Abstract

The present work shows the results obtained after rehearsing fatigue in mode III a material composed of epoxy resin with unidirectional carbon fiber reinforcement. For the execution of the tests and has used a test device that has been previously designed and whose validity has been proven. The novelty of this work is that it is the first time that a study of fatigue to fracture is carried out according to mode III in this type of materials. In addition, this fatigue has been made in two different ways. First, it has been loaded in one direction until reaching a certain angle and returning almost to the starting point and, secondly, it has been loaded both in one direction and in the opposite. Hence the first case is called asymmetric fatigue and in the second, symmetrical fatigue. The results obtained are different since the case of loading is, in both cases, substantially different. In both cases, a statistical analysis of the results has been carried out in order to be able to compare the existing differences more properly.

Abstract

In tensile tests, it is assumed that the distribution of strains and stresses is uniform in the test area of the specimen, except for the particular stress states occurring in the vicinity of the grips. This uniformity is subject to the condition that all stresses applied to the interaction surfaces of the specimen with the grips can be reduced to a resultant force whose line of action is at the centroid of the specimen cross-section. However, imperfections of different nature in the experimental tensile tests may cause this resultant to have some eccentricity with respect to the centroid so that, in general, bending is generated in both principal planes of the specimen. In addition, due to the restraint of deformation by the Poisson effect in the grips, tangential stresses perpendicular to the direction of the load are generated, which can cause torsion. The aforementioned effects have been analysed by digital image correlation (DIC) technique on unidirectional carbon/epoxy laminates tested in longitudinal tension and transverse tension.