Paper number 157


Peter Shyprykevich1, H. Thomas Hahn2, Milan Mitrovic2

1 FAA William J. Hughes Technical Center
AAR-430, Atlantic City Int'l Airport, NJ 08405, USA
2 Mechanical and Aerospace Engineering Department
University of California at Los Angeles
Engineering IV, Los Angeles, CA 90095-1597, USA

Summary Results of an extensive testing program, which addressed the damage accumulation in composite structures under repeated loads, are described. The test program consisted of constant amplitude fatigue with and without preload, low-high and high-low constant amplitude blocks, various stress ratios, and a transport wing spectrum with and without elimination of low loads. Test coupons included unnotched, with center holes, and those with impact damage. These were selected to simulate damage initiation sites commonly found in composite aircraft structure. Threshold strain levels for damage initiation were established by constant amplitude testing, in terms of maximum strain amplitude or strain range, for the three damage initiation sites. The threshold strain data generated by constant amplitude loading was a reliable guideline in predicting damage accumulation under spectrum loading.
Keywords damage accumulation, repeated loads, composite laminates, spectrum fatigue, open hole damage, impact damage, threshold strain levels

Theme : Mechanical and Physical Properties ; Fatigue

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