This paper describes a method for characterizing composite materials subjected to mode III delamination fracture using a custom-designed testing device and test equipment which allows loads or displacements to be applied to the test specimen in two directions, one axial and the other torsional. To verify the method’s functionality experimentally, a composite material made up of an epoxy matrix and unidirectional carbon-fiber reinforcement was used in conjunction with an image analysis device for the purpose of determining the displacement field in the crack front of a double cantilever beam test specimen. According to the results, this test method permits almost pure mode III fracture tests to be carried out, as the mode II component is practically negligible. Another feature of the method is the improvement in the quality and ease of inserting the specimen in the device, thus permitting more repetitive results to be obtained with less dispersion.
The delamination phenomenon is one of the major failure mechanisms in composite materials formed by the stacking of successive layers. The fracture mode that has been studied the least within this phenomenon is mode III, due to the difficulty its simulation involves. A novel test device is presented in this paper that allows laminated composites to be subjected to this mode of loading. Characterization tests were carried out on two materials with different matrices in order to analyse the influence of the type of matrix in the fracture behaviour under mode III-fracture. Furthermore, two analytical models adapted to this test methodology have been used for the determination of the value of the energy release rate for this mode of loading in both materials. The load was applied at different distances from the front of the notch, this being another parameter that was analysed. From the results obtained it follows that the device used in this work allows a dominant mode III and that this result holds for different points of load application studied.
This work comprises a study of the reinforcement capacity provided by the addition of different types of nano-reinforcements of graphene oxide (GO) to epoxy matrices. A range of nanocomposites, resulting from the use of two epoxy matrices (a mono-component system and a bi-component system) and different types of GOs, at different weight percentages were studied and tensile tests were performed on specimens of these materials in order to quantify the variations in their elastic constants and tensile strength. The GO reinforcements used were obtained by means of the modified Hummers method followed by thermal reduction at different temperatures. The aim was to quantify the effect of carbon/oxygen ratio on the reinforcement capacity of GO in order to optimise the manufacturing process. The stiffness of the nanocomposites improved with the addition of TRGO for both matrices, but the tensile strength depended on the matrix.
This paper presents an experimental assessment of the initiation and propagation of interlaminar cracks under mixed mode I/II dynamic fracture loading of a composite material with an MTM45-1 epoxy matrix and unidirectional IM7 carbon-fiber reinforcement. The aims of the experimental program developed for this purpose are to determine, on the one hand, the initiation curves of the fatigue delamination process, understood as the number of load cycles needed to generate a fatigue crack, and on the other, the crack growth rate (delamination rate) for different percentages of static Gc, in both cases for two mode mixities (0.2 and 0.4) and for a tensile ratio R ¼ 0.1. All this with the goal of quantifying the influence of the degree of mode mixity on the overall behavior of the laminate under fatigue loading. The results show that the energy release rate increases with increasing loading levels for both degrees of mode mixity and that the fatigue limit is located around the same percentages. However, crack growth rate behavior differs from one degree of mode mixity to the other. This difference in the behavior of the material may be due to the varying influence of mode I loading on the delamination process.
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