NUMERICAL ANALYSIS OF DELAMINATION GROWTH FOR STIFFENED COMPOSITE LAMINATED PLATES

A study of postbuckling and delamination propagation behavior in delaminated stiffened composite plates was presented. A methodology was proposed for simulating the multi-failure responses, such as initial and postbuckling, delamination onset and propagation, etc. A finite element analysis was conducted on the basis of the Mindlin first order shear effect theory and the von-Krmn nonlinear deformation assumption. The total energy release rate used as the criteria of delamination growth was estimated with virtual crack closure technique (VCCT). A self-adaptive grid moving technology was adopted to model the delamination growth process. Moreover, the contact effect along delamination front was also considered during the numerical simulation process. By some numerical examples, the influence of distribution and location of stiffener, configuration and size of the delamination, boundary condition and contact effect upon the delamination growth behavior of the stiffened composite plates were investigated. The method and numerical conclusion provided should be of great value to engineers dealing with composite structures.

Stress analysis of clamped-free grid composite cylindrical shell under various end loadings

Stress analysis of cylindrical grid-stiffened composite shells was conducted under transverse loading,pure bending,torsion and axial compression under clamped-free boundary condition.Electrical strain gauges were employed to measure the strains in transverse loading case to validate the finite element analysis which was conducted using ANSYS software.Good agreement was obtained between the two methods.It was observed that stiffening the composite shell with helical ribs decreased the average equivalent Von Mises stress on the shell.The reduction of the stress seemed to be higher in the intersection of two ribs.It was also seen that the stress reduction ratio was higher when the structure was under bending compared to torsion and axial compression.The reduction ratio was approximately 75% in pure bending in the intersection point of the ribs,while it was approximately 25% in torsion.Therefore,it is concluded that the presence of the ribs is more effective under bending.Failure analysis was done using Tsai-Wu criterion.The ribs were observed to result in maximum and minimum increase in the failure load of the structure under transverse bending and torsional loading,respectively.

Post-buckling Reliability and Sensitivity Analysis of Composite Stiffened Plates Based on Adaptive Kriging Method

Based on the active learning Kriging(ALK)model and the Hashin failure criterion,this paper proposes a new reliability evaluationmodel for composite stiffened panels,and conducts a reliability analysis on the ultimate bearing capacity.In addition,this paper studies the importance ranking of input variables.By comparing the calculation results of the reliability model proposed in this paper with those of the Monte Carlo method,the accuracy and efficiency of the ALK model are verified by case studies.Finally,the effects of longitudinal elastic modulus and fiber-direction tensile strength on post-buckling failure probability are discussed,which provides significant reference and guidance for the optimization and design of composite stiffened plates.

Nonlinear Bifurcation and Post-buckling Analysis of Cylindrical Composite Stiffened Laminates Based on Weak Form Quadrature Element Method

This paper presents a weak form quadrature element formulation in the analysis of nonlinear bifurcation and post-buckling of cylindrical composite stiffened laminates subjected to transverse loads.A total Lagrangian updating scheme is used in combination with arc-length method,and the branch-switching method is adopted to identify the whole post-buckling procedure of the laminates.The formulation of the shell model and beam model are based on the basic concept of Ahmad.The coincidence of discrete nodes and integration points in quadrature element endows it with compactness and conciseness in the nonlinear buckling analysis of the cylindrical stiffened laminates.Several numerical examples are firstly presented to verify the effectiveness and accuracy of present formulation.Parametric studies on the effects of the height-to-breadth ratio,lamination schemes,positions,distribution,number of the stiffeners on the bifurcation and post-buckling behavior are performed.

An Optimization Approach for Stiffener Layout of Composite Stiffened Panels Based on Moving Morphable Components(MMCs)

An explicit topology optimization method for the stiffener layout of composite stiffened panels is proposed based on moving morphable components(MMCs).The skin and stiffeners are considered as panels with different bending stiffnesses,with the use of equivalent stiffness method.Then the location and geometric properties of composite stiffeners are determined by several MMCs to perform topology optimization,which can greatly simplify the finite element model.With the objective of maximizing structural stiffness,several typical cases with various loading and boundary conditions are selected as numerical examples to demonstrate the proposed method.The numerical examples illustrate that the proposed method can provide clear stiffener layout and explicit geometry information,which is not limited within the framework of parameter and size optimization.The mechanical properties of composite stiffened panels can be fully enhanced.