Scanning electron microscope visualisation of crack initiation and propagation under static and fatigue loading on thermoplastic elastomers

In the present study, the static and fatigue behaviour of two types of co-poly(ether ester)-based thermoplastic elastomers was investigated. By means of static and fatigue tests it could be shown that cracks initiated in a relatively early stage of the process. In this study, special attention was paid to the observation of crack propagation phenomena. The fatigue tests showed that cracks could initiate and propagate over a long period of time since 90% of the fatigue life was spent in the crack stage. Hence, the excellent fatigue properties of co-poly(ether ester)s are due to the material's high resistance to crack growth. Moreover, the microscopic crack processes under static and fatigue loading were investigated. The results of the microscopic analysis concerning crack mouth formation, changes in the crack extension direction due to inelastic deformation induced anisotropy, formation of ripples and curtain like ridges on the crack surfaces etc. are presented and discussed in detail. Finally, models for an explanation of the observed crack propagation phenomena were developed which might also be translated to other types of polymeric engineering materials.