Applied Composite Materials (v.18, #4)

Studying the Tensile Behaviour of GLARE Laminates: A Finite Element Modelling Approach by P. Soltani; M. Keikhosravy; R. H. Oskouei; C. Soutis (271-282).
Numerical simulations based on finite element modelling are increasingly being developed to accurately evaluate the tensile properties of GLARE (GLAss fibre REinforced aluminium laminates). In this study, nonlinear tensile behaviour of GLARE Fibre Metal Laminates (FML) under in-plane loading conditions has been investigated. An appropriate finite element modelling approach has been developed to predict the stress–strain response and deformation behaviour of GLARE laminates using the ANSYS finite element package. The finite element model supports orthotropic material properties for glass/epoxy layer(s) and isotropic properties with the elastic–plastic behaviour for the aluminium layers. The adhesion between adjacent layers has been also properly simulated using cohesive zone modelling. An acceptable agreement was observed between the model predictions and experimental results available in the literature. The proposed model can be used to analyse GLARE laminates in structural applications such as mechanically fastened joints under different mechanical loading conditions.
Keywords: GLARE; Fibre Metal Laminates; Finite element modelling; Tensile behaviour

Time-Variant Simulation of Multi-Material Thermal Pultrusion by Sunil C. Joshi; X. Chen (283-296).
Pultrusion being the viable and economical process for producing constant cross-section composite products, many variants of it are being tried out. This paper embarks on the pultrusion with multi-materials; typically of polymer foam/glass fibre reinforced polymer (GFRP) sandwich panels. Unlike conventional composites pultrusion, this process with more than two material phases, one of them dry, poses a challenge in simulating the thermal co-curing within the die. In this paper, the formulation and development of three-dimensional, finite element/nodal control volume (FE/NCV) approach for such multi-material pultrusion is presented. The numerical features for handling the dry-wet material interfaces, material shrinkage, variations in pull speed and die heating, and foam-to-skin thickness ratio are discussed. Implementation of the FE/NCV procedure and its application in analyzing pultrusion of polymer foam/GFRP sandwich panels with multi-heater environment are presented.
Keywords: Foam sandwich; Pultrusion; Curing; Finite element analysis; Process optimization

Artificial Neural Networks (ANN) have been successfully used in predicting the fatigue behavior of fiber-reinforced composite materials. In most cases, the predictions were obtained for the same material used in training subjected to different loading conditions. The method would be of greater value if one could predict the failure of materials other than those used for training the network. In a recent paper, ANN trained using the experimental fatigue data obtained for composites subjected to a constant stress ratio $$ left( {{hbox{R}} = {sigma_{{ min }}}/{sigma_{{ max }}}} ight) $$ was successfully used to predict the cyclic behavior of a composite made of a different material. In this work, this method is extended to include the stress ratio effect. The results show that ANN can provide accurate fatigue life prediction for different materials under different values of the stress ratio. These results can allow for the development of a materials smart database that can be used for various engineering applications.
Keywords: Artificial neural networks; Composite materials; Fatigue; Stress ratio

High Strain Rate Compressive Tests on Woven Graphite Epoxy Composites by Mohammad Reza Allazadeh; Sylvanus N. Wosu (311-325).
The behavior of composite materials may be different when they are subjected to high strain rate load. Penetrating split Hopkinson pressure bar (P-SHPB) is a method to impose high strain rate on specimen in the laboratory experiments. This research work studied the response of the thin circular shape specimens, made out of woven graphite epoxy composites, to high strain rate impact load. The stress-strain relationships and behavior of the specimens were investigated during the compressive dynamic tests for strain rates as high as 3200 s−1. One dimensional analysis was deployed for analytical calculations since the experiments fulfilled the ratio of diameter to length of bars condition in impact load experiments. The mechanics of dynamic failure was studied and the results showed the factors which govern the failure mode in high strain deformation via absorbed energy by the specimen. In this paper, the relation of particle velocity with perforation depth was discussed for woven graphite epoxy specimens.
Keywords: Compression test; High strain rate; P-SHPB; Woven graphite epoxy; Composites material; Absorbed energy.

Numerical and Experimental Study of the Bleeder Flow in Autoclave Process by Yanxia Li; Min Li; Yizhuo Gu; Zuoguang Zhang (327-336).
In the autoclave process, resin flow is a primary mechanics for the removing of excess resin and voids entrapped in the laminate and obtaining a uniform and void free composite part. A numerical method was developed to simulate the resin flow in the laminate and the bleeder, and the effects of ‘bleeder flow’ on the resin flow and fiber compaction were conducted. At the same time, fiber distribution in the cured laminates was investigated by both experiments and simulations for the CF/Epoxy and CF/BMI composites. The data of the experiments and simulations demonstrated that fibers consolidated and reconsolidated in the laminate and it was impacted by the viscosity and gel time of the resin system. Compared to the post study in which only resin flow in the laminate are considered, these results will deepen the understanding of the consolidation process, resin pressure variation and void control during the autoclave process, which is valuable for the study of the performance of composite parts, provided that fiber distribution does affect some properties of composite material.
Keywords: Polymer-matrix composites; Autoclave process; Resin flow

Firstly, a decision process is undertaken to establish if there is indeed a certification issue. That is situations where flight safety depends on the structural integrity of the repair patch.Secondly, especially if there is a certification issue, a rigorous repair design approach is undertaken, based on a generic data base previously obtained from the testing of bonded joints representing the critical regions in the repair.Thirdly, the actual repair system is validated to ensure the required strength and potential durability has been achieved. This includes Boeing wedge testing, a proven quality control procedure for the adhesive bonding process.Finally, if this approach is considered inadequate then the option is to include proof testing and/or structural health monitoring for assessment of the actual through life structural integrity of the repair system; however, this would only be feasible for special cases where the considerable extra cost and complication can be justified.
Keywords: Bonded repairs; Aircraft; Debonding; Fatigue; Structural health monitoring