Low-velocity impact resistance and acoustic emission evaluation on mechanical failure of carbon fiber weft-knitting-reinforced composites

In this study, the carbon fiber weft-knitting (CFWK)-reinforced composites were prepared and the deformation mechanism during acoustic emission (AE) and low-velocity impact resistance. To fabricate CFWK composites, single-sided 1 x 1 variable plain stitch, double-sided interlock structure, and two inter-ply and intra-ply hybrid structures of the former two stitches were applied for reinforcements in epoxy films via hot-pressing. Moreover, we evaluated the tensile and bending properties during AE and investigated the low-velocity impact properties of CFWK-reinforced composites to evaluate the failure mechanism of composites. Finally, we analyzed the effects of laminating numbers, ply angle, and fabric structure on the properties of CFWK-reinforced composites. Results showed that the composites with 1 x 1 variable plain stitch reinforcement exhibited the highest tensile strength and bending strength (206.22 and 213.43 MPa, respectively) among the composites with a two-layer structure. The tensile fracture strength of [0/90] laying was 35%-50% lower than that of [0/0] laying. In addition, the cluster analysis on AE signal frequency showed that fiber debonding was the main failure mode, accounting for 68% of the total debonding when stretching along the longitudinal direction of the two-ply composite loop. Under the impact energy of 4 J, the maximum load of CFWK-reinforced composites with three-ply interlock increased by 275% compared to that of single-ply composites. Furthermore, the three-ply interlock CFWK-reinforced composites were perforated under impact energy of 10 J.

Automated summary

The results of the study indicate that the carbon fiber weft-knitting composites reinforced with 1 x 1 variable plain stitch exhibited the highest tensile and bending strength among different structures. Different laying directions showed variations in tensile fracture strength. Fiber debonding was identified as the main failure mode through cluster analysis of AE signal frequency. Furthermore, composites with a three-ply interlock structure showed improved low-velocity impact resistance.