Neutron Diffraction Residual Stress Research Articles

Neutron Diffraction Residual Stress Study of a AA2219-T87 Self-Reacting Friction Stir Weld

Neutron Diffraction Residual Stress Study of a AA2219-T87 Self-Reacting Friction Stir Weld

Residual stress and microstructure control in welding of SA508 low alloy steel

Various types of solid-state phase transformation (SSPT) occur during the SA508 steel welding process, especially for multi-pass welding. The multiple thermal cycles lead to a more complex microstructure distribution and significantly influence the residual stress distribution. Therefore, to better control the microstructure and residual stress, it is necessary to optimize the process parameters which are closely related to the welding thermal cycles. This study established a thermo-mechanical-metallurgical multi-field coupling model and then validated it using X-ray and neutron diffraction residual stress measurement tests. Furthermore, the influence of welding heat input and preheating temperature on the formation of phase constituents and the ultimate residual stress field were analyzed in detail, concomitantly with a comprehensive discussion on their underlying mechanisms. The results showed that the increase of heat input expanded the domain occupied by the bainite phase, accompanied by the increase of compressive stress region. Moreover, the rise of preheating temperature promoted the bainite phase transformation, thus decreasing the longitudinal compressive stress and the stress gradient. The variation induced by welding parameters was closely related to the welding cooling rates. To obtain a full bainite and low residual stress condition of welded joint, it becomes imperative to exercise control over cooling rates, maintaining them at approximately 1.0 °C/s.

Neutron diffraction residual stress analysis and mechanical properties of additively manufactured high strength steel hollow sections

Selective laser melting (SLM) is regarded as one of the most attractive metal additive manufacturing (AM) techniques, which has offered a promising solution to fabricating unique members and can be used for a wide range of applications. However, the SLM is often associated with fast cooling rate and a resultant large thermal gradient; which may lead to a large amount of plastic strains and coexistent residual stresses, and sometimes even result in cracking and failure during the fabrication. These plastic strains and residual stresses play crucial roles in determining the mechanical performance of the produced structural members. Plastic strains cannot be directly measured but can be characterized indirectly by hardness values. Thus, it is essential to study the distributions and magnitudes of both residual stresses and hardness in SLM-fabricated members. In the present study, comprehensive experimental studies on micro-hardness, material properties and residual stresses in SLM-fabricated H13 high strength steel hollow sections were conducted. Non-destructive neutron diffraction was utilized to measure residual stresses and their distributions across the wall thickness and over the cross-sections. The effects of both scanning patterns and cross-section geometries on the residual stresses and hardness were also studied. Linear relationships between the hardness values and the material strengths were established for the additively manufactured H13 steel. The Vickers hardness value was found to be highly correlated to the ultimate strength, while it was correlated to the 0.2% tensile proof stress with a small deviation.

Neutron diffraction residual stress determinations in titanium aluminide component fabricated using the twin wire-arc additive manufacturing

In recent years, twin wire-arc additive manufacturing (T-WAAM) technique has been considered as a promising method of fabricating and shaping titanium aluminide components with high efficiency and low cost. However, excessive thermal input of the non-consumable tungsten electrode arc deposition induces significant residual stresses in the buildup component, thus accurate measurement of residual stresses is necessary for T-WAAM buildup part quality assessment. In the present research, non-destructive neutron diffraction residual stresses measurements on as-fabricated and heat-treated T-WAAM produced Ti48Al titanium aluminide components are performed. To exclude the influence of initial large T-WAAM residual stresses on d 0 hkl sample alignment, different d 0 hkl sample dimensions are designed: one is normal thin slice and the other is the meshed sample. According to the obtained results, the conducted post-production heat treatment has partially released initial residual stresses. Also, the meshed design of d 0 hkl sample shows better measurement accuracy than the simple sliced d 0 hkl sample. In addition, T-WAAM fabricated titanium aluminide wall component performs featured tensile-compressive alternating residual stress distribution induced by the layer-by-layer arc deposition.

Neutron diffraction measurements of weld residual stresses in three-pass slot weld (Alloy 600/82) and assessment of the measurement uncertainty

This paper describes in detail two neutron diffraction residual stress measurements, performed on the ENGIN-X neutron scattering instrument at the ISIS facility in the UK and on the SALSA instrument at the Institut Laue-Langevin in Grenoble, France. The measurements were conducted as part of the NeT Task Group 6 (TG6) international measurement round robin on an Alloy 600/82 multi-pass weldment - a slot in an Alloy 600 plate filled with three Alloy 82 weld beads, simulating a repair weld. This alloy/weld combination is considered challenging to measure, due to the large grain size and texture in the weld, and large gradients in the stress-free lattice parameter between the parent and weld metal. The basic principles of the neutron diffraction technique are introduced and issues affecting the reliability of residual stress characterization are highlighted. Two different analysis strategies are used for estimation of residual stresses from the raw data. Chemical composition studies are used to measure the mixing of parent and weld metal and highlight the steep lattice parameter gradients that arise as a consequence. The inferred residual stresses are then compared with three sets of measurements performed on the same plate by other NeT partners on E3 at the HZB in Berlin, STRESS-SPEC at the FRM II in Munich and KOWARI in Sydney. A robust Bayesian estimation average is calculated from the combined five-instrument data set, allowing reliable best estimates of the residual stress distribution in the vicinity of the weldment. The systematic uncertainties associated with the residual stress measurements are determined separately in the weld and parent materials, and compared with those in the NeT TG4 benchmark. This is a three-pass slot-welded plate fabricated from American Iron and Steel Institute AISI 316L(N) austenitic stainless steel, and is normally considered less challenging to measure using diffraction techniques than all nickel welds. The uncertainties in the stress measurements by neutron diffraction for these two weldments seem to be comparable.

Neutron diffraction residual stress determinations in Fe3Al based iron aluminide components fabricated using wire-arc additive manufacturing (WAAM)

The Wire-Arc Additive Manufacturing (WAAM) process is an increasingly attractive method for producing porosity-free metal components. However, the residual stresses and distortions resulting from the WAAM process are major concerns as they not only influence the part tolerance but can also cause premature failure in the final component during service. The current paper presents a method for using neutron diffraction to measure residual stresses in Fe3Al intermetallic wall components that have been in-situ additively fabricated using the WAAM process with different post-production treatments. By using averaging methods during the experimental setup and data processing, more reliable residual stress results are obtained from the acquired neutron diffraction data. In addition, the present study indicates that the normal residual stresses are significant compared to normal butt/fillet welding samples, which is caused by the large temperature gradient in this direction during the additive layer depositions.

Neutron diffraction residual stress analysis during fatigue crack growth retardation of stainless steel

After tensile overloading during fatigue crack growth, retardation of the crack growth rate was significant. Neutron diffraction was employed to examine the evolution of crack-tip residual stress fields during constant-amplitude cyclic loading and during fatigue crack growth following the overload. It was found that the tensile overload induces larger compressive residual stress and zone size near the crack tip in the crack-growth and crack-opening direction. For the maximum crack growth retardation, the largest compressive residual stresses were measured in the region between an overloading point and the current propagating crack tip, for all three of the orthogonal directions. Such large compressive residual stresses in the crack-wake region are thought to reduce the crack tip driving force, thereby retarding the crack propagation rate significantly. Residual stress mapping was performed to examine the effect of the fatigue stress state on the residual stresses in the three different regions from the centerline to the surface, along the through-thickness direction in the compact-tension specimen. Much larger compressive residual stresses were measured at the surface than at mid-thickness. It is thought that larger compressive residual stresses at the surface result from the plane stress condition, resulting in a slower fatigue crack growth rate at the surface of the specimen.

Local Residual Stress Depth Distribution in the Inner Gearing of a Case Hardened Sliding Collar

With respect to residual stress analysis the inner gearing of an automotive sliding collar is a component with a challenging, complex geometry. The accessibility of the tooth root does not exist for conventional measuring approaches. However, the process steps like e.g. broaching and case hardening induce characteristic residual stress distributions, which must be known for the valuation of the mechanical integrity of the parts. For lab X-ray stress analysis approaches according to the sin2ψ-method [1] the ring like structure must be sectioned, which affects the process induced residual stress state. The tooth root is rather small, which further leads to shadowing effects during tilting of the sample. Standard mechanical approaches like incremental hole drilling can be excluded due to the narrow tooth root. Local neutron diffraction residual stress analysis in the tooth root by means of neutron through surface strain scanning at the STRESS-SPEC instrument at the research reactor FRM II, Garching (Germany) was successfully carried out for the inner gearing. A measuring and evaluation strategy is proposed, where special attention is paid to the compensation of the surface effect due to the incomplete immersion of the nominal gauge volume during through surface scanning and to the local variation of the D0-value as a consequence of the case hardening process.

User Influence on Two Complementary Residual Stress Determination Methods: Contour Method and Incremental X-Ray Diffraction

The combination of various residual stress measurement methods is a common practice to complete knowledge that a single measurement method cannot provide. In this study, incremental X-Ray diffraction is combined with the contour method to measure a bent notched specimen to study the methods robustness. A finite element analysis model is built and validated with strain measurement of the bending process thus providing prior knowledge of the residual stress field. Three-dimensional neutron diffraction residual stress measurements are also performed to obtain a reference measurement with a non-destructive method and to validate the simulated stress field. In-depth stress gradient measured by X-ray diffraction is corrected with four different methods that all show good correlation with neutron diffraction measurements. Correction methods, assumptions and uncertainties are discussed and differences are observed on the robustness of the methods. Contour method measurements are performed and results are also in agreement with neutron measurements. The results provided by the contour method are complementary to those of the X-Ray diffraction since, despite a lower accuracy on the edges where X-ray diffraction is performed, the contour method offers the complete cartography of longitudinal stress in a symmetry plane of the bent specimen. Uncertainty of the contour method due to the post-processing procedure is discussed.

High frequency mechanical impact treatment (HFMI) for the fatigue improvement: numerical and experimental investigations to describe the condition in the surface layer

Post-treatment techniques like the high frequency mechanical impact treatment (HFMI) exhibit a significant fatigue life enhancement of welded joints. The effectiveness of this mechanical impact treatment is primarily based on the combination of three effects: the local hardness increase, compressive residual stresses and reduced notch stress concentration at the weld toe. The goal of the present study was to develop a computationally efficient approach for predicting residual stresses induced by the HFMI process on steel specimens. For that purpose, explicit simulations of this post weld treatment technique were performed utilizing the software package ABAQUS. Although, the focus of this study is to find suitable process and material parameters as input for the numerical simulation. For this, the impact velocity, contact force and permanent indentation depth of a pneumatic HFMI-tool were measured. Concerning material modelling, an enhanced combined material model with strain rate dependency was applied. Furthermore, the simulated residual stress field was experimentally validated by X-ray diffraction and neutron diffraction residual stress measurement. The results of the simulations are in good agreement with the experimental results, showing that the material hardening model used for simulation has a high influence on the calculated residual stress values.

Neutron diffraction residual stress analysis of Al2O3/Y-TZP ceramic composites

Residual stress measurements were conducted by time-of-flight neutron diffraction and Rietveld analysis method in Al2O3/Y-TZP ceramic composites fabricated by different green processing techniques (a novel tape casting and conventional slip casting) and with different Y-TZP content (5 and 40vol.% Y-TZP). The results show that the residual stresses in Y-TZP particulates are tensile and the ones in Al2O3 matrix are compressive, with almost flat through-thickness residual stress profiles in all bulk samples. As Y-TZP content increased, tension in Y-TZP phase was decreased but compression in Al2O3 matrix was increased (in absolute value). The values of residual stresses for both phases were mainly dependent on the Y-TZP content in the studied Al2O3/Y-TZP composites, irrespective of sample orientation and fabrication processes (a novel tape casting and conventional slip casting).

굴곡측정법을 이용한 극후판 용접부 잔류응력분포 정량분석

Abstract Residual stresses arising from the materials processing such as welding and joining affect significantly the structural integrity depending on the external loading condition. The quantitative measurement of the residual stresses is of great importance in order to characterize the effects of the residual stresses on the structural safety. In this paper, we introduce a newly devised destructive technique, the contour method (CM), which is applied for the measurements of the residual stress distributions through the thickness of a 80 mm thick steel weld. Residual stresses are evaluated from the contour, which is the normal displacementon a cut surface produced by the relaxation of residual stresses, using a finite element model. The CM provides a two-dimensional map of the residual stresses normal to the cut surface. The CM developed in the present study was validated in comparison with the residual stress distribution determined by a well- established neutron-diffraction residual stress instrument (RSI) instrumented in HANARO neutron research reactor. Key Words : Welding, Residual stress, Contour method, Neutron diffractionISSN 1225-6153Online ISSN 2287-8955

Neutron diffraction residual stress measurements of welds made with pulsed tandem gas metal arc welding (PT-GMAW)

Pulsed tandem gas metal arc welding (PT-GMAW) is being developed to increase productivity and minimise weld-induced distortion in ship-building. The PT-GMAW process was used in pulse–pulse mode to butt-weld two different strength and thickness steels; the residual stress and hardness profiles of the welds are reported and correlated.

Neutron and X-Ray Diffraction Residual Stress Measurements in Aluminium Alloys MIG Welded T-Joints after Friction Stir Processing

Friction Stir Processing (FSP) is a relatively new post-processing technique. Fatigue strength of MIG fillet welds of aluminium alloys can be substantially improved using FSP. Beyond other properties intrinsically tied to fatigue life, especially attention should be paid to the effect of the final residual stress state. In this study the residual stress distribution in T-joints of two aluminium alloys was determined by Neutron and X-ray diffraction. FSP effect on the residual stress state and fatigue life was analysed.

Neutron Diffraction Residual Stress Measurements in Electron Beam Welded Compact Tension Specimens

In a study to investigate the effect of residual stress relaxation on Creep Crack Growth (CCG) a novel fracture mechanics specimen has been designed. Compact Tension, C(T), specimens are fabricated from blocks with Electron Beam (EB) welds such that residual stresses induced during welding are retained in the specimen. Finite element analyses of EB welding and machining processes have been developed to predict the stresses in such C(T) specimens which will drive crack growth in future CCG studies. The residual stresses and strains in these samples have been quantified using the neutron diffraction measurement technique at various stages of the fabrication process and have been used to validate numerical simulations of the fabrication processes.

Structural Characterization and Its Physical Properties of Non-standard A1 Austenite Steel

New austenite stainless steel code-named A1 has been synthesized using the foundry method. The steel was prepared using mineral elements extracted from crude ores in Indonesian mines and commercial scrap materials, in this case ferro scrap, ferro chrome, nickel, manganese, and ferro silicon; all of them were in the granular shape. The starting materials are inserted into an induction foundry furnace that operates on an electromagnetic inductive-thermal system. Moreover, a small quantity of titanium was added to this austenite steel that already has a very low carbon content. The neutron diffraction pattern shows that the material had an fcc crystal structure with lattice parameter of 3.5935 A. Neutron diffraction residual stress and texture measurements were performed on the austenite samples. The residual stress along the [220] crystallographic direction in the A1 alloy is compressive except in the normal direction where it is tensile. Tension as high as -629 MPa was observed in both the axial, transversal and normal directions. No region of high pole densities has been found in the material indicating a weak texture. The average value of the observed hardness is around of 205 on the Vickers scale for original casting sample; and the average hardness value of

Neutron diffraction residual stress measurements on girth-welded 304 stainless steel pipes with weld metal deposited up to half and full pipe wall thickness

The residual stress distribution has been measured in two girth-welded austenitic stainless steel pipe weldments using time-of-flight neutron diffraction. One had weld filler metal deposited up to half the pipe wall thickness, and one had weld metal deposited up to full pipe wall thickness. The aim of the work is to evaluate the evolution in residual stress profile on filling the weld, on which there is little experimental data, and where the selection of the correct hardening model used in finite element modelling can benefit greatly from an understanding of the intermediate residual stresses partway through the welding operation. The measured residual stresses are compared with those calculated by finite element modelling and measured using X-ray diffraction. The results show a change in the measured hoop stress at the weld toe from tension to compression between the half- and fully-filled weld. The finite element results show an overprediction of the residual stress, which may be a consequence of the simple isotropic hardening model applied. The results have implications for the likely occurrence of stress corrosion cracking in this important type of pipe-to-pipe weldment.

Slitting and Contour Method Residual Stress Measurements in an Edge Welded Beam

Welding is known to introduce complex three-dimensional residual stresses of substantial magnitude into pressure vessels and pipe-work. For safety-critical components, where welded joints are not stress-relieved, it can be of vital importance to quantify the residual stress field with high certainty in order to perform a reliable structural integrity assessment. Finite element modeling approaches are being increasingly employed by engineers to predict welding residual stresses. However, such predictions are challenging owing to the innate complexity of the welding process (Hurrell et al., Development of Weld Modelling Guidelines in the UK, Proceedings of the ASME Pressure Vessels and Piping Conference, Prague, Czech Republic, July 26–30, 2009, pp. 481–489). The idea of creating weld residual stress benchmarks against which the performance of weld modeling procedures and practitioners can be evaluated is gaining increasing acceptance. A stainless steel beam 50 mm deep by 10 mm wide, autogenously welded along the 10 mm edge, is a candidate residual stress simulation benchmark specimen that has been studied analytically and for which neutron and synchrotron diffraction residual stress measurements are available. The current research was initiated to provide additional experimental residual stress data for the edge-welded beam by applying, in tandem, the slitting and contour residual stress measurement methods. The contour and slitting results were found to be in excellent agreement with each other and correlated closely with published neutron and synchrotron residual stress measurements when differences in gauge volume and shape were accounted for.

Comprehensive numerical analysis of a three-pass bead-in-slot weld and its critical validation using neutron and synchrotron diffraction residual stress measurements

The current paper presents a finite element simulation of the residual stress field associated with a three pass slot weld in an AISI 316LN austenitic stainless steel plate. The simulation is split into uncoupled thermal and mechanical analyses which enable a computationally less expensive solution. A dedicated welding heat source modelling tool is employed to calibrate the ellipsoidal Gaussian volumetric heat source by making use of extensive thermocouple measurements and metallographic analyses made during and after welding. The mechanical analysis employs the Lemaitre–Chaboche mixed hardening model. This captures the cyclic mechanical response which a material undergoes during the thermo-mechanical cycles imposed by the welding process. A close examination of the material behaviour at various locations in the sample during the welding process, clearly demonstrates the importance of defining the correct hardening and high temperature softening behaviour. The simulation is validated by two independent diffraction techniques. The well-established neutron diffraction technique and a very novel spiral slit X-ray synchrotron technique were used to measure the residual stress–strain field associated with the three-pass weld. The comparison between the model and the experiment reveals close agreement with no adjustable parameters and clearly validates the used modelling procedure.

Neutron Diffraction Residual Stress Measurements in Key-Hole Laser Formed Weldments

There is a new generation of lasers available for materials processing. The new lasers include fibre and disc laser are characterized by very high beam quality at very high power levels providing extremely high energy density. In general laser welding is selected over other welding processes because of the minimisation of the heat input, residual stresses and distortion, for this reason they are increasingly popular over a wide range of industries. The narrowness of the welds makes it challenging to resolve the details of the residual stresses produced by the welding process. Residual strain/stress measurements of two specimens produced using the fibre laser were performed on Engin-X. Across the weld and through thickness distributions are reported in this paper.