NON-LINEAR PROGRESSIVE FAILURE ANALYSIS OF COMPOSITE AEROSPACE - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS NON-LINEAR PROGRESSIVE FAILURE ANALYSIS OF COMPOSITE AEROSPACE STRUCTURES M.Günel 1 and A. Kayran 2* 1 TAI, Ankara, Turkey, 2 Dept. of Aerospace Eng., METU, Ankara, Turkey * Corresponding author (akayran@metu.edu.tr) Keywords : progressive failure analysis, composite aerospace structures, non-linear deformation, material property degradation, Nastran, PCL code Abstract the first ply failure and progression of failure of composite laminates with cut-outs under combined The article presents a study of geometrically non- in-plane and out-of-plane loading and geometrically linear progressive failure analysis of thin walled non-linear deformations. In progressive failure composite aerospace structures subjected to analysis of structures which are exposed to combined in-plane and out-of-plane loadings which especially out-of-plane loads, geometric non-linear are typically encountered in thin walled aerospace effects become prominent when the structure is structures. Different ply and constituent based subjected to large displacement and rotation. In failure criteria and material property degradation addition, in most of the previous studies on schemes have been coded into a PCL code in progressive failure analysis of composite structures, Nastran, and progressive failure analyses of sample single load case is used. Progressive failure analysis composite laminates with cut-outs are executed. of composite laminates under combined in-plane and Case studies are performed to study the effect of out-of-plane loads is particularly important for thin geometric nonlinearity on the first ply failure and walled aerospace structures which are usually progression of failure for laminated composite subjected to combined in-plane and out-of-plane structures under combined in-plane and out-of-plane loads. Therefore, a major objective of the present loadings. study is also to investigate the significance of 1. Introduction geometrically non-linear analysis on the progressive failure response of composite laminates under The use of composite materials in primary aerospace combined in-plane and out-of-plane loading. structures is rapidly increasing. Understanding the For this purpose different ply and constituent based failure response of composite laminates which are failure criteria and material property degradation the building blocks of composite aerospace sub- schemes have been coded into a PCL [5] code in structures is essential in order to exploit the full Nastran and progressive failure analyses of sample strength of composite materials in aerospace composite laminates with cut-outs are executed. structures and design fault tolerant structures. Thin Case studies are performed to study the effect of walled composite aerospace sub-structures, such as geometric nonlinearity on the first ply failure and skin panels of lifting surfaces or pressurized fuselage progression of failure. Different ply and constituent sections, are commonly exposed to combined in- based failure criteria and different material property plane and out-of-plane loadings. Composite degradation schemes, such as sudden degradation laminates with local damages can sustain operating and gradual degradation of material properties, are loads much better than their metallic counterparts. also compared in terms of predicting the first ply Therefore, progressive failure analysis of fiber failure and failure progression. This article presents reinforced thin walled composites is studied widely some sample results. More comprehensive results in the literature to determine the capability of will be presented in the conference. composite structures to sustain loads [1-4]. 2 Description of the PCL code In this article, two dimensional finite element based progressive failure analysis method is used to study The Patran Command Language (PCL) is a

programming language which is an integral part of Fiber failures: ( ) ( ) (1) E , G , G , ν = R * E , G , G , ν the MSC.Patran system. PCL can be used to write 1 12 13 12 1 12 13 12 application or site specific commands and forms, Matrix failures: create functions from all areas of MSC Patran ( ) ( ) including all applications, graphics, the user E , G , G , ν = R * E , G , G , ν ( 2) 2 12 23 21 2 12 23 21 interface and the database, and completely integrate where the material property degradation factor R in commercial or in-house programs. In the current Eqs.(1) and (2) can be adjusted to degrade the study, different ply and constituent based failure criteria and material property degradation schemes properties gradually or suddenly. have been coded into a PCL code which employs For the plane stress state, failure index of the Tsai- Wu ply failure criterion is calculated by [7] linear and non-linear solution types of MSC Nastran depending on the analysis type desired. For the pre- selected failure criterion, failure indices are σ + σ 2 + σ σ F F F (3) 1 1 11 1 12 1 2 calculated based on the strains or stresses at the shell F σ + F σ 2 + F τ 2 = FI 2 2 22 2 66 12 element centers, at the mid plane of plies. In order to where effectively allow material property degradation at 1 1 1 1 1 the ply level, before the failure analysis is initiated, F = − (4) = − F 11 = F 2 1 Y Y X X X T X T C C T C for each element in the finite element mesh distinct − 1 composite laminate properties with distinct two 1 1 = 22 = F (5) F F = 12 66 Y T Y dimensional orthotropic materials for each ply are 2 X X Y Y S C 2 T C T C generated via the PCL code that is developed. Thus, stiffness reduction scheme is implemented easily for In the literature, material property degradation each failed ply by referencing the element property associated with failure predicted by the mode identification and material identification numbers of independent Tsai-Wu failure criterion is the failed ply. Progressive failure analysis continues implemented by identifying a mode of failure, which until the ultimate laminate failure or until a is based on the stress component that contributes prescribed load level is reached. Currently, linear maximum to the failure index. For instance, if the static, large displacement-small strain non-linear maximum contribution to the failure index is due to static (Sol 106) and large displacement-large strain σ fiber direction stress , then fiber failure is 1 non-linear static (Sol 600) solution types of Nastran assumed. Similarly, if maximum contribution to are implemented in the PCL code. σ or shear failure index is due to transverse stress 2 2.1 Progressive failure analysis method τ stress 12 , then matrix failure is assumed. However, In the present study, strains and stresses, which are this method of material property degradation calculated at the mid-plane of the plies by the disregards the contribution of all stress components desired solution type, are used in calculating the and puts the blame on only one stress component in failure indices for the failure criterion selected. order to identify a failure mode. In the present study, Currently, plane stress failure criterion of Hashin [6] material property degradation method used with the and Tsai-Hill failure criterion [7] are implemented in Tsai-Wu failure criterion is modified, and the the PCL code. In this article, results obtained by material property degradation factor, which is Hashin failure criterion are presented. In the selected in the beginning of the analysis, is conference, results obtained by the Tsai-Wu failure manipulated to yield two separate degradation criterion will also be presented. Material property factors that are to be used with the fiber and matrix degradation method that is used with the mode failure modes, which are assumed to occur dependent failure criteria depends on the mode of simultaneously. The decision on the separate failure. For the two dimensional lamination theory degradation factors is based on the relative with the transverse shear deformation effects magnitudes of stress components, which are included, degraded properties for the fiber and responsible for fiber and matrix failures. For this matrix failure modes are given separately by Eqs.(1) purpose, failure indices corresponding to failure and (2) [1]. modes are initially separated as: