A novel numerical simulation method for predicting compressive properties of 3D multiaxial braided composites considering various defects

This paper reports a novel manufacturing process of preparing the Three-Dimensional Multiaxial Braided Composites(3DMBCs) and the effects of various defects generated in the manufacturing process on the compressive mechanical properties of 3DMBCs through the experimental and numerical methods. The five-step fabrication process of the 3D multiaxial braided preform was firstly introduced in detail. Then, the influences of various defects such as voids, waviness, and fiber breakage defects on the compressive properties of 3DMBCs were discussed. It is found that the fiber breakage defect and waviness defects were the two primary factors on the decrease of compressive properties of 3DMBCs. However, void defects in the resin and interface had little effect on the composites. When the fiber breakage defect content was 25% and the waviness was 7°, the composite compressive modulus decreased by 51%. The progressive damage process and failure mechanism of the composite under 90° compressive loading confirmed the validity of the numerical model by comparing with the experiments.

A Novel Strategy to Fabricate Core-Sheath Structure Piezoelectric Yarns for Wearable Energy Harvesters

Wearable and portable electronic devices based on textile structure have been widely used owing to their wearability and comfortableness.However,yarn fineness and the comfort of the fabric cannot satisfy the requirements of smart wearable devices.This work presents a novel strategy to prepare highly integrated PVDF/conductive nylon core-sheath structure piezoelectric yarns for wearable which is fabricated by combining electrospinning strategy with 2D braiding technology.The fineness of single yarns as well as strength are both improved significantly compared to previous works.The piezoelectric outputs of the yarn are still stable after 800 s fatigue test at a frequency of 4 Hz,and the cycle stability can maintain more than 3200 cycles.Furthermore,the piezoelectric yarns are further woven into piezoelectric plain fabric.According to the electrical performance,the length of the piezoelectric yarn and the thickness of the piezoelectric layer would both affect the output electrical performance.The yarn of the 10 cm in length and 600μm in fineness can produce an output voltage of 120 mV.Meanwhile,Both the piezoelectric yarn and the fabric could generate piezoelectric output signals through human movement,such as bending,walking.Therefore,the electrical and mechanical performance of the piezoelectric yarns prepared in our work could be improved significantly,and the comfortableness and durability performance of the piezoelectric fabric can satisfy most wearing requirements,which would provide some help in the field of piezoelectric wearable devices based on yarns and fabrics.