The Study Of Composite Laminated Structure Reliability Based On Support Vector Machine

Currently,there are few researches about the system reliability analysis of composite laminated structure and much fewer considered delamination failure mode.Many of them just analyzed components' not system's reliability.It means that any layer's failure was considered to lead to the system's failure and delamination damage was not considered.There are mainly two reasons.One is that the mechanics methods utilized in the laminated structure reliability's analysis like the classical lamination theory and the first order shear deformation theory can't solve interlaminar stresses properly in many situations.Another is that the explicit form of performance functions to basic stochastic variables of components and failure modes are difficult to give,so relative factors are hard to analyze.To solve the problem of laminated structure system's reliability better,the finite element method based on GLHSDT is utilized as the structure stresses analysis method.SVM in statistics is adopt to present explicit form of performance function to basic stochastic variables and the system reliability analysis model of laminated structure is built.Reliability analysis method for laminated structure considering all kinds of progressive damage mode is proposed.Main contents and results are shown as follows:1.The main thinking and scheme of laminated structure reliability analysis are determined through summarizing and analyzing literatures about lamination theories,methods to explicit performance function and traditional methods to analyze reliability of laminated structure.2.GLHSDT is utilized as mechanics method in reliability analysis,so interlaminar stresses and in-plane stresses can be calculated correctly based on which reliability analysis considering delamination failure is realized.The theory and the finite element based on it are deduced in detail.Expressions of intermediate parameters are presented.The method combining Hammer and Gauss numerical integration method is proposed to calculate multiple integration of element stiffness.The expressions of equivalent nodal points load using Gauss numerical integration method are also deduced.The improved method to put local terms into transverse displacement mode considering transverse normal strain is proposed.The stress calculation especially the interlaminar stress calculation has been completed.3.Directing at the implicit performance function problem in laminated structure reliability analysis,SVM is utilized to train out explicit performance function which can solve the calculation problem of relative parameters between failure modes.Optimal parameters in SVM are chosen by combining grid search method with cross validation method.It is proposed that every variable's sample collection should be normalized separately not integrally.The responding value and the first derivative value expressions of approximated explicit performance function to basic variables after normalizing the training collection are deduced.So reliability index is conveniently to be calculated combining traditional reliability method.4.The system reliability analysis method based on SVM is proposed for laminated structure.The components and system division method is defined first and technician skill to simplify laminated structure reliability analysis is summarized by analyzing the regular changing pattern of stresses.Then the stresses values got through GLHSDT are taken to implicit performance functions to get sample set trained by SVM to get eplicit functions.Advanced first order second moment method is used to calculate components'reliability indexes based on the approximating explicit performance function.The branch and bound method directing at laminated structure is proposed to identify main failure modes.Stiffness reduction model is built aiming at GLHSDT in which constitutive relation matrix is reduced according to the corresponding failure mode.At last bonding method and PNET method are utilized to calculate system reliability degree.At last,it can be concluded that the methods proposed herein to analyze components' and system' reliability of laminated structure considering all kinds of progressive damage mode(matrix crack,fiber breakage and delamination)are feasible and the self-made programs are effective.