Abstract
AbstractThe irreversible deformation behavior of coextruded microlayer composites, consisting of 49 alternating layers of polycarbonate (PC) and styrene—acrylonitrile polymer (SAN), was examined in the triaxial stress state achieved at a semicircular notch during slow tensile loading. Variations in the proportions of PC and SAN were manifest as changes in the relative thicknesses of PC and SAN layers. When the SAN layers were thicker than the PC layers (PC/SAN 25/75 v/v) or the layer thicknesses were about the same (53/47 v/v) the composites were only slightly more ductile than SAN and the deformation behavior of the layers mimicked that of the components. Examination of optical micrographs showed that the damage zone closely resembled that of SAN and consisted of internal notch crazes in the SAN layers that grew out from the notch surface in conformity with a mean stress condition. Shear processes became more evident when the PC layers were thicker than the SAN layers (PC/SAN 65/35 and 74/26 v/v). An unusual transition was observed in the SAN layers from internal notch crazing to interactive crazing and shear banding. The internal notch crazes ceased to grow when they terminated in a pair of microshear bands in the SAN layer. Subsequently a macroscopic shear‐yielding mode was observed as two sets of intersecting slip lines that grew out from the notch surface in both PC and SAN layers. Stress intensification caused by the plastic zone was responsible for the appearance of a second family of internal crazes in the SAN layers that originated in front of the notch tip. © 1993 John Wiley & Sons, Inc.
Published Version
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