In the aerospace industry, composite structures design rules and admissible criteria are not well known for strength sustainability after impact induced damage. Predictive numerical tools are thought to be used to reduce design and certification time and costs, and to determine links between the inner behaviour of the material and the outer designable behaviour of structures. In this frame, it is aimed in this study to compare real tests damage measurements and two kinds of numerical damage predictions: one with geometrical openings for delamination discontinuity modelling, and one without any mesh opening that represents damage in a continuous way. Our attention is focused on two types of pre-impregnated unidirectional materials: T700/M21S and T800/M21S both strain rate sensitive because of a high percentage of thermoplastics in the M21 resin. Quasi-static and dynamic characterization tests have been carried out on balanced angle ply [±θ] laminates using Split Hopkinson's Pressure Bars. A saturation of through ply cracking has been outlined and strain rate effect on T800/M21S coupons' strength has been established up to medium strain rates. User defined cohesive finite elements are implemented in the non-linear explicit finite element analysis (FEA) code LS-DYNA® to model the dynamic delamination opening. At the same time a user defined deterministic continuous damage unidirectional composite material model is developed on the basis of the Matzenmiller-Lubliner-Taylor model widely used for woven composites. Initiation and growth of damage are predicted up to saturation and fracture for various pure and coupled damage mechanisms including delamination and matrix cracking, with criteria based on the experimental characterization. Impact induced damage from experimental measurements and numerical predictions are compared for T800/M21S aeronautical samples impacted at different energy levels. The effect on internal damage and residual indentations of 2 different masses and velocities has been evaluated. It is shown that the cohesive discontinuous delamination and the continuous damage coupling numerical models give both a good prediction of the global flexural behaviour of the structure. Spatial extension in shape and dimensions of damage through the plates' thickness is well predicted by the continuous model while the cohesive model is more diffusive leading to "isotropic" delamination predictions. Also, the continuous model gives better correlations between predicted and measured residual indentations after impact.
| Identifer | oai:union.ndltd.org:univ-toulouse.fr/oai:oatao.univ-toulouse.fr:4272 |
| Date | 20 July 2010 |
| Creators | Ilyas, Muhammad |
| Source Sets | Université de Toulouse |
| Detected Language | English |
| Type | PhD Thesis, PeerReviewed, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | http://oatao.univ-toulouse.fr/4272/ |
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