Abstract
The effect of crack length and of crack wake history on crack closure is investigated in 304L austenitic steel. Tests are run on CT specimens initially pre-cracked at constant applied stress intensity factor range ΔK, at a load ratio R=0.1. After precracking, the crack wakes are machined to obtain 2D physically short cracks. Then propagation of these short cracks is still performed at constant ΔK for length ranging from 0.1 mm up to 4 mm. A numerical analysis of load-displacement data allows improved closure detection for the smaller short cracks. The ratio γ=Kop/Kmax is shown to decrease with decreasing crack length a for a <1.2mm; for a >1.2mm, the long crack domain is reached and γ is shown constant and equal to 0.352 independently of ΔK. For tests usually run at increasing ΔK or decreasing ΔK, γ is dependent on the variation of ΔK with a, and the relation da/dN vs ΔK is shown dependent on the loading history. But in all cases, the crack propagation rates are rationalized in term of ΔKeff.
Published Version
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