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Cite this document
A damage-threshold/fail-safety approach is proposed for ensuring that composite structures are both sufficiently durable for economy of operation, and adequately failsafe or damage tolerant for flight safety. Matrix cracks are assumed to exist throughout the off-axis plies. Delamination onset is predicted using strain energy release rate thresholds. Delamination growth is accounted for in one of three ways: either analytically, using delamination growth laws in conjunction with strain energy release rate analyses incorporating delamination resistance curves: experimentally, using measured stiffness loss; or conservatively, assuming delamination onset corresponds to catastrophic delamination growth. Fail safety is assessed by accounting for the accumulation of delaminations through the thickness. A tension fatigue life prediction for composite laminates is presented as a case study to illustrate how this approach may be implemented. Suggestions are made for applying the damage threshold/fail-safety approach to compression fatigue, tension/compression fatigue, and compression strength following low-velocity impact.
damage tolerance, threshold, fail-safe, composite materials, delamination, impact, fatigue, compression, strain energy release rate, fracture mechanics
U.S. Army Aerostructures Directorate, (AVSCOM), NASA Langley Research Center, Hampton, VA