Sensitivity of damage to microstructure evolution occurring during long-term high-temperature annealing in a semi-crystalline polymer
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This study aimed to highlight the role of microstructure evolutions induced by high temperature annealing on damage in a semi-crystalline polymer during long-term applications. It was based on a polar form of poly(vinylidene fluoride) (Tg = −40 °C; Tm = 170 °C) and the long term annealing context dealt with burst resistance tests performed for 1000 h in a temperature range from 95 °C up to 140 °C. A secondary crystallization was observed after annealing by Differential Scanning Calorimetry and a consistent phenomenology was evidenced in Dynamic Mechanical Analysis. A decrease of the amorphous phase mobility and a weak reorganization of primary crystals were observed at the same time. Tensile tests on annealed specimens pointed out modulus and yield stress reinforcement, partial disentanglement in the amorphous phase and a raise of the volume strain. Thermally-induced microstructure evolutions were shown to enhance cavitation and slow down crack opening displacement kinetics. This last effect would result from both a raise of the yield stress in primary crystals and secondary crystallization.
KeywordsCavitation Dynamic Mechanical Analysis Crack Opening Displacement Differential Scanning Calorimetry Thermogram Crack Opening Displacement
Dr. J.L. Gacougnolle must be greatly acknowledged for his constant interest in this study and very precious remarks, as well as Pr. A. Dragon for his help in finalizing this paper. Authors would like to thank Arkema for financial support and PhD grant to D. Girard, and thank Dr. G. Hoschstetter for fruitful discussion.
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