High‐Speed fracture mechanics by photography of polypropylene copolymers

Publisher Website
Google Scholar
Abstract
The use of photography applied to stroboscopy in analyzing the processes inherent to the starting and propagation of cracks in materials is a technique which has proved to be of great interest, especially since it enables one to check and “directly” study the evolution of such phenomena. Using fracture mechanics criteria this technique has been applied to the study of the impact behavior of some polypropylene copolymers at different rubber contents obtained either by blending or by synthesis. This technique makes it possible to determine numerous parameters of fracture mechanics, including C.O.D. (crack opening displacement), C.O.A. (crack opening angle), JIc, the plastic work parameter, determined from the resistance curveR, tearing modulus, and crack propagation velocity. Furthermore, under high strain rate conditions, the value taken on by the coefficient “λ” relating theJ‐integral to C.O.D. (1, 2) were checked for those materials using the equationJ= λ. σy · C.O.D., Hayes and Turner (3) and Boyle (4). From analysis of the materials it was possible to note that the synergetic effect of the EP (ethylenepropylene) rubber increased, especially when present at percentages of more than 10 percent. Annealing the materials, on the other hand, produced an increase in fracture toughness for those products having a low rubber content; however it did not have any effect on those with an elevated rubber content (26 percent).