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Three-point flexure test for unidirectional off-axis composites has been analyzed by the finite element method. The main difficulty of modeling three-point flexure test of this kind of material is due to the bending-twisting coupling that induces the lift-off of the specimen at the fixture supports. In the present work, the contact between the load and support rollers and the specimen has been modeled with linear gap elements. The type of element and refinement of the mesh have been analyzed in order to minimize numerical error. After having selected those parameters, a complete model with discretization of load and support rollers has been developed to simulate different test conditions. The numerical displacement field has been compared with analytical and experimental results obtained previously. Furthermore, the length and location of the contact between specimen and rollers has been numerically predicted in some configurations.

This work evaluates the influence of geometric properties, the length-to-width ratio, named Aspect Ratio, on curvatures in [θ − 90/θ]T carbon/epoxy composite laminates at room temperature due to thermal residual stresses. A new method to determine experimentally thermal residual curvatures in composites laminates by defining small-length increments on the surface of deformed plate has been exposed. [–454/454]T was considered to obtain a simple analytical expression of twisting curvature. A new way to determine transverse coefficient of thermal expansion α2 is proposed in squared laminates based on experimental values of twisting curvatures of [–454/454]T laminates.

SUMMARYThis paper shows the use of the dual integrated force method (IFMD) in finite elements method and its application to composite materials. This method was developed by S.N. Patnaik in isotropic materials, considering not only the equilibrium equations but also the compatibility conditions. In the IFMD, the principal unknowns are the displacements, and the structure of governing equation is similar to the stiffness method. It is shown that the governing equation of the IFMD is the same than in the case of the hybrid method of Pian. The method is applied to two examples, a cantilever beam of orthotropic material loaded at the end and one off-axis tensile test in a unidirectional composite specimen. The results of this method have been compared with the ones obtained from the application of the stiffness method and with analytical results.