Fatigue performance of marine composite doubler plate joints under random load spectra
Publication Name: Proceedings of American Composites Manufacturers Association (ACMA) Composites & Polycon 2009
Composite structures commonly fail at secondary bonded joints due to crack propagation at the bond line of the joint. The crack propagation response of secondary bonded doubler plate joints in fiber-reinforced polymer (FRP) composite panels was investigated due to variable amplitude fatigue produced by vessel design spectra loads. The doubler plate joints were analyzed with respect to lifespan and failure criteria typically used for marine composites. The goal of the study is to characterize crack propagation in secondary bonded doubler plate joints under variable amplitude fatigue produced by design spectra loads for seaframes. The main contribution of the study to the marine industry is to improve current design methods for doubler plate joints in vessels under service conditions. Furthermore, the study serves to gain a better understanding of fatigue life prediction in secondary bonded joints for marine composites. The research method adopted in the study is to determine a fatigue load scale factor, which can be applied to the ultimate quasi-static strength of an FRP composite doubler plate joint. A test method was developed, and a modified MinerÕs Rule approximation was implemented in determining the damage at failure and estimating preliminary load scale factors. Two fatigue spectra were used to model the stress induced over a full 30-year life cycle of the doubler plate joints in seaframes. Preliminary results have yielded insight into how crack propagation in secondary bonded doubler plate joints progresses under variable amplitude fatigue.