Effect of off-axis angle on low-velocity impact and compression after impact damage mechanisms of 3D woven composites

This paper presents the influence of the off-axis angles on the low-velocity impact (LVI) and compression after impact (CAI) damage mechanism of three-dimensional (3D) woven carbon/epoxy composites. Three kind of samples with different angles, 0°, 30° and 45°, of the weft and warp yarn orientation were experimentally tested using the drop weight LVI and quasi-static CAI equipment. X-ray micro-computed tomography (Micro-CT) techniques were used to identify the impact damage volumes, damage distribution and damage modes of 3D woven composites. Results indicated that the off-axis angles have significant effects on the LVI and CAI mechanical behavior and final failure mechanisms. Furthermore, Micro-CT revealed that off-axis samples exhibit more damage volumes and out-of-plane deformation. More importantly, the ultimate CAI strength of all the samples are largely governed by the global buckling. However, the formation of buckling damage in 0° samples runs from one edge of the specimen to the other side, whereas that in 30° and 45° samples mainly occur along the weft direction.