“…The reproducibility of hole-drilling was also studied in a prior publication using shot peened steel specimens and friction stir welded aluminum specimens [9]. A reproducibility experiment is similar to a repeatability experiment, except that measurements are performed at different laboratories rather than at one laboratory.…”
Background: Measurement precision and uncertainty estimation are important factors for all residual stress measurement techniques. The values of these quantities can help to determine whether a particular measurement technique would be viable option. Objective: This paper determines the precision of holedrilling residual stress measurement using repeatability studies and develops an updated uncertainty estimator. Methods: Two repeatability studies were performed on test specimens extracted from an aluminum and titanium shot peened plate. Each repeatability study included 12 hole-drilling measurements performed using a bespoke automated milling machine. Repeatability standard deviations were determined for each population. The repeatability studies were replicated using a commercially available manual hole-drilling milling machine (RS-200, Micro-Measurements). An updated uncertainty estimator was developed and was assessed using an acceptance criterion. The acceptance criterion compared an expected percentage of points (68%) to the fraction of points in the stress versus depth profile where the measured stresses ± its total uncertainty contained the mean stress of the repeatability studies. Results: Both repeatability studies showed larger repeatability standard deviations at the surface that decay quickly (over about 0.3 mm). The repeatability standard deviation was significantly smaller in 2 the aluminum plate (max ≈ 15 MPa, RMS ≈ 6.4 MPa) than in the titanium plate (max ≈ 60 MPa, RMS ≈ 21.0 MPa). The repeatability standard deviations were significantly larger when using the manual milling machine in the aluminum plate (RMS ≈ 21.7 MPa), and for the titanium plate (RMS ≈ 18.9 MPa). Conclusions: The single measurement uncertainty estimate met a defined acceptance criterion based on the confidence interval of the uncertainty estimate.
“…The reproducibility of hole-drilling was also studied in a prior publication using shot peened steel specimens and friction stir welded aluminum specimens [9]. A reproducibility experiment is similar to a repeatability experiment, except that measurements are performed at different laboratories rather than at one laboratory.…”
Background: Measurement precision and uncertainty estimation are important factors for all residual stress measurement techniques. The values of these quantities can help to determine whether a particular measurement technique would be viable option. Objective: This paper determines the precision of holedrilling residual stress measurement using repeatability studies and develops an updated uncertainty estimator. Methods: Two repeatability studies were performed on test specimens extracted from an aluminum and titanium shot peened plate. Each repeatability study included 12 hole-drilling measurements performed using a bespoke automated milling machine. Repeatability standard deviations were determined for each population. The repeatability studies were replicated using a commercially available manual hole-drilling milling machine (RS-200, Micro-Measurements). An updated uncertainty estimator was developed and was assessed using an acceptance criterion. The acceptance criterion compared an expected percentage of points (68%) to the fraction of points in the stress versus depth profile where the measured stresses ± its total uncertainty contained the mean stress of the repeatability studies. Results: Both repeatability studies showed larger repeatability standard deviations at the surface that decay quickly (over about 0.3 mm). The repeatability standard deviation was significantly smaller in 2 the aluminum plate (max ≈ 15 MPa, RMS ≈ 6.4 MPa) than in the titanium plate (max ≈ 60 MPa, RMS ≈ 21.0 MPa). The repeatability standard deviations were significantly larger when using the manual milling machine in the aluminum plate (RMS ≈ 21.7 MPa), and for the titanium plate (RMS ≈ 18.9 MPa). Conclusions: The single measurement uncertainty estimate met a defined acceptance criterion based on the confidence interval of the uncertainty estimate.
“…The round robin activity by Lord et al. [17] was also aimed at verifying the IHD measurements, by performing independent measures on similarly prepared sampled, to be then compared. The procedure proposed in the present paper, to have a verified IHD residual stress measure, is immediate and the required equipment extra cost is small.…”
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
“…For the intercomparison a simple component was required that would have a reasonably high stress with good repeatability while providing a significant measurement challenge and yet could be produced cost effectively in the numbers required for the first intercomparison exercise. From previous experience (Lord et al , 2002; Grant et al , 2005) a shot peened stainless steel plate was chosen to meet all these criteria.…”
Section: Introductionmentioning
confidence: 99%
“…Some inherent variability due to the shot peening process is to be expected, but the scatter in the results may also be due to material effects, since stainless steel is known to be a problematic material to measure using XRD due to the preferred orientation effects. For this reason it was considered to be a challenging material to examine, and therefore a useful extension to previous intercomparison and validation exercises (Lord et al , 2002; Grant et al , 2005). To reduce the effect of material variability in the intercomparison, Figure 1.…”
Residual stresses impact on a wide variety of industrial sectors including the automotive, power generation, industrial plant, construction, aerospace, railway and transport industries, and a range of materials manufacturers and processing companies. The X-ray diffraction (XRD) technique is one of the most popular methods for measuring residual stress (Kandil et al., 2001) used routinely in quality control and materials characterization for validating models and design. The VAMAS TWA20 Project 3 activity on the “Measurement of Residual Stresses by X-ray Diffraction” was initiated by NPL in 2005 to examine various aspects of the XRD test procedure in support of work aimed at developing an international standard in this area. The purpose of this project was to examine and reduce some of the sources of scatter and uncertainty in the measurement of residual stress by X-ray diffraction on metallic materials, through an international intercomparison and validation exercise. One of the major issues the intercomparison highlighted was the problem associated with measuring residual stresses in austenitic stainless steel. The following paper describes this intercomparison, reviews the results of the exercise and details additional work looking at developing best practice for measuring residual stresses in austenitic stainless steel, for which X-ray measurements are somewhat unreliable and problematic.
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