Damage development in woven fabric composites during tension-tension fatigue

Impacted woven fabric composites were tested in tension-tension fatigue. In contrast to results from static testing, the effects of low energy impact damage in a fatigue environment were found to be the critical element leadi ng to failure of the specimen. This difference emphasizes the need to ident ify and understand the fatigue damage mechanism. A relatively new non-destr uctive inspection technique using infrared thermography was found to be a v ery useful tool in detecting damage initiation and growth. Furthermore, thi s technique supplies valuable information to the characterization of the op erating fatigue damage mechanism(s). Fatigue leads to a degradation of material properties. Consequently, in con nection with impact induced local stress raisers, fatigue produces continuo usly changing non-uniform stress fields because of stress redistribution ef fects. Other models addressing evolution of fatigue damage in composite mat erials have not been able to simulate evolving nonuniform stress fields. Th erefore. in the second part of this paper, an analytical/numerical approach capable of addressing these issues is also proposed.