FATIGUE OF IMPACT DAMAGED CARBON FIBRE COMPOSITES

Abstract

The sensitivity of carbon and glass fibre composite aircraft materials to low-level impact damage leads to some concern about possible long-term degradation of these materials by fatigue, particularly under compressive loading. As for metals, the testing of these materials must be carried out under realistic flight by flight loading, and for composites such testing is complicated by the fact that these materials display good fatigue properties combined with a higher level of scatter than for metals. The duration of fatigue tests can be much greater than for metals, and the testing techniques considerably more complex due to the need to test using predominatly compressive loading. This paper investigates the effects of using a modified loading spectrum to accelerate fatigue testing of carbon-fibre composite laminates, examines the growth rates of realistic impact damage in tests which represent flight by flight loading of an aircraft wing, and discusses briefly some of the problems associated with compression fatigue testing of composites.