Procedure to Perform a Validated Incremental Hole Drilling Measurement: Application to Shot Peening Residual Stresses

Abstract

The paper describes a test rig designed to check and assess the accuracy of the incremental hole drilling (IHD) method. An external load produces a controlled linearly through thickness variable uniaxial stress field (reference bending stress), known with good accuracy, that can be applied and removed at each hole increment. After the separation between the bending relaxed strain from the residual stress relaxed strain, it is possible to reproduce the bending stress distribution in order to have complete confidence of the residual stress measurement. The bending verification of the IHD method was already proposed by other investigators before, but residual stress measurements were then performed on independent configurations. The proposed testing procedure gives a 'real time' verification of the residual stress measurement. Any experimental malfunctioning due to the operator inexperience, or any error during the stress calculation from the relaxed strain would produce an evident difference between the expected reference bending stress and the IHD bending stress output. Moreover, the reference bending stress helped for understanding that the not perfect hole cylindrical shape causes an underestimate of the predicted stress near the surface. A zero depth offset correction was proposed. This correction was tested on the reference bending stress, and then applied to the residual stress prediction. Three shot peening residual stresses IHD measurements were successfully validated by means of the bending stress; moreover, they were in good agreement with independent X-ray diffraction measures also proposed in the paper

An indentation-based technique to determine in-depth residual stress profiles induced by surface treatment of metal components

“…Perfect plasticity with yield limit close to the ultimate material strength is assumed to simulate the response of the hardened material layer at reloading. In fact, the considered surface treatments induce relatively large plastic deformation of usually rather ductile metals 8,31 …”

“…Mechanical treatments commonly considered to improve wear or fatigue performances of structural components induce axis‐symmetric RS states in isotropic materials, with the characteristic in‐depth profile schematically represented in Fig. 1 (see Refs [4–8]). Characteristic parameters of such a distribution are: the surface RS value ; the maximum stress , which occurs at the depth ; the depth , where RS reverse their sign.…”

“…In fact, the considered surface treatments induce relatively large plastic deformation of usually rather ductile metals. 8,31 In the numerical model, the continuous RS distribution described by relation (1) is approximated by the piecewise uniform pattern shown in Fig. 5, in FE layers 5 μm thick.…”

“…cal and reliable identification tool for typical in-depth RS profiles produced by induction surface hardening, gravity, shot and laser peening. [4][5][6][7][8] Compared to the alternative techniques most frequently employed in this field, like hole drilling, X-ray diffraction or strain relaxation method in combination with layer removal, 4,[8][9][10] indentation has the advantage of being reliable, fast, economical and, in most cases, non-destructive, as it involves only small material portions. Furthermore, the test can be performed on different control volumes, directly on the structural component, also in service by portable equipment, without any need to extract material specimens (see e.g.…”

Integral Method Coefficients and Regularization Procedure for the Ring-Core Residual Stress Measurement Technique

“…The material is cut at the center and the relieved strain measured at the periphery for the hole-drilling, while the opposite for the ring-core. The hole-drilling is more widespread being dedicated to superficial stresses [1][2][3][4][5][6]. The ring-core, introduced many years ago [7,8], has diameters and also depth much larger ( Fig.…”