Mechanisms associated with transient fatigue crack growth under variable-amplitude loading: An experimental and numerical study

摘要: An experimental and numerical study has been made of the mechanisms fatigue crack growth crack-closure behavior in an αβ titanium alloy Ti-4A1-4Mo-2Sn-0.5Si (IMI 550), following both single block tensile overloads. Closure immediately behind front (near-tip closure) was found to be main factor controlling load-interaction effects. Single overloads were remove near-tip closure, slightly reduce far-field closure along length, resulting initial acceleration rates. Subsequent delayed retardation rates accompanied by increase load, due enlarged compressive residual stress overload plastic zone. High/low caused greater than same magnitude, this attributed changes degree wake crack. Numerical predictions such transient behavior, based on a modified Dugdale model, are close agreement with results, terms observed opening displacements. Load-interaction effects most severe when baseline intensity range (ΔK) threshold (ΔKTH), or, maximum (Kmax) approached fracture toughness material. At low ΔK levels, magnitude delay sensitive microstructure enhanced coarse-grained β-heat-treated microstructures compared standard fine-grained microstructures. Based these mechanistic sequences suggested explain cycles.