PSI - Issue 71

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

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As discussed in the previous section, the analysis is done on the strap, and due to symmetry, the half strap is considered for the entire analysis. The dimension of the strap is 60 mm x 60 mm, with a thickness of 3 mm, shown in Fig. 2. Six rivet holes with a 2.5 mm radius are arranged in a 3-2-1 pattern with the 15 mm pitch. Row one (R1) has rivet hole H1, row two (R2) contains rivet holes H2 and H3, and row three (R3) has holes H4, H5, and H6. The radius of the pin had increased according to the % of interference level (0.1% and 0.15%). Seam crack has been considered to simulate the crack length. In this study, the crack length 2a is calculated as the summation of the rivet hole diameter and the crack length extending beyond the perimeter of either side of the rivet hole. Throughout this study, the top crack tip was designated as 'crack tip-1' and the bottom crack tip as 'crack tip-2.' In this study, mild steel is used for all the components. The mechanical properties are E = 200 GPa, ν = 0.3, σ y = 250 MPa and σ ut = 450 MPa [Hithendra and Prakash, (2021)]. 2. Numerical Modeling The numerical study is carried out to determine the Stress Intensity factor (SIF) for the Lozenge pattern riveted joints arranged in a 3-2-1 fashion. The initial location and direction of the crack were determined by using the maximum principal stress direction. The crack propagation direction was calculated according to the maximum energy release rate criterion. Three different interference levels, 0%, 0.1%, and 0.15 %, were considered at different locations across the holes. The SIF and crack propagation angle ( ̃ ) is recorded against each crack increment. In this study, one approximate crack path has been determined for each case. 2.1. Specimen Geometry & Material:

Fig. 2. Geometry of the specimen

Fig. 3. Mechanism of a seam crack in ABAQUS [(Smith, 2009)]

2.2. Crack Initiation and Modeling

An initial through-thickness crack of 0.5 mm is given in the direction of maximum principle stress. The 'Seam' crack is used in ABAQUS ® /CAE 2023 to model the crack. A seam is nothing but an edge for 2D or a face for 3D analysis with overlapping nodes. At the time of analysis, these nodes are separated from each other, and the solver treats this as a crack. In ABAQUS ® , a seam crack is always referred to for the contour integral analysis. Fig. 3 shows how the independent nodes on the seam are separating from each other by assigning the seam crack to a sketched partition line on a face under tensile loading [Smith, (2009)]. 2.3. Evaluation of Stress Intensity Factor In this study, SIF is numerically evaluated using ABAQUS ® software. The contour integral module in ABAQUS ® can calculate different contour integrals, such as J-integral, Ct-integral, T-stress, and SIF. For linear elastic fracture mechanics (LEFM), SIF represents a crack's severity, describing the crack tip's local stress and displacement field. The J-integral and energy release rate (G) can be used interchangeably for linear material behaviour. SIF is related to the energy release rate, G, by the following equation (1) for plane stress conditions and (2) for plane strain conditions. = 2 (1) = 2 (1− 2 ) (2) Crack tip singularity is taken care of by moving the mid-side nodes of the edge of the elements shared with the crack tip to a quarter-point distance. 2.4. Crack Path Estimation