Issue 78

V. Pisarev et alii, Fracture and Structural Integrity, 78 (2026) 96-117; DOI: 10.3221/IGF-ESIS.78.06

The essence of our approach resides in “preventive regularization”, which aids in eliminating the difficulties related to correct inversion process. The application of two measurement points for determination of hole-diameter increments along principal stress directions yields an unequivocal solution to the properly posed inverse problem in an explicit form. It employs the solution of linear algebraic equations system with minimal possible condition number CondA  2.8 Availability of this parameter provides quantitative estimation of absolute error inherent in a determination of each principal stress component for any measurement point [22. 24]. For instance, at point 5 of Sp_75 this error equals to 1 2     8.0 MPa. It means that: Inequalities (1) conservatively describe the upper possible limit of the error made in the course of residual stresses determination. Estimations (1) are obtained for uncertainty in fringe order counting   N   =0.5 fringe. Such accuracy can be reliably reached by using high-scaled interference images. Quite optimistic estimations of errors inherent to the final results (1), especially for 2  component, directly prove the reliability of the involved approach to residual stress determination in contact interaction area. It should be also noted that none of existing experimental methods of residual stress characterization, such as X-ray stress analysis using the sin 2 ψ method, the micro-ring-core technique via Focused Ion Beam milling and Digital Image Correlation, the contour method, the strain gauge method, and the hole drilling method with digital image correlation technique, is not capable of direct quantitative uncertainty estimations. Before considering the distributions of the residual stress components over the thickness of the specimen, it should be recalled once again that two different coupons were used for this purpose, namely Sp_75 and Sp_75-Back. The diameters of all four contact dimples are almost identical. The coordinates of the drilling points on side B, opposite the contact dimple, were determined by appropriate geometric measurements. Such an experimental procedure undoubtedly introduces some errors that must be taken into account when comparing the values of the residual stress components referred to opposite specimen’s faces. 1  / 1  =0.19 and 2  / 2  =0.06. (1)

(a)

(b)

(c) Figure 13: Possible distributions of the residual stress components over the thickness of the conditional sample Sp_75+Sp_75-Back.

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