PSI - Issue 61

Onur Ali Batmaz et al. / Procedia Structural Integrity 61 (2024) 305–314 Onur Ali Batmaz et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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3. Implementation of flexural boundaries In our specific problem involving the transverse line-impact on beam clamped specimens, a straightforward approach for BCs is to constrain the displacement degrees of freedom at the corresponding nodes, a method previously employed by Topac et al. (2017). While such BCs effectively reproduce experimental failure patterns, a detailed comparison of in situ experimental and computational deformation and strain fields reveals that such rigid constraining results in a stiffer flexural response, significantly influencing the dynamic characteristics of damage. In this regard, we propose a heuristic approach that replicates the experiment supports by employing spring elements at the corresponding boundary nodes. In the FE model, we utilize translational spring elements (denoted as CONN3D2 in the ABAQUS) to connect boundary nodes to the rigid ground where each spring element has two translational degrees of freedom, horizontal and vertical. The aim of this approach is to eliminate the artificial effects that influence the aspects of the global and local failure processes arise from the idealization of BCs. Figure 3 provides an overview of the heuristic approach employed to determine the spring constants that most accurately represent the experimental boundaries. We determine the stiffness of these springs through a minimization process, aiming to reduce discrepancies between experimental data and simulations. This iterative process involves the extraction of horizontal and vertical displacements along a vertical path near the boundaries, and shear strains along the beam's centerline from the simulations. These values are then compared with experimental measurements obtained through Digital Image Correlation (DIC) for the same impactor position. The process begins with an initial pseudo-random selection of spring constants and proceeds with iterative adjustments until the error between the simulation results and DIC measurements falls below a predefined threshold of 5%. Aligning with experimental observations, the modeling of spring configurations takes into account the following considerations: • The horizontal response of the top boundary springs is related to the tangential contact between the beam and the top fixture plates. This implies a tension-compression symmetric definition for the finite horizontal spring constant ( ℎ, + = ℎ, − ≠0 ). • The vertical response of the top boundary springs is related to the normal contact or separation between the beam and the top fixture plates. Under compression, the springs are modelled to simulate the normal contact situation with a finite vertical spring constant ( , − ≠ 0). Under tension, the springs are modelled to simulate the separation of the mating surface by setting the vertical spring constant to zero ( , + =0 ).

Figure 3. A heuristic approach to replicate the experiment boundaries through the assembly of spring elements at the boundary nodes.