A detailed investigation of damage and failure mechanisms of composite laminates under low-velocity impact (LVI) by experimental tests and numerical modeling is presented. Five impact energy levels were investigated on composite laminates by drop-weight tests. Permanent indentations were measured, and delamination areas of each interface induced by each LVI event were captured using an ultrasonic C-scan. The 3D volume elements with a user-defined, material-based finite element model (FEM) has been applied to predict the LVI event considering damage modes, including intra-ply damage and inter-ply damage. The results of the FEM were found to agree well with experimental observations. Internal damage of the laminate during the impact process was analyzed. For thick laminates, the initiation of damage is observed at the first layer, and then spreads from the impact surface to the back, leading to a pine-type damage pattern as the thickness increases. Frequency-sweep vibration tests of composite laminates subjected to LVI events were studied under a “fixed ends” boundary condition. Our results show that it is reasonable to use frequency-sweep vibration experiments to evaluate the damage of laminates subjected to LVI events.

The effect of scratch damage on the tension properties of carbon fiber plain weave laminates has been studied in detail using digital image correlation (DIC) and acoustic emission (AE). A range of scratch lengths was machined onto different laminates. The bearing capacity of the laminates was then compared with that of unaltered samples. The strain field distributions near the scratches were measured and analyzed as a function of scratch length with DIC. Initiation and propagation of damage were monitored during the tensile tests using AE. Failure sites and morphologies were observed and analyzed. The results show that superficial scratches have little effect on the strength of plain weave laminates when the scratch length is less than 80% of the specimen width. Scratches affect the distribution of strain near the scratch but not far away from the scratch or at the back face of the sample. Not all samples broke from the scratch site but instead broke from the free edge of the sample or close to the gripping region.