Effects of microvoiding on tensile deformation and fracture of polyoxymethylene

Abstract

Interrupted tensile tests were performed on different notch profile polyoxymethylene specimens at 160°C primarily in order to provide sample material for morphological and structural examinations. Scanning electron microscopy and small angle X-ray scattering were employed to examine the contribution of microvoids and other forms of damage to the large scale tensile deformation behaviour. It was established that the nucleation of spherical microvoids occurs during tensile deformation in the pre-yielding region. It was also concluded that voiding is well established by the yield point, while the formation of new microvoids is a continuous process during subsequent deformation. The interrupted tests clearly demonstrated the different stages in the formation, growth and coalescence of voids to form a continuous fracture path leading to fibrillation of the material and ultimately to fracture. Simple finite element models were used to predict the evolution of stress triaxiality with increasing deformation in the notched specimens.