Correlation between macroscopical viscoelastic behaviour and micromechanisms in strained α polyvinylidene fluoride (PVDF)

Links between macroscopical behaviour and micromechanisms of deformation (constrained amorphous shearing, crystalline lamellae slip or unfolding, micro-voiding) are studied in uniaxial tension and creep tests performed on apolar PVDF at different strain rates (tensile tests), stresses (creep tests) and temperatures. Volume changes are simultaneously measured to take into account cavitation processes. The major influence of amorphous phase shearing and its competition with cavitation are described for temperatures ranging from ambient up to 100 degrees C. Concepts of crystallite unfolding are introduced and used to understand particularities of high temperature deformation. Unfolding processes are suggested to be responsible for the different long-term behaviour (creep kinetics and fracture). (C) 2000 Elsevier Science S.A. All rights reserved.