Failure Analysis of ±45° Off-Axis Woven Fabric Composite Specimens

The purpose of this research is to evaluate the mechanical response of eight harness satin woven graphite/polyimide composite specimens using the ±45° test. A series of tensile tests have been conducted at room temperature to evaluate the effect of specimen width as well as monotonic, progressive, and multiple loadings on the response of the composite specimens. Acoustic emission techniques have been employed to monitor damage initiation and progression in the specimens at different stages of loading. In addition, nonlinear finite element computations have been conducted to determine stress distributions in the ±45° fabric specimens. It has been shown that the specimen width effect is strong and should not be ignored in a failure analysis of the fabric composite using the ±45° test. The shear strength of the composite determined from the maximum loads increases substantially with the width of the specimen. It has also been shown in this research that the initiation of intralaminar damage in the graphite/polyimide composite can be monitored using acoustic emission. The initiation of interlaminar damage can be determined either from the characteristic knees on the load/displacement diagrams or from the acoustic emission data.