Residual Stress Measurement Techniques Research Articles

Weld Residual Stress Measurement Using Portable XRD Equipment in a Shipyard Environment

Weld residual stress plays an important role in the production and operating performance of ship structures. Various factors such as background noise, vibration, movement during ship construction, a layer of primer on the plate surface, and a layer of paint after ship construction bring challenges to measure weld residual stress in a shipyard. Three large test panels made of DH-36, High-strength low-alloy steel (HSLA), HSLA-65, and HSLA-80 steels were fabricated to examine the feasibility of using commercially available portable x-ray diffraction (XRD) equipment to measure residual stress in a shipyard environment. The measured results show that portable XRD equipment provided reliable measurements, with the shipyard environment effects, on the panels made of DH-36 and HSLA-65. On the other hand, the primer affected the accuracy of measured residual stress on the panel made of HSLA-80, but electropolishing could have been used to remove the primer to achieve a good measurement. 1. Introduction Welding is one of the most important manufacturing processes in shipbuilding and inevitably induces residual stress and distortion on ship structures. In addition, flame straightening, often used to remove distortion in the final stage of shipbuilding, can result in even higher residual stress because of higher constraints after ship structures are assembled. It is well known that residual stress affects the buckling strength, fatigue performance, corrosion resistance, and dimensional stability of ship structures. As shipbuilding has been increasingly using thinner and higher strength materials such as HSLA-80 and HSLA-100 to reduce weight and increase mobility, residual stress plays an even more important role in the operating performance of ship structures. Understanding the residual stress evolution from raw material to a completed ship during service is critical to improve the ship's performance. Multiple methods have been developed to measure residual stress which can be classified into three categories: nondestructive techniques, semidestructive techniques, and destructive techniques. The common nondestructive techniques include x-ray diffraction (XRD) (Gou et al. 2015), neutron diffraction (Kartal et al. 2006; Palkowski et al. 2013), magnetic method, ultrasonic methods (Bray & Junghans 1995), and impact-indentation method (Lin et al. 2005; Choi et al. 2010; Zhu et al. 2015). The semidestructive techniques include holedrilling and ring-core methods, and the destructive techniques include block removal, splitting, layering, and contour methods (Tebedge et al. 1973; Leggatt et al. 1996). The U.S. Nuclear Regulatory Commission and the Electric Power Research Institute organized an international round robin program to measure weld residual stress in pressurized water reactor primary cooling loop components containing dissimilar metal welds (Fredette et al. 2011; Rathbun et al. 2011). Neutron diffraction, deep-hole drilling, XRD, surface-hole drilling, ring-core method, and contour method were used to measure residual stress in this program. The measured results between different measurement techniques were compared and validated against each other. In addition, a round robin study in Europe was conducted to investigate the accuracy of the XRD method from March 2012 to December 2013 (GKN & DAkkS 2014). Thirty laboratories and companies determined the residual stresses in the surface of two reference samples. Statistical evaluation of all results found that the XRD method has a good measurement accuracy. The robust means are between 4.7 and 6.3 MPa and the robust deviations are between 3.1 and 4.0 MPa. These studies have greatly improved the residual stress measurement techniques.

A novel creep test rig to study the effects of long-range residual stress, elastic follow-up and applied load

One of the many challenges in the behaviour of structures is to understand if the presence of residual stress plays an important role in contributing to failure of a structure operating at high temperature. Assessments of the high-temperature integrity of practical structures are based on experiments carried out using standard laboratory-scale creep test specimens tested under either load- or displacement-controlled conditions. In practice, structures are subjected to combinations of residual and applied stresses which in turn lead to mixed boundary conditions. Conventional laboratory creep tests do not represent these circumstances. The purpose of this paper is to describe the design of a novel test rig to introduce long-range residual stresses at high temperature. The concept of rig is based on three-bar structure with an initial misfit introduced into the central bar to represent a long-range residual stress and could be characterised easily without using time-consuming residual stress measurement techniques. Initial results demonstrated that the magnitude and the interaction of the residual stress with the applied loading is a function of the initial misfit displacements and the relative stiffness of the components of the system. Additionally, the subsequent behaviour of the system, with and without the application of additional loading, is governed by (a) the degree to which the misfit is accommodated by plastic and creep strain and (b) the elastic follow-up provided by the system. The paper describes the design of a test rig and laboratory tests conducted to validate the concept.

Residual stress measurement by strain gauge and X-ray diffraction method in different shaped rails

Abstract It is well known that rails are the most important part of railway infrastructure. Besides good wear and fatigue resistance, appropriate residual stress value in rails is required to improve performance of rails. The knowledge of residual stress types and distributions gives prediction the mechanical properties of materials for manufacturer. This study aims to make comparison between destructive and non-destructive residual stress measurement techniques and to investigate the influence of rail head geometry on residual stress by the use of two different quality rails. One of the rails is R260 grade and the other one is R260 grooved rail. In addition to residual stress measurement with strain gauge (cutting) and X-ray diffraction method, microstructures of the specimens were examined. Results show that grooved rail has higher residual stress and different types of stress were observed for samples which are supported by X-ray and strain gauge method.

Multiscale Measurements of Residual Stress in a Low-Alloy Carbon Steel Weld Clad with IN625 Superalloy

Abstract Fatigue fracture is one of the major degradation mechanisms in the low-alloy 4330 carbon steel pumps that are utilized in the hydraulic fracturing process operating under cyclic loading conditions. A weld cladding technology has been developed to improve the ability of these components to resist fatigue crack initiation by cladding them with a secondary material. This process introduces a residual stress profile into the component that can be potentially detrimental for fatigue performance. The cladding technology under examination is a low-alloy 4330 carbon steel substrate weld that is clad with the nickel-chromium–based superalloy IN625 and is investigated herein using several experimental residual stress measurement techniques. Understanding the magnitude and distribution of residual stress in weld clad components is of the utmost importance to accurately assess the performance of the component in service. This study summarizes the results of residual stress measurements that were determined using X-ray diffraction, i.e., hole drilling based on electronic speckle pattern interferometry, deep-hole drilling, and the contour method, to obtain the residual stress distributions from the surface of the weld clad, through the clad layer, and into the substrate material. The results of deep-hole drilling and the contour method show large-scale tensile residual stress in the clad layer and compressive residual stress in the majority of the substrate. However, the X-ray diffraction and hole drilling methods indicate the presence of short-scale compressive residual stress on the surface and near the surface of the clad layer. It was shown that these measurement techniques are complementary in assessing the residual stress profile throughout the entire component.

Micro-slotting technique for reliable measurement of sub-surface residual stress in Ti-6Al-4V

Micro-slotting, a relaxation residual stress measurement technique, has recently been shown to be an effective method for measuring local residual stresses in a variety of materials. The micro-slotting method relies on a scanning electron microscope–focused ion beam system for milling and imaging, digital image correlation software to track displacements due to residual stress relaxation after milling, and finite element analysis for displacement–stress correlation and calculation of the original stress state in the imaged region. The high spatial resolution of the micro-slotting method makes it a promising technique for obtaining near-surface residual stress data in Ti-6Al-4V components for input into fatigue life models and crack growth simulations. However, use of the micro-slotting method on this alloy has yet to be evaluated against more established measurement techniques. In this study, spatially resolved sub-surface residual stress measurements were obtained on shot peened and low-stress surface-machined Ti-6Al-4V planar coupons using the micro-slotting method and were compared to measurements obtained using the conventional X-ray diffraction depth profiling technique. The sub-surface measurements were in good agreement for the shot peened sample. Observed differences in the measured near-surface residual stresses on the surface-machined sample were attributed to the larger measurement volume of the X-ray diffraction method, suggesting that the micron-sized measurement volume of the micro-slotting method may be more suitable for capturing shallow stress profiles and steep stress gradients. Prior to performing the micro-slotting measurements, finite element modeled displacements were used to verify the measurement procedure and to address uncertainties in the milled slot geometries. The results of this study demonstrated the validity of the micro-slotting procedure and established the technique as a reliable method for measuring sub-surface residual stresses in Ti-6Al-4V.

Establishment of Residual Stress Measurement Technique and Promotion of Industrial Application of Neutron to Industry

Establishment of Residual Stress Measurement Technique and Promotion of Industrial Application of Neutron to Industry

X‐Ray Diffraction Technique for Residual Stress Measurement in NiCrMo Alloy Weld Metal

In the present work, residual stresses in nickel‐based (Ni 625) superalloy weld metal of a 9%Ni steel‐welded joint were measured by X‐ray diffraction (XRD). This technique presents some difficulties in performing measurements in coarse and preferentially oriented weld metal microstructures. It is proposed a preliminary surface treatment by rotating steel wire brushing to perform the stress analysis through XRD technique possible for this kind of material. Stress measurements with proposed XRD technique showed that the stress state in Ni 625 weld metal on the outside surface of the welded joint is characterised by tensile stresses in the transverse and longitudinal directions, while compressive transverse and tensile longitudinal residual stresses are developed in the root pass region.

Two-Dimensional Mapping of In-plane Residual Stress with Slitting

This paper describes the use of slitting to form a two-dimensional spatial map of one component of residual stress in the plane of a two-dimensional body. Slitting is a residual stress measurement technique that incrementally cuts a thin slit along a plane across a body, while measuring strain at a remote location as a function of slit depth. Data reduction, based on elastic deformation, provides the residual stress component normal to the plane as a function of position along the slit depth. While a single slitting measurement provides residual stress along a single plane, the new work postulates that multiple measurements on adjacent planes can form a two-dimensional spatial map of residual stress. The paper uses numerical simulations to develop knowledge of two fundamental problems regarding two-dimensional mapping with slitting. The first fundamental problem is to estimate the quality of a slitting measurement, relative to the proximity of a given measurement plane to a free surface, whether that surface is the edge of the original part or a free surface created by a prior measurement. The second fundamental problem is to quantify the effects of a prior slitting measurement on a subsequent measurement, which is affected by the physical separation of the measurement planes. The results of the numerical simulations lead to a recommended measurement design for mapping residual stress. Finally, the numerical work and recommended measurement strategy are validated with physical experiments using thin aluminum slices containing residual stress induced by quenching. The physical experiments show that two-dimensional residual stress mapping with slitting, under good experimental conditions (simple sample geometry and low modulus material), has precision on the order of 10 MPa. Additional validation measurements, performed with x-ray diffraction and ESPI hole drilling, are within 10 to 20 MPa of the results from slitting.

Residual stress analysis and finite element modelling of repair-welded titanium sheets

An innovative finite element modelling approach has been tested to investigate the effects of weld repair of thin sheets of titanium alloy, taking into account a pre-existing stress field in the components. In the case study analysed, the residual stress fields due to the original welds are introduced by means of a preliminary sequentially-coupled thermo-mechanical analysis and considered as pre-existing stress in the sheets for the subsequent repair weld simulation. Comparisons are presented between residual stress predictions and experimental measurements available from the literature, with the aim of validating the numerical procedure. As a destructive sectioning technique was used in the reference experimental measurements, an investigation is also presented on the use of the element deactivation strategy when adopted to simulate material removal. Although the numerical tool is an approximate approach to simulate the actual material removal, the strategy appears to predict a physical strain relaxation and stress redistribution in the remaining part of the component. The weld repair modelling strategy and the element deactivation tool adopted to simulate the residual stress measurement technique are shown to predict residual stress trends which are very well correlated with experimental findings from the literature.

An optimisation study of the modified deep-hole drilling technique using finite element analyses applied to a stainless steel ring welded circular disc

A circular disc containing a partial ring weld was devised to create high levels of residual stress in a relatively small specimen. The aim of the study was to utilise the complex residual stress generated within the weld and to extend the recently developed novel application of the deep-hole drilling technique in measuring residual stresses well over yield stress. This paper presents (1) finite element analysis (FEA) simulation of the residual stresses due to partial welding in an austenitic stainless steel circular disc, (2) measurement of residual stress using non-destructive and semi-destructive techniques and (3) simulation of the semi-destructive residual stress measurement technique. Comparison is made between the FEA predicted residual stress in the weld, the measurements and the reconstructed residual stresses of the measurements. The purpose of the residual stress measurement was to validate the FEA predicted weld residual stress in the circular disc. The FEA simulation of the measurement method was used (1) to explain any discrepancy between the measured and FEA predicted stresses and (2) to further modify and extend the present deep-hole drilling technique and improve its accuracy. The close correlations confirmed the suitability of new modifications made in the deep-hole drilling technique to account for plasticity when measuring near yield residual stresses present in a component.

Numerical and Experimental Study on the Residual Stresses in the Nitrided Steel

In the present work, residual stresses distribution in the gas nitrided AISI 4140 sample has been studied using finite element (FE) simulation. The nitrogen concentration profile is obtained from the diffusion-controlled compound layer growth model, and nitrogen concentration controls the material volume change through phase transformation and lattice interstitials which results in residual stresses. Such model is validated through residual stress measurement technique—micro-ring-core method, which is applied to the nitriding process to obtain the residual stresses profiles in both the compound and diffusion layer. The numerical and experimental results are in good agreement with each other; they both indicate significant stress variation in the compound layer, which was not captured in previous research works due to the resolution limit of the traditional methods.

High Spatial Resolution Evaluation of Residual Stresses in Shot Peened Specimens Containing Sharp and Blunt Notches by Micro-hole Drilling, Micro-slot Cutting and Micro-X-ray Diffraction Methods

The moderately high lateral RS gradients (on the order of tens of MPa/μm) near shot peened notches in conjunction with the shallow treatment depth (some hundreds of microns) limit the application of far-field and/or high resolution synchrotron diffraction residual stress measurement techniques. Recently proposed Focused Ion Beam – Scanning Elecron Microscope – Digital Image Correlation (FIB-SEM-DIC) based micro mechanical stress relaxation methods for the measurement of residual stress at the micron scale became suitable techniques for local evaluation of residual stresses and stress gradients in shot peened specimens. In this paper ultra-high resolution (~0.5–0.8 μm depth and 5–10 μm lateral resolution) mechanical relaxation stress measurements were used to evaluate the stress variation local to individual peening dimples in ceramic (60–120 μm diameter beads) shot peened Al-7075-T651 double notched samples having 0.15, 0.5 and 2.0 mm radii using Micro-Hole Drilling (μHD), Micro-Slot Cutting (μSC) and micro X-ray Diffraction (μXRD) methods. The micron-sized sampling volumes enabled the stress to be evaluated in individual impact craters (dimples) showing significant point-to-point variation (~ +/−150 MPa) (with certain dimples even recording tensile stresses). After around 30 μm of layer removal the heavily deformed region had largely been removed and the stress profile became much more homogeneous. At this depth the μHD and μSC results were in good accord with those from μXRD measurements which sample over a much larger volume (~40 μm depth × 50 μm laterally) showing an in-plane compressive stress of around 150 MPa far from the notches with the residual stress rising to about 200 MPa at a blunt (2 mm) notch and 500 MPa for a sharp (0.15 mm) one. Further, these recorded variations of residual stresses were correlated with microstructural features, e.g. grains, networks of sub-surface cracks, intermetallics and highly deformed sub-surface regions, revealed by large volume Serial Sectioning Tomography using Plasma Xe+ Focus Ion Beam – Scanning Electron Microscope (PFIB-SEM), EDS and EBSD maps. This allowed for the first time characterize large volume (100 × 66 × 30 μm3) of shot peened regions with resolution of dozens of nanometers and correlate residual stress depth profiles with 3D microstructural features. Finally, in (Benedetti et al. 2016, Int. J. Fatigue) these RS measurements are used to reconstruct the RS field through finite element (FE) analyses.

Residual Stress Measurements Using Elasto-Plastic Indentation and ESPI

This paper presents a method for residual stress measurement using elasto-plastic contact indentation. This method for measuring residual stresses uses data on normal displacements in a bulging area around indentation. It is shown that magnitude and distribution of normal displacements is affected by magnitude and sign of residual stresses. Basic equations describing formation of bulging area around indentation are presented. To record distribution of displacements ESPI-method is used. The main elements of the technique for residual stress measurement using developed method are shown. The method is recommended to be used in the practice of scientific research organizations in the development, improvement and debugging techniques for renovation and hardening of parts.

Assessment of Weld Residual Stress Measurement Precision: Mock-Up Design and Results for the Contour Method

Recent experimental work has shown residual stress measurements in welded material to be difficult. To better assess the precision of residual stress measurement techniques, a measurement article was designed to allow repeated measurements of a nominally identical stress field. The measurement article is a long 316L stainless steel plate containing a machine-controlled eight-pass slot weld. Measurements of weld direction residual stress made with the contour method found high tensile stress in the weld and heat-affected zone, with a maximum near 450 MPa and compressive stress away from the weld, a typical residual stress profile for constrained welds. The repeatability standard deviation of repeated contour method residual stress measurements was found to be less than 20 MPa at most spatial locations away from the boundaries of the plate. The repeatability data in the weld are consistent with those from a previous repeatability experiment using the contour method in quenched aluminum bars. A finite-element simulation and neutron diffraction measurements were performed for the same weld and provided results consistent with the contour method measurements. Much of the material used in the work remains available for use in assessing other residual stress measurement techniques, or for an interlaboratory reproducibility study of the contour method.

Residual Stress Measurements in Dissimilar Weld Metal

This paper describes measurements of residual stress in thin slices removed from the wall of a pressurizer safety/relief nozzle, which is a cylindrical welded component found in a nuclear power pressurized water reactor. Because the slices comprise a cross-section through a dissimilar metal weld that joins the low-alloy steel pressurizer to a stainless steel safe-end, the residual stress measurements are difficult. Typical welds have large grains and preferred orientations, along with chemical and phase gradients, that challenge diffraction techniques using neutron or x-ray beams. Welds also contain spatial gradients of residual stress that challenge mechanical release techniques like contour, slitting, and hole drilling. Therefore, the paper describes the application of, and compares the results from, three applicable residual stress measurement techniques: slitting, electronic speckle pattern interferometry hole drilling, and neutron diffraction. The results of slitting and neutron diffraction are in rough agreement, while the results from hole drilling are significantly different. An uncertainty analysis shows that slitting results had the smallest uncertainty, followed by hole drilling, and that neutron diffraction results had large uncertainty, particularly in the weld.

A critical comparison between XRD and FIB residual stress measurement techniques in thin films

Residual stress has a significant effect on the performance of thin films, in terms of adhesion, hardness, wear and fatigue resistance. Thus, when assessing innovative coatings or new deposition technologies, it is important to perform residual stress evaluation by means of a suitable and reliable technique.X-ray diffraction (XRD) is one of the commonly used techniques, because it is non-destructive, surface sensitive and phase selective. However, it is subject to certain limitations: X-ray diffraction allows stress evaluation (i.e. its indirect deduction from the measured diffraction profile) only in case of crystalline materials, and the results may be subject to aberrations in the presence of texture or stress gradients often occurring in thin films.Recently, a new class of methods for residual stress evaluation has been proposed, based on incremental focused ion beam (fib) milling, combined with high-resolution in situ scanning electron microscopy (SEM) imaging and full field strain analysis by digital image correlation (DIC).The aim of the present paper is to explore in some detail the significance of the stress values obtained for the same coating by X-ray diffraction and focused ion beam milling, and to demonstrate that the analysis of residual stress depth gradients is possible by using FIB-DIC techniques. Finally, a comparative assessment of the weaknesses and strengths of the two techniques will be carried out. For this purpose, a chromium nitride highly textured thin film sample was chosen. The residual stress state evaluation by the two methods was carried out for the coating deposited by the cathodic arc evaporation (CAE-PVD) technique.Although many significant differences were identified between the X-ray diffraction and focused ion beam milling methods, careful consideration of the gauge volumes and weighting demonstrated that satisfactory agreement was obtained. The analysis highlighted the importance of the issues related to (a) probe-to-sample interaction volume (gauge volume), (b) film texture, and (c) the elastic anisotropy. All these factors must be taken into account in order to enable valid comparisons to be drawn.

An Experimental Investigation into Additive Manufacturing-Induced Residual Stresses in 316L Stainless Steel

Additive manufacturing (AM) technology provides unique opportunities for producing net-shape geometries at the macroscale through microscale processing. This level of control presents inherent trade-offs necessitating the establishment of quality controls aimed at minimizing undesirable properties, such as porosity and residual stresses. Here, we perform a parametric study into the effects of laser scanning pattern, power, speed, and build direction in powder bed fusion AM on residual stress. In an effort to better understand the factors influencing macroscale residual stresses, a destructive surface residual stress measurement technique (digital image correlation in conjunction with build plate removal and sectioning) has been coupled with a nondestructive volumetric evaluation method (i.e., neutron diffraction). Good agreement between the two measurement techniques is observed. Furthermore, a reduction in residual stress is obtained by decreasing scan island size, increasing island to wall rotation to 45 deg, and increasing applied energy per unit length (laser power/speed). Neutron diffraction measurements reveal that, while in-plane residual stresses are affected by scan island rotation, axial residual stresses are unchanged. We attribute this in-plane behavior to misalignment between the greatest thermal stresses (scan direction) and largest part dimension.

Residual stress measurements in a P92 steel-In625 superalloy metal weldment in the as-welded and after post weld heat treated conditions

Residual stress measurements have been undertaken in a multi-pass circumferential double J butt-weld made from a P92 martensitic steel pipe using an In625 superalloy weld metal. Stresses were evaluated in the as welded condition and after post weld heat treatment. The deep hole drilling and neutron diffraction techniques were used to provide through thickness measurements for the parent, weld metal and heat affected region for the as-welded and the post weld heat treated conditions. The use of multiple residual stress measurement techniques provides an understanding of the stress distributions as well as increasing confidence in the reliability of the measurements. The results presented are discussed with respect to the residual stress magnitude and location as well as with respect to the effectiveness of the post weld heat treatment procedure.

Residual Stress Measurement Using the Hole Drilling Technique on Components outside the ASTM E837 Standard

The hole drilling technique is probably the most widely used residual stress measurement technique. The ASTM E837 standard covers hole drilling measurements for thin and thick specimens. VEQTER have encountered several cases when the specimen was between the thick and thin specification. In order to gain a greater understanding of the sensitivity of the analyses and accurately measure the residual stresses using the hole drilling technique within intermediate thickness specimens and within thin specimens containing non-uniform residual stresses a study was performed.

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

The ring-core method allows the determination of residual stresses at high depth from the surface. The numerical calculation integral method, commonly used for the hole-drilling, can also be applied to the ring-core. The integral method coefficients were obtained for several depth steps after axial-symmetric FE simulations with harmonic load. These coefficients were then validated with a 3D finite element model. Finally, an application was reported, showing the performance of the Tikhonov regularization on experimental data.