Geometry-dependent fracture behavior of glassy polymer films: Insights from mode I and mode III tearing of polyimide films

Abstract

Through in-plane (mode I) and trouser (mode III) tearing experiments conducted on polyimide film, and the Essential Work of Fracture theory, the influence of geometry (film thickness, orientation, geometric ratio, and pre-crack patterns) on the fracture behavior is studied. The result shows that polyimide film displays brittle fracture macroscopically, but presents localized microplasticity on the fracture surface examined by scanning electron microscopy. The fracture behavior of polyimide films exhibits a pronounced geometry-dependence and the ranking of the influencing factors is: thickness > orientation = geometric ratio > pre-crack pattern. The fracture toughness for mode III fractures is only 9 % − 15 % of that for mode I, highlighting mode III as the most critical and hazardous fracture mode for polyimide films.