Failure of Composites Under Combined Loading

The response of polymer matrix composites under combined proportional axial and torsional loading has been studied. Experiments were performed on solid cylindrical specimens of glass/vinylester and carbon/vinylester composites at a fiber volume fraction, Vf equal to 50%. The specimens were loaded under displacement and rotation control in a proportional manner. The Budiansky-Fleck kinking model was specialized to the case of a solid cylindrical specimen and the predictions were compared to the experimental results. It was found that the compression strength of carbon composites is approximately a linear function of the applied rotation but in the case of glass composites the compression strength is initially unaffected due to shear. At a critical value of shear, the compression strength is seen to diminish rapidly. This suggests that the Budiansky-Fleck model might not be suitable for predicting the effect of shear on compression strength of glass fiber composites.