Failure analysis of +/- 45 degrees off-axis woven fabric composite specimens

The purpose of this research is to evaluate the mechanical response of eigh t harness satin woven graphite/polyimide composite specimens using the +/- 45 degrees test. A series of tensile tests have been conducted at room temp erature to evaluate the effect of specimen width as well as monotonic, prog ressive, and multiple loadings on the response of the composite specimens. Acoustic emission techniques have been employed to monitor damage initiatio n and progression in the specimens at different stages of loading. In addit ion, nonlinear finite element computations have been conducted to determine stress distributions in the +/- 45 degrees fabric specimens. It has been s hown that the specimen width effect is strong and should not be ignored in a failure analysis of the fabric composite using the +/- 45 degrees test. T he shear strength of the composite determined from the maximum loads increa ses substantially with the width of the specimen. It has also been shown in this research that the initiation of intralaminar damage in the graphite/p olyimide composite can be monitored using acoustic emission. The initiation of interlaminar damage can be determined either from the characteristic kn ees on the load/displacement diagrams or from the acoustic emission data.