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Dissertations / Theses on the topic 'Contact Mechanics'
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1
Parel, Kurien Stephen. "An analysis of contact stiffness and frictional receding contacts." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:3c29863a-b0cf-4870-851d-261be72f457f.
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The tangential contact stiffness for ground Ti-6Al-4V surfaces is measured to linearly decrease with the application of tangential load. At the beginning of the application of tangential load, for ground surfaces, the ratio of the tangential contact stiffness to the normal contact stiffness is seen to be approximately half the Mindlin ratio. This is consistent with many other published experimental studies. Measurements of normal contact stiffness for ground surfaces conform to a model that posits a linear relationship between normal contact stiffness and normal load. An equivalent surface roughness parameter is defined for two surfaces in contact; and the normal contact stiffness for ground surfaces is observed to be inversely proportional to this parameter. Single asperity models were constructed to simulate the effect of different frictional laws and plasticity on the tangential displacement of an asperity contact. Further, multi-asperity modelling showed the effect of different normal load distributions on the tangential behaviour of interfaces. In addition, normal contact stiffness was modelled for a grid of asperities taking into account asperity interactions. A receding contact problem for which the required form of the distributed dislocations is bounded-bounded was solved. Then, a fundamental 2D frictional receding contact problem involving a homogeneous linear elastic infinite layer pressed by a line load onto a half-plane of the same material was analysed. This was done by the insertion of preformed distributed dislocations (or eigenstrains), which take into account the correct form of the separation of the interface at points away from the area of loading, along with corrective bounded-bounded distributions. The general method of solution was further refined and adapted to solve three other receding contact problems. The solutions demonstrated the robustness and applicability of this new procedure.
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Ma, Lifeng. "Contact mechanics for coated systems." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409112.
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Lundvall, Olle. "Contact mechanics and noise in gears /." Linköping : Univ, 2004. http://www.bibl.liu.se/liupubl/disp/disp2004/tek862s.pdf.
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Pitteroff, Roland. "Contact mechanics of the bowed string." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387739.
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Siles, Brügge Oscar. "Contact mechanics at the molecular scale." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/18786/.
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A better understanding of the adhesive interactions between surfaces at the molecular scale is of growing importance as miniaturization efforts continue. To this end, Lifshitz theory of continuum mechanics was used to calculate the interaction energies between hydrocarbon surfaces in over 200 liquids, and compared to those obtained from the Hunter model of hydrogen bond solvation thermodynamics. In alkanes, amines, and primary alcohols, both theories yielded comparable results. However, in cases where the refractive index between interacting phases diverges greatly, a large disparity between the Lifshitz work of adhesion and Hunter free energy of complexation was found. In addition to some of the liquids showing differing results between the two theories, binary mixtures of benzyl alcohol and methanol were also identified for further experimental analysis. Slight modifications were applied to Lifshitz to allow for predictions of polar surfaces, and these too were compared to those provided by the Hunter model. Using force spectroscopy and friction force microscopy the tribological properties of hydrocarbon self-assembled monolayers, in the liquids identified previously, were investigated. While interactions in non-polar liquids were well described by both Lifshitz theory and the Hunter model, the former was found to consistently underestimate the work of adhesion in polar liquids, especially in water (Wad > 40 mJ/m2). In contrast, good agreement was generally obtained between the Hunter model and the experimentally obtained interaction energies. This was also true for binary mixtures of benzyl alcohol and methanol, where Lifshitz theory was completely unable to predict the form of the interaction. Friction-load plots were also obtained for the same systems of non-polar surfaces, and the form of their relation in different media was found to be dependent on the previously obtained adhesive energies. At interaction energies below 6 mJ/m2 linear friction-load relationships were observed, while yielding sublinear plots at work of adhesion values above this, corroborating the idea that friction can be considered to consist of load- and area-dependent terms. Mechanochemical removal of NPEOC photoprotecting groups from surfaces with adsorbed OEG-NPEOC-APTES monolayers using an AFM probe was also performed, with feature sizes up to 20 nm being achieved. The dependence on the width and depth of the patterned features on the applied load was investigated, with a positive relation being found for both, up to a critical load; no such change was observed with increasing write speeds. Changing the tip chemistry and environment (i.e. via immersion in different liquids) yielded no change in the size and quality of the patterns obtained, suggesting the lithographic process relies solely on the physical interaction between tip and sample surface. Modification of the surface through derivatization using TFAA and GFP indicates that only the NPEOC protecting group is being removed. Density functional theory was employed to investigate possible reaction pathways of the usual photodeprotection pathway of NPEOC-APTES, and how the mechanical interaction of the tip with the surface may promote one of these to occur without a high energy photon. It was discovered that a compression of the NPEOC leads to a shift in the UV/Vis absorbance spectrum towards higher wavelengths, and it is suggested that the mechanochemical deprotection of OEG-NPEOC-APTES SAMs occurs via this mechanism.
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King, Christopher David S. M. Massachusetts Institute of Technology. "A coupled contact-mechanics computational model for studying deformable human-artifact contact." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118672.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 199-205).
Gas-pressurized spacesuits are necessary for human spaceflight, most notably for extravehicular activity (EVA). Legacy EVA suits have been primarily rigid, and operation in such suits can result in significant metabolic expense, or even injury, for the wearer. To reduce these effects, modern spacesuits are more flexible, through the incorporation of more softgood materials and specially designed joint interfaces such as hip bearings. However, modeling the effects of human-suit interaction for these softgood materials is challenging due to the highly deformable nature of the suit coupled with the deformable nature of the human. To enable improved analysis and design of modern spacesuits, a computational model that can resolve the structural deformations of the suit and human resulting from contact interactions is developed. This thesis details the development and validation of a coupled contact-mechanics solver architecture for use in studying the effects of human-artifact interaction, particularly with respect to pressurized softgood exosuit design. To resolve contact and structural mechanics interactions for a deformable human and artifact, a finite element model is developed. First, the SUMMIT computational framework is employed for resolving the structural deformations of the system, and is coupled to an explicit contact mechanics scheme. The explicit contact scheme is implemented so as to resolve both external- and self-contact problems. Next, the model architecture is integrated to enable parallelization of both the structural deformation and contact systems, and computational scaling investigated. A computational trade study is performed to benchmark the coupled contact-mechanics method against a simpler rigid body model employing a penalty method. Following this, the model is validated against experimental data for various artifact contact problems. The explicit coupled contact-mechanics model is found to effectively capture contact interactions of the experimental data, with improved fidelity for deformable contact interactions. With careful tuning of the system properties, the coupled contact-mechanics model enables an architecture for an integrated human-suit analysis and design model.
by Christopher David King.
S.M.
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Almqvist, Andreas. "Rough surface elastohydrodynamic lubrication and contact mechanics." Licentiate thesis, Luleå, 2004. http://epubl.luth.se/1402-1757/2004/035.
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Walls, Kenneth Cline. "Multi-material contact for computational structural mechanics." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2008m/walls.pdf.
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Liu, Shubin Carleton University Dissertation Engineering Aerospace. "Boundary element analysis in contact fracture mechanics." Ottawa, 1994.
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Christensen, Peter W. "Computational nonsmooth mechanics : contact, friction and plasticity /." Linköping : Department of mechanical engineering, 2000. http://catalogue.bnf.fr/ark:/12148/cb40921031z.
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Bonari, Jacopo. "Novel interface discretisation methods for contact mechanics." Thesis, IMT Alti Studi Lucca, 2021. http://e-theses.imtlucca.it/326/1/Bonari_phdthesis.pdf.
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This thesis’ main scope is the presentation of two different
methodologies for the analysis of contact problems involving morphologically complex or rough surfaces. Both approaches rely on the Finite Element Method (FEM) as the
chosen computational framework. They hinge on the definition of an interface finite element used to model the space encompassed by two solids incontact. This kind of interface element is shared with the field of non-linear fracture
mechanics, employed for the simulation of non-linear crack
growth according to Cohesive Zone Model (CZM). Here, for
the first time, the formulation is extensively applied to contact mechanics. With no further modifications, the interface
element is suited for the solution of contact problems involving smooth and conformal interfaces, exploiting a node-to node
approach and a penalty formulation for the enforcement
of the contact constraints. The element is enriched with specific characteristics that allow for the solution of rough contact problems yet maintaining a very simple mesh discretisation, both using a single-scale and a multiscale approach. In
the single-scale approach, a novel methodology is exploited
that considers an equivalent flat interface and accounts for
the actual geometry by a suitable correction of the standard
normal gap. In the multi-scale approach, the Boundary Element Method (BEM) is exploited for solving, at a micro-scale,
the normal contact problem of a rough rigid indenter making contact with an elastic half-space, according to a far-field displacement determined by the deformation imposed at a
macro-scale. The solution in terms of averaged pressure and
mean separation is then passed back to the macro-scale.
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Everitt, Carl-Magnus. "Initiation of rolling contact fatigue from asperities in elastohydrodynamic lubricated contacts." Licentiate thesis, KTH, Hållfasthetslära (Avd.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-222371.
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Rolling contacts are utilized in many technical applications, both in bearings and in the contact between gear teeth. These components are often highly loaded, which makes them susceptible to suffer from rolling contact fatigue. This work focuses on the rolling contact fatigue mechanism of pitting. In order to attain a better understanding of why pitting initiates and grows, detailed simulations of rolling contacts have been performed. In particular the contact between two gears in a truck retarder was here used as a case study. The investigated contact experienced elastohydrodynamic lubrication conditions since the load was high enough to causes the surfaces in contact to deform and the viscosity of the lubricant to increase significantly. In Paper A it was investigated if surface irregularities in the size of the surface roughness are large enough to cause surface initiated fatigue. The investigation focused on the pitch line since small surface initiated pits were found here even though there was no slip present. Since there were pits present at the pitch line, it is important that the theories of pitting can explain the development of pits also in the absence of slip. The conclusion of the work was that surface irregularities of the size of normal surface roughness are enough to cause surface initiated fatigue at the pitch line. In Paper B it was investigated why pits are more likely to initiate in the dedendum of pinion gears than in the addendum. In both areas slip is present but in different directions. In the dedendum the friction from slip is against the rolling direction which enhances the risk for pitting. The investigation was performed by studying the effect of the temperature rise in the contact caused by the slip. The conclusion drawn was that the temperature rise in the contact explained why pitting was more common in the dedendum than in the addendum.Rullande kontakter förekommer i många applikationer, till exempel i lager och mellan kugghjulständer. Både lager och kugghjul utsätts ofta för höga laster vilket gör att dess ytor löper stor risk att utmattas, vilket kallas rullande kontaktutmattning. Denna studie fokuserar på pitting, även kallat spalling, vilket är en typ av rullande kontaktutmattning där en utmattninsspricka växer fram som får delar av ytan att ramla av. För att få en bättre förståelse varför pittingskador uppkommer har noggranna simuleringar utförts av rullande kontakter. Kontakten mellan två tänder på kugghjul i en lastbilsretarder har används som underlag då många pittingskador påträffats på dem. För att minska friktionen och nötningen i kontakten mellan kuggtänderna användes smörjmedel. De höga lasterna lastbilsretardern utsattes för deformerade kuggarnas ytor elastiskt samtidigt de kraftigt ökade viskositeten hos smörjmedlet. Dessa förhållanden gör att kontakten kallas för elastohydrodynamiskt smord, vilket på engelska förkortas till EHL. I Artikel A undersöktes om små ytojämnheter kan orsaka ytinitierade pittingskador. Eftersom skadan påträffats i friktionslösa kontakter, så som vid rullcirkeln på de undersökta kugghjulen, är det viktigt att teorierna som förklarar uppkomsten inte är beroende av friktion. Undersökningen fokuserade därför på förhållandena vid rullcirkeln. Slutsatsen från arbetet var att små ytojämnheter, av samma storleksordning som ytojämnheterna på de undersökta kugghjulen, är tillräckligt stora för att orsaka utmattningsskador. I Artikel B undersöktes varför det är vanligare att pitts initieras i dedendum än addendum på drivande kugghjul. Kontakten på båda sidorna om rullcirkeln slirar svagt åt olika håll. Att kontakten slirar skapar friktion som är motriktad rullriktningen i dedendum vilket ökar risken för pittingskador. För att undersöka varför dessa förhållanden ökar risken för skador fördjupades analysen av kontakten genom att inkludera temperaturfältet. Simuleringarna visade att temperaturen ökar genom kontakten vilket orsakar en asymmetrisk spänningsfördelning. Denna asymmetriska spänningsfördelning gör att ytojämnheter i dedendum är troligare att orsaka skador än ytojämnheter i addendum.
QC 20180213
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Peng, Wei. "Contact Mechanics of Multilayered Rough Surfaces in Tribology." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1002737061.
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Tvedt, Kristofer Eugene 1963. "Determination of contact stress using gap finite element method." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278152.
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The gap finite element uses the Richard equation to account for the nonlinearity in the boundary condition changes during deformation. This is accomplished by replacing the boundary nonlinearity with an equivalent material nonlinearity within the finite element program and using an incremental solution method. The gap element is developed as a special element with easily obtainable input parameters. The gap element is used to predict high stresses in local areas related to the contact of structural bodies. The major advantage to using a finite element solution with a gap element over a classical solution is in the ease of combining the contact stress with other stresses in a structural body.
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Neukirch, Sebastien. "Enroulement, contact et vibrations de tiges élastiques." Habilitation à diriger des recherches, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00667562.
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Ce mémoire présente plusieurs études sur l'équilibre, la stabilité et les vibrations de poutres élastiques en grande rotation. Le modèle utilisé est d'abord présenté de deux manières différentes : les équations de Kirchhoff sont introduites (i) comme une théorie directe de Cosserat, (ii) par une approche asymptotique 3D->1D. Une étude relativement complète des équilibres avec et sans auto-contact d'une poutre sous contrainte de tension et torsion et encastrée en ses deux extrémités est ensuite exposée. Le modèle est d'autre part appliqué au sur-enroulement de la molécule d'ADN et aux expériences sur molécule individuelle. Le cas d'une poutre naturellement courbe enroulée autour d'un obstacle cylindrique est ensuite traité. Les équations d'équilibre obtenues sont appliquées au cas d'une plante grimpante autour d'un tuteur ainsi qu'aux configurations dimériques de la protéine kératine. Enfin la dynamique d'une poutre plane est analysée sous deux angles différents : (i) le relâchement d'une poutre console qui donne lieu au phénomène de renforcement de courbure, et (ii) les vibrations d'une poutre post-flambée, encastrée en ses deux extrémités, avec comparaison des cas extensibles et inextensibles. La conclusion mentionne quelques problèmes d'intérêt qui seront l'objets d'études futures.
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Man, Kim Wai. "Boundary element analysis of contact in fracture mechanics." Thesis, University of Portsmouth, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317864.
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Burke, Dave. "The mechanics of the contact phase in trampolining." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/16744.
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During the takeoff for a trampoline skill the trampolinist should produce sufficient vertical velocity and angular momentum to permit the required skill to be completed in the aerial phase without excessive horizontal travel. The aim of this study was to investigate the optimum technique to produce forward somersault rotation. A seven-segment, subject-specific torque-driven computer simulation model of the takeoff in trampolining was developed in conjunction with a model of the reaction forces exerted on the trampolinist by the trampoline suspension system. The ankle, knee, hip, and shoulder joints were torque-driven, with the metatarsal-phalangeal and elbow joints angle-driven. Kinematic data of trampolining performances were obtained using a Vicon motion capture system. Segmental inertia parameters were calculated from anthropometric measurements. Viscoelastic parameters governing the trampoline were determined by matching an angle-driven model to the performance data. The torque-driven model was matched to the performance data by scaling joint torque parameters from the literature, and varying the activation parameters of the torque generators using a simulated annealing algorithm technique. The torque-driven model with the scaled isometric strength was evaluated by matching the performance data. The evaluation produced close agreement between the simulations and the performance, with an average difference of 4.4% across three forward rotating skills. The model was considered able to accurately represent the motion of a trampolinist in contact with a trampoline and was subsequently used to investigate optimal performance. Optimisations for maximum jump height for different somersaulting skills and maximum rotation potential produced increases in jump height of up to 14% and increases of rotation potential up to 15%. The optimised technique for rotation potential showed greater shoulder flexion during the recoil of the trampoline and for jump height showed greater plantar flexion and later and quicker knee extension before takeoff. Future applications of the model can include investigations into the sensitivity of the model to changes in initial conditions, and activation, strength, and trampoline parameters.
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Reisse, Franziska. "Effect of malalignment on knee joint contact mechanics." Thesis, Anglia Ruskin University, 2014. http://arro.anglia.ac.uk/550363/.
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Osteoarthritis (OA) is a debilitating joint disease that leads to significant pain, loss of mobility and quality of life. Knee malalignment results in increased joint pressure, which is a primary cause for OA progression. High Tibial Osteotomy (HTO) is a surgical procedure to correct malalignment and redistribute load in the knee joint, reduce peak pressure and delay OA progression. However, clinical outcomes have been unpredictable. Therefore, the aim of this study was to determine the relationship between malalignment and knee contact mechanics. A 3D computational model was created from magnetic resonance images of a cadaveric knee joint. A ligament tuning process was conducted to determine material properties. Finite element analyses were conducted, simulating end of weight acceptance during walking. Different wedge geometries were virtually removed to simulate malalignments from 14° valgus to 16° varus. Contact mechanics were sensitive to soft tissue material properties. In-vitro experiments were compared with computational modelling of the same specimen. Percent full-scale errors for contact force and pressure were less than 8%, demonstrating a unique subject-specific model validation. The native alignment of the cadaveric knee (1° varus) had medial and lateral compartment peak pressures of 4.28 MPa and 2.42 MPa, respectively. The medial:lateral force ratio was 70%:30%. Minimum contact stress did not occur at a Mechanical Axis Deviation (MAD) of zero millimetres nor at the Fujisawa Point, which are common targets for HTO correction. Results showed very strong correlations (r >0.94) between MAD and joint contact loading. This study is the first to demonstrate the relationship between stress (normal, shear, contact pressure) and MAD in a subject-specific model. This is a prerequisite for the development of a tool that could help surgeons make informed decisions on the degree of realignment required to minimise peak joint loading, thereby delaying OA progression.
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Reisse, Franziska. "Effect of malalignment on knee joint contact mechanics." Thesis, Anglia Ruskin University, 2014. https://arro.anglia.ac.uk/id/eprint/550363/1/FReisseThesis_final.pdf.
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Osteoarthritis (OA) is a debilitating joint disease that leads to significant pain, loss of mobility and quality of life. Knee malalignment results in increased joint pressure, which is a primary cause for OA progression. High Tibial Osteotomy (HTO) is a surgical procedure to correct malalignment and redistribute load in the knee joint, reduce peak pressure and delay OA progression. However, clinical outcomes have been unpredictable. Therefore, the aim of this study was to determine the relationship between malalignment and knee contact mechanics.
A 3D computational model was created from magnetic resonance images of a cadaveric knee joint. A ligament tuning process was conducted to determine material properties. Finite element analyses were conducted, simulating end of weight acceptance during walking. Different wedge geometries were virtually removed to simulate malalignments from 14° valgus to 16° varus.
Contact mechanics were sensitive to soft tissue material properties. In-vitro experiments were compared with computational modelling of the same specimen. Percent full-scale errors for contact force and pressure were less than 8%, demonstrating a unique subject-specific model validation. The native alignment of the cadaveric knee (1° varus) had medial and lateral compartment peak pressures of 4.28 MPa and 2.42 MPa, respectively. The medial:lateral force ratio was 70%:30%. Minimum contact stress did not occur at a Mechanical Axis Deviation (MAD) of zero millimetres nor at the Fujisawa Point, which are common targets for HTO correction. Results showed very strong correlations (r >0.94) between MAD and joint contact loading.
This study is the first to demonstrate the relationship between stress (normal, shear, contact pressure) and MAD in a subject-specific model. This is a prerequisite for the development of a tool that could help surgeons make informed decisions on the degree of realignment required to minimise peak joint loading, thereby delaying OA progression.
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Dalvi, Siddhesh Narayan. "UNDERSTANDING CONTACT MECHANICS AND FRICTION ON ROUGH SURFACES." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron158957808488289.
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Hua, Xijin. "Contact mechanics of metal on polyethylene hip replacements." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5568/.
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Metal-on-ultra high molecular weight polyethylene (UHMWPE) total hip replacement (THR) has been the most popular and clinically successful hip prosthesis to date. The long-term performance of THR depends on both the tribological characteristics and biomechanical behaviour of the prosthesis. This project focused on understanding the contact mechanics and mechanical behaviour of cemented and cementless metal-on-UHMWPE THRs under different conditions using a computational approach. Three-dimensional (3D) computational models of THRs with realistic pelvic bone were developed. Two typical bearings, the Charnley hip and the Pinnacle cup system, were investigated. The effect of different factors on the contact mechanics and cement stresses for Charnley THR were examined. Additionally, the contact mechanics and mechanical behaviour of Pinnacle THR under daily activities, standard and microseparation conditions were analysed. The cup angles and penetration depths in the cup, and the sizes of the components were found to have a significant effect on the contact mechanics and cement stresses for Charnley THR. The stresses at the bone-cement interface for the Charnley THR with outer diameter of 40 mm were predicted to be higher than that of 43 mm, the difference was found to be consistent with the clinical observation of different aseptic loosening rates. The cup angles and radial clearances were found to have a synergistic effect on the contact mechanics of Pinnacle THR. Edge loading on both articulating surface and backside surface of the liner was observed during some daily activities due to steep cup inclination angles and smaller radial clearance. The introduction of microseparation into the gait cycle, especially when combined with steep cup inclination angles, resulted in concentrated stresses and plastic deformation in the liner, which would cause potential damage to the liner. Therefore, it is critically important to reduce the levels of rotational and translational mal-positioning of the components clinically.
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Salehi, Shahin. "Machine Learning for Contact Mechanics from Surface Topography." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76531.
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Kollepara, Kiran Sagar. "Low-rank and sparse approximations for contact mechanics." Thesis, Ecole centrale de Nantes, 2022. http://www.theses.fr/2022ECDN0030.
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Les stratégies typiques de modélisation réduite de la mécanique des contacts utilisent des approximations de rang inférieur. L’hypothèse sous-jacente est l’existence d’un sous-espace et d’un sous-cône de faible dimension pour les champs de déplacement et de pression de contact, respectivement. Cependant, la pression de contact présente un caractère local, car la zone de contact peut varier en fonction de paramètres tels que le chargement ou la géométrie. Dans cette thèse, la pertinence des approximations de rang faible pour la mécanique des contacts est étudiée et des voies alternatives fondées sur des techniques de régression parcimonieuses sont explorées. Il est montré que la nature locale de la pression de contact conduit à une perte de la séparabilité, limitant ainsi la précision des méthodes de rang faible. Par la suite et pour atténuer les problèmes d’inséparabilité, les approximations utilisant des dictionnaires contenant un grand nombre d’atomes sont étudiées. Deux stratégies sont établies àl’aide de méthodes d’approximation parcimonieuses. L’une est fondée sur une approche d’ensemble actif où les éléments du dictionnaire sont sélectionnés de manière gloutone, et l’autre sur des approximations d’enveloppes convexes qui éliminent le besoin d’appliquer explicitement des contraintes de non-pénétration. Enfin, les méthodes de réduction non linéaires sont explorées. Elles permettent d’enrichir le dictionnaire en utilisant des interpolations nonlinéaires, réduisant ainsi le coût de calcul associé à la construction du dictionnaire dans la phase hors-ligneTypical strategies for reduced modelling of contact mechanics use low-rank approximations.The underlying hypothesis is the existence of low-dimensional subspace and subcone for the displacement and contact pressure fields, respectively. However, the contact pressure exhibits a local nature, as the contact position can vary with parameters like loading or geometry. The adequacy of low-rank approximations for contact mechanics is studied and alternative routes based on sparse regression techniques are explored. It is shown that the local nature of contact pressure leads to a loss in linear separability, thereby limiting the accuracy of low-rank methods. Subsequently, approximations using overcomplete dictionaries to mitigate the inseparability issues is investigated. Two strategies are devised using sparse approximation methods. One is based on an active-set approach where the dictionary elements are selected greedily, and another is based on convex hull approximations where the non-penetration constraints need not be explicitly enforced. Lastly, the non-linear dimensionality reduction framework is explored. The snapshot set computed in the training phase is enriched at a low complexity using non-linear interpolations, thereby reducing the burden of creating overcompletedictionaries in the offline phase
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Wilson, W. Everett Jackson Robert L. "Surface separation and contact resistance considering sinusoidal elastic-plastic multiscale rough surface contact." Auburn, Ala, 2008. http://hdl.handle.net/10415/1490.
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Jelagin, Denis. "Frictional Effects on Hertzian Contact and Fracture." Doctoral thesis, KTH, Hållfasthetslära (Avd.), 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4535.
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This thesis addresses normal axisymmetric contact of dissimilar elastic solids at finite interfacial friction. It is shown that in the case of smooth and convex but otherwise arbitrary contact profiles and monotonically increasing loading a single stick-slip contour evolves being independent of loading and profile geometry. This allows developing an incremental procedure based on a reduced problem corresponding to frictional rigid flat punch indentation of an elastic half-space. The reduced problem, being independent of loading and contact region, was solved by a finite element method based on a stationary contact contour and characterized by high accuracy. Subsequently, a tailored cumulative superposition procedure was developed to resolve the original problem to determine global and local field values for two practically important geometries: flat and conical profiles with rounded edges and apices. Results are given for relations between force, depth and contact contours together with surface stress distributions and maximum von Mises effective stress, in particular to predict initiation of fracture and plastic flow. It is also observed that the presence of friction radically reduces the magnitude of the maximum surface tensile stress, thus retarding brittle fracture initiation. Hertzian fracture through indentation of flat float glass specimens by steel balls has been examined experimentally for a full load cycle. It has been observed that if the specimen survived during loading to a maximum level it frequently failed at decreasing load. It has been proposed by Johnson et al. (1973) that the underlying physical cause of Hertzian fracture initiation during load removal is that at unloading frictional tractions reverse their sign over part of the contact region. Guided by these considerations a robust computational procedure has been developed to determine global and local field values in particular at unloading at finite friction. In contrast to the situation at monotonically increasing loading, at unloading invariance properties are lost and stick-slip regions proved to be severely history dependent and in particular with an opposed frictional shear stress at the contact boundary region. This causes an increase of the maximum tensile stress at the contour under progressive unloading. It is shown that the experimental observations concerning Hertzian fracture initiation at unloading are at least in qualitative correlation with the effect friction has on the maximum surface tensile stress. A contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been further investigated analytically and numerically for a wider range of material parameters and contact geometries. With the issue of Hertzian fracture initiation in mind, results concerning the influence of the friction coefficient and compliance parameters on the absolute maximum surface tensile stress during a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation. Fracture loads are measured with steel and tungsten carbide spherical indenters in contact with float glass specimens at monotonically increasing loading and during a load cycle. Computational predictions concerning the fracture loads are given based on Hertz and frictional contact theories combined with a critical stress fracture criterion. The computational results obtained for frictional contact are shown to be in better agreement with experimental findings as compared to the predictions based on the Hertz theory. The remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen’s surface. In order to account for the influence of the random distribution of these defects on the fracture loads at monotonic loading, Weibull statistics was introduced. The predicted critical loads corresponding to 50% failure probability were found to be in close agreement with experimentally observed ones.QC 20100729
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Rehermann, Pablo F. Sanz. "Modeling rock folding with large deformation frictional contact mechanics /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Ajibose, Olusegun K. "Nonlinear dynamics and contact fracture mechanics of high frequency percussive drilling." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=61011.
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Shellock, Matthew R. "Contact analysis of nominally flat surfaces." Thesis, Monterey, Calif. : Naval Postgraduate School, 2008. http://handle.dtic.mil/100.2/ADA483610.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2008.Thesis Advisor(s): Kwon, Young W. "June 2008." Description based on title screen as viewed on September 2, 2008. Includes bibliographical references (p. 51). Also available in print.
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Votsios, Vasilis. "Contact mechanics and impact dynamics of non-conforming elastic and viscoelastic semi-infinite or thin bonded layered solids." Thesis, Loughborough University, 2003. https://dspace.lboro.ac.uk/2134/11815.
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The thesis is concerned with the contact mechanics behaviour of non-conforming solids. The geometry of the solids considered gives rise to various contact configurations, from concentrated contacts with circular and elliptical configuration to those of finite line nature, as well as those of less concentrated form such as circular flat punches. The radii of curvature of mating bodies in contact or impact give rise to these various nonconforming contact configurations and affect their contact characteristics, from those considered as semi-infinite solids in accord with the classical Hertzian theory to those that deviate from it. Furthermore, layered solids have been considered, some with higher elastic modulus than that of the substrate material (such as hard protective coatings) and some with low elastic moduli, often employed as tribological coatings (such as solid lubricants). Other bonded layered solids behave in viscoelastic manner, with creep relaxation behaviour under load, and are often used to dampen structural vibration upon impact. Analytic models have been developed for all these solids to predict their contact and impact behaviour and obtain pressure distribution, footprint shape and deformation under both elastostatic and transient dynamic conditions. Only few solutions for thin bonded layered elastic solids have been reported for elastostatic analysis. The analytical model developed in this thesis is in accord with those reported in the literature and is extended to the case of impact of balls, and employed for a number of practical applications. The elastostatic impact of a roller against a semi-infinite elastic half-space is also treated by analytic means, which has not been reported in literature. Two and three-dimensional finite element models have been developed and compared with all the derived analytic methods, and good agreement found in all cases. The finite element approach used has been made into a generic tool for all the contact configurations, elastic and viscoelastic. The physics of the contact mechanical problems is fully explained by analytic, numerical and supporting experimentation and agreement found between all these approaches to a high level of conformance. This level of agreement, the development of various analytical impact models for layered solids and finite line configuration, and the development of a multi-layered viscoelastic transducer with agreed numerical predictions account for the main contributions to knowledge. There are a significant number of findings within the thesis, but the major findings relate to the protective nature of hard coatings and high modulus bonded layered solids, and the verified viscoelastic behaviour of low elastic modulus compressible thin bonded layers. Most importantly, the thesis has created a rational framework for contact/impact of solids of low contact contiguity.
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Heuer, Dennis, Norbert Schwarzer, and Thomas Chudoba. "Contact Mechanics in Dentistry: A systematic investigation of modern composite materials used for fillings." Universitätsbibliothek Chemnitz, 2006. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200600133.
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Nowadays, high demands are made on filling materials in modern dentistry: Durability, Reliability &Aesthetic Requirements
Thus, a group of physicists and an independent practicing dentist investigated 11 different teeth fillings (composite materials) as used in modern
dental practices according to their stability and ability to withstand contact loadings.
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Wei, Deheng. "Granular Mechanics Across Length Scales: Contact, Breakage, Fracture, and Permeability." Thesis, University of Sydney, 2021. https://hdl.handle.net/2123/24546.
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Particle morphology is of pivotal importance in granular materials at different length scales. This thesis begins with quantification and reconstruction of real particle shapes, then studies various kinds of granular material behaviour influenced by morphology features.
The project background and related previous work are introduced in Chapters 1 and 2, respectively. Chapter 3 is firstly concentrated on reconstructing particle shapes using Spherical Harmonics (SH). DEM clumps are also used to approximate realistic particle shapes to simulate sand column collapse. The efficiency of SH analysis between different coordinate systems in FEM mesh qualities and reconstruction are also compared. Chapter 4 is on contact behaviour of rough spheres with different morphology features. Via FEM simulation, benchmarked with Hertzian solution, a semi-analytical model is proposed.
In Chapter 5, to highlight the influences of contact curvature on single particle crushing behaviour, a rotational point loading in FDEM, benchmarked with an in-situ XCT experiment, is proposed. In Chapter 6, experiments of failure modes of cemented sands under different loading paths and the quantification of fracture fabric are conducted. FDEM simulations, benchmarked with a combined in-situ experiment with XCT and diffraction, of meso-scale concrete are also conducted. Effects of realistic aggregate morphology on overall concrete are investigated. In Chapter 7, permeability of uniformly graded 3D printed grains, is experimentally studied. Modified Kozney-Carman equation is also proposed. Chapter 8 concludes this work by summarising the findings and implications and provides an outlook on future works.
This dissertation presents a new comprehensive understanding of granular behaviour influenced by its morphology features. Via the proposed framework combining both experimental and numerical information, it is helpful to design and optimise of various granular materials with specific morphology features.
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Hodaei, Mohammad. "Multi Scale Contact Mechanics of Bio-Mechanical Systems with inclusion of roughness effect- Fractal Analysis." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/dissertations/1064.
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Contact mechanics of rough surfaces and surface wear will be considered. Two types of failures are considered. The first involving rapidly growing failure and the second fatigue type surface failure as a result of repetitive application of load cycle. The first type of failure will be identified based on surface hysteresis energy loss in a load/unload cycle or examination of fracture toughness of the material near its rough surface. The above approach will be used to examine both types of failure in joint implants in the human body. These include consideration of implants for hip, ankle, spine and knee. In this case rapid and/or fatigue failures will be considered and related to anticipated implant life cycle based on implant recipient's tolerance level. Hence surface fidelity in terms of the biological host's tolerance of toxicity level due to wear will be used to develop life cycle prediction of an implant. The second application, rapid and fatigue wear will be examined in commonly used mechanical systems that include spur and helical gearing and rolling element bearings.
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Buchan, Lawrence Lewis. "Open MRI investigation of contact mechanics in cam femoroacetabular impingement." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52576.
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Cam femoroacetabular impingement (FAI) is a mechanical process thought to cause of hip osteoarthritis (OA). In cam FAI, it is thought that a ‘cam deformity’ on the femoral head-neck junction intrudes into the intra-articular joint space, inducing elevated mechanical force on acetabular cartilage. However, few experimental studies have measured contact mechanics in FAI. Open MRI in functional positions has potential to directly and non-invasively assess cam FAI, but MRI measures have not been related to mechanics. This thesis asked, in cadaver hips positioned in a simulated anterior impingement posture: (1) Does open MRI show intrusion of a cam deformity into the intra-articular joint space? (2) Is a cam deformity associated with elevated acetabular contact force? (3) Are MRI measures of cam FAI related to acetabular contact force?
Cadaver hips (cam, n=9; controls, n=3) were positioned in a simulated anterior impingement posture, then imaged using open MRI with multi-planar reformatting. The β-angle was measured at 72 locations about the circumference of the femoral neck, and a binary ‘MRI cam-intrusion sign’ was defined (positive if βmin<0°). Hips were then instrumented with a piezoresistive sensor before conducting six repeated impingement trials, measuring acetabular contact force (F), centroid location, and distribution. A binary ‘contact-force sign’ (positive when F>20N) defined elevated contact force.
Minimum β-angle ranged from 1.4° to -28.5° in cams versus 4.6° to -0.2° in controls. Cam hips were significantly more likely than controls to have a positive MRI cam-intrusion sign (p=0.0182, Fisher’s exact test) and positive contact-force sign (p=0.0083). There was a significant relationship between the MRI cam-intrusion sign and contact-force sign (p=0.033).
This thesis established that open MRI measures of cam FAI relate to contact mechanics, indicating that open MRI has significant potential to investigate the biomechanics of cam impingement. Open MRI can be used to establish treatment guidelines and understand why some hips develop OA and some do not.Applied Science, Faculty of
Graduate
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Zdero, Radovan. "A new diagnostic ultrasound technique for studying TKR contact mechanics." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0001/NQ42992.pdf.
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Jackson, Monique I. "The mechanics of the table contact phase of gymnastics vaulting." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/6330.
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A computer simulation model of the table contact phase of gymnastics vaulting was developed to gain an understanding of the mechanics of this phase of the vault. The model incorporated a gymnast and a vaulting table, and used a novel two-state contact phase representation to simulate the interaction between these two bodies during the table contact phase. The gymnast was modelled in planar form using seven segments, with torque generators acting at the wrist, shoulder, hip and knee joints. The model also allowed for shoulder retraction and protraction, displacement of the glenohumeral joint centre and flexion/extension of the fingers. The table was modelled as a single rigid body that could rotate. The model was personalised to an elite gymnast so that simulation outputs could be compared with the gymnast's performance. Kinematic data of vaulting performances were obtained using a optoelectronic motion capture system. Maximal voluntary joint torques were also measured using an isovelocity dynamometer, and a torque - angle - angular velocity relationship was used to relate joint torques to joint angles and angular velocities. A set of model system parameters was determined using a gymnast-specific angle-driven model by matching four simulations to their respective performances concurrently. The resulting parameters were evaluated using two independent trials, and found to be applicable to handspring entry vaults. The torque-driven model was successfully evaluated, and shown to produce realistic movements, with mean overall differences between simulations and recorded performances of 2.5% and 8.6% for two different handspring entry vaults. The model was applied to further understanding of the mechanics of the table contact phase of gymnastics vaulting. Optimisation showed that there was limited potential (1.3%) for the gymnast to improve performance through technique changes during the table contact phase. However, with additional changes in configuration at table contact post-flight rotation could be increased by 9.8% and post-flight height could be increased by 0.14m. Angular momentum was found to always decrease during the table contact phase of the vault, although the reductions were less when maximising post-flight rotation.
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Acito, Vito. "In situ X-ray computed tomography for soft contact mechanics." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2023. http://www.theses.fr/2023ECDL0054.
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L'aire de contact réelle AR entre deux solides en contact est une quantité fondamentale qui contrôle le comportement de frottement d'une interface de contact. Bien que la plupart des techniques expérimentales visant à mesurer cette quantité soient basées sur le contraste optique entre les régions en contact et hors contact, ces méthodes sont limitées par la transparence optique requise par au moins l'un des deux corps en contact. En outre, ces techniques ne permettent d'accéder qu'à l'interface de contact sans fournir d'informations sur d'autres quantités physiques importantes telles que la déformation globale ou les phénomènes hors contact à la surface. À partir de quelques travaux pionniers, nous proposons la tomographie à rayons X (XRCT) in-situ comme méthode alternative pour surmonter ces limites et accéder à la morphologie complète du contact en 3D avec des paires de contacts potentiellement non transparentes. Dans toutes les études précédentes, les analyses ont été effectuées sur des surfaces complexes sans se concentrer sur des examens préliminaires des limites de la XRCT (comme l'estimation des erreurs dans la mesure de AR). Dans ce cadre, nous avons proposé l'utilisation d'un système modèle composé d'une sphère lisse en élastomère (PDMS) et d'une plaque rigide lisse (en PMMA) pour simplifier le problème et souligner les avantages et les inconvénients de cette méthode expérimentale. Nous nous sommes d'abord concentré sur la mesure in-situ de l'évolution de AR au cours d'un essai de compression et de cisaillement réalisé sur notre système modèle. Les résultats ont été comparés à ceux d'un dispositif opto-mécanique 2D déjà maîtrisé. Enfin, à partir de la reconstruction en 3D in-operando du contact modéle indenté cisaillé, nous avons pu extraire les champ de déplacement, déformation et contraintes dans le contact par corrélation numérique des volumes (DVC) en utilisant comme marqueurs des particules préalablement dispersés dans le PDMS. Tous ces résultats ont été mis en regard des prédictions théoriques de modèles de la littératureThe real contact area AR between two solids in contact is a fundamental quantity that controls the frictional behavior of a contact interface. Although most experimental techniques aimed at measuring this quantity are based on the optical contrast between in-contact and out-of-contact regions, these methods are limited by the optical transparency required for least one of the two contacting bodies. Furthermore, these techniques only provide access to the contact interface without providing information on other important physical quantities such as the global deformation or the out-of-contact phenomena at the surface. Building on some pioneering work, we propose in-situ X-ray tomography (XRCT) as an alternative method to overcome these limitations and access the full 3D contact morphology with potentially non-transparent contact pairs. In all previous studies, analyzes were performed on complex surfaces without focusing on preliminary examinations of the limitations of XRCT (such as estimating errors in measuring AR). In this context, we proposed the use of a model system composed of a smooth elastomer sphere (PDMS) and a smooth rigid plate (PMMA) to simplify the problem and highlight the advantages and disadvantages of this experimental method. We first focused on measuring in-situ the evolution of AR during a compression and shear test carried out on our model system. The results were compared to those of a 2D opto-mechanical device already mastered. Finally, from the in-operando 3D reconstruction of the indented and sheared contact , we were able to extract the displacement, deformation and stress fields in the contact by digital correlation of volumes (DVC) using as markers particles previously dispersed in PDMS. All these results were compared to theoretical predictions from models in the literature
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Shariati, Hossein. "Mechanical modeling of granite subjected to contact loading." Licentiate thesis, KTH, Hållfasthetslära (Avd.), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-263592.
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The mechanical properties of Bohus granite subjected to contact loading is investigated based on experimental and numerical results. An elasto-plastic constitutive material model combined with a damage description is employed. The material model parameters are determined based on experimental results. Any kind of inelastic deformation except the tensile failure is described by a linear Drucker-Prager (DP) plasticity model with variable dilation angle. As for the damage description, an anisotropic damage model (DFH model) is considered to account for the tensile failure (i.e. mode I fracture). The resulting constitutive model is implemented numerically to simulate the mechanical behavior of the material under indentation loading up to its load capacity. In paper A, the DP material model parameters are calibrated based on quasioedometric tests performed in an earlier work. It is described how the yield surface and dilation angle are determined from this test. The calibrated material model is implemented numerically in a commercial finite element software. The numerical model is validated based on quasi-static spherical indentation tests performed in this work. The force-penetration (P-h) response of the material is recorded during the indentation tests. Moreover, a high speed camera is utilized to observe the specimen surface around the contact area during the indentation test. It is detected that the observed load-drops in the P-h response correspond to material removals on the specimen surface. The tested specimens are also scanned by X-ray tomography to investigate the fracture pattern. In paper B, the anisotropic DFH damage model is employed in order to predict the fracture pattern observed in the indentation test. The chosen damage model considers the heterogeneity in the material tensile strength. It is described how the statistical distribution of the tensile strength is calibrated. The calibrated DFH model is combined with the DP model and the resulting DP-DFH model is utilized to simulate the P-h response and the fragmentation process of Bohus granite subjected to quasi-static contact loading.Examinator: Professor Mårten Olsson, KTH, Stockholm
QC 20191108
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Kruntcheva, Mariana. "Dynamics of circular cylindrical shells in contact with fluid." Thesis, Robert Gordon University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245161.
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Krithivasan, Vijaykumar Jackson Robert Lloyd. "Finite element analysis of three-dimensional elasto-plastic sinusoidal contact and inclusion in a multi-scale rough surface contact model." Auburn, Ala., 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SPRING/Mechanical_Engineering/Thesis/Krithivasan_Vijaykumar_55.pdf.
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Liu, Ming. "FINITE ELEMENT ANALYSIS OF THE CONTACT DEFORMATION OF PIEZOELECTRIC MATERIALS." UKnowledge, 2012. http://uknowledge.uky.edu/cme_etds/15.
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Piezoelectric materials in the forms of both bulk and thin-film have been widely used as actuators and sensors due to their electromechanical coupling. The characterization of piezoelectric materials plays an important role in determining device performance and reliability. Instrumented indentation is a promising method for probing mechanical as well as electrical properties of piezoelectric materials.
The use of instrumented indentation to characterize the properties of piezoelectric materials requires analytical relations. Finite element methods are used to analyze the indentation of piezoelectric materials under different mechanical and electrical boundary conditions.
For indentation of a piezoelectric half space, a three-dimensional finite element model is used due to the anisotropy and geometric nonlinearity. The analysis is focused on the effect of angle between poling direction and indentation-loading direction on indentation responses.
For the indentation by a flat-ended cylindrical indenter, both insulating indenter and conducting indenter without a prescribed electric potential are considered. The results reveal that both the indentation load and the magnitude of the indentation-induced potential at the contact center increase linearly with the indentation depth.
For the indentation by an insulating Berkovich indenter, both frictionless and frictional contact between the indenter and indented surface are considered. The results show the indentation load is proportional to the square of the indentation depth, while the indentation-induced potential at the contact center is proportional to the indentation depth.
Spherical indentation of piezoelectric thin films is analyzed in an axisymmetric finite element model, in which the poling direction is anti-parallel to the indentation-loading direction.
Six different combinations of electrical boundary conditions are considered for a thin film perfectly bonded to a rigid substrate under the condition of the contact radius being much larger than the film thickness. The indentation load is found to be proportional to the square of the indentation depth.
To analyze the decohesion problem between a piezoelectric film and an elastic substrate, a traction-separation law is used to control the interfacial behavior between a thin film and an electrically grounded elastic substrate. The discontinuous responses at the initiation of interfacial decohesion are found to depend on interface and substrate properties.
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McKeon, James Christopher P. "Tomography applied to Lamb wave contact scanning nondestructive evaluation." W&M ScholarWorks, 1998. https://scholarworks.wm.edu/etd/1539623370.
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The aging world-wide aviation fleet requires methods for accurately predicting the presence of structural flaws that compromise airworthiness in aircraft structures. Nondestructive Evaluation (NDE) provides the means to assess these structures quickly, quantitatively, and noninvasively. Ultrasonic guided waves, Lamb waves, are useful for evaluating the plate and shell structures common in aerospace applications. The amplitude and time-of-flight of Lamb waves depend on the material properties and thickness of a medium, and so they can be used to detect any areas of differing thickness or material properties which indicate flaws. By scanning sending and receiving transducers over an aircraft, large sections can be evaluated after a single pass. However, while this technique enables the detection of areas of structural deterioration, it does not allow for the quantification of the extent of that deterioration. Tomographic reconstruction with Lamb waves allows for the accurate reconstruction of the variation of quantities of interest, such as thickness, throughout the investigated region, and it presents the data as a quantitative map. The location, shape, and extent of any flaw region can then be easily extracted from this Tomographic image. Two Lamb wave tomography techniques using Parallel Projection tomography (PPT) and Cross Borehole tomography (CBT), are shown to accurately reconstruct flaws of interest to the aircraft industry. A comparison of the quality of reconstruction and practicality is then made between these two methods, and their limitations are discussed and shown experimentally. Higher order plate theory is used to derive analytical solutions for the scattering of the lowest order symmetric Lamb wave from a circular inclusion, and these solutions are used to explain the scattering effects seen in the Tomographic reconstructions. Finally, the means by which this scattering theory can be used to develop Lamb wave Tomographic algorithms that are more generally applicable in-the-field, is presented.
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ELKILANI, YASSER SHAWKI. "A HYBRID ELASTICITY AND FINITE ELEMENT METHOD FOR THREE-DIMENSIONAL CONTACT PROBLEMS WITH FRICTION." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1055167472.
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Gomez, Miguel J. "Optimization-based analysis of rigid mechanical systems with unilateral contact and kinetic friction /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/6793.
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Patil, Amit. "Inflation Mechanics of Hyperelastic Membranes." Licentiate thesis, KTH, Strukturmekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160707.
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The applications of inflatable membrane structures are increasing rapidly in the various fields of engineering and science. The geometric, material, force and contact non-linearities complicate this subject further, which in turn increases the demand for computationally efficient methods and interpretations of counter-intuitive behaviors noted by the scientific community. To understand the complex behavior of membranes in biological and medical engineering contexts, it is necessary to understand the mechanical behavior of a membrane from a physics point of view. The first part of the present work studies the pre-stretched circular membrane in contact with a soft linear substrate. Adhesive and frictionless contact conditions are considered during inflation, while only adhesive contact conditions are considered during deflation. The peeling of membrane during deflation is studied, and a numerical formulation of the energy release rate is proposed. It is observed that the pre-stretch is having a considerable effect on the variation of the energy release rate. In the second part, free and constrained inflation of a cylindrical membrane is investigated. Adhesive and frictionless contact conditions are considered between the membrane and substrate. It is observed that the continuity of principal stretches and stresses depend on contact conditions and the inflation/deflation phase. The adhesive traction developed during inflation and deflation arrests the axial movement of material points, while an adhesive line force created at the contact boundary is responsible for a jump in stretches and stresses at the contact boundary. The pre-stretch produces a softening effect in free and constrained inflation of cylindrical membranes. The third part of the thesis discusses the instabilities observed for fluid containing cylindrical membranes. Both limit points and bifurcation points are observed on equilibrium branches. The secondary branches emerge from bifurcation points, with their directions determined by an eigen-mode injection method. The occurrence of critical points and the stability of equilibrium branches are determined by perturbation techniques. The relationship between eigenvalue analysis and symmetry is highlighted in this part of the thesis.QC 20150227
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Gokay, Kemal. "Contact Mechanics Of Graded Materials With Two Dimensional Material Property Variations." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606527/index.pdf.
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ABSTRACT
CONTACT MECHANICS OF GRADED MATERIALS WITH TWODIMENSIONAL
MATERIAL PROPERTY VARIATIONS
Gökay, Kemal M.S., Department of Mechanical Engineering Supervisor: Asst. Prof. Dr. Serkan Dag September 2005, 62 pages Ceramic layers used as protective coatings in tribological applications are known to be prone to cracking and debonding due to their brittle nature. Recent experiments with functionally graded ceramics however show that these material systems are particularly useful in enhancing the resistance of a surface to tribological damage. This improved behavior is attributed to the influence of the material property gradation on the stress distribution that develops at the contacting surfaces. The main interest in the present study is in the contact mechanics of a functionally graded surface with a two &ndash
dimensional spatial variation in the modulus of elasticity. Poisson&rsquo
s ratio is assumed to be constant due to its insignificant effect on the contact stress distribution [30]. In the formulation of the problem it is assumed that the functionally graded surface is in frictional sliding contact with a rigid flat stamp. Using elasticity theory and semi-infinite plane approximation for the graded medium, the problem is reduced to a singular integral equation of the second kind. Integral equation is solved numerically by expanding the unknown contact stress distribution into a series of Jacobi polynomials and using suitable collocation points. The developed method is validated by providing comparisons to a closed form solution derived for homogeneous materials. Main numerical results consist of the effects of the material nonhomogeneity parameters, coefficient of friction and stamp size and location on the contact stress distribution.
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Andres, Michael [Verfasser]. "Dual-dual formulations for frictional contact problems in mechanics / Michael Andres." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2011. http://d-nb.info/1014363608/34.
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Hallberg, Hofstrand Erik. "Flexographic post-printing of corrugated board : contact mechanics and print quality /." Karlstad : Department of Chemical Engineering, Karlstads universitet, 2006. http://www.diva-portal.org/kau/theses/abstract.xsql?dbid=537.
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Zhou, Yunong [Verfasser]. "Modelling contact mechanics with improved Green's function molecular dynamics / Yunong Zhou." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2020. http://d-nb.info/1228858713/34.
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FEINAUER, CHRISTOPH. "The Statistical Mechanics Approach to Protein Sequence Data: Beyond Contact Prediction." Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2640930.
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The recent application of models from inverse statistical mechanics to protein sequence data in has been a large success. In my thesis, I will build upon these models but also use them beyond their original aim of residue contact prediction. This includes the improvement of contact prediction itself by extending the models, the application of the methods in the wider scope of protein interaction networks and the prediction of further biological characteristics from the extracted information.
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Kudawoo, Ayaovi Dzifa. "Problèmes industriels de grande dimension en mécanique numérique du contact : performance, fiabilité et robustesse." Phd thesis, Université de Provence - Aix-Marseille I, 2012. http://tel.archives-ouvertes.fr/tel-00773642.
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Ce travail de thèse concerne la mécanique numérique du contact entre solides déformables. Il s'agit de contribuer à l'amélioration de la performance, de la fiabilité et de la robustesse des algorithmes et des modèles numériques utilisés dans les codes éléments finis en particulier Code_Aster qui est un code libre développé par Électricité De France (EDF) pour ses besoins en ingénierie. L'objectif final est de traiter les problèmes industriels de grande dimension avec un temps de calcul optimisé. Pour parvenir à ces objectifs, les algorithmes et formulations doivent prendre en compte les difficultés liées à la mécanique non régulière à cause des lois de Signorini-Coulomb ainsi que la gestion des non linéarités dûes aux grandes déformations et aux comportements des matériaux étudiés. Le premier axe de ce travail est dédié à une meilleure compréhension de la formulation dite de " Lagrangien stabilisé " initialement implémentée dans le code. Il a été démontré l'équivalence entre cette formulation et la formulation bien connue de " Lagrangien augmenté ". Les caractéristiques mathématiques liées aux opérateurs discrets ont été précisées et une écriture énergétique globale a été trouvée. Une réflexion a été mise en oeuvre en vue de renforcer de manière faible la condition cinématique sur la normale dans la zone de contact via les techniques d'optimisation sans contraintes. La nouvelle formulation est dite de " Lagrangien augmenté non standard ". Trois nouvelles stratégies basées sur le Lagrangien augmenté ont été implémentées. Il s'agit de la méthode de Newton généralisée : c'est une méthode d'optimisation qui permet de résoudre toutes les non linéarités du problème en une seule boucle d'itérations. La méthode de Newton partielle est une méthode hybride entre la méthode historique du code appelée méthode de point fixe et la méthode de Newton généralisée. Enfin, on a mis en place une façon originale de traiter le cyclage : ce phénomène apparaît souvent au cours de la résolution du problème et il entraîne la perte de convergence des algorithmes. La stratégie nouvelle permet d'améliorer la robustesse des algorithmes.