Progressive Failure Analysis Of Composite Laminates And Biaxial Test Fixture Design

Due to the good performance such as high specific strength and stiffness,low weight, ability to manufacture complex geometries and other factors,the use of composite materials in aerospace, aviation, medicine, mechanics,building, automotive and civil engineering industry has increased rapidly inrecent years, but the inherently anisotropic structure and the complicacy ofthe failure process make the prediction of the composite materials seem verydifficult. As a result, an accurate predict method becomes very imperative.The theory of strength analyses, which contains four parts: theconstitutive model, calculating the stresses, failure criteria and the stiffnessdegradation method, was reviewed in this paper. To get the more accurateresults needs to select the proper failure criteria and stiffness degradationmethod. Also in some material systems, the module in the tension andcompression loading conditions is different, this should not just be ignored.This paper has done some research in these fields: Firstly, in the aspect ofthe stiffness degradation method, a simple method was proposed based onthe model of individual unidirectional ply within the laminated composite.The model simplified Zinoviev’s theory about the individual unidirectionalply under transverse loading and shear loading. Hashin criterion wasemployed to predicting the failure of individual ply in the laminates. With the help of increment method, a program written in MATLAB was compliedto analysis the failure behavior of the composite laminates. The GraphicalUser Interface (GUI) of the program is designed. With this program, thefailure of composite laminates of various lay-up and materials was predicted.Results demonstrated that, on the premise of maintaining the high accuracyof Zinoviev’s theory, the model simplified the calculation process and couldbe easily applied to further study. Secondly, considering the bimodular ofthe composite materials, the parameter in the constitutive model wasselected due to the loading case (tension or compression) and a UMATprogram was written based on the simplified Zinoviev’s theory. At the sametime, a new mechanism for biaxial tension tests was developed for loadingan in-plane composite laminate specimen simultaneously in two principaldirections in this paper. A composite cruciform specimen for biaxial testingis also designed. Due to the difficulties in determining the failure zone, anew method is proposed based on the Tsai-Wu theory. Taking all the factorsincluding the corner fillet, geometry of the arms and thickness intoconsideration, a Finite Element Method (FEM) parametric modelingtechnique is coupled with a modified ant colony optimization (ACO) tooptimize the shape of the specimen. The optimization result shows that theoptimized specimen in this paper can achieve a uniform strain field andmeet the requirements of the failure zone, so the specimen of this type canbe applicable to the biaxial tests.