Characterization of Impact Induced Delamination in Composite Laminates — An Experimental and Finite Element Study

The present paper summarizes the investigation of the impact responses of crossply carbon fiber composites at various levels of low velocity impact. The studies mostly focus on the evaluation of contact force and energy absorbed through dynamic impact tests and detection of 3 D impact damage using high resolution ultrasonic C-Scans and microscopic examinations. The size, shape, and position of impact-induced damage have been identified in each layer by providing a 3 D image of the low velocity impact damage. The residual compression and flexural strengths of damaged specimens after impact were determined from static compression and flexural tests. Delamination appealed to be the most critical damage parameter due to the low-velocity impact in composite laminates. The composite plate with a penny-shape internal crack was modeled by the finite element method using a 3-D layered structural element. The delamination in the form of a penny shaped crack was simulated by eliminating the constraints of adjacent nodes between layers. The response of the composite plate under the influence of a compressive load with various sizes of delamination have been studied. The stress contours of the plate were simulated for various sizes of delamination in the composite plate. The results show that the magnitude of the contact force increased 62 % as the energy of the impact force increased from 2 joules to 10 joules. The impact damage appeared to initiate beyond 2 J and the shape of the impact induced delamination at 10 J showed an elliptical shape in layers closer to the unimpacted surface. The shape of the delaminations gradually become smaller and circular in layers closer to the impacted surface. The compression strength of the unimpacted sample is almost eight times higher than it is in the sample impacted at ten joules.