A Study of the Effects of Prestrain on the Tensile Properties of Filamentary Composites

Abstract

A study of the effect of mechanical prestraining on the tensile behavior of metal matrix composites was conducted. Using both a two-member cylindrical composite simulation model and actual filamentary composites, the stress and strain distribution was followed during cool-down from the compositing temperature, through the prestrain cycle, and during subsequent reloading. The prediction of the behavior of the model composites during unloading from the prestrained state was found to be complicated by compressive plastic flow of the matrix during the unloading. By using experimentally measured effective stress-effective strain curves, the Bauschinger effect exhibited by model composites was well described. The model composites used to validate the analysis consisted of maraging steel—OFHC copper concentric cylinders. Prestraining of copper-tungsten filamentary composites was investigated both experimentally and analytically to verify the applicability of the model to real fiber composites. It was established that prestrain into the elastic-plastic behavioral region was successful in increasing the load-carrying capacity of composites with a 20 percent volume fraction of tungsten. The analytical technique used to describe the behavior of the cylindrical composites was used to rationalize the behavior of the filamentary composites. It was shown that the ameliorating effect of prestraining was due to the alteration of the net residual stress state of the matrix from an “as fabricated” tensile state to one of compression after prestraining.