PSI - Issue 37

Md Niamul Islam et al. / Procedia Structural Integrity 37 (2022) 217–224 Md Niamul Islam et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 1. Print orientation and layer stacking for quasi-isotropic structure.

2.2. Mechanical characterisation tests Chacón et al. (2019) and Wang et al. (2019) showed that printing parameters significantly change the properties of AM parts, so mechanical tests were performed to obtain the elastic-plastic material properties and capture the failure behaviour. Tensile tests were carried out based on ASTM 638-14 using 2 mm thick specimens (Fig. 2a) and a testing speed of 5 mm/min. Accordingly, cylindrical specimens of diameter 7.5 mm and height 15 mm (Fig. 2b) were tested under compression at a testing speed of 0.9 mm/min, following ASTM D695-15. Also, dynamic mechanical analyses (DMA) were performed in flexure (3-point bending) for a frequency sweep of 1-150 Hz at 25°C as per ASTM D5023-15, using rectangular specimens of dimensions 64 mm × 13 mm × 3 mm (Fig. 2c). For each experiment, 5 samples were tested to obtain valid results.

Fig. 2. Specimens for tensile (a), compression (b) and DMA (c) tests.

2.3. Ballistic impact test and modelling

Ballistic impact tests were carried out using an in-house gas gun (Fig. 3) with 100 mm × 100 mm × 2.5 mm AM plates and 9 mm spherical steel projectiles. A total of 5 different plates were tested, with the velocity of the projectiles ranging from 95 m s -1 to 120 m s -1 and the calculated energy at impact between 14 J to 20 J. The experimental boundary conditions of the ballistic impact tests were modelled in a simple configuration using FEA in Abaqus. Four layers of thickness 0.5 mm were stacked as shown in Fig. 4 to create a 2 mm thick plate. The material ’s elastic-plastic behaviour was incorporated in tabular form and the explicit solver was used to perform the analysis. Hashin damage model was used for the target’s material and the steel spherical projectile was given an impact velocity of 100 m s -1 , i.e. the impact energy was 15.5 J. The damage model was implemented in FE simulations through a user-subroutine (VUMAT) to account for the fracture behaviour as it predicts the anisotropic damage in fibre-reinforced composites with elastic-brittle behaviour. The model considers four different failure modes: fibre tension, fibre compression, matrix tension, and matrix compression (Duarte et al., 2017). The projectile