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Oscillation properties of delaminated structures are governed by dissipative impact-like contacts in the debonded region. The contribution focuses on the numerical simulation of this special type of contact. A robust and efficient contact strategy is presented mainly based on the theory of sudden impacts embedded in Finite Element methods.

Within the classical dynamics of mechanical systems physical effects in boundary layers of contacting bodies are fundamental. Examples are impact motion or frictional contact. Usually the dynamics in boundary layers is given on other time and length scales than the dynamics of the system itself.

If the coefficient of friction is sufficiently large, elastic contact problems can exhibit ‘wedged’ solutions in which the body remains in a state of stress in the absence of applied loads. In this paper, we demonstrate that the critical coefficient of friction for wedging to occur is also the lowest real eigenvalue of a certain nonlinear eigenvalue problem. Possible strategies for solving this eigenvalue problem are discussed.

The wedged configuration with Coulomb friction (i.e. a nontrivial equilibrium state of a linear elastic body in a frictional unilateral contact with a rigid body under vanishing external loads), which is considered here in a 3-D continuous framework, was firstly studied in [1]. A supremal functional defined on the set of admissible normal displacement and tangential stresses is introduced. The infimum of this functional defines the critical friction coefficient for the wedged problem (WP). For friction coefficients with > (WP) has at least a solution and for < (WP) has no solution.

The review of a very broad research program carried out at Technion on different aspects of the fundamental contact and friction problem is presented.

A new mechanism of dynamic instability is found, generated by the thermo-elastic deformations. In particular, it is found that even if coupling between dynamics and heat transfer seems apparently very weak (due to the very different time scales involved), the dynamic modes become unstable for arbitrarily small speeds, in a simple model involving an elastic layer compressed between two rigid plates and sliding out-of-plane. The present analysis neglects the effect of out-ofplane deformations and possible stick-slip in that direction.

Friction occurs in the contact between tyre and road. The friction of rubber material on dry surfaces is dominated by hysteresis and adhesion effects. Hysterisis friction is characterised by the energy dissipation within the visco-elastic material, which is caused by its deformation while passing the surface roughness. Hysteresis effects are modelled by an extended linear visco-elastic material with several Maxwell elements. The development of a model in the time domain allows to consider nonlinear effects. Additionally temperature effects are taken into account based on the WLF-transformation. Adhesion forces originate from molecular bindings between the contact partners. This effect is simulated by applying a modified model of Achenbach on real surfaces. The temperature distribution within the friction contact region is investigated experimentally as well. Furthermore global stick-slip vibrations of a rubber block element are investigated using a global contact model. Numerical results are compared with experiments performed on a tribometer test rig.

The modeling of rubber frictional properties on rough surfaces is of considerable importance for the prediction of tire traction properties. The presented work consists in a physically based model describing the dynamic contact and the sliding friction of elastomers on rough surfaces. The self-affine character of rough substrates is analytically treated with correlation functions which depend on three surface descriptors. This allows a generalization of the concepts introduced by Greenwood and Williamson and a quantitative estimation of the velocity dependent real area of contact. The hysteresis friction can be modelled in the frame of this theory, originating from the energy losses due to the local deformation of the rubber from the surface asperities during dynamic contact. The experimental results show that the frictional behaviour under wet conditions is fairly described by the hysteresis friction. The transition from wet to dry friction is explained via an adhesion component assumed to be related with the real area of contact. This approach is also confirmed by the experiment and gives a deeper insight in the relationship between the material viscoelastic properties, the surface roughness and the frictional behavior.

This paper presents a model for unsteady longitudinal slippage of a loaded rubber wheel. The aim of modelling was to calculate the dynamical contact behavior in a numerical efficient way. Further on, simulation results are compared to experimental data.

Friction of tyres is a major contributor to automotive safety. Usually friction if most demanded on wet roads. Several theories have been proposed about the physical origins of dry and wet friction. They tend to evaluate the respective contributions of adhesion forces and dissipative mechanisms at the relevant scales. We discuss their achievements and limitations. The relevance of taking into account these physical mechanisms to improve the simulation of tire friction problems is addressed.