Weld Residual Stress Measurement Research Articles

Stress biaxiality-based residual stress assessment in welded T-joints using the blind-hole method

The blind-hole method is widely used to measure the welding residual stress (WRS) in welded steel structural connections such as T-joints. To enhance the test accuracy, a rapid WRS evaluation method considering stress level and biaxial stress ratio was developed and validated. The proposed method was applied to measure the WRS distributions of T-joints in steel truss bridges, and a finite element model (FEM) simulating the WRS was verified by the test results. On this basis, the effects of welding parameters and geometric configuration of T-joints on WRS were analyzed by the validated FEM. The results show that the maximum error from ignoring the hole edge plasticity or stress biaxiality is about 20%, and the proposed method can effectively reduce the WRS measurement error caused by the above factors. The results of the experiment and FE analysis demonstrate that the WRSs in T-joint are in an obvious biaxial stress state, which further proves that it is necessary to consider stress biaxiality in calibration for the blind-hole method.

Study on the relationship between the root welding residual stress and the root-failure fatigue strength of Plug Welded specimens

It is difficult to examine the relation between the root notch welding residual stress (WRS) and the root-failure fatigue strength because of the difficulty in the direct root WRS measurement. The root WRS can be calculated by thermal elastic-plastic finite element analysis (TEPFEA), but its accuracy has not been fully verified yet. In this study, root-failure fatigue tests, in which direct root WRS measurement can be performed, are carried out. Plug welded (PW) specimens with backing plates are used in those tests, and the root WRS in as-welded (AW) and stress-relieved (SR = PWHT) specimens are measured using X-ray diffraction (XRD) method by cutting off the backing plate. The measured WRSs are compared with those calculated by TEPFEA. It is found that the root WRSs in the PW specimens estimated by TEPFEA become much larger than those measured when creep strain is neglected. The SR specimen’s fatigue strength improvement ratio is estimated by using the mean stress effect formulas developed for toe-failure cases (IIW Fatigue Recommendations and MIL-HDBK-5D). The estimated improvement ratio shows fair agreement with that measured.

Determination of the three-dimensional welding residual stress in a thick plate T-welded joint using the stepwise eigenstrain-contour method

The stepwise eigenstrain-contour method (SECM) for determining three-dimensional welding residual stress (WRS) was developed based on conventional eigenstrain-contour method. A thick plate T-welded joint specimen was manufactured and its three-dimensional WRS was measured via the SECM. The SECM was then verified by the superposition method, which obtains the three-dimensional WRS on the cut surface by superposing the measurement results of the hole-drilling method and the standard contour method. Finally, the three-dimensional eigenstrain field and WRS field in the thick plate T-welded joint specimen were comprehensively analyzed. The results show that the SECM greatly improves the reconstruction accuracy of the WRS components in non-principal directions of the welded joint, thus extending the standard contour method to three-dimensional WRS measurement. Overall, the three-dimensional WRS in the specimen presents self-equilibrated tension-compression distribution. The peak longitudinal, transverse and vertical WRSs on the whole mid-length section of the specimen are 382.3 MPa (0.92 σy), 152.7 MPa (0.37 σy) and 105.8 MPa (0.26 σy) respectively, which usually appear near the bottom of weld zone. The transverse and vertical WRSs are usually smaller than the longitudinal WRS, and the WRS in the flange is generally greater than that in the web.

Measurements of residual stresses in a welded orthotropic steel deck by the hole-drilling method considering stress biaxiality

Welding residual stress (WRS) significantly affects the fatigue cracking of orthotropic steel deck. In this paper, the influence of strain release coefficients (SRC) calibration methods on the WRS measurement results of the hole-drilling method was studied; then the WRSs of an orthotropic steel deck were measured by the hole-drilling method considering stress biaxiality. High-value WRSs are greatly overestimated, when the SRC are calibrated via the formula method and experiment. The uniaxial FEM calibration ignoring the stress biaxiality still leads to a peak WRS error of 11.48%. Considering the influence of stress biaxiality on SRC, the average peak WRS is 496.3 MPa, appearing at the weld centerline on the deck; as the distance from the weld centerline increases, the WRSs gradually decrease until to the compressive stress; the WRS distribution of the deck top surface is approximately M-shaped with two tensile WRS areas around the weld; the WRSs on the deck bottom surface have a similar distribution trend to those on the top surface; the WRSs of the U-rib are obviously smaller than those of the deck. The transverse WRS distribution is similar to that of longitudinal WRS, while its value is far less than longitudinal WRS.

In situ studies of full-field residual stress mapping of SS304 stainless steel welds using DIC

Large tensile residual stress is detrimental to the structural integrity of welded structures. As a result, it is very important to understand the residual formation during the welding process. In this paper, a new non-contact welding residual stress measurement technique based on digital image correlation (DIC) is proposed as a way to investigate residual stress formation. To investigate the stress evolution of the welded plate, we conduct a series of experiments by using this new method. High-temperature full-field strain obtained from DIC was computed by incremental theory to acquire stress increment. Stress evolution and residual stress were obtained by superimposing the stress increment. Hole-drilling residual stress measurements for verification were also implemented. The maximum difference, which was 37 MPa between the two methods demonstrated that this new technique was able to characterize the full-field welding residual stress during the welding process.

Weld Residual Stress Measurement on Ship Structures

Weld residual stresses on ship structures were significantly investigated by using a three-step approach. Step 1 is to measure residual stress on small samples in laboratories to validate measurement methods, step 2 is to measure residual stress on three test panels made of DH36, HSLA-65, and HSLA-80 in a shipyard, and step 3 is to measure residual stress on a large mock-up unit and on a tie-down. Step-1 and step-2 study, presented in the Society of Naval Architects and Marine Engineers-2017 conference, concluded that portable X-ray equipment can be used in a shipyard environment to provide reliable measurements. Residual stress was successfully measured on small welded joints, the DH36 panel, and the HSLA-65 panel, but not on the HSLA-80 panel. The reason for poor measurements on the HSLA-80 panel was that the primer on HSLA-80 surfaces blocked the diffracted X-ray. To achieve a good measurement, mechanical grinding and electropolishing were investigated to remove the primer before measurement. The minimum electropolishing time required to remove the compressive stress induced by mechanical grinding was established by experimental trials. With the electropolishing process, reasonable measurements were achieved on the HSLA-80 panel, a tie-down, and the knuckle joints of the large mock-up unit. This study reports the measured stresses on the HSLA-80 panel, the tie-down, and the knuckle joints. Welding, as one of the most important manufacturing processes in shipbuilding, inevitably induces residual stress and distortion on ship structures. Multiple methods have been developed to measure residual stress with nondestructive and destructive techniques. The common nondestructive techniques include X-ray diffraction (XRD) (Gou et al. 2015; Bandyopadhyay et al. 2018; Monine et al. 2018), neutron diffraction (Palkowski et al. 2013), magnetic method, ultrasonic methods (Bray & Junghans 1995), and impact-indentation method (Zhu et al. 2015). The destructive techniques include hole-drilling and ring-core methods, and the destructive techniques include block removal, splitting, layering, and contour methods (Leggatt et al. 1996).

Fatigue strength assessment of ultra-high-strength steel fillet weld joints using 4R method

A fatigue analysis on experimentally tested transverse fillet-welded non-load-carrying T- and X-joints made of S960 and S1100 ultra-high-strength steel was carried out in the present study. The test data consisted of welded joints in the as-welded, high frequency mechanical impact-treated, and tungsten inert gas-dressed conditions, that were fatigue tested using uniaxial constant amplitude loading with an applied stress ratio of R = 0.1–0.5. The weld geometry and residual stress measurements were carried out, and for each joint, the fatigue strength was assessed using a multiparametric notch stress approach, entitled the 4R method, which incorporates the consideration of four parameters, i.e. notch stress range Δσk(r), applied stress ratio R, material ultimate strength Rm, and residual stress σres in the fatigue assessment. In the 4R method, the local cyclic elastic-plastic behavior at the notch root is obtained, and the Smith-Watson-Topper parameter is applied to conduct a mean stress correction to commeasure all results into a single S-N curve. The results showed that the applied stress ratio had a distinct influence on the fatigue strength capacity for both joints in the as-welded and post-weld treated conditions when using the conventional stress-based approaches, i.e. nominal stress, structural hot-spot stress and effective notch stress concepts. Nevertheless, the 4R method resulted in a good agreement between the experimental test results and the fatigue strength assessments, regardless of the load and joint conditions.

A compensation filter method for extracting surface characteristic from an optical point cloud

Optical devices cannot directly obtain the deformation for welding residual stress (WRS) measurement since it is difficult to get the surface characteristic with a high accuracy of measurement. This paper therefore presents a full-field fast method for WRS measurement based on heterodyne multiple frequency phase shift technology. Furthermore, in order to denoise the acquired point cloud, this paper proposes a novel compensation filter method (CFM) to extract accurate surface topography: specifically, to slice the original point cloud into several independent groups, then smooth each group of the point cloud to obtain the compensation value, and finally to fuse the filtered point cloud with the compensation value to extract surface characteristic. As a result, the simulation and the experiment results show that the CFM can reduce the noise by about 80%. It demonstrates that the novel CFM can maintain the features of the point cloud and remove noise efficiently, indicating the high accuracy of the CFM result and the potential to realize fast WRS measurement.

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.

Weld Residual Stress Measurement on Ship Structures

Weld Residual Stress Measurement on Ship Structures

A Review on Welding Residual Stress Measurement by Hole Drilling Technique and its Importance

A Review on Welding Residual Stress Measurement by Hole Drilling Technique and its Importance

05.03: Weld residual stresses effects in the design of welded plate girders: Simulation and Implementation

ABSTRACTEurocode 3 offers different possibilities on a numerically‐aided design of welded plate girders. In this, a geometrically and materially nonlinear analysis of the imperfect structure (GMNIA) provides the theoretically highest possible degree of realism. A correct implementation of “imperfections” is of critical importance in the practical application of this method. The current design rules are based on long term experience in terms of traditional (“old”) welding procedures and regular (“low strength”) steel grades. Thus, they provide very approximate (but safe) rules for these structures. With the introduction of modern shop welding operations and materials, many of these assumptions seem to be over‐conservative. A revision of these rules is being processed in different national and international research projects. This particular study focusses on the weld residual stresses and their effects in conventional steel S355 and high strength steel S690. Metal active gas (MAG) welding under shop welding conditions was used. The measurement of weld residual stresses on component‐like samples (carried out by the BAM Bundesanstalt für Materialforschung und ‐prüfung in Berlin) has been widely published. The hereupon based (simplified) welding simulation as part of a subsequent structural analysis is shown here. A novel numerical approach how to directly incorporate the results into large structural components models is presented. The capacity analysis is performed on a simple example for weak‐axis buckling. The results indicate significant improvements in the utilization of load‐bearing capacity and underline the superior buckling assignment for the S690 compared to conventional S355. The experimental validation of the findings is currently being prepared.

Investigating optimal cutting configurations for the contour method of weld residual stress measurement

The present work examines optimal cutting configurations for the measurement of weld residual stresses (WRS) using the contour method. The accuracy of a conventional, single-cut configuration that employs rigid clamping is compared with novel, double-embedded cutting configurations that rely on specimen self-constraint during cutting. Numerical analyses examine the redistribution of WRS and the development of cutting-induced plasticity (CIP) in a three-pass austenitic slot weld (NeT TG4) during the cutting procedure for each configuration. Stress intensity factor (SIF) analyses are first used as a screening tool; these analyses characterise lower stress intensities near the cutting surface when double-embedded cutting configurations are used, relative to SIF profiles from a single-cut process. The lower stress intensities indicate the development of CIP – which will ultimately affect back-calculated WRS – is less likely to occur when using an embedded configuration. The improvements observed for embedded cutting approaches are confirmed using three-dimensional finite element (FE) cutting simulations. The simulations reveal significant localised plasticity that forms in the material ligaments located between the pilot holes and the outer edges of the specimen. This plasticity is caused by WRS redistribution during the cutting process. The compressive plasticity in these material ligaments is shown to reduce the overall tensile WRS near the weld region before this region is sectioned, thereby significantly reducing the amount of CIP when cutting through the weld region at a later stage of the cutting procedure. Further improvements to the embedded cutting configuration are observed when the equilibrating compressive stresses in material ligaments are removed entirely (via sectioning) prior to sectioning of the high WRS region in the vicinity of the weld. All numerical results are validated against a series of WRS measurements performed using the contour method on a set of NeT TG4 benchmark weld specimens.

Mitigating cutting-induced plasticity in the contour method, part 1: Experimental

Application of the contour method for the measurement of weld residual stresses (WRS) is prone to inaccuracy due to plastic deformation resulting from the redistribution of typically high (close to yield) WRS during the cutting process. The current work, seeks ways to mitigate cutting-induced plasticity by controlling stress redistribution through optimisation of the contour cutting configuration. The idea of using a stress-informed fracture mechanics approach to find the optimal cutting configuration is introduced. The level of plasticity associated with different cutting configurations is then assessed, allowing control of the location and magnitude of cutting-induced plasticity to occur during the cutting process. A conventional edge-crack cutting configuration is compared with a proposed double-embedded cutting configuration by measuring the longitudinal WRS in two three-pass slot weld specimens (NeT TG4) produced using identical weld procedures. The experimental results show that a novel double-embedded cutting configuration leads to greater accuracy in WRS measurements relative to conventional edge-crack cutting configurations at the expense of higher levels of plasticity being introduced local to small ligaments.

Biaxial Residual Stress Mapping for a Dissimilar Metal Welded Nozzle

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.

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.

Comparison of weld residual stress measurement results in low alloy welds between X-ray diffraction and stress relief methods

In this study, a comparison of weld residual stress measurements between the X-ray diffraction technique and the stress relief technique is performed with the focus on the effect of the thickness on the stress measurement results. As the difference in the thickness becomes smaller, the difference in the stress measurement results also becomes smaller. At the weld center, where the stress gradient is in the thickness direction, the difference in the thickness is not negligible. In other words, it is concluded that the X-ray diffraction method is advantageous because it can evaluate the unique stress generated only in the surface layer.

AL7N01 Butt Joint Welding Residual Stress Measurement by Ultrasonic Method

Analysis the shortage of ultrasonic stress measurement based on Lcr wave in low spatial resolution. Point out it is inapplicable in measuring gradient stress field like welding residual stress field. In this paper, propagation differential method is proposed to solve the low spatial resolution problem on Lcr wave stress measurement, and its theory is introduced. This method can raise the spatial resolution from tens of millimeter to a several millimeter level with out decline the stress resolution. A welding residual stress field of 7N01 aluminum alloy butted joint plate is measured by this method, and its result is compared with hole drilling method. Source of errors is discussed. It is seen that propagation differential method is applicable in welding residual stress measurement.

Internal Welding Residual Stress Measurement Based on Contour Method

The internal welding longitudinal residual stress is measured using contour method for a bead-on-plate welding specimen and a T type welding structure.The welded specimen is cut along a plane perpendicular to the weld line,and the deformed profiles(contours) of the cut surfaces are precisely measured.Then,the measured contours are fitted and taken as displacement boundary conditions to an elastic finite element model to calculate the corresponding stresses normal to the cutting plane.The fitted contours of the cut surfaces with different fitting methods are compared,and the measuring results are also compared with those of three-dimensional thermal-elastic-plastic finite element simulation.Investigated results show that the internal residual stress of thick welded structures can be measured with good precision by the contour method;due to the errors introduced by the electric discharge machining(EDM) and the profile measurement,the subsurface residual stress within 2 mm depth measured by the contour method would be inaccurate in magnitude,but the good distribution trend can be got by the method;broken wire during EDM process can lead to local profile error that produce a abrupt change in measured stress.

Measurement and simulation of temperature and residual stress distributions from friction stir welding AA2024 Al alloy

Finite element (FE) models have been developed to predict residual stress distributions resulting from the friction stir welding (FSW) process. Plates 250 mm × 50 mm × 5 mm in dimension of an Aluminium alloy (AA2024-T4) were butt-joined through FSW. The thermal profiles were monitored in-situ during the welding process using thermocouples. Sequentially-coupled thermo-mechanical simulations have been performed using an instantaneous relative linear velocity based heat source. Post weld residual stress measurements have been obtained using the neutron diffraction technique and were used to verify the finite element results. The thermal profiles measured during welding have been simulated in the FE model. Increasing the tool traversal speed is found to reduce the peak temperatures experienced during welding for a given tool rotational speed. The general trends and magnitudes of the residual stress distributions measured along the weld line have been predicted by the FE model. The residual stress distributions measured and predicted are relatively symmetric and uninfluenced by the range of tool traversal speeds for the cases considered. Further refinement of the material and process model may be required to improve the predictions accuracy. However, effective predictions have been obtained in the FE model presented by treating the material as a continuum without additional complexities.