DAMAGE MECHANISM ANALYSIS OF 2D 1×1 BRAIDED COMPOSITES UNDER UNIDIRECTIONAL TENSION

Coupling with the periodical displacement boundary condition,a representative volume element(RVE) model is established to simulate the progressive damage behavior of 2D1×1 braided composites under unidirectional tension by using the nonlinear finite element method.Tsai-Wu failure criterion with various damage modes and Mises criterion are considered for predicting damage initiation and progression of yarns and matrix.The anisotropic damage model for yarns and the isotropic damage model for matrix are used to simulate the microscopic damage propagation of 2D1×1braided composites.Murakami′s damage tensor is adopted to characterize each damage mode.In the simulation process,the damage mechanisms are revealed and the tensile strength of 2D1×1braided composites is predicted from the calculated average stress-average strain curve.Numerical results show good agreement with experimental data,thus the proposed simulation method is verified for damage mechanism analysis of 2D braided composites.

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.