A methodology for the rapid characterization of Mode II delamination fatigue threshold in FRP composites

A new methodology to measure the Mode II interlaminar fracture in fatigue for FRP composites is developed. The proposed methodology uses a Modified Transvers Crack Tensile (MTCT) specimen and is able to characterize the near threshold behavior in a robust, easier and significantly faster way than standard procedures. Analytical formulae, able to link the crack growth rate to the load or strain amplitudes, were found and verified, and their importance was explained, in particular, for what concerns the characterisation of the near threshold behavior. Experiments were performed both in load and strain control, while the delamination growth was monitored using different techniques including the Thermoelastic Stress Analysis (TSA). Experiments showed the reliability and effectiveness of the proposed procedure, and evidence its suitability and compatibility with current industrial material testing and qualification protocols with particular emphasis to industrial environment where a "no growth" design approach is employed.