Fatigue lifetime of GFRP laminates in critical plane defined by equivalent normal stress

Abstract

The study analyzed the fatigue tests of GFRP laminates [0/(±45)2/0]T of specimens cut at different angles (0°, 30°, 45°, 60°, 90°) in relation to the axis 0. The value of the equivalent stress has been determined according to two popular criteria taken from statics. Assuming the parallelism of the basic fatigue characteristics of the specimens cut at 0° and 90° and defining the values of X, Y and S, which are maximum values of stress in different directions, we modified criteria proposed by Azzi-Tsai-Hill and by Norris. Due to the fact that these criteria are nonlinear due to the components of the stress state, they cannot be applied to operational or non-conforming loads in phase. Therefore, it is proposed to apply a linear relationship for the components of the stress state in the form of the following expression for the equivalent normal stress in the critical plane defined by this stress. As a result, the obtained amplitudes of equivalent stresses were compared with the experimental fatigue life. It has been shown that the newly proposed criterion for reduced stress, can be successfully applied to composite materials.