Electron Bombardment Induced Crack Initiation and Crack Growth in polymers and Polymer Surfaces

Abstract

When a notched, polymeric material is stressed, the notch opens into a wide crack-tip, exposing a region of high stress concentration. The consequences of electron bombardment of the tip of polyisoprene, butyl rubber, Kapton-H®, Teflon®, low density polyethylene, and linear high density polyethylene stressed under vacuum are under investigation. Evidence is presented for electron induced crack growth at stresses below that needed for crack growth due to stress alone. The electron current densities used in these experiments are sufficiently small that thermal heating of the zone near the crack tip tends not to dominate. To provide information on the physical phenomena involved, we present measurements of electron current, gas pressure, and sample load in response to both periodic and stationary electron bombardment of the sample. Video taping of the shape of the crack before and during bombardment are also presented. Experiments involving the bombardment of unnotched polymers under stress are also described, along with measurements of the influence of electron bombardment on the tear energy of an elastomer.