Quasi-static cyclic loading assessment of GFRP single-lap adhesive joints reinforced with z-pins

Abstract

Numerous studies have focused on the bond behavior of z-pinned composite joints under monotonic and fatigue loading. Despite this, research on quasi-static cyclic loading is still limited. In order to improve our understanding of the mechanical behavior of glass fiber reinforced polymer (GFRP) single-lap adhesive joints subjected to quasi-static cyclic loading, an experimental study was conducted, and the effects of z-pinning and the adhesive thickness of the bonding area on the strength and stiffness of joints were examined. In this regard, a series of the single-lap joints with 0.5 and 1 millimeter adhesive thickness without z-pin and reinforced with 9 and 16 z-pins were fabricated and monotonic, quasi-static cyclic, and monotonic after cyclic loadings were applied to each. It was found that in conditions where monotonic loading is only the case, and there is no quasi-static cyclic loading, the use of single-lap joints with 16 z-pins is recommended due to their effect on enhancing the ultimate load. For deciding on the adhesive thickness, the shear stiffness of the joint should be taken into consideration, as thinner adhesive thickness resulted in lower shear stiffness but higher ultimate load with the same number of z-pins. In the presence of quasi-static cyclic loading, inserting 16 z-pins along with 1 mm adhesive thickness is proposed. This number of z-pins significantly increased the ultimate load and the number of cycles the joint could tolerate. The impact of this thickness on reducing the level of stiffness degradation and displacement increment is noticeable as the cyclic loads progress.