Relative influence of microstructure and macroscopic triaxiality on cavitation damage in a semi-crystalline polymer

Abstract

The relative influence of microstructure on mechanical behaviour and cavitation in a semi-crystalline polymer is studied here and compared to the macroscopic triaxiality effect induced by the sample shape. Microstructure effects result from process or annealing. In the later case, DSC and DMA experiments show secondary crystallization, homogenization of primary crystals and decrease of the amorphous phase mobility. Samples shapes exhibiting more or less macroscopic triaxiality are tested in tension before and after annealing at high temperature. More cavitation is observed after annealing – or in slowly cooled down materials – in weakly triaxial structures (dumbbell specimens or diabolo specimens with a large curvature radius). In highly triaxial samples (diabolo specimens with a small curvature radius) no difference are observed between as-received and annealed samples: the macroscopic hydrostatic stress is then of major importance compared to the raise of local hydrostatic stress within the amorphous layer resulting from high-temperature annealing.