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

Abstract

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 × 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 × 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.

Features of acoustic emission and micro‐CT of 3D‐printed continuous Kevlar fiber‐reinforced composites during progressive damage under flexural load

“…For Specimen A, the loads range from 0 to 0.30 kN and 0 to 0.28 kN (averaged failure load) during the first and the second loading stage, and the corresponding load ranges are 0–0.37 and 0–0.34 kN for Specimen B. It is well known that AE signals monitored during the failure process of composites well reflect the generation and evolution of damages, and even can be clustered for the classification and recognition of damage modes 19 . In this study, typical characteristic parameters of AE signals including amplitude, peak frequency, and RA value (the ratio of rising time and amplitude) were selected for the clustering analysis of AE signals based on k‐means algorithm.…”

“…AE technology can collect damage signals generated during failure process of structures in real time, therefore, AE monitoring has been widely used for the damage detection and location of composites and provides meaningful information for the understanding of different damage modes 19,20 . Until now, there have been many reports about the damage monitoring of AE technology to Kevlar fiber‐reinforced composites produced by traditional manufacturing methods 21 .…”

“…AE technology can collect damage signals generated during failure process of structures in real time, therefore, AE monitoring has been widely used for the damage detection and location of composites and provides meaningful information for the understanding of different damage modes. 19,20 Until now, there have been many reports about the damage monitoring of AE technology to Kevlar fiber-reinforced composites produced by traditional manufacturing methods. 21 AE device was employed by Ramasamy et al 22 to investigate the damage evolution of continuous Kevlar fiber-reinforced composites pretreated using phosphoric acid, monitored results indicated that the percentage of AE hits related to delamination damage was reduced for composites after treated.…”

Mechanical properties of interlayer hybrid textile composite materials based on modified aramid and UHMWPE fabrics

“…As a representative fabric type, knitted fabrics have been considered as the reinforcement in composite materials. They have exhibited more outstanding properties than other fabrics of different architectures, such as good elongation and drape, 4 good formability, 5 high energy absorption capability, 6 and great impact resistance 7 …”

“…They have exhibited more outstanding properties than other fabrics of different architectures, such as good elongation and drape, 4 good formability, 5 high energy absorption capability, 6 and great impact resistance. 7 Aramid and UHMWPE fibers both possess the advantages of high specific modulus and high specific strength, and their composite materials have exhibited excellent mechanical properties. 8,9 Owing to lacking polar groups on the surface and presenting a smooth surface morphology, however, these fibers show poor adhesion at the interface with the resin matrix.…”