Heat and strain measurements at the crack tip of filled rubber under cyclic loadings using full-field techniques

International audienceThis study aims at characterizing heat sources during the deformation of the crack tip zone in carbon black filled Styrene Butadiene Rubber (SBR). For this purpose, the thermomechanical response of cracked specimens was investigated using coupled full thermal and kinematic field measurements and a suitable motion compensation technique. The kinematic analysis enabled us to define the zone of influence of the crack and to measure the maximum stretch ratio level. The maximum stretch ratio level at the crack tip is higher than that measured at specimen failure during uniaxial tensile tests, which can be explained by considering the maximum chain extensibility. The calorimetric analysis shows that the high heat source gradient zone is very much more confined than the high temperature gradient zone. The heat sources at the crack tip remain positive and small during unloading, which indicates that mechanical dissipation is high and confined to the crack tip. This result highlights that the material behaves very differently in the crack tip zone compared to homogeneous tests. This proves that it not possible to predict the behavior of the crack tip zone from homogeneous tests. Moreover, it is observed that the mechanical dissipation decreases with the number of first cycles, which highlights the fact that the material is increasingly accommodated. This study provides the first accurate measurement of heat sources at the crack tip of rubber, constituting a new experimental tool in the fracture mechanics of rubber

Numerical-simulation of Stratified Coating Flow By a Variational Method

We present a method for calculating the two-dimensional steady state flow of stratified Newtonian liquids. Lagrange multipliers are used to impose the free surface conditions. When surface tension is not vanishing, contact angles are easily introduced. Inlet and outlet free sections are treated by means of a technique which allows us to calculate layer thicknesses as part of the result. Parametric studies are thereby facilitated. The solution procedure is derived from a variational approach. At each iteration, a linear system is obtained by linearizing the weak form of the problem. A finite element discretization is carried out on this continuous system. The mesh is adapted to the successive configurations of the free boundaries. Ill-shaped elements are corrected by exerting artificial forces on the mesh vertices. The global iterative scheme exhibits a quasi-quadratic convergence. The outflow from a slot and the curtain coating flow are analysed and illustrate the power of the method. (C) 1994 Academic Press, Inc

Analysis of the Interface Singularity of a 2-fluid Flow By H and H-p Finite-elements

The h-p method is shown to be a powerful tool for exhibiting the presence of a singularity at the extremity of a liquid-liquid interface without surface tension, in a Newtonian isothermal layered flow. Numerical results indicate that no pressure continuity seems to hold on the interface separation line