Analytical evaluation of the two-rail shear test method for composite materials

Linear three-dimensional finite element analyses were conducted to evaluate various rail and specimen configurations of the two-rail shear test procedure. Additional analytical evaluations were performed to investigate the effects of specimen aspect ratio, material orientation, loading direction, and the rigidity of the rails on stress distributions. Shear stresses were found to be distributed uniformly over a large region in the specimen gage section for most of the models analyzed, but normally accompanied by significant transverse and axial normal stresses. The results indicated that an axial loading applied to a test fixture of uniform steel rails and a test specimen with aspect ratio of 6 was the preferred test procedure. Simple test specimens of trapezoidal and rectangular geometries, and specimens with tabs, were chosen for further evaluation. Also, the new Wyoming-Modified Two-Rail Shear test fixture was established based on these analyses.