Effect of friction on the hysteresis loops from three-point bending fatigue tests of fibre-reinforced composites

In uni-axial fatigue tests on fibre-reinforced composites, the stress–strain hysteresis loop can be used as a measure for stiffness degradation and energy dissipation. In case of three-point bending fatigue tests, the hysteresis loop of the bending force versus midspan displacement can yield similar information. In this paper, it is shown that the shape of the hysteresis loop can be affected significantly by friction at the supports, especially for large deflections. As such, the area of the closed hysteresis loop is no longer a measure for energy dissipation and damage growth. Three-point bending fatigue tests have been compared to static bending tests with different support conditions. Finally finite element analyses have confirmed that friction can be identified as an important parameter affecting the shape of the hysteresis curve.