A modified loading method for separating the effect of residual stress on fatigue crack growth rate of welded joints

Abstract

A novel loading method is proposed to remove the effect of residual stress on measured fatigue crack growth rate in welded joint, using which the influence of empirical crack growth rate correlation equations on the results can be avoided. The total stress intensity factor range and the effective stress ratios corresponding to the combined effect of applied and residual stress are kept constant during the fatigue crack growth test, by changing the applied maximum and minimum loads with the increase of crack length and changes in residual stress based on the superposition rule. The feasibility of the proposed method was validated by tests of compact tension specimens containing residual stresses introduced by four‐point bending. The loading method was then applied to a test of welded compact tension specimen with coupled effect of residual stress and microstructure change on fatigue crack growth rate. The fluctuation in the separated crack growth rate reflects the effect of microstructure change on fatigue crack growth rate.

Residual stress/strain evolution due to low‐cycle fatigue by removing local material volume and optical interferometric data

“…Relationships (7) and (8) give the following distribution of circumferential residual strains along the secondary hole edge:…”

Theoretical and experimental study on optimal cropping load control strategy of duralumin alloy AlCu4Mg1 based on linear elastic fracture mechanics

“…20 Fatigue crack growth rate is measured. 21 Yet due to the lack of fatigue crack growth rates for various materials and the determination method of the stress intensity factor amplitude boundary point in each zone, the satisfactory results cannot be obtained by dividing the fatigue life into zones. Besides, the new cropping theory is not perfect, so it is necessary to put forward the reasonable cropping theory and apply it to the machinery manufacturing industry.…”

Fatigue surface crack propagation and intersecting cracks in connection with welding residual stresses

“…The residual stress as well as the microstructural change has a significant combined effect on fatigue crack propagation (eg, Fratini et al). To avoid this combined effect by separating the effect of the welding‐induced residual stress on fatigue crack propagation rate, the loading method can be used . Not focusing on the effect of welding process parameters and microstructural changes, we will concentrate on the effect of welding residual stress on fatigue crack propagation, which should be taken into account for predicting fatigue life.…”

“…To avoid this combined effect by separating the effect of the welding-induced residual stress on fatigue crack propagation rate, the loading method can be used. 8,9 Not focusing on the effect of welding process parameters and microstructural changes, we will concentrate on the effect of welding residual stress on fatigue crack propagation, which should be taken into account for predicting fatigue life. Numerical and experimental analyses of welded joints were performed to understand and describe the effect of residual stress on Nomenclature: Δa, crack increment; q T , correction function; C, n, m, Paris, Forman material constants; C T , constant in correction function; E, Young modulus; K, stress intensity factor; ΔK, stress intensity factor range; N, number of cycles; R, stress intensity factor ratio; s, crack front coordinate; T, nonsingular T-stress; x, y, z, Cartesian crack tip coordinates; r, θ, polar crack tip coordinates; X, Y, Z, Cartesian global coordinates; ν, Poisson ratio; σ Y , yield stress Subscripts: app, applied; ell, ellipse; max, maximum; min, minimum; res, residual; C, critical distributions of the stress intensity factor along the crack front and fatigue crack propagation rate.…”