Дисертації з теми "Failure strength"
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1
Weernink, Corinne M. "Heart failure and respiratory muscle strength." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0001/MQ42222.pdf.
2
Björklund, Oscar. "Ductile Failure in High Strength Steel Sheets." Doctoral thesis, Linköpings universitet, Hållfasthetslära, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-105213.
Анотація:
Developments in computer-aided engineering and the rapid growth of computational power have made simulation-driven process and product development efficient and useful since it enables detailed evaluation of product designs and their manufacturing processes. In the context of a sheet metal component, it is vital to predict possible failure both during its forming process and its subsequent usage. Accurate numerical models are needed in order to obtain trustworthy simulation results. Furthermore, the increasing demands imposed on improved weight-to-performance ratio for many products endorse the use of high-strength steels. These steels often show anisotropic behaviour and more complex hardening and fracturing compared to conventional steels. Consequently, demand for research on material and failure models suitable for these steels has increased. In this work, the mechanical and fracture behaviour of two high-strength steels, Docol 600DP and Docol 1200M, have been studied under various deformation processes. Experimental results have been used both for material characterisation and for calibration of fracture criteria. One major requirement as concerns the fracture criteria studied is that they should be simple to apply in industrial applications, i.e. it should be possible to easily calibrate the fracture criteria in simple mechanical experiments and they should be efficient and accurate. Consequently, un-coupled phenomenological damage models have been the main focus throughout this work. Detailed finite element models including accurate constitutive laws have be used to predict and capture material instabilities. Most of the fracture criteria studied are modifications of the plastic work to fracture. Ductile tensile and ductile shear types of fracture are of particular interest in sheet metal applications. For these fractures the modification of the plastic work relates to void coalescence and void collapse, respectively. Anisotropy in fracture behaviour can be captured by the introduction of a material directional function. The dissertation consists of two parts. The first part contains theory and background. The second consists of five papers.
3
Farrell, Robert William. "Structural Features Related to Tree Crotch Strength." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/32619.
Анотація:
Crotches were cut out of red maple (Acer rubrum), callery pear (Pyrus calleryana), and sawtooth oak (Quercus acutissima) trees (2.5â -7â d.b.h.) and then pulled apart in an engineering testing machine to identify physical parameters correlated with crotch strength. Parameters measured included the diameter of the branch and of the trunk above and below the crotch, angle of the branch and branch bark ridge, and the length of the crotch and the branch bark ridge. The force required to break each sample was used to calculate breaking strength based on the formula for bending stress. Each parameter was tested for correlation with crotch strength within the individual species and for the three species combined. The ratio of branch diameter over crotch width had the highest correlation coefficient for crotch strength. Branch angle was also correlated with crotch strength but not as highly as the ratio of the diameters. V-shaped crotches (those with included bark) were significantly weaker than U-shaped crotches for all species. The ratio of the two stem diameters greatly influenced the manner in which the crotches broke. In crotches where the branch diameter was 2/3 the size of the trunk or smaller, the crotch broke by being pulled directly out of the trunk. Crotches with branches more than 2/3 the diameter of the trunk broke when the trunk split longitudinally and had significantly lower strength values. These results indicate that increased crotch strength results from a small branch diameter relative to that of the trunk.Master of Science
4
Björklund, Oscar. "Modelling of Failure in High Strength Steel Sheets." Licentiate thesis, Linköpings universitet, Hållfasthetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-77759.
Анотація:
In this theses the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M are studied. Constitutive laws and failure models are calibrated and veried by the use of experiments and numerical simulations. For the constitutive equations, an eight parameter high exponent yield surface has been adopted, representing the anisotropic behaviour, and a mixed isotropic-kinematic hardening has been used to capture non-linear strain paths. For ductile sheet metals three dierent failure phenomena have been observed: (i) ductile fracture, (ii) shear fracture, and (iii) instability with localised necking. The models for describing the dierent failure types have been chosen with an attempt to use just a few tests in addition to these used for the constitutive model. In this work the ductile and shear fracture have been prescribed by models presented by Cockroft-Latham and Bressan-Williams, respectively. The instability phenomenon is described by the constitutive law and the nite element models. The results obtained are in general in good agreement with test results. The thesis is divided into two main parts. The background, theoretical framework, mechanical experiments and nite element models are presented in the rst part. In the second part, two papers are appended.In publication incorrect ISBN: 9789175198955
5
De-Vilder, Saskia Joan. "Controls on the evolution of strength and failure style in shallow rock slope failures." Thesis, Durham University, 2018. http://etheses.dur.ac.uk/12819/.
Анотація:
Rock fall failure comprises fracturing through zones of intact rock, known as rock bridges, and kinematic release along discontinuity surfaces. Understanding controls on magnitude – frequency relationships of rockfalls, and their associated failure characteristics aids susceptibility analysis and interpretation of pre-failure deformation. For failure to occur, these rock bridges must have been weakened, with this damage accumulation driven by a suite of weathering processes. This thesis aims to explore the spatial and temporal controls on weathering induced strength degradation and its subsequent influence on the mechanics of rockfall detachment. Within this, it examines the role of gravitational ambient stress, as dictated by slope topography and rock mass structure, which recent research suggests influences the efficiency of weathering processes. The project integrates field observations, analogue experiments and numerical modelling over varying spatial scales. Terrestrial laser scanning and gigapixel photography are combined to forensically map rock bridge attributes within rockfall detachment surfaces. The role of slope geometry and rock mass structure in concentrating stress is assessed via conceptual finite element models. Finally, samples are subjected to stress conditions induced by the slope structure and environmental conditions in a series of weathering analogue experiments. Together, these results indicate that weathering significantly reduces intact rock strength with areas of stress concentration purely a mechanical control on rockfall release rather than a temporal control on weakening. Weaker rock is characterised by substantial post-peak strength, which requires multiple stages of brittle fracture before ultimate failure occurs. This in turn influences the stages of failure required through rock bridges before final failure, with this number of rock bridges dependent on rockfall size. Mechanically, failure mode is dependent on rock bridge proportion, distribution and location for individual rockfalls. A conceptual model describes magnitude-frequency characteristics and the observable pattern of pre-failure deformation expected for different stages of weathering.
6
Alkhalil, M. F. S. "Strength of filament wound structures under complex stresses." Thesis, University of Manchester, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387260.
7
Prasad, Hanasoge Saraswathi Deepthi. "Bearing strength and failure behavior of hybrid composite laminates." Thesis, Linköpings universitet, Konstruktionsmaterial, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-170914.
Анотація:
Composite layups have been continuously used over many years in various applications. It is necessary to optimize its composition by studying various parameters influencing the mechanical properties and studying the failure behavior. In this master thesis, the objective was to test five different plies manufactured using thick and thin plies and various combinations of thick and thin laminates called hybrid laminates. Bearing tests are performed for five layups with each layer has its thickness varying from 40μm to 130μm, and a combination called hybrid laminate, and the results from the tests are investigated. The resulting system has a good performance with onset damage above 700 MPa and an ultimate failure above 1130 MPa, using fibers' full potential. Also, the different failure modes like fiber kinking, matrix crack, delamination, and their effect on the layup's strength are investigated using fractography. This paper also investigates the influences of the thickness of the laminate on the strength of hybrid composites jointed using different mechanisms, and its failure modes are checked. Results from this experiment are used to validate in the form of FEM model, which is a part of an internal project at RISE SICOMP AB. This thesis is suitable for an engineering student in mechanical engineering, material science interested in composite materials and fractography.
8
Noury, Pourya. "On failure of high strength steel bridge roller bearings." Doctoral thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-65215.
Анотація:
This thesis is concerned with failure analysis of high strength steel bridge roller bearings.Paper Adescribes how the commonly used Hertz formulas for contact stresses underestimate the actual stresses in practice due to temperature differences, misalignments and other construction-related conditions. In this paper, finite element analyses of bridge roller bearings were carried out to investigate the accuracy of the traditional roller bearing design rules in view of issues such as girder deformability, misalignment imperfections and material nonlinearity. The results first indicated that roller bearings develop contact stress concentrations at the outer edges of the rollers. Second, it was shown that the contact stresses are very sensitive to misalignment imperfections between the bridge girder and the abutment. Third, it was shown that the roller bearings develop inelastic deformation at relatively low loads in relation to the design load.In Paper B, the finite element method was employed to gain an understanding of the behaviour of a cracked bridge roller bearing in service. The cracked roller was considered as a two-dimensional edge-cracked disk subjected to a diametrical compressive line load. The crack parameters, stress intensity factor Mode I, KI and Mode II ,KII were calculated for the relevant load configuration and angle of disk rotation. The calculated data for KIwere also used to check the accuracy of approximate stress intensity factor solutions reported earlier for Mode I. For plain Mode I loading very good agreement was found between the obtained results and data presented in Schindler and Morf (1994). Paper Cis aimed at finding the likely failure mechanism of a bridge roller bearing made of high strength martensitic stainless steel. Spectroscopy and finite element stress analysis of the roller indicated that an initial radial surface crack, found at an end face of the roller and close to the contact region, was induced by stress corrosion cracking (SCC). The initial crack subsequently changed shape and increased in size under growth through fatigue and finally formed a quarter-circle radial crack centred on the end face corner of the roller. Numerically computed stress intensity factors for the final crack showed that crack loading was predominantly in Mode II. For a crack size as observed on the fracture surface, the maximum service load, as specified by the manufacturer, enhanced by a certain roller bearing misalignment effect, was sufficient for failure through fracture.InPaper D, after a brief summary of the history of high strength stainless steel bearings, the paper reviews service experience of failed bearings in Sweden and elsewhere. Accompanying finite element analyses were performed in order to gain better insight into the likely failure mechanism. Finally, thiscomprehensive review leads to a conclusion that identifies the causes of the failures occurred and makes some recommendations.
9
Zhang, Xuesong, and n/a. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion." Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20051104.153239.
Анотація:
Failure criteria play a vital role in the numerical analysis of reinforced concrete structures. The current failure criteria can be classified into two types, namely the empirical and theoretical failure criteria. Empirical failure criteria normally lack reasonable theoretical backgrounds, while theoretical ones either involve too many parameters or ignore the effects of intermediate principal stress on the concrete strength. Based on the octahedral shear stress model and the concrete tensile strength under the state of triaxial and uniaxial stress, a new failure criterion, that is, the simplified unified strength theory (UST), is developed by simplifiing the five-parameter UST for the analysis of reinforced concrete structures. According to the simplified UST failure criterion, the concrete strength is influenced by the maximum and intermediate principal shear stresses together with the corresponding normal stresses. Moreover, the effect of hydrostatic pressure on the concrete strength is also taken into account. The failure criterion involves three concrete strengths, namely the uniaxial tensile and compressive strengths and the equal biaxial compressive strength. In the numerical analysis, a degenerated shell element with the layered approach is adopted for the simulation of concrete structures. In the layered approach, concrete is divided into several layers over the thickness of the elements and reinforcing steel is smeared into the corresponding number of layers of equivalent thickness. In each concrete layer, three-dimensional stresses are calculated at the integration points. For the material modelling, concrete is treated as isotropic material until cracking occurs. Cracked concrete is treated as an orthotropic material incorporating tension stiffening and the reduction of cracked shear stiffness. Meanwhile, the smeared craclc model is employed. The bending reinforcements and the stirrups are simulated using a trilinear material model. To verify the correctness of the simplified UST failure criterion, comparisons are made with concrete triaxial empirical results as well as with the Kupfer and the Ottosen failure criteria. Finally, the proposed failure criterion is used for the flexural analysis of simply supported reinforced concrete beams. Also conducted are the punching shear analyses of single- and multi-column-slab connections and of half-scale flat plate models. In view of its accuracy and capabilities, the simplified UST failure criterion may be used to analyse beam- and slab-type reinforced concrete structures.
10
Colavito, Kyle Wesley. "Peridynamics for Failure and Residual Strength Prediction of Fiber-Reinforced Composites." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311300.
Анотація:
Peridynamics is a reformulation of classical continuum mechanics that utilizes integral equations in place of partial differential equations to remove the difficulty in handling discontinuities, such as cracks or interfaces, within a body. Damage is included within the constitutive model; initiation and propagation can occur without resorting to special crack growth criteria necessary in other commonly utilized approaches. Predicting damage and residual strengths of composite materials involves capturing complex, distinct and progressive failure modes. The peridynamic laminate theory correctly predicts the load redistribution in general laminate layups in the presence of complex failure modes through the use of multiple interaction types.This study presents two approaches to obtain the critical peridynamic failure parameters necessary to capture the residual strength of a composite structure. The validity of both approaches is first demonstrated by considering the residual strength of isotropic materials. The peridynamic theory is used to predict the crack growth and final failure load in both a diagonally loaded square plate with a center crack, as well as a four-point shear specimen subjected to asymmetric loading.This study also establishes the validity of each approach by considering composite laminate specimens in which each failure mode is isolated. Finally, the failure loads and final failure modes are predicted in a laminate with various hole diameters subjected to tensile and compressive loads.
11
Manger, Christopher I. C. "Failure of notched woven GFRP composites : damage analysis and strength modelling." Thesis, University of Surrey, 1999. http://epubs.surrey.ac.uk/738/.
12
Wu, Yang. "Experimental and numerical study on failure strength of aspirated cell membrane." Thesis, University of Iowa, 2017. https://ir.uiowa.edu/etd/6018.
Анотація:
The objective of this work is to develop an innovative and quantitative method to study cell failure under fluidic pressure to understand cell membrane mechanical properties. Due to lack of experimental data related to cell failure property, the current research focuses on investigating the cell failure using a micro pipette aspiration experiment method to elaborate gradually increasing hydrostatic pressure to the cell causing the membrane to deform and eventually rupture. Based on our observation, the prostate cancer cells (PC-3) deformed into a deflated and flattened shape under higher hydrostatic pressure (249 Pa) while prostate epithelial cells (PrEC LH) cells generate a spherical and rounded shape. The stress along the cell membrane was estimated from the curvature data captured from the 2D microscopic images for each pressure magnitude to quantify the damage before rupture state. From the results, non-transformed prostate epithelial cells (PrEC LH) presented a stiffer and rupture resilient property compared to transformed prostate cancer cells (PC-3) which presented a softer and vulnerable property. Besides, the alteration of shape of the aspirated membrane directly affected the stress distribution over the membrane and as a result, provoked membrane failure. Multiple pieces of research have shown a higher stiffness of healthy cells compared to cancer cells including one of the previous studies done by our group which have also found that cancer cell tends to become stiffer after exposing to fluid shear stress. The discovery of this cellular behavior and novel numerical quantification method of cell failure could advance the study of cancer cell membrane failure, cellular matrix structure, response to mechanical loadings and potentially foundation in developing new treatment for cancer other than destructive chemical treatment.
13
Wang, Yueyue. "Theoretical experiment of GISSMO failure model for Advanced High Strength Steel." Thesis, Högskolan Väst, Avdelningen för produktionssystem (PS), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-11658.
Анотація:
When developing an electric vehicle, it is essential to evaluate the deformation in and around the battery box for different crash scenarios, and it is necessary to develop a more advanced model that would take into account all the stress modes. Thanks to the excellent properties of Advanced High Strength Steel (AHSS) combine with high strength for more safety and weight reduction for less exhaust emission, AHSS is more and more commonly used in automobile industry. The material employed in this project is DOCOL 900M and it is a martensitic steel with yield strength higher than 700MPa. The focus of the current work is to describe the experimental setup for the GISSMO model used in LS-DYNA. A number of experimental methods and theories have been reviewed. Different geometries of the test specimens under different stress triaxialities have been discussed. The study also compares the accuracy and robustness of each of the testing methods and setups. The effect of anisotropy of materials on the mechanical properties was studied. Some summaries about how to reduce errors in the experiment under the conditions of low costing and high efficiency have been discussed. According to the stress-strain response of ductile materials, the parameters of plasticity model can be calibrated. The material can be implemented in finite element software to calibrate the parameters of damage and the prediction of material failure can be achieved. The experiment and simulation are always good to be used together in the research.
14
Maguire, Dawn Laurel. "Failure mechanisms in VLSI bonds subjected to mechanical and environmental stresses." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/30523.
15
Gebhart, Tristan Reyes. "POST-LIQUEFACTION RESIDUAL STRENGTH ASSESSMENT OF THE LAS PALMAS, CHILE TAILINGS FAILURE." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1662.
Анотація:
Assessment of post-liquefaction residual strength is needed for the development of empirically-based, predictive correlations for earthquake engineering design. Previous practice commonly assigned negligible strengths to liquefied materials for engineering analysis, producing overly-conservative designs. Increasingly available case history data, and improved analytical tools have allowed for more accurate and less overly-conservative estimation of soil residual strength, improving empirical predictive models. This study provides a new case history to the limited suite of (approximately 30) liquefaction failure case histories available for post-liquefaction in-situ strength predictive correlations.
This case history documents the Las Palmas gold mine tailings dam failure, resulting from seismic-induced liquefaction during the moment magnitude 8.8 February 27, 2010 Maule, Chile earthquake; the sixth largest since 1900. Forensic analysis provides reasonably well-constrained values of 1) back-calculated representative post-liquefaction residual strength, 2) representative penetration resistance, and 3) representative vertical effective stress along the suspected liquefied failure surface.
This study employs the incremental momentum method to incorporate momentum effects of a moving soil mass. The incremental momentum method requires a series of cross sections animating the geometry of failure progression from initiation to termination, converging on the observed final geometry. Using interpreted soil strength characteristics, an iterative procedure approximates the back-calculated value of post-liquefaction residual strength.
Findings of this case history plot well with existing empirical deterministic regression charts and are in general agreement with previous, related efforts. Results yield representative, well-constrained values of: 1) post-liquefaction residual strength ≈ 173 psf, 2) penetration resistance of N1,60,CS ≈ 5 and N1,60 ≈ 2.5, and 3) vertical effective stress ≈ 4,300 lb/ft2, or ≈ 2.0 atm.
16
Hamil, Stephen J. "Reinforced concrete beam-column connection behaviour." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/1523/.
17
McClain, Michael Patrick. "A micromechanical model for predicting tensile strength." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-10052007-143117/.
18
Eman, Jesper. "Study and characterization of localization and failure behaviour of ultra high strength steel." Licentiate thesis, Luleå : Luleå tekniska universitet/Tillämpad fysik, maskin- och materialteknik/Hållfasthetslära, 2007. http://epubl.ltu.se/1402-1757/2007/23/.
19
Rae, Philip John. "Quasi-static studies of the deformation, strength and failure of polymer bonded explosives." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621753.
20
Haberle, Jurgen. "Strength and failure mechanisms of unidirectional carbon fibre-reinforced plastics under axial compression." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/11390.
21
Hughes, Philip Daniel. "Development and clinical application of tests of respiratory muscle strength." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391625.
22
Junaideen, Sainulabdeen Mohamed. "Failure of saturated sandy soils due to increase in pore water pressure." Thesis, Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B30708540.
23
Dong, Xudong. "Stress distribution and failure mode of dental ceramic structures under Hertzian indentation." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22989560.
24
Hess, Paul E. "Uncertainty in marine structural strength with application to compressive failure of longitudinally stiffened panels." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-01242009-063009/.
25
Patten, Scott. "Inelastic Analysis of Tripping Failure of Stiffened Steel Panels due to Stiffener Flange Transverse Initial Eccentricity." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/32505.
Анотація:
This thesis studies the present methods used to predict the ultimate tripping strength of stiffened panels under compressive axial stress. The current methods involve the use of a bifurcation, or eigenvalue, approach to predicting failure stress. The effects of initial transverse eccentricity of the stiffener are ignored using such a method. Six panels were modeled and tested with ABAQUS, a finite element software package, and the results were compared to output from ULSAP, a closed-form ultimate strength analysis program. The ultimate strengths predicted by ABAQUS changed with the influence of initial deflection of the stiffener flange, while the results from ULSAP did not change. This thesis attempts to use beam-column analysis on the imperfect stiffener flange to predict the tripping strength. It was determined that the procedure presented in this thesis does not accurately model the true failure mode of stiffeners in tripping. The resulting ultimate strengths are extremely conservative and neglect the importance of the stiffener webâ s role in tripping. Future work is recommended to expand on these findings and to incorporate the influence of the stiffener web into a beam-column solution.Master of Science
26
Zeeshan, Muhammad. "Tensile Strength of Bonded Lap-mitered Butt-Joints between Layered CFRP Bands : -In collaboration with RUAG Space AB." Thesis, KTH, Lättkonstruktioner, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-172209.
Анотація:
Joints in structures always cause strength reduction. The percentage of strength reduction depends upon the selection of several factors such as: type of joint (i.e. adhesive or mechanical), technique of joint (i.e. lap joint, butt joint etc.), geometry of joint, mode of load application etc. Here in this research, the strength of adhesively bonded butt joints with several geometries, later referred as joint angles, is investigated under uniaxial tension loading. Adhesively bonded simple butt joints, where joints are placed perpendicular to the loading direction are in common practice mainly because of ease in manufacturing process. But when the joint is fabricated with an angle respective to the loading direction, the geometry of the joint itself affects the strength of the joint significantly. Without going too deep into other factors that affects the joint strength such as manufacturing techniques, manufacturing defects, material behavior etc. only the geometry of the joint is considered and it is evaluated whether it is worth to change the joint geometry or not. The significant issue in adhesive joint technology is the prediction of joint strength. However, an approach similar to plastic yield criterion later referred as elastic limit offset method (attempted for 0.025% offset) is considered to estimate the linear elastic limit. Since RUAG Space AB (the industry for which this project is performed) is only interested in the linear elastic regime of the stress-strain curve, therefore the elastic limit offset method is considered to be the suitable one. The present work is concerned with the study of adhesively bonded angled butt joint vs. strength behavior. The strength of adhesively bonded butt joints is examined for several butt joint angles under uniaxial tensile loading. The employed butt joint angles are: 0°, 30°, 45°, 60° and 75°. The main objective of the current investigation is to find the joint angle that has the highest strength or the highest capability of load transfer. In addition to the above, the influence of the joint on the stress field, joint strength and type of failure is also evaluated using DSP (Digital Speckle Photography) technique and simulated using well known finite element tool, ABAQUS. It is observed that specific strength of the joint is greatly influenced with joint angle. The 45° joint showed the highest elasticity and failed like ductile behavior whereas 75° joint showed the lowest elasticity and failure was purely brittle. Moreover, post-failure inspection of fractured surfaces showed cohesive failure (failure within adhesive layers) for 0°, 30°, 45° and 60°whereas 75° showed composite or adherend failure. The simulation is performed for each joint angle. However to validate the model only 45° and 75° joints results are compared with experimental results and plotted in the report. The simulation results of these angles showed good agreement with the experimental ones. Moreover, the stress fields for each joint angle are captured (from ABAQUS), showing that all joints are susceptible to inter-laminar shear. Besides, the relative slip between the top and middle adherends is also calculated, the results show that, the 45° joint has higher tendency of relative slip than others.
27
Krishna, Chalavadi Sai. "Parameter identification of GISSMO damage model for DOCOL 900M high strength steel alloy : Usage of a general damage model coupled with material modeling in LS-DYNA for Advanced high strength steel crashworthiness simulations." Thesis, Högskolan Väst, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-11745.
28
董旭東 and Xudong Dong. "Stress distribution and failure mode of dental ceramic structures under Hertzian indentation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31241621.
29
Mohan, Preethi. "Bond strength evaluation of two resin cements with two adhesives and analysis of mode of failure." Connect to resource online, 2009. http://hdl.handle.net/1805/2079.
Анотація:
Thesis (M.S.D.)--Indiana University School of Dentistry, 2009.Title from PDF t. p. (viewed Feb. 9, 2009) Advisor(s): Jeffrey A. Platt, Chair of the Research Committee, Tien-Min Gabriel Chu, Michael A. Cochran, Bruce A. Matis, Burak Taskonak, B. Keith Moore. Curriculum vitae. Includes abstract. Includes bibliographical references (leaves 71-76).
30
Duthoit, Jeremy. "A micromechanics-based method for off-axis strength prediction of unidirectional laminae - Approach for a nonlinear rubber based lamina." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/34367.
Анотація:
In this study, a micromechanics-based method is developed to predict the off-axis strength of unidirectional linear elastic laminae. These composites fail by matrix cracking along a plane parallel to the fiber direction. The stresses in the matrix are calculated using a local stress analysis based on a concentric cylinder model. This model consists of a unique fiber embedded in matrix; both constituents are represented by cylinders. A finite element model is also constructed and the results of the two models compared. The stresses and strains from the concentric cylinder model are averaged over the volume of the matrix and used in a local failure function. This failure function has the form of a reduced and normalized strain energy density function where only transverse and shear terms are considered. The off-axis strength prediction method is validated using data from the literature.
This failure function will be used in the near future for composites with a matrix having nonlinear properties. Experimental tensile tests on steel-cord/rubber laminae and laminates as well as on the nonlinear rubber matrix were performed. Stress-strain behavior and off-axis strength data were obtained. An approach for off-axis strength prediction for these laminae is defined based on a finite element stress analysis. The finite element analysis approach is motivated by the one used for linear composites.Master of Science
31
Tehrani, Mohammad Jafari. "Micromechanical Analysis of Strength of Polymer Networks with Polydisperse Structures." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1491913532934372.
32
Majumdar, Prasun Kanti. "Strength and Life Prediction of FRP Composite Bridge Deck." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/27285.
Анотація:
Fiber reinforced polymer (FRP) composites are considered very promising for infrastructure applications such as repair, rehabilitation and replacement of deteriorated bridge decks. However, there is lack of proper understanding of the structural behavior of FRP decks. For example, due to the localization of load under a truck tire, the conventionally used uniform patch loading is not suitable for performance evaluation of FRP composite deck systems with cellular geometry and relatively low modulus (compared to concrete decks). In this current study, a simulated tire patch loading profile has been proposed for testing and analysis of FRP deck. The tire patch produced significantly different failure mode (local transverse failure under the tire patch) compared to the punching-shear mode obtained using the conventional rectangular steel plate. The local response of a cellular FRP composite deck has been analyzed using finite element simulation and results are compared with full scale laboratory experiment of bridge deck and structure. Parametric studies show that design criteria based on global deck displacement is inadequate for cellular FRP deck and local deformation behavior must be considered.
The adhesive bonding method is implemented for joining of bridge deck panels and response of structural joint analyzed experimentally. Strength, failure mode and fatigue life prediction methodologies for a cellular FRP bridge deck are presented in this dissertation.Ph. D.
33
Bardelcik, Alexander. "Effect of Pre-Bending and Hydroforming Parameters on the Formability of Advanced High Strength Steel Tube." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2829.
Анотація:
With increasing fuel costs and the current drive to reduce greenhouse gas emissions and fuel consumption, a need to reduce vehicle weight is apparent. Weight reduction can be achieved by replacing conventionally stamped structural members with hydroformed parts. The weight reduction can be further enhanced by reducing the thickness of the hydroformed members through the use of advanced high strength steel (AHSS). A primary limitation in hydroforming AHSS, is the limited ductility or formability of these materials. This limitation becomes acute in multi-stage forming operations in which strain path changes become large making it difficult to predict formability. Thus, the focus of the current work is to study the effects of pre-bending on the subsequent hydroformability of Dual-Phase DP600 steel tubes. As part of this effort, the effect of key bending and hydroforming process parameters, bending boost and hydroforming end-feed, have been studied in a parametric fashion. Multi-step pre-bending and hydroforming experiments were performed on 76. 2 mm (3. 0") OD tubes with a wall-thickness of 1. 85mm (DP600). Experiments were also performed on 1. 74mm Interstitial Free (IF) steel tube, which provided a low strength, high formability baseline material for comparison purposes. A fully instrumented servo-hydraulic mandrel-rotary draw tube bender was used in the pre-bending experiments in which various levels of boost were applied. The results showed that increased boost reduced the major (tensile) strain and thinning at the outside of the bend. At the inside of the bend, the compressive minor strain became larger and thickening increased.
Hydroforming of the straight and pre-bent tubes was conducted using various levels of load-control end-feed (EF). For both straight and pre-bend tube hydroforming, an increase in hydroforming EF resulted in increased burst pressure and corner-fill expansion (CFE). The effect of bending boost on CFE was also measured. For a given hydroforming EF case, a tube bent with greater boost achieved a higher burst pressure and consequently a greater CFE which increased the hydroformability of the material. Pre-bending was shown to consume a considerable amount of the formability of the tube in the hydroforming experiments. For the same EF case, the pre-bent tubes could only achieve a fraction of the straight tube CFE at burst.
The pre-bending and hydroforming experiments were complimented by finite element simulation in the hope of providing additional insight into these processes. The finite element (FE) models were able to accurately predict the strain and thickness changes imposed during pre-bending. The models were able to accurately predict the CFE, EF displacement, and strain and thickness distributions after hydroforming.
The extended stress-based forming limit curve (XSFLC) failure criterion was applied to predict failure (onset of necking) during hydroforming, which was measured as the burst pressure in the experiments. For straight tube hydroforming, the XSFLC predicted the correct failure pressure versus hydroforming EF load trend, but over predicted the failure pressures. In pre-bend hydroforming, the models were able to capture the effect of bending boost and hydroforming EF on the hydroformability of the tubes. The XSFLC was able to capture the drop in formability for bending versus straight tube hydroforming, but was unable to capture the failure pressure versus hydroforming EF load trend or magnitude. Further work is required to make the XSFLC applicable to straight and pre-bend hydroforming.
34
Bonetti, Rodolfo Arturo. "Ultimate Strength of the Local Zone in Load Transfer Tests." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/31392.
Анотація:
An improved equation is presented for the prediction of the ultimate strength of the local zone in Load Transfer Tests. The derivation of this new formulation is the result of the investigation of the ultimate bearing strength of plain and reinforced concrete blocks, concentrically loaded. A total of 199 bearing tests were performed on plain and reinforced concrete prisms to evaluate the variables involved in the bearing problem. A finite element analysis of a typical square block loaded with different bearing areas was performed. Two equations, one for plain concrete and the other for reinforced concrete were derived using the Mohr failure criterion.
The performance of the derived equations was evaluated against actual test data. The results of this evaluation showed very good agreement between the predicted ultimate strength and the actual test strength for both plain and reinforced concrete. For plain concrete specimens the ratio Ptest/Ppred was 1.05 with a coefficient of variation of 9 percent. In the case of reinforced concrete blocks the ratio Ptest/Ppred was 1.00 with a coefficient of variation of 14 percent.Master of Science
35
Noorian-Bidgoli, Majid. "Strength and deformability of fractured rocks." Doctoral thesis, KTH, Mark- och vattenteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155719.
Анотація:
This thesis presents a systematic numerical modeling framework to simulate the stress-deformation and coupled stress-deformation-flow processes by performing uniaxial and biaxial compressive tests on fractured rock models with considering the effects of different loading conditions, different loading directions (anisotropy), and coupled hydro-mechanical processes for evaluating strength and deformability behavior of fractured rocks. By using code UDEC of discrete element method (DEM), a series of numerical experiments were conducted on discrete fracture network models (DFN) at an established representative elementary volume (REV), based on realistic geometrical and mechanical data of fracture systems from field mapping at Sellafield, UK. The results were used to estimate the equivalent Young’s modulus and Poisson’s ratio and to fit the Mohr-Coulomb and Hoek-Brown failure criteria, represented by equivalent material properties defining these two criteria. The results demonstrate that strength and deformation parameters of fractured rocks are dependent on confining pressures, loading directions, water pressure, and mechanical and hydraulic boundary conditions. Fractured rocks behave nonlinearly, represented by their elasto-plastic behavior with a strain hardening trend. Fluid flow analysis in fractured rocks under hydro-mechanical loading conditions show an important impact of water pressure on the strength and deformability parameters of fractured rocks, due to the effective stress phenomenon, but the values of stress and strength reduction may or may not equal to the magnitude of water pressure, due to the influence of fracture system complexity. Stochastic analysis indicates that the strength and deformation properties of fractured rocks have ranges of values instead of fixed values, hence such analyses should be considered especially in cases where there is significant scatter in the rock and fracture parameters. These scientific achievements can improve our understanding of fractured rocks’ hydro-mechanical behavior and are useful for the design of large-scale in-situ experiments with large volumes of fractured rocks, considering coupled stress-deformation-flow processes in engineering practice.QC 20141111
36
Scott-Emuakpor, Onome Ejaro. "Development of a novel energy-based method for multi-axial fatigue strength assessment." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1196280356.
37
Maghsoudloo, Arash. "Nonlinearity Of The Residual Shear Strength Envelope In Stiff Clays." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615551/index.pdf.
Анотація:
During shearing of stiff clays, plate-shaped clay particles are parallel-oriented in the direction of shear reaching the minimum resistance of &ldquoresidual shear strength&rdquo
. The residual shear strength envelopes of stiff clays are curved, but for practical purposes represented by linear envelopes. This study investigates the nonlinearity of the residual shear strength envelope using experimental evidence (i) from laboratory reversal direct shear tests on two stiff clays (Ankara clay and kaolinite) at 25 to 900 kPa effective normal stresses and (ii) from laboratory data collected from literature. To evaluate the importance of nonlinearity of the envelope for geotechnical engineering practice, by limit equilibrium method, (a) case histories of reactivated landslides are analyzed and (b) a parametric study is carried out. Conclusions of this study are: (1) The residual shear strength envelopes of both Ankara clay and kaolinite are nonlinear, and can be represented by a power function (cohesion is zero). (2) At least 3 reversals or cumulative 20 mm shear displacement of direct shear box is recommended to reach residual condition. (3) Empirical relations between plasticity index and residual friction angle can accurately estimate the residual strength of stiff clays. (4) Nonlinearity is especially important for landslides where average effective normal stress on the shear plane is less than 50 kPa, both for translational and rotational failures. For such slopes using a linear strength envelope overestimates the factor of safety (more significantly for the case of high pore pressures). (5) As the plasticity index increases, the power &ldquo
b&rdquo
of the nonlinear shear strength envelope decreases, indicating more significant nonlinearity. For less plastic materials, using linear and nonlinear shear strength envelopes does not affect the factor of safety.
38
Post, Nathan L. "Reliability based design methodology incorporating residual strength prediction of structural fiber reinforced polymer composites under stochastic variable amplitude fatigue loading." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/26492.
Анотація:
The research presented in this dissertation furthers the state of the art for reliability-based design of composite structures subjected to high cycle variable amplitude (spectrum) fatigue loads. The focus is on fatigue analyses for axially loaded fiber reinforced polymer (FRP) composites that contain a significant proportion of fibers in the loading direction and thus have fiber-direction dominated failure. The four papers presented in this dissertation describe the logical progression used to develop an improved reliability-based methodology for fatigue-critical design. Throughout the analysis extensive experimental fatigue data on several material systems was used to verify the assumptions and suggest the path forward.
A comparison of 12 fatigue model approaches from the literature showed that a simple linear residual strength approach (Broutman and Sahu) provides an improvement in fatigue life prediction compared to the Palmgren-Miner rule, while more complex residual strength models did not consistently improve on Broutman and Sahu. Evaluation of the effect of load history randomness on fatigue life was made using experimental results for spectra in terms of the first order autocorrelation of the stress events. For approximately reversed Rayleigh distributed fatigue loading, load sequence was not critical in the material behavior. Based on observations of empirical data and evaluation of the micro-mechanics deterioration and failure phenomena of FRP composites under fatigue loading, a new residual strength model for the tension and compression under any load history was proposed. Then this model was implemented in a stochastic framework and a method was proposed to enable calculation of the load and resistance factor design (LRFD) parameters for realistic reliabilities with relatively few computations. The proposed approach has significant advantages over traditional lifetime-damage-sum-based reliability analysis and provides a significant step toward enabling more accurate reliability-based design with composite materials.Ph. D.
39
Karafillis, Pavlina. "Characterizing the failure of parachute seams : the impact of stitch concentration and strain rate on ultimate tensile strength." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112571.
Анотація:
Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (page 29).
Parachutes are commonly used in space mission landings. With increasing payloads, parachutes are getting larger, bearing larger loads and operating at faster speeds. Designing these devices requires a knowledge of aerodynamics, fluid flow, and the mechanical properties of cloth. A brief overview of the basics of parachute design are described. There are many possible failure modes, but catastrophic failures are caused by failures at the weakest point of the parachute, the seam. Seams are characterized by a seam efficiency, a percentage of the strength of the cloth used to stitch the seam together. In this study, seams and cloth were tested to failure on an Instron 5582 to experimentally determine their respective Ultimate Tensile Strengths (UTS). The ratio of the seam UTS to the cloth UTS was used to determine seam efficiency. Results indicated no clear relationship between strain rate and seam efficiency in the range tested. However, a strong relationship between stitch concentration and seam efficiency was established. A best fit curve was developed and with an an R2=0.80. In order to better understand the failure mode, the open source Matlab function Ncorr was also used to provide a visualization of the strain on the coupons during testing. The results of the digital correlation analysis performed by Ncorr are also reported, and indicate the importance of transverse and shear strain in causing catastrophic failure.
by Pavlina Karafillis.
S.B.
40
Ríos, Bayona Francisco. "Analytical and numerical approaches to estimate peak shear strength of rock joints." Licentiate thesis, KTH, Jord- och bergmekanik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-248019.
Анотація:
In Sweden, there exists a large number of dams. Many of them are founded on rock masses normally affected by the presence of sub-horizontal rock fractures, which makes sliding along rock joints under the dam foundation one of the most critical failure mechanism. Various attempts have been made to relate the peak shear strength of rock joints to measurable parameters. However, the uncertainty in the determination of the shear strength of rock joints is nonetheless still significant.The main aim of this thesis is to investigate, develop and apply analytical and numerical techniques for estimation of peak shear strength of natural and unfilled rock joints. In a first step, the peak shear strength of several natural and unfilled rock joint was calculated by using surface aperture measurements from high-resolution optical scanning and a modified version of the analytical criterion previously developed by Johansson and Stille in 2014. In a second step, PFC2D was utilised to perform numerical shear tests on two-dimensional profiles selected from high-resolution optical scanning on unweathered and perfectly mated tensile induced rock joints.The results from the analytical approach show that the calculated peak shear strengths of the analysed samples are in good agreement compared with the laboratory investigations. Conversely, the obtained results from the numerical approach show lower peak shear strengths in the analysed two-dimensional profiles compared with the conducted laboratory shear tests.The analytical approach together with the advanced techniques to measure surface roughness available today, may be a possible way forward towards a methodology to determine peak shear strength of large-scale natural rock joints in-situ.Bergsprickors skjuvhållfasthet är en avgörande faktor för att kunna bestämma säkerheten mot gliding för dammar där sub-horisontella utbredda bergsprickor existerar. Samtidigt är parametern svår att bestämma då den påverkas av flera faktorer som sprickytans råhet, vittringsgrad, normalspänning, skala samt passning. Skjuvhållfasthet av bergsprickor kan bestämmas genom att använda empiriska och analytiska brottkriterier samt numeriska metoder. Problemet med de befintliga metodikerna är att de inte beaktar inverkan från sprickans passning. Detta innebär att hållfastheten riskerar att överskattas.Det övergripande syftet med denna licentiatuppsats är att studera, utveckla och tillämpa analytiska och numeriska metoder för uppskattning av skjuvhållfasthet för naturliga och ofyllda bergsprickor. I ett första steg beräknades skjuvhållfastheten för ett antal naturliga och ofyllda bergsprickor. Detta gjordes genom att mäta aperturen baserat på högupplöst skanning och en vidareutvecklad version av det analytiska kriteriet som föreslogs av Johansson och Stille 2014. I ett andra steg användes PFC2D för att genomföra numeriska skjuvtester på två-dimensionella sprickprofiler baserat på högupplöst skanning av perfekt passade och draginducerade bergsprickor.Resultaten från uppskattad skjuvhållfasthet med den analytiska metodiken visar på en bra överensstämmelse i jämförelse med de utförda skjuvförsöken. Resultaten från de utförda analyserna med PFC2D visar på en något lägre skjuvhållfasthet än vad som observeras i verkligheten.Den utvecklade analytiska metodiken, tillsammans med de avancerade tekniker som idag finns för att mäta sprickytornas råhet, bedöms kunna utgöra ett första steg mot att bättre kunna bestämma den storskaliga skjuvhållfastheten för bergsprickor i fält.
QC 20190402
41
Akhtar, Mohammad Farhan. "Numerical Investigation of High Strength Structural Steel Gravity Columns at Elevated Temperature." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613748386003217.
42
Dorribo, Dorribo Daniel. "Development of mechanism-based models for resistance spot weld failure simulation of multi-material advanced high strength steel sheets." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/461803.
Анотація:
The automotive industry is constantly involved in the development of new projects aimed at reducing weight, fuel consumptions and costs while improving passengers¿ safety. In order to achieve these increasing demands, Advanced High Strength Steels (AHSS) have been introduced in recent years reducing vehicle structure weights and improving the crashworthiness. With the increase in the bearing capacity of crash-relevant structural components, the sheet metal joining techniques such as adhesive bonding and resistance spot welding (RSW) become critical. In order to develop the vehicle structure in these new projects, full-vehicle crash finite element simulations are usually performed. Simplified beam-like models are currently used in these simulations (with thousands of spot welds) to represent RSW joints response. The maximum bearing force of these models are fitted using large experimental campaigns, considering all the main factors that have the highest influence on the fracture response of a welded joint. The objective of this thesis is twofold: (1) to develop a model that is able to partially replace the extensive experimental campaign in providing parameters for the crash simulation simplified spot weld models, and (2) to gain understanding of spot weld joints failure response in order to improve the current simplified models.
To achieve these objectives, a detailed spot weld model for the prediction of spot weld failure in joints in AHSS sheets is presented. The presented model includes a definition of the local material properties as well as the geometry features of a spot weld. In addition, an industrially suited fracture criterion, i.e. robust and without a long-term calibration, is used for the prediction of maximum force. An energetic fracture criterion based on the use of elastic-plastic fracture-mechanics is identified as the better suited for the prediction of spot weld failure and joint bearing capacity. The J-integral is evaluated in the weld notch and this value is compared with a material parameter, the fracture toughness, in order to obtain the joint maximum force.
The presented detailed FE spot weld model is validated to joints of two different steel grades of the AHSS family usually present in the current vehicle structure, a hot formed martensitic boron-alloyed steel (22MnB5) and a cold formed dual phase steel (DP 980). The validation is performed comparing the results obtained with the finite element model and the experimental results extracted from an extensive loading test experimental campaign where the main factors that have an influence in the spot weld fracture response are considered. The obtained simulated critical forces of the loading tests present good agreement with the experimental ones in all tested configurations.
Finally, based on the presented finite element spot weld model, some recommendations are exposed for extending the model for new combinations and loading conditions. The proposed procedure can be used to reduce the long-term characterization campaigns used to calibrate the joints of a new AHSS grade, where fracture is triggered by stress concentration ahead of a notch. Furthermore, some recommendations for the future structure design are given taking into account the information obtained with the present model.La industria del automóvil está constantemente involucrada en el desarrollo de nuevos proyectos persiguiendo la reducción de pesos, consumos de combustible y costes, así como mejoras en seguridad. Par alcanzar estas demandas, en los últimos años los llamados aceros avanzados de muy alta resistencia (AHSS) se han introducido reduciendo el peso de la estructura de los vehículos y mejorando su respuesta en caso de accidente. Con la mejora de la resistencia de los componentes estructurales relevantes durante un impacto a alta velocidad, las técnicas de unión de chapas de metal, como los adhesivos o los puntos de soldadura por resistencia (RSW), han pasado a tener un papel crucial. Para desarrollar la estructura de estos nuevos proyectos, se realizan habitualmente simulaciones de elementos finitos de vehículo completo. En estas simulaciones, con miles de puntos de soldadura, se usan modelos simplificados en los que la fuerza máxima según la unión y el caso de carga es obtenida mediante extensas campañas experimentales. Esta tesis tiene dos objetivos principales: (1) desarrollo de un modelo capaz de reemplazar parcialmente las extensas campañas experimentales que proveen de parámetros a los modelos simplificados de puntos de soldadura usados para la simulación de choque, (2) mejor comprensión de la respuesta a fallo de las uniones soldadas por puntos para mejorar los actuales modelos simplificados. Par cumplir estos objetivos se presenta un modelo detallado de elementos finitos. El modelo incluye la definición de las propiedades mecánicas locales así como las características geométricas de un punto de soldadura. Además, para la predicción de la fuerza máxima se aplica un criterio de fractura adecuado a la industria, es decir, robusto y a la vez sin la necesidad de una larga calibración. Se identifica un criterio energético de fractura basado en la mecánica de fractura elasto-plástica como el más adecuado para obtener la capacidad de carga de las uniones. La fuerza máxima de las uniones se obtiene al evaluar la concentración de tensiones alrededor de la entalla de soldadura mediante la integral J y comparándola con un parámetro del material (tenacidad de fractura). El modelo presentado es validado para uniones soldadas de dos tipos de aceros de la familia de los AHSS presentes habitualmente en la estructura de los vehículos modernos, un acero martensítico al boro estampado en caliente (22MnB5) y un acero de fase dual de estampación en frio (DP 980). Esta validación se realiza comparando los resultados de fuerza máximas obtenidos por el modelo de elementos finitos con los resultados experimentales obtenidos de una extensa campaña experimental donde se tienen en cuenta los principales factoras que tienen influencia en la fractura. Los resultados de las fuerzas críticas obtenidas de los ensayos experimentales de carga presentan una gran concordancia con la simulación para todas las configuraciones testeadas. Finalmente, basándose en el modelo detallado presentado se proponen algunas recomendaciones para extenderlo para nuevas combinaciones y condiciones de carga, así como recomendaciones sobre el diseño de estructuras teniendo en cuenta como se cargas los puntos de soldadura en distintas condiciones. El procedimiento propuesto puede ser usado para reducir las extensas campañas experimentales empleadas en la caracterización de uniones en nuevos tipos de aceros de alta resistencia, donde la fractura es desencadenada por concentración de tensiones alrededor de la entalla de soldadura.
43
Elsayed, Adham Fawzy [Verfasser]. "Comparison between the fracture strength and failure mode of lithium disilicate, zirconia and titanium implant abutments / Adham Fawzy Elsayed." Kiel : Universitätsbibliothek Kiel, 2018. http://d-nb.info/1166654567/34.
44
Sterley, Magdalena. "Characterisation of green-glued wood adhesive bonds." Doctoral thesis, Linnéuniversitetet, Institutionen för teknik, TEK, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-18606.
Анотація:
The gluing of unseasoned wood, called green gluing, is a relatively new sawmill process, implying a radically changed order of material flow in the production of value-added wood-based products. It facilitates the enhancement of raw material recovery and value yield by integrating defect elimination and gluing already before kiln drying. The present study evaluates green glued adhesive bonds in flatwise glued beams and finger joints. The main part of this work deals with green gluing using a moisture curing polyurethane adhesive (PUR). Standardised test methods and specially designed, small scale, specimens were used for the determination of the strength, fracture energy and the ductility of both dry- and green glued bonds in tension and in shear. Using the small scale specimens it was possible to capture the complete stress versus deformation curves, including also their unloading part. An optical system for deformation measurement was used for the analysis of bond behaviour. The influence of moisture content during curing and temperature after curing on the adhesive chemical composition and on the mechanical properties was investigated. Furthermore, the moisture transport through the adhesive bond during curing was tested. Finally, microscopy studies were performed for analysis of bond morphology and fracture. The results show that two significant factors influence the shear strength of green glued bonds: wood density and adhesive spread rate. Bonds which fulfil the requirements according to EN 386 could be obtained within a wide range of process parameters. The small specimen tests showed that green glued PUR bonds can reach the same strength and fracture energy, both in shear and in tension, as dry glued bonds with the same adhesive amount. The local material properties of the bonds could be determined, thanks to the failure in the tests taking place within the adhesive bond itself and not in the wood. Following process factors were shown to cause lower bond strength: a) a low adhesive spread rate, b) high pressure and c) short pressing time in combination with low wood density and high moisture content. Moreover, the heat treatment of the cured PUR adhesive during drying influenced the chemical composition of the adhesive, providing for higher strength, stiffness and Tg of the adhesive, caused by an increased amount of highly ordered bidentate urea.
45
Sigley, R. H. "Failure mechanisms under complex loading of glass-reinforced polyester composites and their matrices : The effect of superposed hydrostatic pressures up to 300 MPa on axial tensile and compressive strengths, and in-plane shear properties of unidirectional." Thesis, University of Bradford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234245.
46
Sterley, Magdalena. "Green gluing of wood." Licentiate thesis, KTH, Civil and Architectural Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1737.
47
Tinl, Nicholas E. "An Investigation of the Bearing Strength of Bolted Connections in Aluminum and Titanium Alloys." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1322506214.
48
Stewart, Scott William. "Rock mass strength and deformability of unweathered closely jointed New Zealand greywacke." Thesis, University of Canterbury. Civil Engineering, 2007. http://hdl.handle.net/10092/1224.
Анотація:
Closely jointed greywacke rock masses are widespread throughout both the North and South Islands of New Zealand and much of New Zealand's infrastructure is constructed upon greywacke rock masses. This thesis deals with determining the rock mass strength of unweathered closely jointed New Zealand greywacke rock masses. Currently, the estimation of rock mass strength and deformability is reasonably well predicted through the use of such empirical failure criteria as the Hoek-Brown failure criterion and empirical expressions to predict deformability. However, previous studies upon predicting the strength and deformability of unweathered closely jointed New Zealand greywacke rock masses has shown that existing empirical methods of determining strength and deformability are unsatisfactory. The problem with predicting rock mass strength and deformability moduli of New Zealand greywacke and the lack of adequate data to calibrate a failure criterion was the starting point for this work. The objective of this thesis was to increase the knowledge of intact and defect properties of closely jointed greywacke, develop reliable rock mass data with which to calibrate a failure criterion and improve the ability to estimate the rock mass strength of greywacke rock masses. A review of existing failure criteria for rock masses was conducted and of these criteria, the Hoek-Brown rock mass failure criteria was selected to calibrate to both the intact rock and rock mass failure data, because of its broad acceptance in the rock mechanics community. A database of greywacke properties was developed based on previous studies upon unweathered greywacke around New Zealand and is attached to the thesis as an Appendix. The database included descriptions of greywacke defect properties and mechanical properties of the intact rock and joints. From this database, inputs could be justified for numerical modelling and later analyses of failure criteria. Records from the construction archives of the Benmore and Aviemore hydroelectric power projects in the South Island of New Zealand were reviewed to obtain information and results from a series of shear tests carried out on unweathered closely jointed greywacke in the 1960s. Data on rock mass strength at failure and rock mass deformability were extracted from these records to assess the predictability of the failure criterion and deformability expressions. Problems experienced during the shear tests at the Aviemore dam site created doubt as to the actual rock mass strengths achieved at failure. The behaviour of these tests was studied using the finite difference code FLAC. The work was aimed at investigating the potential for transfer of shear force between the two concrete blocks sheared in each test and the impact shear force transfer had upon the likely normal stresses beneath each block at failure. The numerical modelling results indicated that a combination of preferential failure occurring in one direction, and doubt in the actual normal load applied to the concrete blocks during testing lead to premature failure in the blocks sheared upstream. The blocks sheared in the opposite direction failed at normal stresses that are reflective of the strength of an unweathered greywacke rock mass, but these results could be explained by failure occurring along defects therefore not satisfying the assumptions of homogeneity typically required of a rock mass failure criterion. The Hoek-Brown failure criterion for intact rock was investigated by fitting it to the largest intact greywacke datasets. For a full set of test data (i.e. including tensile data), the Mostyn & Douglas (2000) variant of the Hoek-Brown failure criterion gave the best fit for a full set of rock mass data. A multiple regression method was developed which improved the fitted curve to intact data in the tensile region and gave the best estimate of tensile strength if no existing lab results for tensile strength were available. These results suggest that the Hoek-Brown failure criterion is significantly limited in its applicability to intact NZ greywacke rock. Hoek-Brown input parameters different to those suggested by Hoek et al (2002) are recommended for using the Hoek-Brown failure criterion for intact NZ greywacke. For closely jointed NZ greywacke rock masses, the results from the shear tests at Aviemore and Benmore were separated into different GSI classes and Hoek-Brown envelopes fitted to the datasets by multiple regression. Revised expressions were proposed for each Hoek-Brown input parameter (mb, s, ab) as a function of the GSI. The resulting revised Hoek-Brown failure envelopes for NZ greywacke offer a significant improvement on the existing criterion used to predict the strength of NZ greywacke intact rock and rock masses. The differences in the behaviour of the reaction blocks that failed before the test blocks and the reduction in rock strength due to sliding along defects from that predicted could be reasoned from recorded observations and the behaviour of the concrete blocks during the shear tests. This study has clearly illustrated the need for continued research in this area. This includes (1) a means of assessing the role of defects upon the shear strength of closely jointed greywacke rock mass into a failure criterion, (2) further modelling of the in-situ shear tests by a discrete element procedure to expressly determine the role of the defect on failure, (3) more testing on rock masses to obtain more data to calibrate a rock mass failure criterion, and (4) more studies on predicting the strength of extremely disturbed rock masses.
49
Petrie, Elizabeth Sandra. "Rock Strength of Caprock Seal Lithologies: Evidence for Past Seal Failure, Migration of Fluids and the Analysis of the Reservoir Seal Interface in Outcrop and the Subsurface." DigitalCommons@USU, 2014. https://digitalcommons.usu.edu/etd/2072.
Анотація:
This research characterizes the nature of fractures in Paleozoic and Mesozoic caprock seal analogs exposed in central and south-eastern Utah. The results of this research show evidence for fluid flow and mineralization in the subsurface as well as reactivation of fractures suggesting that the fractures act as a loci for fluid flow through time. The heterolithic nature of the caprock seals and meso-scale (cm to m) variability in fracture distributions and morphology highlight the strong link between the variation in material properties and the response to changing stress conditions. The variable connectivity of fractures and the changes in fracture density at the meso-scale plays a critical role in subsurface fluid flow. The presence or formation of new fractures can result in seal bypass systems, which can cause failure of hydrocarbon traps, CO2 geosequestration sites, waste and subsurface fluid repositories. An integrated approach of field, borehole geophysical, burial and stress history modeling, rock strength testing, and numerical modeling are used to understand the effects changing material properties, rock strength, and stress history have on sealing capacity. Simplified stress history models derived from burial history curves are combined with laboratory derived rock properties to understand the importance variations in rock properties and differential and effective mean stress have on the mechanical failure of fine-grained clastic sedimentary rocks. Burial history and rock strength data show that in units that experience similar burial depths and changing mechanical property exert a control on deformation type. Geomechanical models reveal changes in local strain magnitudes at locked mechanical interfaces, suggesting that elastic mismatch between layers results in differential strain distribution. Characterization of fracture patterns, rock strength variability and the modeled changes in subsurface strain distribution is especially important for understanding the response of low-‐permeability rocks to changing stress in the subsurface, and is applicable to multiple geo-engineering scenarios such as exploitation of natural resources, waste disposal, and management of fluids in the subsurface. The analyses presented in this dissertation provide analog fracture data for fine-grained clastic rocks and a dataset for better understanding the importance of heterogeneity in low permeability rocks.
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Erdogan, Hakan. "Improvement Of Punching Strength Of Flat Plates By Using Carbon Fiber Reinforced Polymer (cfrp) Dowels." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612728/index.pdf.
Анотація:
Due to their practical application, flat-plates have been commonly used slab type in constructions in recent years. According to the investigations that were performed since the beginning of the 20th century, the vicinity of the slab-column connection is found to be susceptible to punching failure that causes serious unrepairable damage leading to the collapse of the structures. The objective of this study is to enhance the punching shear strength of slab-column connections in existing deficient flat plate structures. For this purpose, an economical and easy to install strengthening method was applied to ¾scale flat-slab test specimens. The proposed strengthening scheme employs the use of in house-fabricated Carbon Fiber Reinforced Polymer (CFRP) dowels placed around the column stubs in different numbers and arrangements as vertical shear reinforcement. In addition, the effect of column aspect ratio on strengthening method was also investigated in the scope of this study. Strength increase of at least 30% was obtained for the CFRP retrofitted specimens compared to the companion reference specimen. Three-dimensional finite element analyses of test specimens were conducted by using the general purpose finite element analyses program. 3-D finite element models are successful in providing reasonable estimates of load-deformation behavior and strains. The experimental punching shear capacities and observed failure modes of the specimens were compared with the estimations of strength and failure modes given by punching shear strength provisions of ACI 318-08, Eurocode-2, BS8110-97 and TS500. Necessary modifications were proposed for the existing provisions of punching shear capacity in order to design CFRP upgrading.