Measurements of the craze-bulk interfacial active zone

Abstract

The width of the active zone, a region of strain softened material at the craze-bulk interface, was measured as a function of temperature in polystyrene (PS) using a gold decoration technique. Thin trilayer films of PS (total thickness 0.6 μm) with a central layer of buried gold “islands” were made. The films were strained at a controlled rate and various temperatures. When the films crazed, the gold particles act as markers which reveal the deformation of the PS. The strain in the PS could be seen in transmission electron microscopy (TEM) as a change in areal density of the gold particles. The width of the active zone was determined by measuring the distance between the edge of the change in areal density of the gold particles and the craze-bulk interface. It was found that the width of the active zone was a function of the distance behind the craze tip at room temperature. The width of the active zone was ∼10 nm at the craze tip and increased linearly to a value of ∼25 nm at a distance 250 to 300 μm from the craze tip. The active zone width was independent of the distance from the craze tip for distances greater than 300 μm. The active zone width at the craze tip is in good agreement with previously reported results. The higher strain rates at the craze tip are believed to be responsible for the change in the width of the active zone as a function of distance behind the craze tip. The active zone width increased linearly with increasing temperature from 25 nm at room temperature to 60 nm at 93 °C. The increase in the active zone width can be accounted for by the decrease in strain softening of PS at higher temperatures.