Abstract

In the current study, extensive experimental investigations were carried out on quasi-isotropic Carbon Fiber Reinforced Plastic (CFRP) composite laminates simulating low-velocity impact. Laminates made of three different layups were subjected to impact in the range of 3–30 Joules and their transient response were measured in the form of displacement, energy, velocity and load as functions of time. From these parameters estimates were made of the energy required to initiate damage, onset of delamination and consequent generation of multiple delaminations and their growth. Further, the laminates were tested using ultrasonic NDE technique to quantitatively determine both projected as well as layerwise delamination. From the results obtained, for the range of impact energies tested, threshold energy value for different layups was found to vary from 1.655 to 2.132 Joules/mm. Further, BVID (energy level at which damage is barely visible at the point of impact) was found to be 2.5 Joules/mm. Qualitative indications of damage were observed from load-time plots by sudden drops in load. Ultrasonic evaluation further confirmed these indications. Accurate measure of delamination distribution was obtained by processing the raw scan data using image processing technique. Based on the quantitative data obtained an empirical relation between impact energy and delamination was established.

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