Strength Analysis Of Woven Composites With Holes Based On Multi-scale Method

The advantage of fiber reinforced composites is that the fibers,as the main load-bearing structure,are closely and continuously distributed in the material,and the opening destroys the continuity,and creates stress concentration area around the opening,which leads to the early failure of the whole structure.Therefore,it is of great significance to correctly understand and evaluate the failure mechanism and mechanical properties of perforated composites for structural safety design.With the popularization of woven composites,the mechanical properties of their openings have attracted much attention due to the existence of warp and weft yarns.In this paper,the prediction method and failure mechanism of open hole tensile properties of plain woven composites are studied through the combination of experiments and multi-scale simulation analysis.Firstly,the quasi-static tensile test of plain woven composites with different opening sizes and different shapes is carried out.The trend of ultimate load and equivalent modulus of plain woven composites before and after opening is obtained.The digital image correlation(DIC)full field strain testing technology and AE damage monitoring technology are used,The strain field distribution and damage state change around the orifice were obtained to evaluate the damage evolution behavior of plain woven composites under different opening conditions.Based on the point stress criterion(PSC),the characteristic length of the width to diameter ratio of the specimen is obtained,and the opening strength of the round hole is predicted theoretically.This part provides the experimental basis for the multi-scale progressive damage analysis.Secondly,the geometric parameters of the periodic unit cell of plain woven composites were obtained by optical microscope.Based on the python script written by texgen software,the high fidelity meso unit cell model was established,and the periodic boundary was imposed on it and the local coordinate direction of the material was given.Using the load equation proposed by Hashin and Hou as the failure criterion of fiber bundle and the maximum principal stress criterion as the failure criterion of matrix,combined with the exponential damage evolution of fiber bundle and the linear damage evolution of matrix in the form of equivalent displacement,the UMAT subroutine is compiled t o analyze the progressive damage of plain woven composites at meso scale.Compared with the experimental results,it is proved that the proposed model can effectively predict the stiffness and strength of plain woven composites.Finally,from the perspective of macro opening,the two-dimensional damage failure criterion based on strain failure proposed by Linde et al.Is extended to the three-dimensional form.Combined with the nonlinear damage evolution,the macro progressive damage finite element study of plain woven composites is carried out.Compared with the experimental results,it is proved that the macro progressive damage model established in this paper can effectively predict the open hole tensile strength of plain woven composites,which also show s that the multi-scale progressive damage analysis model established in this paper is reliable.Based on the strength of the opening obtained by the macro progressive damage analysis,the feature length of the finite element analysis is obtained by linear elastic analysis and pixel method.The PSC strength prediction method based on the finite element analysis is established.Through the parametric study on the shape of elliptical opening,it can be seen that for small aperture specimens,increasing the notch length along the load direction is conducive to improving the overall bearing capacity of the structure.