PSI - Issue 66

Akash Shit et al. / Procedia Structural Integrity 66 (2024) 247–255 Shit and Prakash/ Structural Integrity Procedia 00 (2025) 000–000

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stress linear elastic fracture mechanics (LEFM) analysis is conducted on the strap where initial cracks tend to manifest [Liu et al., (2020)], using Abaqus®/CAE 2023 software package. 2.1. Specimen Geometry and Material In this study one standard cruciform specimen is considered as the approximate representation of a strap plate of a riveted butt joint. The strap plate is connected on its four sides using a 3-2-1 Lozenge pattern riveted connection. The specimen geometry is adopted from the study of bi-axial fatigue behavior of a box-welded joint by [Takahashi et al., (2003)] and the fatigue surface crack growth study under biaxial loading by Morishita et al., (2021). The modified specimen dimensions with 3-2-1 Lozenge pattern riveted connection used in this study is shown in Fig. 1(a); the numbering of rivet holes at various positions is shown in Fig. 1(b). The thickness of the strap plate is 10 mm. The diameter of each rivet hole is 30 mm. In this investigation, the total crack length, denoted as ‘2a’, and is determined by adding the diameter of the rivet hole to the length of the crack extending outward from the perimeter on either side of the rivet hole. For the crack tips, at positions H1, H3, H4, and H5, the upper crack tip is referred to as 'crack tip-1', while the lower crack tip is referred to as 'crack tip-2'. At position H13, the left crack tip is designated 'crack tip-1', and the right crack tip is designated 'crack tip-2'. The study is conducted utilizing the material property of mild steel, viz.,E = 200 GPa, ν = 0.3, σ y = 250 MPa and σ ut = 450 MPa, for both plate and rivets. a b

Fig. 1. (a) Specimen geometry [Takahashi et al., (2003), Morishita et al., (2021)] (b) Hole locations

2.2. Numerical Modeling of Crack Initiation and Propagation Throughout the analysis, the crack is modeled as a seam in Abaqus®/CAE. This seam is treated as a unique feature edge in 2D analysis or a unique feature face in 3D analysis. The distinctive characteristic of the seam edge is that overlapping nodes are assigned along this edge or face during meshing. These nodes will separate during the analysis, creating discontinuities equivalent in size to the seam [Smith, (2009)]. After determining the location and direction of the maximum principal stress for a specific rivet hole, by applying appropriate boundary conditions, an initial through-thickness crack of 1 mm is then introduced in the identified direction. In this study, the Maximum Energy Release Rate (MERR) based crack advancement criterion is used to predict the crack propagation angle of the preexisting initial crack. Starting with an initial crack length of 32 mm (2a) oriented along the maximum principal stress direction, each crack tip is advanced by 1 mm, following the direction indicated by the MERR. This iterative crack advancement process is continued until the crack length reaches 50 mm.