PSI - Issue 14

P Rama Subba Reddy et al. / Procedia Structural Integrity 14 (2019) 676–683 Author name / Structural Integrity Procedia 00 (2018) 000–000

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lower laminate thickness, the effect of matrix and fiber-matrix interfacial strength is not significant. However, with increase of thickness, the laminates have shown different energy absorption. E-glass/phenolic composite laminate has shown higher energy absorption than E-glass/epoxy composite laminate at 20mm and 25mm thick. This can be attributed that the laminate which has got lower fracture energy for delamination has performed better at higher thickness. The data suggest that delamination is a major energy absorption mechanism for higher ( ≥20mm)

thickness laminate. 4. Failure analysis 4.1. Failure analysis at different depth levels

Failure analysis studies on post impacted composite laminates have shown usual failure modes such as matrix cracking, shear cutting, tensile failure and delamination. Detailed analysis on failure modes of composites under ballistic impact conditions as a function of impact velocity and laminate thickness were reported along with high speed video images in our previously published work by Reddy et al. (2015). In the present study, failure behaviour of laminate at different depth levels is studied by using ultrasonic C-scan analysis technique. Fig.5 shows damage pattern in 10mm and 25mm thick laminates at different depth levels starting from left which is strike face , towards the right side showing different depth levels to the rear side of the laminate. It is observed that from front to rear side of the laminate, the damage area is increased. This trend is similar in both the laminates however, E-glass/phenolic laminate has shown more damage area than E-glass/epoxy laminate.

Fig.5 Damage at different depth level for 10mm (top) and 25mm (below) thick laminates