Contact mechanics | EPFL Graph Search

Contact mechanics is the study of the deformation of solids that touch each other at one or more points. A central distinction in contact mechanics is between stresses acting perpendicular to the contacting bodies' surfaces (known as normal stress) and frictional stresses acting tangentially between the surfaces (shear stress). Normal contact mechanics or frictionless contact mechanics focuses on normal stresses caused by applied normal forces and by the adhesion present on surfaces in close contact, even if they are clean and dry. Frictional contact mechanics emphasizes the effect of friction forces. Contact mechanics is part of mechanical engineering. The physical and mathematical formulation of the subject is built upon the mechanics of materials and continuum mechanics and focuses on computations involving elastic, viscoelastic, and plastic bodies in static or dynamic contact. Contact mechanics provides necessary information for the safe and energy efficient design of technical

Contact Mechanics for Hyperelastic Materials

Youssef Eddebbarh

Understanding the mechanical behavior of soft materials is of great importance for many applica-tions, especially for bioengineering and clinical applications. Hertzian theory is frequently used to characterize the mechanical properties of such materials. However, these materials undergo large deformations resulting in non-linear stress-strain response, which cannot be accurately captured by Hertzian contact. These materials are also rate sensitive, where at high velocities, external e˙ects such as air can influence the mechanical response. In this study, we experimentally in-vestigated the contact response of a soft spherical impactor on a rigid substrate and by using the principle of Total Internal reflection, we directly measured the contact radius. The e˙ects of specimen size, loading rate and boundary conditions were also examined and we found that, for the studied velocities, only the boundary conditions a˙ects both the radius-displacement and load-displacement relationships, leading to deviations from the theory at di˙erent indentation depths. We finished by setting up an experiment consisting of a pendulum for studying the e˙ects of high velocities and the influence air.

2021

Couplage d'une loi d'adhésion à une loi de contact avec frottement pour l'étude de la décohésion dans les matériaux composites

Christian Talon

In this thesis, an original law of adhesion is developed and then coupled to the classical law of unilateral contact with threshold friction, in order to study the phenomenon of fibre/matrix debonding in composite materials. This tribological law is developed within the framework of standard generalized materials adapted to interfaces. Thus, the law is derived from a free energy potential ψc and a dissipation potential Φc. The adhesive interface is interpreted as a bundle of links connecting the two contact surfaces. Each link is assumed to have a plastic behavior with softening and damage, caused by stretching, to represent the loss of adhesion. An internal variable ga measuring an irreversible adhesive gap is introduced and associated by energetic duality to an adhesive stress pa. The ranges of ga and pa are limited by two characteristic constants of adhesion, gM and pM respectively. pM is the maximum adhesive tension below which the links remain elastic. Above this limit, debonding and damage of the links occur as ga increases. Once ga reaches the value gM, total rupture of the adhesive bond occurs. This adhesion law is then mounted in parallel to the contact and friction laws into a unique law. The law is regularized using either the approximate penalty method or the exact augmented Lagrangian method, in option. The regularized laws are implemented in a node-to-node contact element of the finite element code TACT. The adhesive force is computed by means of a predictor-corrector with projection algorithm for integrating the evolution of ga, and the relevant Jacobian tensors required for the resolution of non-linearities by the iterative scheme of Newton are calculated. This is accomplished for the penalty and the augmented Lagrangian regularizations. A traction test of a glass/epoxy interface in the normal direction is designed and used to experimentally determine the parameters pM and gM of such an interface (pM directly and gM indirectly). Numerical simulations of adhesion between a rigid punch and an elastic half-space enable the comparison of the proposed model of adhesion to the classical theories of adhesion. A numerical simulation of the standard pull-out test of a fibre embedded in a matrix is then performed, and the numerical shear distribution along the interface is compared to the analytical one existing for this experiment. The results are in good agreement with existing ones. Finally, a crack propagation in a fibrous composite is simulated.

EPFL2002

Couplage d'une loi d'adhésion à une loi de contact avec frottement pour l'étude de la décohésion dans les matériaux composites

Christian Talon

EPFL2002