PSI - Issue 71

Akash Shit et al. / Procedia Structural Integrity 71 (2025) 50–57

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1. Introduction Starting from the Industrial Revolution, mechanical components have played a pivotal role in improving the human lifestyle along with the rapid modernization of the world. Riveting is a crucial permanent fastening process due to its greater strength, reliability, and ease of fabrication. Throughout the operation, due to the fatigue loading, inherent flaws often originate at the high-stress concentration area, like the rivet holes. The crack initiation at the riveted joint depends upon various parameters like the rivet type, clamping force, local stress concentration factor, fretting fatigue, secondary bending for lap joints, and environmental effects [Schijve, (1992)] [Silva et al., (2000)]. Therefore, numerous investigations have been carried out to enhance the fatigue life of the components. [Pinho et al., (2005)] found a significant reduction in SIF due to the compressive residual stress field around the rivet holes by cold working. [Moreira et al., (2007)] reported for a single-column three rows riveted lap joint load transfer primarily occurs through the first and last rivets. The significant effect of back pitch and rivet diameter on the fatigue life and SIF is found by [Liu et al., (2020b)] and [Hithendra and Prakash, (2021)]. Stop-drilled holes in front of the crack tip significantly improve the total fatigue life [Song and Shieh, (2004)]. The presence of ancillary holes ahead of the stop drilled hole can further reduce the stress concentration factor depending on their position and size [Murdani et al., (2008)]. Fatigue crack retrofitting also helps to reduce SIF significantly [YuanZhou et al., (2019)]. Lozenge pattern riveted joints are known for their better strength and stability due to the even load distribution across the rivets. The studies on lozenge pattern riveted joints reported the limiting interference level between rivet pin and holes up to which the SIF decreases [Hithendra and Prakash, (2021)]. The most beneficial interference level to minimize SIF for different crack configurations at Lozenge joint is also reported [Hithendra and Prakash, (2021)]. Previous studies on lozenge-pattern riveted joints assume crack propagation along the plane perpendicular to the loading direction, but crack propagation does not follow a defined path. This study employs the maximum principal stress direction for the initial crack location and the maximum energy release rate (MERR) criterion for further crack advancement. The SIF and crack path deviation in 3-2-1 lozenge-pattern riveted joints are analyzed under the MERR criterion. Various interference levels are incorporated to assess their influence on the crack path and SIF. According to the literature, initial cracks first emerge on the straps of the riveted butt joint due to the high-stress zone [Liu et al., (2020)]. Because of that, this study focuses on the strap, as shown in Fig. 1(b). In butt joints, the load is transferred from the plate to the straps by the pins. So, for the analysis of the straps, we can consider that the rivets of one half are fixed, and the rivets of the other half are subjected to loading. Due to the symmetry of the strap plate, this condition is equivalent to the edge-loaded half-strap plate with all six rivets fixed [Hithendra and Prakash, (2021)]. The final half strap model shown in Fig. 1(c) is used for the analysis by assuming 100 % load transfer. The star marks on the rivets in Fig. 1(b) and (c) represent the fixed boundary condition. a b c

Fig. 1. (a) 3-2-1 lozenge pattern double strap riveted butt joint; (b) simplified upper strap geometry with rivets of the left half fixed and loads acting on the right half of the rivets; (c) edge-loaded half-strap geometry with fixed rivets [Hithendra and Prakash, (2021)] Nomenclature

Half Crack Length, mm Elastic Modulus, GPa Poisson’s Ratio Applied Stress, MPa Tensile Yield stress, MPa Ultimate Tensile Strength, MPa Energy Release Rate, Mode I Stress Intensity Factor, Mode II Stress Intensity Factor, Geometric Factor