PSI - Issue 60

Rajagurunathan M et al. / Procedia Structural Integrity 60 (2024) 517–524 Rajagurunathan and Prakash./ Structural Integrity Procedia 00 (2024) 000–000

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the damages on cross-ply (0/90) 2s and quasi-isotropic (0/45/-45/90) s composite laminates can be classified into three stages. At low impact energy levels of 2.6 J and 10.4 J, only delamination occurred. At moderate levels of impact energy (23.4 J), both the delamination and matrix cracking were observed. For high energy impact (41.5 J and 65 J), severe delamination, matrix damage and fiber damage were found. From the results, it was observed that the damage in the region under the impactor occurs mainly due to fiber damage and matrix cracking; these damages propagated as delamination between laminae. The contours of matrix damage due to tension and compression at different energy levels are shown in Fig. 3. From the contours, the top laminas are mostly affected by matrix compression whereas bottom layers are affected due to matrix tension. At low and moderate impact energy levels, there is no significant damage to the fiber. The contour plots of the fiber damages due to tension and compression for the (0/90) 2s and (0/45/-45/90) s laminates impacted with 65 J are shown in Fig. 4. It was noted that the fiber damages are found in all laminas and the total fiber damage volumes on cross-ply and QI laminates are predicted as 188.56 mm 3 and 30.16 mm 3 respectively under 65 J of impact energy. It is also noted that the top and bottom laminas had more bending deformation and stresses, which causes delamination and matrix damage. From the contours of the fiber compressive damages, it was found that the fiber damages due to compression is less than tension. In the cross-ply laminate, a small compressive damage is observed in all laminae except the bottom lamina. But in quasi-isotropic laminate, first two plies are affected by fiber compressive damages. The fiber compressive damage variables in the rest of the laminae did not reach the critical value. Due to the low impact energy, the delamination damage was seen at areas near the impact locations. As the impact velocity increased, the delamination area increased and its shape gradually changed from the initial peanut shape to an irregular shape. The delamination pattern at low (10.4 J) and high energy (65 J) levels on the cross-ply and QI laminates are shown in Fig. 5. In both the laminates, severe delamination was seen at the bottom interfaces. At 65 J of impact energy, the total delamination areas between laminae in (0/90) 2s and (0/45/-45/90) s are calculated as, 6071mm 2 and 10411mm 2 respectively.

a) b) Fig. 3. Evolution of matrix damage for different impact energy levels on: a) (0/90) 2s ; b) (0/45/-45/90) s laminate.

a) b) Fig. 4. Fiber damage evolution at 65 J of impact on laminate: a) (0/90) 2s ; b) (0/45/-45/90) s .

4.1. Impact force-time histories The numerically predicted impact force-time curves under five different impact energy are shown in Fig. 6. From these graphical representations, it was observed that the impact forces on cross-ply laminates are higher than QI laminates at all impact energies. Since the 90 o laminas are oriented along the shorter side of the composite specimen, at low impact energies (2.6 J and 10.4 J), the force-time history was found as to be a smooth sinusoidal curve. The force-time history curve of moderate impact energy (23.4 J) showed some oscillations when the impact