PSI - Issue 71

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

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The main objective of this study is to predict the crack propagation path at different crack locations under different interference levels. After analyzing the initial 6 mm crack that lies along the maximum principal stress direction, a further 0.5 mm extension is given to both the crack tip according to the maximum energy release rate direction. This crack propagation technique is called the virtual crack extension approach based on the distribution of strain energy release rate at the crack tip presented by [Hellen, (1975)]. This repetitive crack advancement procedure is continued till the 17 mm crack length. The approximate deviation of the MERR-based crack path from the plane perpendicular crack path is found by plotting the spatial coordinates in loading and transverse direction of the crack path on an X-Y plot, keeping the center of the respective holes as the origin. After that, one linear line was fitted through the crack path coordinates. The angle of deviation is calculated from the equation of that straight line. The governing equation for a straight line is, = + (3) Where c is the y-intercept and m is the gradient that can be represented as = 2 − 1 2 − 1 (4) = (5) This is the angle of that line with the positive X-axis. And (90 ° − ) , is our desired angle of deviation from the Y-axis (assumption of crack path perpendicular to the loading direction). 2.5. Load and Boundary Conditions The plate and pins are created as 2D planar parts, and the entire analysis is conducted by following the plane stress linear elastic fracture mechanics approach. All the pins are connected with their respective holes by standard surface to-surface contact behaviour with a friction coefficient of 0.2. A force of 14,400 N was applied to induce a remote stress of 80 MPa at the right end edge of the plate, directed outward perpendicular to the thickness surface [Hithendra and Prakash, (2021)]. All the pins were fixed in all directions. Initially, for no interference level to predict the crack path, all three rows were studied by inserting initial cracks at H1, H2, H4, and H5. However, later, to find the impact of MERR-based crack advancement on SIF, only H4 and H5 are studied because R3 is more severe than R1 and R2, as reported by [Hithendra and Prakash, (2021)] in their studies. They further found that only 0.1% and 0.15% interference levels are the most beneficial to reducing the SIF [Karakampalle and Prakash, (2021)]. So, in this study, only these two interference levels are considered. 2.6. Meshing Fracture mechanics analysis using seam crack required conformal and focused mesh. A structured focus mesh is created by creating an appropriate partition of the geometry to meet the requirement as shown in Fig. 4(c). The global element size is 1 mm for the entire model, and to achieve fine mesh around the hole to capture the proper stress distribution, a 0.25 mm element size is employed. The element type used in this study is CPS8, representing an 8 node biquadratic plane stress quadrilateral element. Fig. 6 represents the meshed model used in the analysis. a b c

Fig. 4. Mesh parameter validation (a) Theoretical model with center crack (b) Equivalent fea model (c) Typical mesh for the current model The finite element analysis results were compared with the available theoretical solution to validate the model and select the appropriate mesh parameters. The SIF at both the crack tip of a central crack (2a) for a plate of width b,