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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damage patterns. These regular mesh sizes were halved in the fine mesh model (0.10×0.10×0.15 mm³), and in-plane sizes of cohesive elements were adjusted accordingly. A comparative analysis of the results from the regular and fine mesh models revealed insignificant differences, with a maximum force deviation of less than 2% and similar matrix cracking patterns. Given the strong agreement in impact responses, damage sequence, and patterns between regular and fine mesh model results, all subsequent investigations are conducted using regular mesh sizes to minimize computational cost. The elastic and strength-related properties of Hexcel 913C/HTS unidirectional (UD) prepreg used in the simulations are provided in Table 1. It is worth noting that when laminae are constrained by laminae with varying fiber orientations, their strength is enhanced in comparison to that of unidirectional laminates (Parvizi et al., 1978). This increased strength is commonly referred as “in - situ strength”. To determine the values of in-situ strength, we have followed the methodologies outlined in the works of Camanho et al. (2006) and Catalanotti (2019). Contact and friction models are employed for two primary interactions: between the steel impactor and the composite beam, and among the composite layers in cases of self-contact. The built-in contact algorithms and friction models are provided by Abaqus (Hibbitt et al., 2016). When dealing with self-contact between composite layers, the general contact algorithm with the penalty contact method is employed, excluding interactions involving the impactor and the composite beam. To enhance computational efficiency by predefining contact pairs, the surface-to-surface contact type with the penalty contact method is utilized for interactions between the steel impactor and the composite beam. Friction is accounted for in all contacting surfaces and interfaces by applying the built-in Coulomb's friction model. Specifically, we set the Coefficient of Friction (COF) to 0.3 for contact between the steel impactor and the composite (Lopes et al., 2009a) and 0.5 in cases of self-contact among composite layers (Schön, 2000). In the experiments, the specimen was clamped with steel plates 25 mm from both ends. One straightforward approach is to simplify these experimental boundary conditions by considering them as fixed supports, an approach employed by Topac et al. (2017). Specifically, the end portions of the bottom surface are constrained in both longitudinal and transverse directions, while the end portions of the top surface are fixed only in the longitudinal direction to accommodate the specimen's contraction due to Poisson's ratio effect. Although the use of these so-called fixed supports accurately reproduces experimental failure patterns, a detailed comparison of in situ experimental and computational deformation and strain fields reveals that such rigid constraining led to a stiffer flexural response, which significantly affects dynamic damage characteristics. Instead of adopting this idealized boundary conditions approach involving fixed supports, we propose a heuristic method to replicate the experimental boundaries through the assembly of spring elements at the corresponding boundary nodes. Further details regarding this proposed boundary conditions approach are provided in Section 3.

Figure 1. FE model and a representative meshed section.