PSI - Issue 75

Andrew Halfpenny et al. / Procedia Structural Integrity 75 (2025) 219–233 Author name / Structural Integrity Procedia (2025)

224

6

= { max{ , 0 + 1 ∙ + 2 ∙ 2 + 3 ∙ 3 } if ≥0 0 + 1 ∙ 0 −2 ∙ 1 if <−2 where 0 = (0.825 − 0.34 + 0.05 2 ) ∙ [cos ( 2 ∙ )] 1 if −2≤ <0

(14)

(15) 1 = (0.415 − 0.071 ) ∙ 2 =1− 0 − 1 − 3 3 =2 0 + 1 −1 where and are parameters obtained through tests that represent the plane stress/strain constraint factor and the ratio of maximum applied stress to the flow of stress, respectively. The threshold stress intensity range, ∆ ℎ , is defined as: ∆ ℎ =∆ 0 ∙ √ + 0 [ 1− (1− 0 ) ∙ (1 − )] 1+ ℎ ∙ (16) where ∆ 0 is the threshold stress intensity range at =0 obtained from tests, is the crack length, 0 = 0.0381mm is the intrinsic crack length and ℎ is the threshold coefficient determined from tests. The critical stress intensity, , is function of the thickness and is given by: = 1 ∙ [1+ ∙ −( ∙ 0 ) 2 ] (17) where 1 is the plane strain fracture toughness, and are fitting parameters obtained experimentally, is the plate thickness and 0 is the plane strain reference thickness defined as: 0 =2.5( 1 ) 2 (18) with the yield stress. For values of stress ratio < it was proposed to adjust the effective stress intensity range, ∆ , as: ∆ = { max ∙ (1− min ) if < min max − min otherwise (19) For values of stress ratio > , instead, it was proposed to adjust the maximum stress intensity as: