Residual stress determination by optical interferometric measurements of hole diameter increments

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

“…Reference fringe patterns approach could be used to confirm this assumption. Artificial images, which are constructed for the elastic transition model (5) and experimental stress values for Figure 11C, D. Comparison of real interferograms and reference fringe patterns, which are related to the same principal stress directions, demonstrates practically complete coincidence of corresponding images. The same result is obtained for Side A.…”

“…This implies that four principal stress components are essential for complete quantitative describing of the residual stress state. 5 To attain this end, hole diameter increments Δu and Δv along principal stress direction σ 1 and σ 2 , respectively, must be measured on opposite faces A and B of the plate. When such is the case, residual Relationships (1) represent the transition model that is essential to convert experimentally measured displacement components into required values of residual stress.…”

“…This arrangement provides a way of subsequent recording interference fringe patterns inherent in the ESPI technique on opposite specimen's faces for the same through hole. 5 The optical setup includes two symmetrical illumination directions, lying in the same plane, and one observation direction coinciding with the normal to the plane surface of the object. Direct counting of fringe orders between two basic points in interference fringe patterns gives required values of hole diameter increments Δu and Δv along principal stress directions:…”

“…This estimation directly follows from the comprehensive accuracy analysis of the results inherent in the general approach to residual stress determination, which employs simultaneous measurements of hole diameter increments on opposite faces of thin plate. 4 Considerations, presented in, 5 prove that for the residual stress to be reliably determined proceeding from the elastic transition model (1), its value must meet the condition σ i ≤ 0.5σ y (i = 1, 2). Experimental results presented in Table 1 demonstrate values of the residual stress, which reliably fall within the required range.…”

“…Available experience reliably evidences that the centre of the probe hole is located very close to the point of maximal tensile residual stress component directed along the weld. 5,[14][15][16][17][18][19][20][21] The results of determination of residual stress components in all coupons for different stages of lowcycle fatigue are listed in Table 1. Figure 5 contains a graphical representation of the dependencies of maximal residual stress components σ A 2 and σ B 2 , referred to opposite coupon's faces, against of number of loading cycles.…”