Composite materials exhibit various and complex failure behavior. Different formalisms have been used to predict failure. Improvement of old theories and new ones continue to be published. In this paper, the most recent and widely used models are presented. Failure criteria such as Tsai‐Wu, parametric formulations, maximal stress and strain, Hashin criterion, Hart‐Smith criterion, and the method based on kriging are presented. These failure theories may be classified in two categories, depending whether they integrate failure modes or not. The formalism of each theory is briefly described and their application to model failure of composite laminates is discussed by comparing the advantages and limitations of each method. The diversity of experimental failure envelopes, as reported in the literature on composites, is outlined and it is shown that most criteria permit modeling only particular failure properties of composite laminates.
Predicting failure stress and failure modes in composite laminates is very difficult. The choice between failure criteria is complex and there is a lack of experimental study to validate the results obtained. In this paper, a theoretical and experimental study of damage progression and failure modes of graphite-epoxy laminates in three points bending tests is presented. A quasi-isotropic [(± 45/9010)]5 graphite-epoxy composite is investigated. C-scan method and microscopic sectioning permit to monitor damage progression and failure modes during the experiment. Specimens at different failure levels are used to determine damage progression and the effect of geometrical parameters on the successive failures and on failure modes is studied. The progression of damage has been followed experimentally and identified in detail. The theoretical study is based on the classical laminate theory in the case of in-plane loads. A software program has been elaborated for post-failure treatment and experimental results are compared with numerical predictions.
: Liquid composites moulding processes are now widely used in the aeronautical and the aerospace fields. For the automobile sector, this type of processes is more and more used and still has very high potential. Optimizing moulding parameters, particularly the time cycle and improving the quality of the obtained parts, are key to increasing use of this type of process. When closing the mould in the LCM processes, the compression phase followed by the reinforcements' relaxation are important stages that influence all process parameters. This work presents a theoretical modelling based on two approaches. The results are compared to the experimental ones obtained within our laboratory. In the experimental results, the compressibility behaviour of the reinforcements according to their type; number of ply, lubrication and compression speed were studied. The test results highlight the influence of these parameters on the compressibility and the relaxation of the reinforcements and identify the nesting and the anisotropy as being two important factors. For the theoretical modelling, two approaches are proposed. In the first one, based on the equation of continuity, Darcy's law and the Terzhagui model; the total stress in the mould is equal to a viscous stress due to the fluid flow and an elastic stress due to the fibers response. The equation of Chen and Al, used to model elastic stress allows us to predict the compressibility of the impregnated reinforcements. The second approach is a rheological one where the models of Zener, Burger and Maxwell are used. The results analysis highlights the influence of some moulding parameters and fibrous reinforcement's compression rules. A good agreement is noted between the experimental and the theoretical compression curves of the fibrous reinforcements. The rheological model of Maxwell gives the best prediction of reinforcements behaviour in both compression and relaxation phase.
The use of composite materials with continuous fibers in the aeronautic and aerospace industries requires reliable and precise methods for the prediction of failure. Predicting failure stresses and failure modes in composite laminates is very difficult. The choice between failure criteria is complex, and there is a lack of experimental study to validate the result obtained partly because the biaxial tests are still difficult to perform. This work employs a mixed methodology based on a theoretical and an experimental approach to develop a procedure for the choice and the validation of the failure criterion. The comparison is concerned not only with the macroscopic failure but also with the succession of the failure, the failure mode, and the effect of the geometrical parameters of the test specimen. The most general failure criteria are tested by using two approaches of the stiffness reduction. A finite element code has been elaborated within our laboratory for postfailure treatment. The numerical simulation results are compared with the experimental ones and permit us to make a conclusion on the validity of the failure criteria used.
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