Fatigue Damage of Long Fibre Reinforce Composites

In present times, the use of composite structures is becoming more and more important and their employ can be planned for lightweight but also performing structures. Therefore, dealing with the study of the mechanical behaviour of composite materials, it is important to provide models or laws for fatigue life estimation. The aim of this work is to define and compare the decay of the composite mechanical properties during fatigue, and in particular the damage initiation, of different types of long-fibre reinforced composites. The damage of the composites is evaluated by considering different approaches: the evaluation of the stiffness of the specimens during the experimental tests, the observation of internal defects by scanning electronic microscope of interrupted tests specimens, the surface temperature measurement by the experimental technique of thermography. Object of this study are glass and basalt fibre reinforced plastic laminates, with a polymeric matrix. Rectangular specimens are cut from similar manually laminated plates and static and fatigue experimental tests are performed. The fatigue test results are compared and the mechanical behaviour of the basalt fibre composite is compared with the more used and known glass fibre composites. In particular the high cycle fatigue behaviour is considered and a final discussion on the meaning of fatigue strength data of composite materials is proposed.