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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Article
  • Peer Reviewed
UC Davis Previously Published Works (2003)

This paper describes an improved data reduction scheme for the deep-hole method of residual stress measurement. The deep-hole method uses the changes in diameter of a reference hole, drilled through the thickness of a component, to determine residual stress. The diameter changes result from the removal of a cylindrical core from the component, where the core is larger than and concentric with the reference hole. The new data reduction seeks to determine the unknown eigenstrain distribution that gives rise to the residual stress state and to the reference hole deformations; once the eigenstrain distribution is found, it is input to an elastic finite element analysis to provide the residual stress distribution in the original component. The new data reduction relies on expressing the unknown eigenstrain field in a polynomial basis, and finding the unknown basis function amplitudes from the measured reference hole diameter changes. The new data reduction is compared with the current technique, and it is shown that the proposed scheme offers several advantages to the current method of data reduction.

    Cover page: Improved data reduction for the deep-hole method of residual stress measurement
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2018)
    This article examines the precision of the contour method using five residual stress measurement repeatability studies. The test specimens evaluated include the following: an aluminum T-section, a stainless steel plate with a dissimilar metal slot-filled weld, a stainless steel forging, a titanium plate with an electron beam slot-filled weld, and a nickel disk forging. These specimens were selected to encompass a range of typical materials and residual stress distributions. Each repeatability study included contour method measurements on five to ten similar specimens. Following completion of the residual stress measurements, an analysis was performed to determine the repeatability standard deviation of each population. In general, the results of the various repeatability studies are similar. The repeatability standard deviation tends to be relatively small throughout the part interior, and there are localized regions of higher repeatability standard deviations along the part perimeter. The repeatability standard deviations over much of the cross section range from 5 MPa for the aluminum T-section to 25 MPa for the nickel disk forging. There is a strong correlation between the elastic modulus of the material and the repeatability standard deviation. These results demonstrate the precision of the contour method over a broad range of specimen geometries, materials, and stress states.
      Cover page: Repeatability of Contour Method Residual Stress Measurements for a Range of Materials, Processes, and GeometriesCreative Commons 'BY-SA' version 4.0 license
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2016)
      This paper describes a sequence of residual stress measurements made to determine a two-dimensional map of biaxial residual stress in a nozzle mockup having two welds, one a dissimilar metal (DM) weld and the other a stainless steel (SS) weld. The mockup is cylindrical, designed to represent a pressurizer surge nozzle of a nuclear pressurized water reactor (PWR), and was fabricated as part of a weld residual stress measurement and finite-element (FE) modeling round-robin exercise. The mockup has a nickel alloy DM weld joining an SS safe end to a low-alloy steel cylinder and stiffening ring, as well as an SS weld joining the safe end to a section of SS pipe. The biaxial mapping experiments follow an approach described earlier, in PVP2012-78885 and PVP2013-97246, and comprise a series of experimental steps and a computation to determine a two dimensional map of biaxial (axial and hoop) residual stress near the SS and DM welds. Specifically, the biaxial stresses are a combination of a contour measurement of hoop stress in the cylinder, slitting measurements of axial stress in thin slices removed from the cylinder wall, and a computation that determines the axial stress induced by measured hoop stress. At the DM weld, hoop stress is tensile near the OD (240 MPa) and compressive at the ID (-320 MPa), and axial stress is tensile near the OD (370 MPa) and compressive near the midthickness (-230 MPa) and ID (-250 MPa). At the SS weld, hoop stress is tensile near the OD (330 MPa) and compressive near the ID (-210 MPa), and axial stress is tensile at the OD (220 MPa) and compressive near midthickness (-225 MPa) and ID (-30 MPa). The measured stresses are found to be consistent with earlier work in similar configurations.
        Cover page: Biaxial Residual Stress Mapping for a Dissimilar Metal Welded Nozzle
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2018)
        This article describes the use of complementary residual stress measurements to quantify cold-work stress relief in die forgings used for monolithic unitized aerospace components. Two specimens were used, being nominally identical, but measured at different processing stages: one that was die forged and quenched (high residual stress state) and one having a post-quench, cold-work stress relief (low residual stress state). Multi-component residual stress maps were developed using multiple techniques along a single measurement plane (axes of this plane run parallel to the nominal long-transverse [x-direction] and short-transverse directions [y-direction]). The measurement techniques were energy dispersive X-ray diffraction (EDXRD), neutron diffraction (ND), and primary slice removal (PSR) biaxial mapping. Good agreement was found between the EDXRD and PSR biaxial mapping measurements. In the high-stress specimen, measured stress normal to the measurement plane (z-direction [L]) is highly compressive along the part exterior (-300 MPa) and highly tensile toward the center (250 MPa), as typical of quenched aluminum. Stress along the x-direction has a similar spatial distribution but smaller magnitude (-200 MPa to 130 MPa). The measured stresses in the cold-worked, low-stress specimen are significantly lower, with z-direction and x-direction stresses ranging between -130 MPa and 75 MPa.
          Cover page: Multi-Technique Residual Stress Measurements to Quantify Stress Relief of 7085-T7452 Aluminum Die ForgingsCreative Commons 'BY-SA' version 4.0 license
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2004)

          This paper examines the effects of laser peening on Alloy 22 (UNS N06022), which is the proposed material for use as the outer layer on the spent-fuel nuclear waste canisters to be stored at Yucca Mountain. Stress corrosion cracking (SCC) is a primary concern in the design of these canisters because tensile residual stresses will be left behind by the closure weld. Alloy 22 is a nickel-based material that is particularly resistant to corrosion; however there is a chance that stress corrosion cracking could develop given the right environmental conditions. Laser peening is an emerging surface treatment technology that has been identified as an effective tool for mitigating tensile redisual stresses in the storage canisters. The results of laser-peening experiments on Alloy 22 base material and a sample 33 mm thick double-V groove butt-weld made with gas tungsten arc welding (GTAW) are presented. Residual stress profiles were measured in Alloy 22 base material using the slitting method (also known as the crack-compliance method), and a full 2D map of longitudinal residual stress was measured in the sample welds using the contour method. Laser peening was found to produce compressive residual stress to a depth of 3.8 mm in 20 mm thick base material coupons. The depth of compressive residual stress was found to have a, significant dependence on the number of peening layers and a slight dependence on the level of irradiance. Additionally, laser peening produced compressive residual stresses to a depth of 4.3 mm in the 33 mm thick weld at the center of the weld bead where high levels of tensile stress were initially present.

            Cover page: Assessment of tensile residual stress mitigation in Alloy 22 welds due to laser peening
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2014)
            Residual stresses can be a main cause of fractures, but forensic failure analysis is difficult because the residual stresses are relaxed after fracture because of the new free surface. In this paper, a method is presented for a posteriori determination of the residual stresses by measuring the geometric mismatch between the mating fracture surfaces. Provided the fracture is not overly ductile, so that plasticity may be neglected, a simple, elastic calculation based on Bueckner's principle gives the original residual stresses normal to the fracture plane. The method was demonstrated on a large 7000 series aluminum alloy forging that fractured during an attempt to cut a section into two pieces. Neutron diffraction measurements on another section of the same forging convincingly validated the residual stresses determined from the fracture surface mismatch. After accounting for closure, an analysis of the residual stress intensity factor based on the measured residual stress agreed with the material's fracture toughness and fractographic evidence of the failure initiation site. The practicality of the fracture surface method to investigate various failures is discussed in light of the required assumptions. © 2013 Elsevier Ltd.
              Cover page: Forensic determination of residual stresses and KI from fracture surface mismatch
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2014)
              The fully effective utilization of large aluminum forgings in aerospace structures has been hampered in the past by inadequate understanding of, and sometimes inaccurate representation of, bulk residual stresses and their impact on both design mechanical properties and structural performance. In recent years, significant advances in both computational and experimental methods have led to vastly improved characterization of residual stresses. As a result, new design approaches which require the extraction of residual stress effects from material property data and the formal inclusion of residual stresses in the design analysis, have been enabled. In particular, the impact of residual stresses on durability and damage tolerance can now be assessed, and more importantly, accounted for at the beginning of the design cycle. In an effort to support the development of this next-generation design capability, the AFRL sponsored Metals Affordability Initiative (MAI) consortium has conducted a detailed experimental and analytical study of fatigue crack initiation and fatigue crack growth in aluminum coupons with known, quench induced residual stresses. In this study, coupons were designed and manufactured such that simple 'design features,' such as holes and machined pockets, were installed in locations with varying levels of bulk residual stress. The residual stresses at the critical locations in the coupons were measured using multiple techniques and modeled using detailed finite element analysis. Fatigue crack initiation (FCI) and fatigue crack growth (FCG) tests were performed using both constant amplitude and spectrum loading and the results were compared against computed FCI and FCG lives. © (2014) Trans Tech Publications, Switzerland.
                Cover page: A Detailed Evaluation of the Effects of Bulk Residual Stress on Fatigue in Aluminum
                • Article
                • Peer Reviewed
                UC Davis Previously Published Works (2019)
                One of the primary barriers for adoption of additive manufacturing (AM) has been the uncertainty in the performance of AM parts due to residual stresses/strains. The rapid heating and cooling rates from the thermal history of the laser melting process result in high residual stresses/strains that produce significant part distortion. Efforts to mitigate residual stresses using post-process heat treatments can significantly impact the microstructures of the AM part which may lead to further issues. Therefore, the ability to accurately predict the residual stresses in as-built AM parts is crucial, and rigorous benchmark measurements are needed to validate such predictions. To fill this need, the AM-Bench aims to provide high-fidelity residual stress and strain benchmark measurements in well-characterized AM bridge-shaped parts. The measurements reported here are part of the residual elastic strain benchmark challenge CHAL-AMB2018-01-RS. Residual strains and stresses in this work were measured using neutron diffraction, synchrotron X-ray diffraction, and the contour method. Part deflection measurements were performed using a coordinate measurement machine after the part was partially separated from the build plate. These independently measured results show a high degree of agreement between the different techniques.
                  Cover page: Elastic Residual Strain and Stress Measurements and Corresponding Part Deflections of 3D Additive Manufacturing Builds of IN625 AM-Bench Artifacts Using Neutron Diffraction, Synchrotron X-Ray Diffraction, and Contour MethodCreative Commons 'BY' version 4.0 license
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