Strain Induced Crystallisation during Crack Propagation, Consequence of Thermo-Oxydative Aging

These last years, thanks to progresses in X-ray characterization techniques, Strain Induced Crystallization (SIC) of Natural Rubber (NR) has been deeply studied: a large number of recent publications have explored the influence of intrinsic (materials formulation) and extrinsic (loading conditions, temperature…) parameters on this phenomenon. Fed by all these results, new works in modelling have been launched, which should finally lead to a much better comprehension of SIC. Yet, a lot of these academic studies find their origin in the need to clarify the claimed beneficial role of SIC on the fatigue properties of NR; from this point of view, a lot of work is still necessary. Indeed, fatigue and cracks propagation behaviors involve complex strain fields in the material; cavitation and decohesion (when NR is filled) are known to occur in the crack tip region, which makes more difficult the analysis of SIC mechanisms; in addition, in a lot of industrial applications, the materials submitted to fatigue are also aging, i.e. their structural and chemical characteristics, which are known to control SIC, evolve with time…to a point where it is not sure that SIC still occur or has an impact on their crack propagation and fatigue behavior. Thus, in this presentation, we will begin by a state of the art on SIC mechanisms and the questions which still need to be addressed; then we will show new results on the SIC mechanisms, and more generally on all the microstructural modifications, during crack propagation in NR; the consequences of the material thermo-oxydative aging on these phenomena will also be discussed.