A tensile setup for the IDNS composite shear test

An existing test method, the inclined double notch shear (IDNS-) test, for determination of interlaminar shear properties in thin panels of layered composite materials was developed further. Experimentally observed and unresolved issues with the original IDNS-test setup were addressed. Undesired specimen deformation (and potential instability) is observed at high loads with the original compressive setup, particularly for more compliant materials. Then, testing conditions continuously change throughout a test. Here, a tensile setup which applied a statically determined combination of loads to the doubly notched specimen was used instead. The proper combination of loads minimized the arising stress concentrations at the notch roots while it produced a homogeneous state of true inter-laminar shear stress over the test region. Numerical (FE-) analyses and experimental studies to investigate testing conditions such as: specimen geometry parameters, appropriate loading combinations, and recommendations for optimal test performance in terms of achieved shear strengths and shear strain fields, were performed. In addition to the tensile setup, the possibility to use tilted notches was studied. The tensile IDNS-setup produced more homogeneous fields over the test region, even for short notch distances, further it achieved interlaminar shear strength values in the same range as or even higher than the original setup. Finally, distinctly less specimen deformation was observed with the tensile setup, and thus proper adjustment was much simpler while instability was completely avoided.