Abstract
The aim of this paper is to study the fatigue behaviour of GRP rods manufactured by a modified pultrusion technique. Constant-deflection flexural fatigue tests were performed at zero mean stress, i.e. a cyclic stress ratio R = −1. The frequency of the testing machine was 25 Hz. Failure was defined as a 30% drop in the specimen stiffness (EI). The relationship between the endurance limit and the static flexural strength and fibre volume fraction, V
f, was determined, and the influence of V
f on the induced surface temperature, S-N relationships and failure modes was investigated.
The results show that, in the range of V
f values investigated, as V
f increased fatigue strength increased. The relationship between the residual stiffness ratio (
EI
(EI)
0
) and the normalized fatigue life (
N
N
f
) was independent of stress amplitude (S
a) and V
f. This result was supported by using the residual stiffness ratio as a failure criterion. The predicted values of endurance limit by using the proposed equation gave excellent agreement with the experimental data.