Experimental investigation of the fatigue behavior of adhesively-bonded pultruded GFRP joints under different load ratios

The fatigue response of adhesively-bonded pultruded GFRP double-lap joints was investigated under different loading patterns and experimental results were obtained for three different applied load ratios: R = 0.1, R = 10, and R = -1. The fatigue life of the examined joint configuration is affected by the different loading type, generally being shorter for tensile loads and longer when compressive loads were applied. The dominant failure mode was a fiber-tear failure that occurred in the mat layers of the pultruded laminates for the tensile and reversed loadings, while the failure was driven by a crack in the roving layer in the case of R = 10. A decrease in joint stiffness of approximately 8% was observed for the tensile and reversed loading conditions, while a very limited stiffness degradation of around 2% was recorded under compression. The results proved that there is no correlation between the applied load level and stiffness degradation at failure. Independent of the failure mode, similar crack development was observed, characterized by an initial and final region of accelerated propagation, and a middle part of linear, and slower, crack propagation, corresponding to around 80% of the fatigue life. Considerable differences were observed for the derived fatigue crack growth curves under different load ratios. (C) 2011 Elsevier Ltd. All rights reserved.