Mechanical Response of Aramid/Epoxy under Tensile, Compressive and Shear Loading

The results of an extensive room temperature mechanical characterization of unidirectional aramid/epoxy carried out using three different test methods are summa rized. The three test methods employed in the above investigation were: off-axis tension and compression tests and Iosipescu shear test. The tests were performed under mono tonic and quasi-static cyclic loading conditions in order to determine the initial elastic pa rameters and characterize subsequent nonlinear response, including failure stresses, under combined loading. It is demonstrated that the initial elastic response correlates well with the predictions of the transformation theory. The nonlinear response obtained from the three test methods is essentially dissipative, exhibiting apparent permanent strain accu mulation and hysteresis loops. The extent and character of nonlinearity and dissipation is a function of the applied load with respect to the fiber direction and depends on the sign of the load. The dramatic differences observed in the nonlinear response and failure char acteristics in tension and compression are discussed in terms of different mechanisms operative at the microscale.