PSI - Issue 77

Bruno Pedrosa et al. / Procedia Structural Integrity 77 (2026) 649–656 Bruno Pedrosa/ Structural Integrity Procedia 00 (2026) 000–000

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1. Introduction Fatigue cracks in metallic structures can be acceptable when they do not have significant safety or economic concerns. However, in this scenario, not only do periodic inspections have to be considered, but also the knowledge concerning fatigue crack growth is essential. The mechanisms and the fatigue crack growth rate demand significant attention to set timely inspection periods. In this sense, experimental tests and new analytical models are required to strengthen scientific knowledge about general fatigue crack growth and specific mechanisms. Furthermore, regarding fatigue damages in riveted/bolted shear connections, it is crucial to properly acknowledge fatigue crack propagation mechanisms to establish reliable predictions about the crack behavior. This aspect is especially relevant for cracks emerging in invisible areas, such as the region of the plates covered by bolt heads, nuts, and washers. The fatigue behavior of bolted or riveted connections depends on the stress level to which their components are subjected. Fatigue cracks emerging from the connecting plate are more frequent because geometric discontinuities lead to high stress concentrations. A peak of stress is found at the edges of the bolt hole. This high level of stress can originate from a crack which will propagate perpendicular to the load direction. The load mechanisms of a bolt hole must be appropriately acknowledged to assess the fatigue performance and crack influence on the behavior Mayville et al. (Mayville et al., 1987) developed a model based on beam-on-elastic foundation analysis to calculate the shear force acting at a given bolt hole location. Three bolt hole cracking stages were identified: initiation, corner crack propagation, and through-crack propagation. Wang et al. (Wang et al., 2020) implemented a nonlinear ultrasonic crack detection method in rail-bolted joints. Using the third harmonic presented a linear relation with the crack size. Baarssen et al. (Baarssen et al., 2022) performed an experimental investigation on the net cross-section failure of pre-cracked bolt holes. The ultimate strength was found to be slightly lower than the results of Eurocode 3. However, the number of tests was reduced, and no statistical analysis could be carried out. Claudiu Gudas (Gudas, 2020) developed a numerical approach to account for the effects of crack length on the fastener load transfer and on the far field and bypass loads at each fastener adjacent to the crack. Wan et al. (Wan et al., 2024) investigated the fatigue behaviour of 42CrMo4 high-strength single lap double-bolted joints based on experimental and numerical approaches. The results indicate that fatigue cracks propagated in a complex distribution. On the other hand, cold extrusion forming and bolt preload improve fatigue life. Studer and Taras (Studer & Taras, 2022) studied the hole-bearing resistance of symmetric single-bolt connections considering various steel grades. Experimental and numerical analyses were performed to assess the influence of hardening behaviour on the hole-bearing deformations. Geng et al. (Geng et al., 2025) studied a fatigue strengthening method for fastener hole components based on a non contacting electromagnetic cold expansion process. The falling stage of the pulse current generated a compressive residual stress that contributed to improving the fatigue life of this component. Furthermore, crack growth mechanisms in bolt holes have been studied by several authors. Zhuang (Zhuang, 2000) investigated using the weight function and strip-yield crack closure methods to analyse the fatigue crack growth from tie bolt holes in a disc. These methods have shown a better correlation with experimental data when compared to conventional methods. Dong et al. (Dong et al., 2020) focused on the fatigue crack growth of a corner crack at the edge of a hole and proposed a new FCG equation. Borges et al. (Borges et al., 2020) used a numerical approach based on the plastic crack tip opening displacement to study FCG from notches. Chakherlou et al. (Chakherlou et al., 2010) investigated fatigue crack growth in single-holed plates by means of experimental and numerical approaches. Cao et al. (Cao et al., 2023) developed a stochastic fatigue crack growth (FCG) modelling method for bolt holes. Experimental results on standard FCG specimens were used to describe the stochastic FCG process based on a Wiener failure mechanism analysis. The accuracy of the established model is then verified at the component level. This paper intends to be a valuable contribution to analyzing the fatigue mechanisms in bolt hole details by conducting experimental fatigue tests on representative specimens and addressing different approaches to modelling fatigue life. Fatigue tests on steel plates with a hole aim to evaluate fatigue crack initiation and propagation phases and the fatigue life in which the crack becomes detectable (in a real bolted connection). Several scientific studies in the literature (Jiménez-Peña et al., 2017) have shown that the compressive effect of the bolt head, washer, and nut on the connected plates is beneficial, extending the fatigue life of the detail by reducing fatigue crack growth. The study of bolt hole crack mechanisms using detail without connecting elements allows us to assess the worst-case scenario and a less complex situation.