconstructed history gives the same fatigue life as the original history.Ph. D.
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Holmberg, Erik. "Topology optimization considering stress, fatigue and load uncertainties." Doctoral thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-123008.
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This dissertation concerns structural topology optimization in conceptual design stages. The objective of the project has been to identify and solve problems that prevent structural topology optimization from being used in a broader sense in the avionic industry; therefore the main focus has been on stress and fatigue constraints and robustness with respect to load uncertainties. The thesis consists of two parts. The first part gives an introduction to topology optimization, describes the new contributions developed within this project and motivates why these are important. The second part includes five papers. The first paper deals with stress constraints and a clustered approach is presented where stress constraints are applied to stress clusters, instead of being defined for each point of the structure. Different approaches for how to create and update the clusters, such that sufficiently accurate representations of the local stresses are obtained at a reasonable computational cost, are developed and evaluated. High-cycle fatigue constraints are developed in the second paper, where loads described by a variable-amplitude load spectrum and material data from fatigue tests are used to determine a limit stress, for which below fatigue failure is not expected. A clustered approach is then used to constrain the tensile principal stresses below this limit. The third paper introduces load uncertainties and stiffness optimization considering the worst possible loading is then formulated as a semi-definite programming problem, which is solved very efficiently. The load is due to acceleration of point masses attached to the structure and the mass of the structure itself, and the uncertainty concerns the direction of the acceleration. The fourth paper introduces an extension to the formulated semi-definite programming problem such that both fixed and uncertain loads can be optimized for simultaneously. Game theory is used in the fifth paper to formulate a general framework, allowing essentially any differentiable objective and constraint functions, for topology optimization under load uncertainty. Two players, one controlling the structure and one the loads, are in conflict such that a solution to the game, a Nash equilibrium, is a design optimized for the worst possible load.
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Marsh, Gabriel. "Fatigue load monitoring of offshore wind turbine support structures." Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28278.
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The uptake of renewable energy sources has increased dramatically in recent decades, in response to the contribution to climate change attributed to CO2 emissions from the burning of fossil fuels, the need for governments to maximise the use of domestic energy forms with depleting conventional sources, and to reduce exposure to fuel price volatility. Renewable energy targets set by the European Union have been supported by legislation and economic incentives, and have resulted in a sharp increase in installed wind power capacity in particular. Wind power is seen as a particularly attractive source of renewable energy capacity in the UK due to favourable resources and a competitive cost of energy for onshore sites, with 8.8 GW of capacity currently installed [1]. Constraints from visual and environmental impacts, together with improved wind resources, have led to the acceptance of greater financial costs and the exploitation of offshore sites, with over 5 GW installed to date [1]. Both onshore and offshore, the wind industry now has significant operational experience, with some of the earliest wind farms approaching the end of their design life. Material fatigue is a design critical factor which dictates the safe operational life of wind turbines, but is subjected to numerous areas of uncertainty in the level of environmental loading and structural response, as well as material properties and manufacturing methods. Therefore, a conservative design must be ensured from the outset, which presents the potential for fatigue life extension of installed assets if improved knowledge of their operational experience can be obtained. This thesis details the methodology for a fatigue load assessment of operational offshore wind turbine support structures using measured data, and attempts to quantify areas of loading which contribute to total fatigue damage. The methodologies developed build on existing recommendations for onshore wind turbines to incorporate the additional effects of the offshore environment. Results from measured loading suggest that design fatigue levels can be reduced if operational monitoring is included. Operational experience can allow design conservatism, which is necessary due to uncertainties in structural properties and in levels of stochastic loading, to be more accurately quantified.
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Bernard, Richard Joseph. "The fatigue crack growth behavior of Ti-24A1-11Nb as a function of temperature and load ratio." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/20187.
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Cosack, Nicolai [Verfasser]. "Fatigue Load Monitoring with Standard Wind Turbine Signals / Nicolai Cosack." Aachen : Shaker, 2010. http://d-nb.info/1084535939/34.
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Dahlberg, Johan. "On the asperity point load mechanism for rolling contact fatigue." Doctoral thesis, Stockholm : Hållfasthetslära, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4569.
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Müller, Kolja [Verfasser]. "Probabilistic Fatigue Load Assessment for Floating Wind Turbines / Kolja Müller." München : Verlag Dr. Hut, 2020. http://d-nb.info/121947634X/34.
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Hannes, Dave. "On fatigue crack growth modelling of surface initiated rolling contact fatigue using the asperity point load mechanism." Doctoral thesis, KTH, Hållfasthetslära (Avd.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-141151.
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Load transfer in applications or between machine components is generally achieved through contact. In case of recurrent high contact loads in combination with a rolling motion, i.e. with a relatively small amount of slip, the contact surface may eventually suffer from rolling contact fatigue (RCF). The damage consists then of cracks and craters or spalls, which can cause dysfunctionality of the application leading to inefficiency or increased maintenance costs. Ultimately the damage may cause total failure of the machine component. The damage process is still not fully understood due to the complexity of the problem. Different mechanisms have been suggested to explain initiation and propagation of RCF damage. The current work focused on crack growth modelling of surface initiated RCF in case hardened gear steel. The study was based on the asperity point load mechanism, which emphasizes the importance of the surface roughness in the damage process. Asperities on the contact surface act as stress raisers inducing locally high tensile surface stress when entering the contact. Improved understanding of the damage process and further validation of the asperity point load mechanism was achieved. In Paper A, the crack path of surface initiated RCF was simulated in the symmetry plane of the damage with the trajectory of the largest principal stress in the uncracked material. The mode I fracture mechanism was found applicable as well as linear elastic fracture mechanics (LEFM). The evolvement of the asperity contact parameters during the load cycle was determined through a finite element (FE) contact model based on an equivalent contact geometry. The predicted RCF crack path agreed with experimental spall profiles both in entry details as in overall shape. An experimental series was performed in Paper B to investigate the crack closure behaviour in presence of large negative minimum loads. The experimental results suggested a crack closure limit close to zero. The choice of the equivalent mixed-mode stress intensity factor range and especially the crack closure limit had a significant effect on the predicted RCF or spalling life. The two-dimensional crack growth model was further developed in Paper C and used to investigate the influence of asperity size, friction and residual surface stress on the simulated RCF damage. The simulations agreed qualitatively with experimental observations where reduced surface roughness, improved lubrication and compressive residual surface stress increased RCF resistance. In Paper D, a three-dimensional stationary crack was studied using an FE model and a simplified RCF load. A new crack geometry was proposed allowing the investigation of the spall opening angle of the typical vshaped damage. Crack arrest through crack closure was suggested as explaining mechanism. A qualitative study indicated increased spread of the surface damage with increased friction. The results also depended on the crack inclination angle. The different studies supported the asperity point load mechanism to explain not only fatigue initiation but also fatigue crack propagation.QC 20140210
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Majdič, Petr. "Napěťová, deformační a bezpečnostní analýza statoru generátoru zatíženého nehomogenní teplotou." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231962.
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This thesis deals with stress, strain and reliability analysis of synchronous generator stator including an inhomogeneous temperature field. Using the finite element method, stress and strain are calculated, and from these values safety against yield strength is determined, which is followed by the life calculation of the most stressed weld joint and the determination of its possible damage during the period required by the customer.
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Fellows, Lesley. "Fatigue crack growth under variable stress ratios and complex load history." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325898.
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Prinsloo, Etienne Pieter Willem. "Fatigue equivalent static load: Methodology for the design of vehicle structures." Diss., University of Pretoria, 2003. http://hdl.handle.net/2263/25966.
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This study is concerned with the design of vehicle structures through the use of Fatigue Equivalent Static Loads (FESL). A large percentage of failures of mechanical structures can be attributed to fatigue. Furthermore, it is also generally accepted that defective structural design is mostly caused by insufficient knowledge of the input loading. The fatigue loads experienced by vehicle structures are especially difficult to quantify. In the current competitive markets, it is essential to use a pro-active, timely and cost effective process to solve fatigue related problems. The heart of the FESL methodology is the ability to condense a large amount of input load data into a single fatigue load. This is achieved by calculating the damage of the measurements and converting it to an equivalent stress, through the use of a calibration matrix obtained from a unit-load finite element analysis. A Fatigue Equivalent Static Load can now be determined, and the vehicle structure can be evaluated for durability.Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2003.
Mechanical and Aeronautical Engineering
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Allsop, Steven Christopher. "Hydrodynamic modelling for structural analysis of tidal stream turbine blades." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/33219.
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The predictable nature of the tides offers a regular, reliable source of renewable energy that can be harnessed using tidal stream turbines (TSTs). The UK's practically extractable tidal stream energy resource has the potential to supply around 7 % of the country's annual electricity demand. As of 2016, the world's first commercial scale arrays have been deployed around the UK and France. The harsh nature of the marine operating environment poses a number of engineering challenges, where the optimal turbine design solution remains under investigation. In this thesis, a numerical model is developed to assess the power production and hydrodynamic behaviour of horizontal axis tidal turbines. The developed model builds upon well established and computationally efficient Blade Element Momentum Theory (BEMT) method for modern three-bladed wind turbines. The main novel contribution of this thesis is extending the application to an alternative design of a ducted, high solidity and open centre TST. A validation study using measurements from multiple different scale model experimental tank tests has proven the applicability of the model and suitability of the imposed correction factors. The analytical modifications to account for ducted flow were subsequently indirectly verified, where predictions of turbine power and axial thrust forces under optimal operating speeds were within 2 % of those using more advanced computational fluid dynamics (CFD) methods. This thesis presents a commercial application case of two turbines designed by OpenHydro, examining the BEMT performance with a sophisticated blade resolved CFD study. A comparison of results finds that the model is capable of predicting the average peak power to within 12 %, however it under predicts thrust levels by an average of 35 %. This study concludes that the model is applicable to ducted turbine configurations, but is limited in capturing the complex flow interactions towards the open centre, which requires further investigation. The computational efficiency of the newly developed model allowed a structural analysis of the composite blades, thus demonstrating it is suitable to effectively evaluate engineering applications. Stresses are seen to be dominated by flap-wise bending moments, which peak at the mid-length of the blade. This tool will further enable EDF to perform third party assessments of the different turbine designs, to aid decision making for future projects.
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Bailey, Chris A., T. McInnis, K. Sato, B. Johnston, Z. Sha, and Michael H. Stone. "Is a 20 Kg Load Sufficient to Simulate Fatigue in Squat Jumps?" Digital Commons @ East Tennessee State University, 2014. https://dc.etsu.edu/etsu-works/4564.
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