Impact properties of laminated composites with stitching fibers

In order to characterize the outstanding performance of three-dimensional (3D) composites, the low velocity impact test has been carried out. 3D fiber structures have been achieved by using the automated tape placement (ATP) process and a stitching method. Materials for the ATP and the stitching process were carbon/epoxy prepreg tapes and Kevlar fibers, respectively. Two-dimensional (2D) composites with the same stacking sequence as 3D counterparts have also been fabricated for the comparison of damage tolerance. For the assessment of damage after impact loading, specimens were subjected to C-scan nondestructive inspection. Compression-after-impact (CAI) tests were conducted to evaluate residual compressive strength. The damage area of 3D composites was greatly reduced (30–40%) compared with that of 2D composites. Although the CAI strength did not show drastic improvement for 3D composites, the ratio of retained strength was 5–10% higher than 2D samples. The effect of stitching on the impact performance was negligible above the energy level of 35 J.