Dissertations / Theses: 'Steel bridges, the fatigue crack propagation'

1

Montezuma, Marcos FÃbio VerÃssimo. "Modelagem Computacional da PropagaÃÃo de Trincas em Vigas de Pontes de AÃo sob Carregamento CÃclico de Amplitude VariÃvel." Universidade Federal do CearÃ, 2002. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7297.

Full text

Abstract:

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior
Pontes de aÃo normalmente estÃo sujeitas a carregamentos cÃclicos de amplitude variÃvel, com tipo e freqÃÃncia de trÃfego ao acaso. Dessa forma, a nucleaÃÃo e a propagaÃÃo de trincas nos elementos estruturais de uma ponte podem ser resultantes das flutuaÃÃes de carregamentos. ApÃs determinar a localizaÃÃo e o tamanho de uma falha existente, tem-se de imediato a preocupaÃÃo com a previsÃo de sua propagaÃÃo a fim de se ter um tempo conveniente para o reparo. Desta maneira, os conceitos de mecÃnica da fratura e fadiga sÃo fundamentais para o correto entendimento do problema. Neste trabalho Ã feito o desenvolvimento de um modelo computacional para a anÃlise do crescimento de trincas utilizando-se os modelos do Valor MÃdio QuadrÃtico e Ciclo-a-Ciclo. Nas simulaÃÃes realizadas, observa-se a influÃncia dos carregamentos de amplitudes variÃveis sobre a previsÃo de vida da estrutura. Foram consideradas como variÃveis de entrada do programa, diferentes tamanhos iniciais de trincas e diferentes histÃrias de carregamentos. Dessa forma, pÃde-se avaliar a dispersÃo dos resultados de previsÃo de vida da estrutura, com a variaÃÃo dos diferentes parÃmetros de entrada.
Steel bridges are usually subject to variable amplitude cyclic loading, with type and frequency of traffic at random. Thus, the nucleation and propagation of cracks in structural elements of a bridge may be due to fluctuations in shipments. After determining the location and size of a fault existing, has the immediate concern to the prediction of its propagation in order to have a convenient time for repair. Thus, the concepts of fracture mechanics and fatigue are essential for a proper understanding of the problem. This work is done by developing a computational model for the analysis of crack growth models using the mean square value and Cycle-by-cycle. In the simulations, we observe the influence of variable amplitude loading on the expected life of the structure. Were considered as input variables of the program, different initial crack sizes and different loading histories. Thus, we could evaluate the dispersion of expected life of the structure with the variation of different input parameters.

APA, Harvard, Vancouver, ISO, and other styles

2

Abdelwahab, Kemal, and Mohamed Abdirizag Farah. "Spricktillväxt i stålkonstruktioner på grund av utmattning." Thesis, KTH, Byggteknik och design, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-259364.

Full text

Abstract:

Stålbroars approximativa livslängd bestäms av stålets utmattningshållfasthet, då utmattning är en av de främsta anledningarna till att livslängden begränsas. I Sverige existerar ett antal broar som närmar sig slutet av sin livslängd, samtidigt som behovet för kapacitet och kraven på broarna ökar. Flertalet av dessa broar är i behov av upprustning. Däremot är det inte möjligt ur vare sig ett ekonomiskt- eller miljöperspektiv att byta ut alla broar, och därför behöver de broar som är mest kritiska prioriteras. Vid utmattningsdimensionering av stålbroar beaktas hela spänningsvidden, oavsett om spänningarna är i drag eller tryck. En spricka propagerar endast vid dragspänningar, vilket innebär att tryck- spänningar egentligen inte bör vägas in i samband med dimensionering. Detta innebär att en del stålbroar skulle kunna ha en längre livslängd än vad den traditionella dimensioneringen ger. Spänningsintensitetsfaktorn 𝐾 används inom brottmekaniken för att förutspå spänningsintensiteten i närheten av sprickspetsen, och appliceras till linjärelastiska material. Det finita elementprogrammet Abaqus användes när brodetaljen modellerades och analyserades. Brodetaljen representerar en balk med en påsvetsad anslutningsplåt, som utsätts för trafiklasten på en bro och en temperaturlast för att simulera egenspänningar. Detaljen representerar problematiken med utmattning i stålkonstruktionsdelar. Motivet för denna studie är att inga sprickor har hittats under inspektioner av liknande detaljer, det till trots att en del stålbroar teoretiskt sett förbrukat sin livslängd. Studien genomfördes med en mer avancerad modell än vad som vanligtvis skapas för bedömning av utmattning, med syftet att modellera verkligheten mer korrekt. Resultaten visar hur egenspänningarna bidrar till dragspänningar, vilket leder till sprickpropagering i modellen. Vid spricklängden 9,5 mm övergår spänningarna från drag till tryck, och då upphör spricktillväxten. Resultaten visar även att utmattningssprickor kan växa i stålkonstruktionsdelar som i huvudsak utsätts för nominella tryckspänningar, ifall höga egenspänningar uppstår vid anslutningsplåten.
Steel bridges estimated service life is determined by the fatigue strength of the steel, since fatigue is one of the main reasons for limiting the service life. In Sweden there is a number of bridges that approach the end of their service life, while the need of increasing the capacity and demands on bridges grows. The majority of these bridges is in need of reparation. On the other hand, it is not possible either from a financial- or environmental perspective to replace all bridges, and therefore the bridges that are most critical needs priority. In the case of fatigue design calculation of steel bridges, the entire stress range is taken into account, regardless of whether the stresses are in tension or pressure. A crack propagates only at tensile stresses, which means that pressure should not really be considered in the design calculations. This means that some steel bridges could have a longer life span than the traditional design calculation gives. The stress intensity factor K is used within the fracture mechanism to predict the stress intensity near crack tip, and is applied to linear elastic materials. The finite element program Abaqus was used when the bridge detail was modeled and analyzed. The bridge detail represents a beam with a welded connection plate, which is exposed to traffic load at the bridge and a temperature load to simulate residual stresses. The detail represents the problem of fatigue in steel structural parts. The motive for this study is that no cracks have been found during inspections of similar details, despite the fact that some steel bridges theoretically have consumed their longevity. The study is conducted with a more advanced model than usually created for assessment of fatigue, with the purpose of modeling the reality more correctly. The results show how the residual stresses cause tensile stresses, which leads to crack propagation in the model. At a crack length of 9,5 mm, the stresses change from tension to compression, and then the crack growth ceases. The results also indicate that fatigue cracking can grow in steel structural parts that are mainly exposed to compressive nominal stresses, if tensile residual stresses appear at the connection plate.

APA, Harvard, Vancouver, ISO, and other styles

3

Abdul-Salam, Ezzet Hameed. "Fatigue crack propagation in mild steel." Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291749.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Guirgis, Sameh. "Fatigue crack propagation in steel components at resonance." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ62216.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Horne, Michael R. "Rayleigh Wave Acoustic Emission during Crack Propagation in Steel." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28780.

Full text

Abstract:

An investigation was conducted of the existence of seismic surface pulses (SSP) on crack faces in near-failure fatigue. An SSP has components of various modes of wave propagation. The component with the largest amplitude is a Rayleigh surface wave pulse. The possibility that these surface modes have much higher amplitudes than bulk modes of acoustic emission (AE) was illustrated by an idealized thought experiment relating an SSP on a half-space to the response of crack faces to crack extension. A number of aspects of AE monitoring in finite objects were investigated. Attributes of surface wave propagation on the edge of a specimen were found to be easier to monitor than other modes of wave propagation. Wavelet analysis was used to compare the characteristics of brittle AE with other sources. A new testing paradigm was developed to reduce interference from secondary sources of AE and enhance the investigation of AE from critical crack behavior. Unique specimen design features were developed, data acquisition features sought and validated, a dead weight load frame was modified, and data analysis procedures were developed. Criteria based on velocity, frequency content, amplitude and shape were devised to determine if an AE event is an SSP. The tests were designed to mimic load conditions on structures such as bridges and hence investigate the difference between AE generated in field conditions and that of typical laboratory conditions. Varieties of steel, from very ductile to very brittle, were tested. It was concluded that plastic zone formation, considered a secondary source of AE, was found not to interfere with the SSP activity. The SSP was found experimentally to have 2-3 times the amplitude of the bulk wave AE. The lack of sufficient AE did not allow for determination of conclusive changes in the AE as the specimens approached failure. However, it was found that brittle crack extension in fatigue and ductile failure can produce wave propagation resembling the SSP.
Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

6

Keller, Scott. "Creep-Fatigue Crack Initiation and Propagation of a Notched Stainless Steel." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5659.

Full text

Abstract:

Premature failures of vital gas turbine components, such as blades and vanes, have been the result of increasing demands of power generation facilities. As power needs fluctuate throughout the day, operators are quickly firing up gas turbines as a means of providing instant power. Traditionally, these engines run at constant operating conditions; however, contemporary operating conditions call for these engines to be applied on an “as necessary” basis. The result of the cyclic startup and shutdown of gas turbines has led to a phenomenon known as creep-fatigue (CF). A coupling of two primary failure mechanisms in gas turbines, CF conditions exacerbate the mechanisms of creep and fatigue, ultimately leading to a premature failure of components. Traditionally, independent creep and fatigue analyses are conducted to determine the limiting life factor of gas turbines. Recently, fracture mechanics approaches have been successfully used in extending the traditional analyses to include fatigue- and creep-crack growth analyses. Founded on existing approaches to creep-fatigue crack growth analyses, including experimental elastic and plastic fracture mechanics approaches, a coupled creep-fatigue crack initiation and propagation model is developed. To bring these models to fruition, the current study utilizes the development of an experimental setup capable of subjecting a modified fracture specimen to creep-fatigue conditions. With two test temperatures key to turbine components, a blunt notch compact tension specimen was subjected to trapezoidal load waveforms with various lengths of holds at maximum load. A developed direct current potential drop (DCPD) system was used to monitor crack initiation and crack lengths throughout the duration of tests. Numerical simulations on a representative specimen were conducted, to correlate and predict key fracture mechanics parameters used in the development of creep-fatigue crack initiation and propagation models. Metallurgical analysis of specimens was conducted, implementing both optical and scanning electron microscopy. From the experimental and numerical studies, a model for both the initiation and propagation of cracks on a single specimen is furnished. Through the use of elastic-plastic fracture mechanics parameters, the proposed models are observed to predict crack initiation and replicate crack propagation rates based on the experimental conditions. Assisting in the implementation of the proposed models, intended uses and applications for the models are provided, simplifying the life prediction analyses for components expected to fail due to creep-fatigue service conditions.
Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering

APA, Harvard, Vancouver, ISO, and other styles

7

Donohoe, C. J. "Corrosion fatigue of a high strength low alloy steel." Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322985.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Trask, David Anthony. "Experimental and numerical investigation into fatigue crack propagation models for 350WT steel." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0003/MQ31652.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Kaneko, Yoshihisa. "Fatigue Crack Propagation and Cyclic Deformation in Ferritic Stainless Steel Single and Bicrystals." Kyoto University, 1998. http://hdl.handle.net/2433/77916.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

Callister, D. R. "A study of fatigue crack propagation in quenched and tempered and controlled rolled HSLA steels." Thesis, Cranfield University, 1987. http://dspace.lib.cranfield.ac.uk/handle/1826/4444.

Full text

Abstract:

A range of HSLA steels reflecting the two major processing routes, quench and tempering and controlled rolling, have been tested in fatigue to assess their potential wider application in the offshore Industry. The six steels chosen have a wide range of yield strenghts (470 to 690Nmm-2), fracture toughness (31 to 260J at -40°C) and carbon equivalent values (0.19 to 0.33). Fatigue testing has in general been carried out at low frequency (0.5Hz) and high load ratio (0.6) however some tests have been conducted at very low frequency (0.1Hz) and low load ratio (0.1). An in-air study was first used to assess the fatigue performance of all six parent plates. Five steels were welded by the Submerged Arc Welding process at high heat input (1.5kJmm -1) to evaluate the Heat Affected Zone (HAZ) fatigue performance. A new test was devised to grow a fatigue crack through a single pass, bead on plate-, HAZ whilst maintaining a constant stress intensity range. The surface crack length was continuously monitored and recorded to an accuracy of 0.01mm. A corrosion fatigue study evaluated the performance of one controlled rolled and one quenched and tempered steel at three levels of impressed current cathodic protection. Extensive metallographic examination was made to study the influence of microstructural features and types on fatigue crack propagation. Techniques used include optical microscopy, scanning electron microscopy, fatigue crack and surface replication and crack profile digitising. These techniques give an assessment of crack path deviation and branching, the influence of precipitates and inclusions, and an indication of the mode of fatigue crack propagation. The wide range of microalloyed HSLA steels tested have shown a significant improvement in fatigue crack propagation resistance over structural steels conforming to BS 4360 grade 50D. Typically an improvement by a factor of two has been observed. Whilst the observed increase in fatigue life was slightly reduced by high heat input welding the slope of the Paris curves remained unaffected thus indicating a similar stress intensity range sensitivity in the HAZ to that shown by the parent plate. The newly developed crack monitoring system coupled to a computer controlled fatigue testing machine has shown a wide variation in fatigue crack propagation rates through a heat affected zone microstructural gradient. Growth rates have increased by a factor of ten in localised coarse grained microstructural regions compared to the adjacent weld metal and outer heat affected zone. The corrosion fatigue study has also indicated that in general HSLA steels retain their superiour fatigue resistance compared to structural steels and in particular respond more favourably to cathodic protection. Both in-air and corrosion fatigue studies have indicated that the controlled rolled steel microstructures developed mainly for line pipe application has the greatest potential for increased use offshore.

APA, Harvard, Vancouver, ISO, and other styles

11

Baxter, David Paul. "Investigation of a brittle cleavage fracture mode during fatigue crack propagation in a duplex stainless steel." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388383.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Shah, Sayyid Masoodur Rahman. "Investigation of crack propagation in X38CrMoV5 tool steel at room temperature and 600°C on small scale specimens." Toulouse 3, 2010. http://thesesups.ups-tlse.fr/1098/.

Full text

Abstract:

Les outillages de mise en forme à chaud, sont soumis à des chargements thermomécaniques sévères, qui endommagent leur surface. Une nouvelle méthode de caractérisation de l'endommagement par fatigue est proposée. Des éprouvettes de dimensions réduites, représentatives de la surface, ont été utilisées. Les essais de propagation de fissure en fatigue sur l'acier à outil X38CrMoV5 traité à 47 HRC sont réalisés à la température ambiante et à 600°C. Les effets de l'épaisseur de l'éprouvette, du rapport de charge et de la température ont été étudiés. Différents paramètres de propagation de fissure ont été établis à l'aide de la simulation numérique. Une méthode de mesure de l'ouverture en fond de fissure, utilisant une caméra numérique et un microscope à longue portée, a été développée. Les images acquises sont ensuite traitées par corrélation d'images pour mesurer l'ouverture de fissure. Un modèle de propagation de fissure basé sur l'ouverture en fond de fissure a été développé
Forging and high pressure die casting processes impose heavy mechanical loads on die materials and tools damaging their surface during production. This study proposes a novel method of characterisation of the surface damage of tool steels using thin specimens. Fatigue crack propagation experiments are carried out on the tool steel X38CrMoV5 at ambient temperature as well as at 600°C. The effect of specimen thickness, load ratio and temperature on the fatigue crack propagation is studied. Different fatigue crack propagation parameters are established using numerical simulations. A method of crack tip opening displacement measurement is developed. This method is based on image acquisition with the help of a digital camera and a long distance microscope followed by an image correlation procedure, to measure the crack opening displacements. A fatigue crack propagation model based on crack opening displacement is developed and compared with traditional propagation models

APA, Harvard, Vancouver, ISO, and other styles

13

Shibanuma, Kazuki. "Reformulation of XFEM and its application to fatigue crack simulations in steel structures." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120941.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Millar, Peter G. "Corrosion fatigue crack propagation behaviour of a high strength low alloy steel in a synthetic sea water environment." Thesis, Cranfield University, 1986. http://dspace.lib.cranfield.ac.uk/handle/1826/4443.

Full text

Abstract:

The corrosion fatigue crack propagation behaviour of a high strength low alloy steel, N-A-XTRA 70, in a synthetic sea water solution was tested using S. E. N. specimens subjected to a loading frequency of 0.1 Hz and a load ratio of 0.6. In order to simulate the conditions encountered by a thumbnail type crack several specimens from each of the microstructural types tested, namely parent plate, heat affected zone and heat treated material, had their crack sides covered by transparent plastic covers. Severe overprotection and slight underprotection conditions were produced using cathodic protection potentials of -1400, -1300, -1200 and -700 mV (S. C. E. ). The Paris relationship da/dN = CLKm was found to be a useful tool in describing the crack propagation rate data. Results obtained, presented in the form of plots of log da/dN against log AK, show that for parent plate, H. A. Z. and heat treated material, covering the crack sides of specimens produces enhanced corrosion fatigue crack propagation rates, at cathodic protection potentials of -1400 and -1300 mV (S. C. E. ), when compared to non covered specimens. This trend was also true for H. A. Z. specimens at a potential of -700 mV (S. C. E. ). For parent plate specimens, however, covering the crack sides at a potential of -700 mV (S. C. E. ) produced reduced crack propagation rates over non covered specimens. It is believed restriced oxygen access may account for these results. Plots of the Paris exponent m and constant C for the three microstructures tested produced three lines of the form m= alnC +b where a and b were found to be dependent upon material parameters. Comparison of results with BS 4360: 50D revealed that N-A-XTRA 70 exhibited superior fatigue performance when tested in air but behaved worse under conditions of free corrosion.

APA, Harvard, Vancouver, ISO, and other styles

15

Khan, Mushtaq Ahmad. "A study of fatigue crack nucleation and propagation properties of a B.S. 4360 - 50D structural steel by ultrasonic methods." Thesis, Brunel University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261124.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Recho, Naman. "Amorçage et propagation d'une fissure de fatigue des éléments de structures métalliques soudés." Paris 6, 1987. http://www.theses.fr/1987PA066198.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Liu, Jikai. "Influence of metallurgical phase transformation on crack propagation of 15-5PH stainless steel and 16MND5 low carbon steel." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00833206.

Full text

Abstract:

Ou study focuses on the effects of phase transformations on crack propagation. We want to understand the changes of fracture toughness during welding. In this work, fracture toughness is expressed by J-integral. There are many experimental methods to obtain the critical toughness JIC but they are impractical for our investigation during phase transformation. That is the reason why we have proposed a method coupling mechanical tests, digital image correlation and finite element simulation. The fracture tests are implemented on pre-cracked single edge notched plate sample which is easy for machining and heat conduct during phase transformation. The tests are conducted at different temperatures until rupture. Digital image correlation gives us the displacement information on every sample. Each test is then simulated by finite element where the fracture toughness is evaluated by the method G-Theta at the crack propagation starting moment found by potential drop method and digital image correlation technical. Two materials have been studied, 15Cr-5Ni martensitic precipitation hardening stainless steel and 16MND5 ferritic low carbon steel. For these two materials, different test temperatures were chosen before, during and after phase transformation for testing and failure characterization of the mechanical behavior. Investigation result shows that metallurgical phase transformation has an influence on fracture toughness and further crack propagation. For 15-5PH, the result of J1C shows that the as received 15-5PH has higher fracture toughness than the one at 200°C. The toughness is also higher than the original material after one cycle heat treatment probably due to some residual austenite. Meanwhile, pure austenite 15-5PH at 200°C has higher fracture toughness than pure martensitic 15-5PH at 200°C. For 16MND5, the result also proves that the phase transformation affects fracture toughness. The as received material has bigger J1C than the situation where it was heated to 600°C. On the other hand, the material at 600°C just before isothermal bainite transformation after the austenitization during cooling process also has higher fracture toughness than the one at 600°C before austenitization. These two conclusions are consistent well with the result of 15-5PH. But the final situation of 16MND5 after one cycle heat treatment has a slightly smaller J1C than the receiving situation. It means that one cycle heat treatment hasn't an significant influence on 16MND5fracture toughness. Conclusions show that one should pay attention to the heating period before austenitization of the substrate material when people do the welding as the higher temperature will bring the lower fracture toughness during this process. While during cooling period, the fracture toughness doesn't change a lot during, before or after the cooling induced phase transformation. Even for 15-5PH, it has a better fracture toughness after the martensite transformation than before.

APA, Harvard, Vancouver, ISO, and other styles

18

Gautrelet, Christophe. "Développement et exploitation d'un banc vibratoire en flexion pour les essais de fatigue Linearity investigation from a vibratory fatigue bench Fatigue curves of a low carbon steel obtained from vibration experiments with an electrodynamic shaker." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMIR21.

Full text

Abstract:

Dans le but de fournir des données expérimentales pour alimenter les modèles numériques développés au Laboratoire de Mécanique de Normandie, nous avons mis en place un banc d'essais uniaxiaux en fatigue vibratoire permettant de tester des structures à grand nombre de cycles. Après la rédaction d’un cahier des charges pour définir les caractéristiques d’excitations et de mesures, une étude de qualification de ce moyen d’essais est présentée afin d’obtenir les plages de performance basée sur l’hypothèse de linéarité du système. Ensuite, pour vérifier la faisabilité en fatigue, nous avons réalisé une étude visant à établir une courbe de caractérisation d’un acier bas carbone. Néanmoins, ce banc d’essais ne permet pas de distinguer les phases d’initiation de fissure, de propagation et de rupture. Nous avons donc proposé quelques pistes pour évaluer le nombre de cycles à fissuration : la première est basée sur la variation de pente de l’amplitude de déformation mesurée à partir de jauges de déformation et la seconde utilise le décalage de la fréquence de résonance. Nous avons ainsi proposé un modèle simple de dommage non linéaire basé sur la variation de la fréquence de résonance qui permet également d'évaluer les nombres de cycles à la rupture des spécimens. La durée de vie en fatigue expérimentale obtenue par ce modèle est confrontée avec celle en fatigue obtenue par un modèle de dommage issu de la littérature
The aim of Laboratory of Mechanics of Normandy is to provide experimental data to enhance the numerical models developed for structural design. Therefore, we have set up a vibration-based uniaxial bending bench for testing structures under a high cycle fatigue. After setting up specifications to specify the characteristics of the excitations and measurements, a qualification investigation of this test bench is presented in order to obtain the performance ranges based on the assumption of the system linearity. Then, to verify the feasibility in fatigue, we conducted a study to establish a characterization curve of a low carbon steel. Nevertheless, this test bench does not distinguish the phases of initiation, propagation and fracture of the crack. We have therefore proposed some ways to assess the cycle number of crack initiation: the first one is based on the slope variation of the strain amplitude measured from strain gauges and the second one uses the resonant frequency drop. We have thus proposed a simple model of nonlinear damage based on the variation of the resonant frequency which also makes it possible to evaluate the cycle number at fracture of the specimens. The experimental fatigue life obtained by this model is compared with the fatigue life obtained by a damage model provided by the literature

APA, Harvard, Vancouver, ISO, and other styles

19

Zeghloul, Abderrahim. "Comparaison de la propagation en fatigue des fissures courtes et des fissures longues." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37619253w.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Linder, Jan. "Fatigue strength of engineering materials - the influence of environment and porosity : the use of linear elastic fracture mechanics to assess the influence of environment and porosity on the fatigue strength for engineering materials /." Doctoral thesis, KTH, Industriell ekonomi och organisation (Inst.), 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4195.

Full text

Abstract:

The objective of this work was to use LEFM in order to assess the detrimental influence of surrounding chloride-containing environments for stainless steels, hardened steel as well as for a cast aluminium alloy. An additional aim was also to use LEFM to assess the influence of porosity on the fatigue properties for different commercial cast aluminium alloys and manufacturing methods. The environmental influence on fatigue performance was mainly evaluated from fatigue crack growth measurements using compact tension (CT) specimens. In addition, fatigue performance in the high cycle regime was studied using spot welded specimens and smooth specimens. Corrosion fatigue tests for stainless steels were performed in different chloride-containing aqueous solutions and compared to the behaviour in air. Variables, which have been investigated, included temperature, redox potential and fatigue test frequency. The environmental influence on fatigue performance has also been compared to localised corrosion properties. Fatigue crack propagation rates were found to be higher in 3% NaCl than in air for all stainless steels investigated. The highest alloyed austenitic steel, 654SMO, showed the least influence of the environment. For duplex stainless steels the environment enhanced fatigue crack propagation rate to a higher degree than for austenitic stainless steels. This is explained by a material-dependent corrosion fatigue mechanism. In the high cycle regime, fatigue properties for spot welded stainless steels specimens were found to be decreased between 30%-40% due to the presence of 3% NaCl. For the hardened steel 100CrMnMo8 a fracture mechanics approach was employed for prediction of corrosion fatigue properties. In this model corrosion pit growth rate and the threshold stress intensity factor for fatigue crack propagation are needed as input parameters. For the high pressure die cast aluminium alloy the environmental influence of fatigue initiation through pre-exposure of smooth specimens was studied. Depending on environment used for pre-exposure, fatigue strength was found to be reduced by up to 50 % compared to the fatigue strength in air. Fatigue strength reduction was clearly associated to corrosion pits in the aluminium material. A fracture mechanics model was further successfully used to predict the environmental influence. The influence of porosity on the fatigue strength for the cast aluminium alloys tested has been described by a Kitagawa diagram. In design, the Kitagawa diagram can be used to predict the largest allowable pore size if the load situation in the component is known. The size of the porosity could either be evaluated directly from x-ray images or from metallographic prepared cross-sections using a method of extreme value analysis
QC 20100907

APA, Harvard, Vancouver, ISO, and other styles

21

Tolunguc, Burcu. "Microstructural And Mechanical Characterization Of Duplex Stainless Steel Grade 2205 Joined By Hybrid Plasma And Gas Metal Arc Welding." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614001/index.pdf.

Full text

Abstract:

In the present study, the applicability of the hybrid plasma arc welding, in which a keyhole is responsible of deep penetration and a filler wire electrode supplies a high deposition rate, was examined. The microstructural evolutions in grade 2205 duplex stainless steel plates joined by keyhole and melt-in techniques were investigated. The specimens obtained from welded plates having thickness of 8 mm were examined via optical and scanning electron microscopy. Metallographic investigations were supported by X-ray diffraction and energy dispersed spectra analyses by characterizing the phases formed after welding. Impact toughness properties, hardness profiles, and crack propagation behavior of welding zones were quantitatively and qualitatively compared for mechanical characterization. Fracture characteristics were determined via scanning electron microscopy examinations. It was observed that single-pass HPA weldment seemed to be free of secondary austenite precipitation in acicular form, which is inevitable in multi-pass conventional arc welding methods. Besides &delta
-ferrite was successfully kept under 70%, which is presented as a limit to not to deteriorate the mechanical properties of DSS. High linear welding speed and high power density supplied by HPAW presented narrower weld metal and heat affected zone with not only lower hardness but also higher impact toughness energies. Synergic effect of the keyhole formed by a plasma arc and the metal transfer supplied by gas metal arc gave reasonable dilution in the weld metal. Furthermore, fatigue crack growth tests revealed that crack propagation rates in HPAW joints were comparable to GMAW joints.

APA, Harvard, Vancouver, ISO, and other styles

22

Suyitno, Budhi-Muliawan. "Etude du comportement en fatigue d'aciers à dispersoïdes." Poitiers, 1988. http://www.theses.fr/1988POIT2342.

Full text

Abstract:

Etude experimentale sur un acier micro-allie dans deux etats microstructuraux bainitique et ferrito-perlitique, soumis a des essais d'endurance, de fatigue oligocyclique et de fissuration. Comparaison avec les resultats obtenus sur un acier conventionnel dans un etat trempe-revenu. Influence de l'environnement (air, vide, azote et traces de vapeur d'eau) et de la frequence d'essai. Discussion du role fragilisant de la vapeur d'eau. Proposition d'un modele de propagation sous environnement actif

APA, Harvard, Vancouver, ISO, and other styles

23

Ouarabi, Mohand Ouramdane. "Influence de la fréquence de chargement sur la résistance à l'amorçage et la croissance des fissures de fatigue dans des aciers utilisés dans des applications mécaniques exigeantes." Thesis, Paris 10, 2018. http://www.theses.fr/2018PA100034.

Full text

Abstract:

Les essais de fatigue peuvent être effectués dans une gamme de fréquences similaire, mais les fréquences les plus élevés sont généralement préférables afin de réduire le temps de test et d'obtenir des résultats dans une période raisonnable. La question reste à savoir si un effet de fréquence existe. Cette étude traite de l'effet de la fréquence de chargement sur la résistance à l'amorçage et à la propagation des fissures sur 3 matériaux (M800HY, CP1000 et DP1180) utilisés dans le domaine automobile. Deux rapports de charge (R=-1 et 0.1) et cinq fréquences de chargement (25 Hz, 30 Hz, 150 Hz et 20 kHz) ont été étudiés. Tout d'abord, nous avons réalisé des calculs par élément finis en dynamique pour dimensionner les éprouvettes et calculer l'étendue du facteur d'intensité de contrainte durant la propagation de la fissure de fatigue. Ensuite, nous avons réalisé des essais d'amorçage et de propagation. Indépendamment de la fréquence de chargement,l'amorçage de la fissure de fatigue est toujours surfacique à cause des concentrations de contraintes dues au processus de laminage ou de l'électro-galvanisation. L'observation des faciès de rupture sur éprouvettes testées à 30 Hz et 20 kHz montre que le mode de propagation est transgranulaire avec quelques localisations de rupture intergranulaire ou par clivage sur la nuance DP1180. Les stries de propagations sont présentes sur les faciès d'éprouvettes M800HY et absentes sur les faciès des deux autres nuances. La nuance DP1180 présente une meilleure résistance à l'amorçage et à la propagation de la fissure de fatigue. Concernant l'effet de la fréquence de chargement, globalement l'amorçage de la fissure de fatigue est dépendante de la fréquence de chargement, par contre, la propagation est indépendante de la fréquence
Fatigue tests can be performed in a similar frequency range, but the higherfrequencies are generally preferable to reduce the test time and obtain results within areasonable time. The question remains whether a frequency effect exists. This study dealswith the effect of the loading frequency on fatigue strength and crack growth of 3 steels(M800HY, CP1000 and DP1180) used in automotive industry. Two load ratios (R = -1 and0.1) and five load frequencies (25 Hz, 30 Hz, 150 Hz and 20 kHz) were studied. First, weperformed dynamics finite element method to calculate the dimensions of the specimens(to vibrate with a resonance at 20 kHz), and, the stress intensity range as a function of the length of crack. Then, we have done some test on fatigue crack initiation and propagation. Whatever the loading frequency, the initiation of the fatigue crack is always on the surfacebecause of the stress concentrations due to the rolling process or the electro-galvanization.The observation with SEM of fracture surface of the specimens tested at 30 Hz and 20 kHzshows that the mode of propagation is transgranular with some locations of intergranularfailure or by cleavage on DP1180 grade. The fatigue striation on fracture surface arepresent on the M800HY and absent on the other two materials. The grade DP1180 has abetter resistance to the initiation and propagation of the crack. Regarding the effect ofloading frequency, overall the initiation of the fatigue crack is dependent on the loadingfrequency, however, the propagation is independent of the loading frequency

APA, Harvard, Vancouver, ISO, and other styles

24

Jendoubi, Khemaïs. "Mesures locales et globales des paramètres mécaniques gouvernant la fissuration par fatigue." Poitiers, 1987. http://www.theses.fr/1987POIT2312.

Full text

Abstract:

Etude sur l'alliage d'aluminium a haute resistance 2024t351 et sur l'acier inoxydable aisi316. Determination, par mesures locales a l'aide de microjauge, du champ de deformation existant au voisinage de la pointe de fissure pour differentes conditions de chargement. Mesures globales a l'aide d'un capteur de deplacement a lames monte sur l'axe de chargement, de l'energie q dissippee par cycle et le facteur d'intensite de contraintes effectif. Mesure de l'ouverture de fissure par microscopie electronique a balayage. Proposition de la modelisation experimentale du champ de deformation pour des facteurs d'intensite de contrainte correspondant aux valeurs de la loi de paris

APA, Harvard, Vancouver, ISO, and other styles

25

Solignac, Marie-Paul. "Etude du comportement a la fissuration en fluage et en fatigue d'aciers inoxydables austenitiques z2 cnd 17-12 (316 l) a 550 c." Paris 6, 1986. http://www.theses.fr/1986PA066540.

Full text

Abstract:

Description du comportement du materiau en fluage par une loi puissance. Etude des relations entre la vitesse de propagation et les parametres mecaniques. Prevision de la duree de vie. En fatigue, etude de l'influence des parametres experimentaux et de certains traitements (vieillissement, ecrouissage) sur la fissuration. Etude par microscopie electronique des modes de rupture, ainsi que de la microstructure necessaire a la comprehension du comportement de l'acier

APA, Harvard, Vancouver, ISO, and other styles

26

DOQUET-DARIDON, VERONIQUE. "Comportement et endommagement de deux aciers a structure cubique centree et cubique a faces centrees, en fatigue oligocyclique, sous chargement multiaxial non-proportionnel." Paris, ENMP, 1989. http://www.theses.fr/1989ENMP0137.

Full text

Abstract:

Precision des mecanismes de durcissement cyclique anormal manifeste par certains materiaux sous chargement non proportionnel, ainsi que des reductions d'endurance qui l'accompagnent. Etude dans le cas de l'acier inoxydable austenitique 316 l et d'un acier doux

APA, Harvard, Vancouver, ISO, and other styles

27

Scharnweber, Michael. "Initiierung und Ausbreitung kurzer Ermüdungsrisse in ein- und zweiphasigem Edelstahl." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-143798.

Full text

Abstract:

In der vorliegenden Arbeit wurden Untersuchungen zum Initiierungs- und Ausbreitungsverhalten kurzer Ermüdungsrisse in einem austenitischen sowie einem austenitisch-ferritischen Edelstahl durchgeführt. Dazu erfolgten zyklische Verformungsexperimente sowohl ex situ als auch in situ im Rasterelektronenmikroskop. Die Auswertung der Experimente erfolgte im Rasterelektronenmikroskop sowohl abbildend in verschiedenen Modi als auch über Rückstreuelektronenbeugungsmessungen. Bezüglich der Rissinitiierung wurde eine Häufigkeitsverteilung der Rissinitiierungsorte für beide Stähle erstellt. Die dabei ermittelte stark unterschiedliche Häufigkeit für die transkristalline Rissinitiierung in der austenitischen Phase konnte mit der unterschiedlichen Textur und Mikrostruktur der beiden Stähle in Zusammenwirken mit den elastischen Eigenschaften der beiden Phasen erklärt werden. Für die Rissausbreitung wurde gezeigt, dass eine Korrelation zwischen der Risslänge und der Rissausbreitungsrate besteht, aus der hervorgeht, dass die Übergangsrisslänge zwischen den Bereichen der mikrostrukturell und mechanisch kurzen Risse etwa einen Korndurchmesser beträgt. Anhand der in situ Messung der (plastischen) Rissöffnung und -scherung wurden die Unterschiede im Rissausbreitungsverhalten in den verschiedenen Phasen herausgearbeitet. Für die austenitische Phase ergibt sich dabei ein öffnungsdominierter und für die ferritische Phase ein scherungsdominierter Mechanismus. Die im Ferrit auftretenden zwei unterschiedlichen Ausprägungen der Oberflächenrisspfade („rau“ und „glatt“) konnten mit der Orientierung der jeweils risstragenden Körner korreliert werden. In Zusammenwirken mit der beobachteten Systematik der Anordnung der Gleitspuren um kurze Risse im Ferrit sowie einer Analyse der Spannungsverteilung um die Rissspitze wurde ein Modell des Rissausbreitungsmechanismus\' erstellt sowie die bisher in der Literatur vorherrschende These des Einfachgleitens widerlegt. Schließlich konnte die Barrierenwirkung von Korn- und Phasengrenzen sowohl anhand der Messung der Rissausbreitungsrate als auch der plastischen Rissöffnung bzw. -scherung gezeigt und daraus Rückschlüsse auf die Ausdehnung der plastischen Zone vor der Rissspitze gezogen werden. Gleichzeitig wurde dabei die Korrelation zwischen Rissausbreitungsrate und plastischer Rissöffnung bzw. -scherung nachgewiesen.

APA, Harvard, Vancouver, ISO, and other styles

28

Holáň, Libor. "Šíření dlouhých únavových trhlin v austenitické oceli při smykových módech II a III." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2013. http://www.nusl.cz/ntk/nusl-234164.

Full text

Abstract:

This work is focused on the realization of experiment allowing simultaneous loading under mode II and III in a single circular specimen. Proposed experiment allowed to minimize crack closure during the cyclic loading and obtained values of thresholds of stress intensity range can be considered to be very close to effective values. This was attained by means of an unique experimental devices and procedure of preparation of pre-crack of specimen with circumferential notch, which was made of stainless austenitic steel. The obtained values were compared with theoretical models with the support of molecular dynamics and ab-anitio calculation. Based on observation was found out, that fatigue crack propagation is controlled by decohesion model in austenitic steel. The morphology of fracture surfaces was studied by means of optical chromatographie and 3D stereophotogrammetry, which allowed a comparison of created morphology under shear modes II and III. Morphology of fracture surface formed (static and cyclic loading) by pre-crack was also studied by means of selected roughness parameters. The mechanism of deflection (kink) of crack growth under mode II was defined.

APA, Harvard, Vancouver, ISO, and other styles

29

Kusko, Chad S. "Fatigue crack propagation of stainless steel welds /." Diss., 2002. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3048963.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Achilles, Roy Derrick. "Corrosion fatigue crack propagation in pressure vessel steel." Thesis, 2014. http://hdl.handle.net/10539/15247.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Tau, Lin, and 陶霖. "Microstructural Effects of AISI 4130 Steel on Hydrogen Assisted Fatigue Crack Propagation." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/20031903768876510369.

Full text

Abstract:

博士
國立臺灣大學
材料科學(工程)研究所
84
The main objective of this research has been to carry out a systematic study on the influences of various microstructures of a popular structural steel, AISI 4130 steel, on hydrogen-enhanced fatigue crack propagation. Some important effects have been discussed in this work, including those of microstructure, strength, hydrogen permeation, tempering temperature for tempered martensitic structures, and isothermal treating temperature for bainitic structures. In this work, some conclusions could be outlined: (1) For ferrite/pearlitic structures, the distribution of ferrite/pearlite along the path of hydrogen penetration affected hydrogen diffusivity deeply. Then the results of hydrogen diffusivity can be applied to explain the hydrogen-assisted fatigue crack propagation behavior of the banded and random ferrite/ pearlite structures successfully. (2) The variation of hydrogen-assisted fatigue crack growth rates of specimens sampled from different orientations for banded ferrite/ pearlitic structure was very significant, slight for random in the random ferrite/pearlitic structure. (3) A similar hydrogen-enhanced fatigue crack growth behavior and a transgranular fracture mode were found in bainitic structures, though they have different tensile strength and hydrogen permeation rate. (4) The hydrogen-assisted fatigue crack propagation rate of tempered martensitic structures increased as yield strength increased. In higher strength tempered martensites, an irregular fracture mode, in which the intergranular crack propagated easily near surface of specimen, was found. (5) The microstructural effect was the dominant factor on the hydrogen-assisted fatigue crack growth behavior. Alternatively, the strength effects could not been featured systematically.

APA, Harvard, Vancouver, ISO, and other styles

32

Ferreira, João Pedro Mota. "Pre-strain effects on fatigue crack propagation behaviour of a pressure vessels steel." Dissertação, 2017. https://hdl.handle.net/10216/106334.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Ferreira, João Pedro Mota. "Pre-strain effects on fatigue crack propagation behaviour of a pressure vessels steel." Master's thesis, 2017. https://hdl.handle.net/10216/106334.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

Zhang, Jun-Hao, and 張峻豪. "The mean stress effect on Fatigue crack propagation rate and thershold for interstitial-free steel." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/93f4ve.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Curle, Ulyate Andries. "Near-threshold fatigue crack growth behaviour of mild steel in steam during rotating bending." Diss., 2007. http://upetd.up.ac.za/thesis/available/etd-12192007-150550.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

(6620411), Leslie E. Campbell. "A Benchmark for Evaluating Performance in Visual Inspection of Steel Bridge Members and Strategies for Improvement." Thesis, 2019.

Find full text

Abstract:

Visual inspection is the primary means of ensuring the safety and functionality of in-service bridges in the United States and owners spend considerable resources on such inspections. While the Federal Highway Administration (FHWA) and many state departments of transportation have guidelines related to inspector qualification, training, and certification, an inspector’s actual capability to identify defects in the field under these guidelines is unknown. This research aimed to address the knowledge gap surrounding visual inspection performance for steel bridges in order to support future advances in inspection and design procedures. Focusing primarily on fatigue crack detection, this research also considered the ability of inspectors to accurately and consistently estimate section loss in steel bridge members.

Inspection performance was evaluated through a series of simulated bridge inspections performed in representative in-situ conditions. First, this research describes the results from 30 hands-on, visual inspections performed on full size bridge specimens with known fatigue cracks. Probability of Detection (POD) curves were fit to the inspection results and the 50% and 90% detection rate crack lengths were determined. The variability in performance was large, and only a small amount of the variance could be explained by individual characteristics or environmental conditions. Based on the results, recommendations for improved training methods, inspection procedures, and equipment were developed. Above all, establishment of a performance based qualification system for bridge inspectors is recommended to confirm that a satisfactory level of performance is consistently achieved in the field.

Long term, managing agencies may eschew traditional hands-on bridge inspection methods in favor of emerging technologies imagined to provide improved results and fewer logistical challenges. This research investigated the potential for unmanned aircraft system (UAS) assistance during visual inspection of steel bridges. Using the same specimens as in the hands-on inspections, four UAS-assisted field inspections and 19 UAS-assisted desk inspections were performed. A direct comparison was made between performance in the hands-on and UAS-assisted inspections, as well as between performance in the two types of UAS-assisted inspections. Again, significant variability was present in the results suggesting that human factors continue to have a substantial influence on inspection performance, regardless of inspection method.

Finally, to expand the findings from the crack detection inspections, the lower chord from a deck truss was used to investigate variability in the inspection of severely corroded steel tension members. Five inspectors performed a hands-on inspection of the specimen and four engineers calculated the load rating for the same specimen. Significant variability was observed in how inspectors recorded thickness measurements during the inspections and engineers interpreted the inspection reports and applied the code requirements.

APA, Harvard, Vancouver, ISO, and other styles

37

Scharnweber, Michael. "Initiierung und Ausbreitung kurzer Ermüdungsrisse in ein- und zweiphasigem Edelstahl." Doctoral thesis, 2013. https://tud.qucosa.de/id/qucosa%3A28094.

Full text

Abstract:

In der vorliegenden Arbeit wurden Untersuchungen zum Initiierungs- und Ausbreitungsverhalten kurzer Ermüdungsrisse in einem austenitischen sowie einem austenitisch-ferritischen Edelstahl durchgeführt. Dazu erfolgten zyklische Verformungsexperimente sowohl ex situ als auch in situ im Rasterelektronenmikroskop. Die Auswertung der Experimente erfolgte im Rasterelektronenmikroskop sowohl abbildend in verschiedenen Modi als auch über Rückstreuelektronenbeugungsmessungen. Bezüglich der Rissinitiierung wurde eine Häufigkeitsverteilung der Rissinitiierungsorte für beide Stähle erstellt. Die dabei ermittelte stark unterschiedliche Häufigkeit für die transkristalline Rissinitiierung in der austenitischen Phase konnte mit der unterschiedlichen Textur und Mikrostruktur der beiden Stähle in Zusammenwirken mit den elastischen Eigenschaften der beiden Phasen erklärt werden. Für die Rissausbreitung wurde gezeigt, dass eine Korrelation zwischen der Risslänge und der Rissausbreitungsrate besteht, aus der hervorgeht, dass die Übergangsrisslänge zwischen den Bereichen der mikrostrukturell und mechanisch kurzen Risse etwa einen Korndurchmesser beträgt. Anhand der in situ Messung der (plastischen) Rissöffnung und -scherung wurden die Unterschiede im Rissausbreitungsverhalten in den verschiedenen Phasen herausgearbeitet. Für die austenitische Phase ergibt sich dabei ein öffnungsdominierter und für die ferritische Phase ein scherungsdominierter Mechanismus. Die im Ferrit auftretenden zwei unterschiedlichen Ausprägungen der Oberflächenrisspfade („rau“ und „glatt“) konnten mit der Orientierung der jeweils risstragenden Körner korreliert werden. In Zusammenwirken mit der beobachteten Systematik der Anordnung der Gleitspuren um kurze Risse im Ferrit sowie einer Analyse der Spannungsverteilung um die Rissspitze wurde ein Modell des Rissausbreitungsmechanismus\' erstellt sowie die bisher in der Literatur vorherrschende These des Einfachgleitens widerlegt. Schließlich konnte die Barrierenwirkung von Korn- und Phasengrenzen sowohl anhand der Messung der Rissausbreitungsrate als auch der plastischen Rissöffnung bzw. -scherung gezeigt und daraus Rückschlüsse auf die Ausdehnung der plastischen Zone vor der Rissspitze gezogen werden. Gleichzeitig wurde dabei die Korrelation zwischen Rissausbreitungsrate und plastischer Rissöffnung bzw. -scherung nachgewiesen.

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Steel bridges, the fatigue crack propagation'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles