Impact and post-impact properties of hybrid-matrix laminates based on carbon fiber-reinforced epoxy and elastomer subjected to low-velocity impacts

The presented study investigates the impact behavior of hybrid matrix (HyMa) composite laminates under low-velocity impact loads. In the specific HyMa material system, carbon fiber-reinforced EPDM-rubber layers are combined with conventional carbon fiber-reinforced epoxy layers in a co-curing autoclave process. HyMa specimens with 1, 3 and 5 interlayers of fiber-reinforced elastomer (FRE) (21 plies in each specimen, 4.58 mm specimen thickness) and reference specimens were subjected to low-velocity impacts and compression after impact tests. Specimen response and damage were analyzed based on force-time curves, force-displacement curves, visual damage inspection, ultrasonic C-scans, micrographs and compression strength. Low-velocity impact experiments at different energy levels (16 J, 20 J, 25 J and 30 J) showed that peak forces, visual damage area and projected damage area could be dramatically reduced with increasing number of FRE layers. Energy absorption increased up to 21% and impact tolerance was significantly enhanced using HyMa laminates. We found that two main effects influenced the impact behavior: shear decoupling by the reinforced elastomer layers leading to higher deformation compliance and fiber fracture as a pronounced damage mechanism.