Influence of stress ratio on residual stress evolution near cold-expanded hole due to low-cycle fatigue by crack compliance data

Abstract

Modified version of the crack compliance method is used for determination of stress intensity factor (SIF) related to narrow notches emanating from cold-expanded holes. These notches are inserted at different stages of low-cycle fatigue under constant external load. It is shown how residual SIF values, generated by residual stress field influence, can be separated from total experimental SIF values. Residual SIF values, obtained at different stage of low-cycle fatigue with the same stress range Δσ = 350 MPa but different stress R = –0.4 and R = –1.0, provide quantitative description of residual stress evolution near cold-expanded hole. It shown that maximal residual stress relaxation of order 20 per cent occurs at 95 lifetime per cent for both loading programs.

Damage accumulation near the cold-expanded hole due to high-cycle fatigue by crack compliance method

“…This procedure has been substantiated in Ref. [19] by revealing linear character of dependencies of NMOD and SIF values, obtained in the residual stress field, from externally applied stresses. This fact opens a way to implement the linear superposition principle for evaluation of residual SIF values.…”

“…It seems quite natural to expand the above described methodology for quantifying damage accumulation in the vicinity of a cold-expanded hole. Remarkable capabilities of combining the crack compliance method and measurements of deformation response by ESPI to describe low-cycle fatigue influence on the evolution of fracture mechanics parameters, which are inherent in narrow notches inserted near cold-expanded holes, have been previously demonstrated [18][19]. The main difference between plain and cold-expanded hole resides in a presence of the residual stress field in the second case.…”

Residual stresses near cold-expanded hole at different stages of high-cycle fatigue by crack compliance data

“…Numerous numerical and experimental methods have been developed and implemented to solve the first from above problems [3][4][5][6][7][8][9][10]. A set of both experimental and numerical works concerns residual stress evolution [11][12][13][14][15][16][17][18]. Required data are available for restricted spectrum of loading cycle parameters.…”

“…Required residual SIF values are derived from the relationships developed for modified version of the crack compliance method [19]. In previous papers modified version of the crack compliance method has been implemented for residual stress characterization near cold-expanded holes [17,18]. The objects of investigations were plane rectangular specimens measuring 180×30×5 mm with centred cold-expanded holes of diameter 2 = 4.0 mm.…”

“…This means that a direct implementation of narrow notch inserting to quantitatively reveal residual stress level is quite difficult due to very high fringe density along the notch borders. To overcome this problem, specimens were subjected to constant tensile loading before a notch inserting [17,18]. This approach has two drawbacks.…”