Intrinsic Threshold Stress Intensity of Additive Manufactured Metals

Abstract

Intrinsic, closure-free, threshold stress intensity, ΔKth,i, is uniquely related to a certain computable near-tip residual stress, σ*; σ* is sensitive to applied stress ratio at given Kmax under constant-amplitude loading and, particularly so, to load history under variable-amplitude loading. ΔKth,i will vary significantly, depending on load conditions, rendering its characterization under controlled σ* crucial. Experiments on additive manufactured (AM) PH1 steel and 18Ni300 maraging steel confirm the possibility of characterizing the relationship between ΔKth,i and σ* using small-size compact tension, C(T), specimens. This opens the way for material characterization from miniature specimens cut out from smaller components. Application of the relationship between ΔKth,i and σ* leads to improved assessment of the structural integrity of AM components through residual crack growth analysis as well as specification of allowable defect size. It can serve as an input for optimization of AM process parameters.