Effect of thermal cycles on the deformation state at the crack tip of crystallizable natural rubber
Résumé
This paper deals with the effect of temperature variations on crack tip kinematicsin rubbers, especially in crystallizing rubbers. In such materials, the high deformation levelencountered at the crack tip engenders the formation of crystallites. As a consequence, thecrack tip is reinforced and resists crack growth. However, this phenomenon is signicantly affectedby variations in material temperature. This is classically observed at the macroscopicscale in terms of crack propagation rate and path. In this study, the effect of temperature isstudied at the local scale, by measuring the change in the kinematic eld at the crack tip duringthermal cycles. Results show that, in crystallizable natural rubber, the effect of temperaturedepends on the stretch ratio atained in the zone under consideration. In slightly stretchedzones, the stretch ratio increases with the increase in temperature, whereas it decreases inhighly stretched zones. This highlights the competition between the effects of the variationsin internal energy and in entropy on the thermomechanical response. Moreover, if crystallitesform in highly stretched zones, the increase in temperature leads to crystallite melting,which increases the stretch ratio. This is explained by the fact that crystallites act as llers byconcentrating the stress and therefore by increasing the apparent stiffness of the material.
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