An assessment of through-thickness shear tests for initiation of fatigue failure

Two different tests have been evaluated for their potential to provide data on through-thickness failure initiation of carbon/epoxy prepreg composites under shear fatigue loading; the Short Beam Shear test and the Double Notched Shear test. These tests were selected based on their simple geometry and ease of detection of damage onset. Results of extensive fatigue test programmes, including multiple R-ratios, are presented. A detailed study of damage initiation in the short beam shear test was conducted through Computed Tomography X-ray scanning of interrupted tests. Comparison between the two different test methods showed a steeper S-N curve for the double notched shear tests. Non-linear finite element analyses were performed to better understand and explain the test results.