Crack Propagation Evaluation of Polymer Composite FRP Panels Subjected to Static and Cyclic Loading

This paper summarizes a multiphase analytical and experimental study on evaluating the propensity for small delaminations in fiber-reinforced-plastic (FRP) composite panels to propagate under both static and cyclic (wind) loads. Finite-element modeling, employing orthotropic plane strain/stress elements, was used with the crack closure method to determine the energy stored at the crack tips. Crack propagation tests were conducted to obtain energy release rates at crack tips. The results of these test were compared with the calculated energy demands to evaluate the propensity of interlaminar flaws to propagate under service loads. Retention of static strength after fatigue load was determined by prototype tests with load magnitudes and cycles approximating the full service life of the panels. Finally, available design procedures for fatigue strength were evaluated in light of test findings. Results of the study indicated that small interlaminar flaws in the FRP composite panels have low probability of propagating under design loads. Fatigue testing and available design formulations confirmed the structural safety of the panels under long-term cyclic wind loads.