Fatigue and Fracture of Titanium Aluminides

DeLuca, Daniel P.; Cowles, B. A.; Haake, F. K.; Holland, K. P.

doi:10.21236/ada226737

Cited by 24 publications

(1 citation statement)

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“…Recently a new class of structural composites has been developed in which the matrix is relatively brittle, so that matrix ductility does not blunt microcracks; yet sufficiently ductile that appreciable mechanical fatigue is known to occur in the unreinforced matrix [5]. Typical of these new composites are relatively brittle intermetallics, e.g.…”

Section: Introductionmentioning

confidence: 99%

Crack Bridging in the Fatigue of Fibrous Composites

Cox

Marshall

1991

Fatigue Fract Eng Mat Struct

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Recent observations of fatigue cracks bridged by continuous fibers in titanium alloy and titanium aluminide composites are compared to analogous observations in fiber-reinforced ceramics under monotonic loading. Three failure modes have been identified under axial loading in each case: longitudinal failure (failure parallel to the fibers) and noncatastrophic and catastrophic mode I failure (failure normal to the fibers). The criteria for transition from one failure mode to another are reviewed. Models developed previously to describe the failure of fiber-reinforced ceramics are extended to describe the mechanics of mode I fatigue crack growth. The extension is straightforward as long as the fibers do not fail in the crack wake, i.e. the failure mode is noncatastrophic mode I failure. NOMENCLATURE a = crack length x = crack position normal to crack front u = normal crack opening displacement p = tractions applied by bridging ligaments po = maximum of p ( u ) f = fiber volume fraction p = fiber radius E,, Em, E = moduli of fibers, matrix, and composite v = Poisson's ratio for the composite t = interfacial friction stress 1 = relaxation length for stress transfer from fibers to matrix CL = coefficient defined in equation (3) u, = applied stress K, = applied stress intensity factor KtiP = net crack tip stress intensity factor K,, = mode I1 crack tip stress intensity factor Kb = reduction in stress intensity factor due to bridging G =weight function w = specimen dimension u, = critical stress for steady-state matrix crack extension J, = critical crack tip fracture energy N = elapsed fatigue cycles N , = fatigue cycles since crack front passed position x R = load ratio up), op, cR = residual stresses

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Section: Introductionmentioning

confidence: 99%