Ductile–brittle failure of amorphous glassy polymers: A phase-field approach

Abstract

Optimal use and design of amorphous glassy polymers in goods have become a significant task in the key industrial sectors ranging from micro-electronics to aerospace and medical industry. Depending on the microstructure, temperature level and the external loading rate to which these polymers are subjected, the fracture response may change from ductile to brittle or vice versa. While the ductile response is manifested by diffuse shear zones exhibiting volume-preserving inelastic deformations, the brittle response is revealed by very small crack-like defects containing a sequence of fibrillar bridges and elongated micro-voids, thereby resembling the void formation consisting of nucleation and growth stages. Their formation is driven by tensile straining followed by volumetric inelastic deformations. The present study is concerned with the description of shear yielding and crazing in terms of their respective evolution equations. Besides, an extension towards the modeling of the fracture is employed via the crack phase-field approach, accounting for ductile and brittle failure concomitantly. This is granted by the novel failure criterion that features a critical amount of plastic strain and void volume fraction. Such a modality simultaneously models the macroscopic crack initiation and growth leading to ductile or brittle fracture, as such purports to be more physically grounded compared to extant models in the literature. The predictive performance of the proposed model has been demonstrated by fitting of various extant experimental data of homogeneous and inhomogeneous tests in relation to initial boundary value problems.