An integrated method for off-axis tension and compression testing of unidirectional composites

This study presents an integrated method suitable for off-axis tension and compression testing in unidirectional composites, and its application to the testing of in-plane shear characterization. A new rotating-grip test fixture, incorporating the attractive features of the existing pinned-end fixture and hydraulic wedge grips, has been developed. The proposed gripping system consists of two sets of jaw faces, each with a pair of self-aligning bearings that allows for loading in the axial and radial directions. Finite element analysis and experiments were performed to evaluate the effectiveness of the rotating-grip test fixture. Results from numerical calculations show that this method reduces stress concentrations near the end and produces relatively uniform stress distributions in the specimen gage section. Mechanical testing results show a considerable increase in the measured shear properties of composites, compared with the existing end grip systems. The results indicated that the new test fixture is significantly better than the conventional fixture, and is also comparable to the method of the oblique end-tab for off-axis testing.