Mechanisms of interactive crazing in PC/SAN microlayer composites

Abstract

AbstractMechanisms are proposed for the two types of interactive crazing that have been observed in PC/SAN microlayer composites when the PC layer thickness is on the micron‐size scale. It is demonstrated that when the PC layer is thin enough the deformation zone that forms at a craze tip can interact with the next‐neighboring SAN layer. By measuring the dimensions of the craze tip in scanning electron micrographs, it was found that the craze‐tip opening does not depend on the SAN layer thickness, i.e., the length of the SAN craze. Consequently, the size and shape of the resulting plastic zone in the PC layer are also independent of layer thickness. The zone that forms in the PC layer consists of a colinear plastic zone together with a pair of micro‐shearbands that grow at an angle of about 45°. When the PC layer is less than 6 μm, the elastic stress concentration from the colinear plastic zone increases the probability of crazing in the neighboring SAN layer with the formation of craze doublets that consist of two aligned crazes in neighboring SAN layers. By taking into consideration the Weibull distribution of crazing, a craze doublet fraction comparable to the 30% observed experimentally was predicted with a stress intensification factor in the range of 1.03–1.05. When the PC layer thickness is less than 1.3 μm, the length of the colinear plastic zone is comparable to the PC layer thickness. Formation of a craze at the point of impingement of the plastic zone on the neighboring SAN layer leads to craze arrays with many aligned crazes in neighboring SAN layers. At higher strains, the micro‐shearbands grow through the PC layers and extend into several adjacent SAN and PC layers. This produces a change in deformation mechanism in the SAN layers at the yield instability, from craze opening to shear yielding. © 1994 John Wiley & Sons, Inc.