Abstract
This paper presents the effect of loading and unloading duration on the fatigue damage process of plain woven GFRP. Specimens were subjected to three kinds of rectangle wave loading having different combinations of loading and unloading duration. All loading waves had the same maximum cyclic stress. Fatigue life, modulus decay, AE events and residual strength were measured. In-situ observation of internal damage of GFRP was conducted using an optical microscope with a video recording system.
From the study, the following conclusions were obtained. The fatigue life is influenced by not only loading duration but also unloading duration. The fatigue life is short in the case that loading or unloading duration is long. Modulus decay in the fatigue process is affected by unloading duration, while it is not affected by loading duration. The residual strength is independent on both loading and unloading duration. In the case of short loading duration, debonding in the weft bundle becomes wide with an increase of number of cycles, but the rate is low. Few of debonding in the weft bundle propagate transversely and few AE events are detected in the case of short unloading duration regardless of loading duration. Both loading and unloading duration affect the growth mode of debonding in the weft bundle. These effects of loading and unloading duration on fatigue damage process may be explained by the difference in growth mode of debonding in the weft budle.
