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In the present work, neutronographic in situ diffraction stress analyses during uniaxial loading and subsequent unloading were carried out on the two duplex stainless steels X2CrNiMoN22-5-3 and X3CrNiMoN27-5-2 with nominal phase fractions for ferrite:austenite of 50:50% and 70:30%, respectively. In addition to the different phase fractions, the two steels also differed in their phase-specific crystallographic texture. The load-partitioning behaviour and the phase-specific micro (residual) stress evolution for total strains up to about 9% were investigated. The results indicated that for both materials under load, the phase-specific stress in the ferrite phase was significantly higher than in the austenite phase, while no texture development through the plastic deformation could be observed.

Journal of materials science 57(48), 22082-22098 (2022). doi:10.1007/s10853-022-07997-w, Published by Springer Science + Business Media B.V, Dordrecht [u.a.]

Near interfacial residual stresses are investigated in a joint composed of aluminum alloy and dual phase steel. A small step neutron diffraction scan was initially performed to determine the weld interface position along the measured transverse cross section. Residual stress measurements were then performed in three orthogonal directions for steel and aluminum using {211} and {311} diffraction peaks, respectively. The small step scan enables to identify the wavy nature of the interface, which has been subsequently combined in the residual stress calculation. The resultant of all three components of the residual stresses is almost zero along the mid-thickness of the steel plate, validating the estimated stresses. Near the interface, residual stresses on the steel reveal an “M” shape distribution while in the aluminum sheet they show a “W” shape. The interfacial residual stresses in the steel originate from the thermomechanical processing condition, phase transformation and the mismatch in the coefficients of thermal expansion (CTE). At the vicinity of the interface, the aluminum plate presents a distribution of residual stresses similar to a superposition of residual stresses resulting from an arc welding and the effect of mismatch in CTE.

Residual stresses (RS) are often induced through quenching of aluminum alloys and present a potential risk of developing crack or distortion in subsequent manufacturing processes. Study of methods to minimise the RS in quenched components is of practical importance. In this paper, cold rolling (CR) has been carried out to remove the RS in quenched AA7050 blocks. The CR effect on relaxing RS in quenched AA7050 blocks has been evaluated via the neutron diffraction (ND), X-ray diffraction (XRD) and contour techniques. The results reveal that although CR transforms near-surface residual stresses from large compression to large tension along the rolling direction, it results in remarkable RS relief in the core part of the material. An integrated finite element model for RS evolution through the CR process was put forward and has been validated by the experimental results.

Superhard silicon carbide bonded diamond materials can be produced by liquid silicon infiltration of diamond containing preforms. These materials can be produced as bulk materials and as layered materials with the SiC bonded diamond only in areas where it is required. In order to understand the behaviour of the materials it is necessary to know the internal stresses in the different phases and at the interface. These stresses were determined by Raman spectroscopy and in the bulk by neutron diffraction using the SALSA instrument in the ILL. In the SiC bonded diamond material the diamond and the remaining Si are under compressive stresses. The SiC-phase is under tensile stresses up to 500 MPa. The Raman investigations and the neutron diffraction resulted in similar results. At the interface between the SiC-bonded diamond and the SiSiC no significant additional stresses could be observed.

Joining various metallic parts becomes crucial to lighten the vehicles for automobile industry and thus reduce the greenhouse gas emission while maintaining crashworthiness. The combination of Al and steels is of an interest due to the lightweight of Al alloys and the high strength of steels. Similarly, to classic welds, dissimilar welds accommodate residual stresses. Their quantification is a challenge using conventional approaches. Dissimilar welds produced by Friction Melt Bonding (FMB) technique [1] are used here to verify two different approaches of measuring residual stresses using neutron diffraction at SALSA (Strain Analyser for Large and Small scale engineering Applications) instrument. Firstly, near interface residual stresses are characterized for an Al/steel joint by considering a pseudo strain correction method. Residual stresses near the interface originate from an inhomogeneous distribution of thermal cycles and from the difference in coefficient of thermal expansion for both Al and steel during the cooling stage. These stresses are characterized using this pseudo strain correction method [2]. On the Al/steel interface, longitudinal residual stresses in the steel side reveal an “M” shape distribution while, on the aluminum side, longitudinal residual stresses show a “W” shape. Secondly, four different welds composed of Al/steel produced with various welding conditions (2 different advancing speed and two different backing plates) are characterized by measuring an average residual stress using an oscillating gauge across the thickness [3]. This second approach is particularly beneficial for thin plates with smaller thickness than the gauge’s diagonal width. It is found that the longitudinal residual stress increases for increasing heat input into the welds. The transverse residual stress on the steel side also becomes slightly tensile with increasing heat input into the welds. Thus, it is preferable to produce dissimilar welds with lower heat input in order to minimize the residual stresses in the welds. These two proposed methods enable to quantify the residual stresses in dissimilar welded joints. [1] C. van der Rest, P.J. Jacques, A. Simar, Scr. Mater., 77 (2014) 25-28. [2] N. Jimenez-Mena, T. Sapanathan, J.-M. Drezet, T. Pirling, P.J. Jacques, A. Simar, J. Mater. Process. Technol., 266 (2019) 651-661. [3] T. Sapanathan, J.-M. Drezet, P. J. Jacques, T. Pirling, A. Simar, doi:10.5291/ILL-DATA.1-02-245

The control of residual stress (RS) remains a challenge in the manufacturing of metallic parts using the laser powder bed fusion process (LPBF). This layer-by-layer manufacturing approach gives rise to complex triaxial RS distributions, which require extensive characterization effort for a broader acceptance of LPBF in industry. This study focuses on the distribution of bulk triaxial RS and surface RS in LPBF austenitic steel 316L. The RS are determined by X-ray and neutron diffraction to characterize the RS distribution. Variations in the LPBF parameters interlayer time (ILT) and scanning velocity and their influence on the temperature distribution and resulting RS is investigated using thermographic data from in situ process monitoring. The RS in the LPBF 316L is tensile at the surface and compressive in the bulk. The RS is directly related to the thermal history of the part as shown by the in situ thermography data. Shorter ILT leads to higher temperatures of the part during the manufacturing, which decrease the RS and RS formation mechanisms. Interestingly, the surface RS does not agree with this observation. This study highlights the benefit of using multiple RS determination methods and in situ thermography monitoring to characterize the RS in LPBF processed parts.

Residual stresses in materials affect their resistance to the initiation of fracture and to subsequent crack growth. Using full-field strain measurements and finite element analysis we demonstrate that the effect of residual stress on a material's crack growth resistance curve can be understood using elastic-plastic fracture mechanics. It is shown that Lei's modified J-integral formulation (Jmod) is a good predictor of the load vs crack extension behaviour of an elastic-plastic material containing residual stresses. Keywords: Residual stress, Fracture, Neutron diffraction, Digital image correlation, Finite element analysis

Neutron diffraction and curvature measurements were conducted to investigate the residual stresses associated with Plasma Transferred Arc Cladding (PTA) of Ti-6Al-4V on a substrate of the same material. The wire-feed PTA coupled with 3-axis CNC machine was used as an Additive Manufacturing (AM) technique to build parts. A combination of the process parameters was chosen to investigate their effects on residual stress evolution. Neutron Diffraction (ND) measurements of residual strains were performed on the SALSA instrument at the Institut Laue-Langevin (ILL), Grenoble, France. Longitudinal stresses were also inferred by using a Coordinate Measurement Machine (CMM) and Euler-Bernoulli beam theorem. Furthermore, Optical Microscopy (OM) of the cross section of the parts was used to analyse the microstructural evolution. The results show the effect of shorter and longer ‘dwell time’ between layers on the evolution of residual stresses.

The residual stresses in heat-treated 7075 aluminium alloy blocks have been characterised using two neutron diffraction strain scanning instruments. The influence of uniaxial cold compression on relieving the residual stress has been determined. Systematically increasing the magnitude of cold compression from 1 to 10% has been shown to have a small beneficial effect on the final residual stress distribution, by reducing the magnitude of the range in the triaxial residual stresses. The effect of an overaging precipitation treatment on the residual stress has also been characterised, and this was found to have a significant stress relieving influence (25–40%). A relationship between the width of the {311} diffraction peaks and the amount of cold compression was also observed.

Batteries & supercaps 4(2), 327 - 335 (2020). doi:10.1002/batt.202000178, The two‐dimensional lithium distribution in the graphite anode was non‐destructively probed by spatially resolved neutron diffraction for a batch consisting of 34 different cylinder‐type (18650) Li‐ion batteries in fully charged state. The uniformity of the lithium distribution was quantified and correlated to the cell specifications/electrochemistry and to intrinsic cell parameters like electrode thickness, position of current collectors, etc. which were obtained by X‐ray micro‐computed tomography. Non‐uniformities in the lithiation state of the anode from a constant plateau have been observed for the majority of the studied cells. Their location corresponds to the positions of current tabs connecting the electrode stripes and areas of incomplete electrode coating at the beginning and the end of the electrode stripes. Four commonly used schemes of current lid connection were identified. Each of them displays its own effect on the uniformity of the lithiation at the anode and, therefore, variation of the intrinsic state‐of‐charge distribution and, most probably, the ageing behavior of the electrodes., Published by Wiley-VCH, Weinheim

The rigidity temperature of a solidifying alloy is the temperature at which the solid phase is sufficiently coalesced to transmit tensile stress. It is a major input parameter in numerical modeling of solidification processes as it defines the point at which thermally induced deformations start to generate internal stresses in a casting. This temperature has been determined for an Al-13 wt.% Cu alloy using in situ neutron diffraction during casting in a dog-bone-shaped mold. This setup allows the sample to build up internal stress naturally as its contraction is not possible. The cooling on both sides of the mold induces a hot spot at the middle of the sample that is irradiated by neutrons. Diffraction patterns are recorded every 11 s using a large detector, and the very first change of diffraction angles allows for the determination of the rigidity temperature. We measured rigidity temperatures equal to 557°C and 548°C depending on the cooling rate for grain refined Al-13 wt.% Cu alloys. At a high cooling rate, rigidity is reached during the formation of the eutectic phase. In this case, the solid phase is not sufficiently coalesced to sustain tensile load and thus cannot avoid hot tear formation.

Nickel-base superalloys are conventionally aged in order to develop a favorable microstructure as well as to relieve residual stresses. Here neutron diffraction was used to follow the evolution of residual stress during aging in Inconel 718 and Udimet 720LI for the first time by a combination of in situ and ex situ measurements. First, the quench-induced stress profiles were determined for different geometries of Inconel 718 forgings confirming that the amplitude of stress is not significantly affected by the thickness of the component. It was followed by in situ residual stress analysis using neutron diffraction during aging/annealing treatments at 650 °C, 720 °C, and 750 °C. Almost 90 pct of stress relaxation was found to occur primarily during heating to the aging temperature as a result of a combination of plasticity and early-stage creep relaxation. Creep-like stress relaxation was observed to evolve at a diminishing rate during the isothermal treatment of Inconel 718 at 720 °C and 750 °C, while no further stress relaxation occurred at 650 °C. This means that a change in hold temperature might have a more immediate impact on stress relaxation than a change in duration of heat treatment. The post-aging ex situ measurements showed that a heat treatment at 750 °C for 8 hours reduced the stresses by approximately 70 pct in Inconel 718. By comparison, when heat treating Udimet 720LI in the same way only a 20 pct stress reduction was observed, which is explained by the higher creep resistance of this alloy.

Residual stresses are often introduced into aluminum alloys through quenching processes performed to generate the required microstructure. Such residual stresses are known to be deleterious to the integrity of the component. Methods to mitigate residual stresses in quenched components are therefore of great importance. Cold rolling has been proposed as an effective technique to remove residual stresses in large components. In this work, the effectiveness of cold rolling in reducing the residual stresses in quenched blocks AA7050 has been quantified using the neutron diffraction technique. Neutron diffraction measurements have been performed on two blocks one quenched and the other quenched & cold rolled block. Comparing the residual stress distributions pre and post rolling it has been found that cold rolling almost eliminates the tensile residual stresses in the core of the block, however it generates large tensile residual stresses d in a shallow region near the surface of the block.

The use of cold drawing processes for tubes is a flexible and well-established technology to reduce tube dimensions and improve their surface quality. However, wall thickness deviations over the circumference in the semi-finished goods – eccentricity – and residual stresses can be disadvantageous. Nevertheless, drawing with die tilting is clearly affecting the eccentricity as well as the residual stress development. In this paper the evolution of residual stresses over the wall thickness in cold drawn copper tubes was measured from the as-received state over the condition in the deformation zone with tilted dies and finally to the drawn tubes by means of neutron diffraction analysis at SALSA facility in Institut Laue-Langevin (ILL), Grenoble. A model was developed and the behavior of the residual stresses was simulated using the finite element method (FEM). The information about the evolution was necessary for the model and its verification. With this model – which is taking into account the influence of eccentricity on the residual stress development – the cost intensive neutron diffraction measurements can be reduced strongly. The verified model was used to calculate the residual stresses for standard drawn tubes and compared to tilted ones. Keywords: Residual stresses, Tube drawing, finite element method, Neutron diffraction, Die tilting, Copper tube

Since all residual stress measurement methods have inherent limitations, it is normally impractical to completely characterise a three-dimensional residual stress field by experimental means. This lack of complete information makes it difficult to incorporate measured residual stress data into the analysis of elastic–plastic fracture without resorting to simplified methods such as the Failure Assessment Diagram (FAD) approach. We propose a technique in which the complete residual stress field is reconstructed from measurements and used in finite element analysis of the fracture process. Residual elastic strains and stresses in three-point bend fracture specimens were measured using neutron diffraction and an iterative method was used to generate a self-consistent estimate of the complete residual stress field. This enabled calculation of the J contour integral for a specimen acted on by both residual stress and an externally-applied load, allowing the interaction between residual and applied stress to be observed in detail.

Multi-pass fusion welding by a filler material (wire) is normally carried out to join thick steel sections used in most engineering applications. Multiple thermal cycles from a multi-pass weld resulted in a variable distribution of residual stress field across the weld and through the thickness. Presence of tensile residual stresses can be detrimental to the integrity and the service behaviour of the welded joint. In addition to a complex distribution of residual stress state, multi-pass welds also form dendritic grain structure, which are repeatedly heated, resulting in segregation of alloying elements. In this research, microstructural refinement with modification of residual stress state was attempted by applying post-weld cold rolling followed by laser processing and then cold rolling. The residual stress was determined non-destructively by using neutron diffraction. Post-weld cold rolling followed by laser processing was carried out to induce recrystallization of the cold rolled grains. Microstructural characterisation indicates a significant grain refinement near the capping pass. However, post-weld cold rolling followed by laser processing reinstates the lock-in stress. In this study, it was demonstrated that a complete recrystallized microstructure with compressive state of stress can be formed when a further cold rolling is applied on the laser processed, recrystallized microstructure.

Rectilinear blocks of the very high-strength aerospace aluminum alloy 7449 were solution treated and cold water quenched. They were then stress relieved immediately by cold compression. The amount of cold compression was systematically varied from 0 to 0.3 %. The amount of plastic strain was limited to well below the industrial standard of ~2 %. The blocks then received a stabilizing aging treatment. The residual stress distribution remaining in the blocks was characterized using neutron diffraction, with the aim of tracking how the through thickness 3-D residual strains and stresses change as cold compression progresses. Stress relief was of the order of 30–50 %, but there was no discernible systematic increase in stress relief as the plastic deformation magnitude was increased. It is suggested that this is mainly due to the differences between the samples being less than the experimental uncertainty of the neutron diffraction strain measurement technique.

Structural integrity assessment of welded joints requires characterising the residual stresses generated during the process. Although measurements can provide a quantitative estimation of the residual stresses, a reliable numerical model offers greater advantages in terms of cost, time and versatility. A validated model can be used to optimise the measurement procedure and thereby aiding in further refinement of the model itself. In the current work, a three-pass tungsten-inert gas welding in an austenitic stainless-steel plate is simulated using a three-dimensional sequentially coupled thermo-mechanical analysis for the purpose of predicting the transient thermal profiles and the final residual stresses as a part of NeT programme. Block-dumped heat transfer analysis was conducted with element activation and deactivation to represent the physical deposition of the weld beads for each pass, followed by a mechanical analysis to predict the stresses. Incremental deep-hole drilling and neutron diffraction techniques at ILL and HZB facilities in Grenoble and Berlin respectively, were employed to measure the residual stresses through the thickness of the sample plate at the center. The predicted thermal history and the residual stresses are verified with the measured thermocouple recordings and the stresses respectively.

Towards the improvement of the understanding of force/stress distribution in granular media under load, a new experimental approach is suggested. Neutron diffraction, a non-conventional experimental technique, has been successfully used to map the evolution of intragranular strains in sand specimens loaded in a novel plane-strain apparatus. Representative preliminary results from recent experiments are presented, focusing on the correlation between the macro- and micro-scale response of the material, to highlight the potential of the experimental approach.

Intergranular strains due to tensile plastic deformation were investigated in a commercially pure Ti. Neutron diffraction has been used to characterize the evolution of residual elastic strain in grains with different crystallographic orientations. Experimental data have been obtained for the macroscopic stress–strain curve and the intergranular strain evolution in the longitudinal and transverse direction relative to the uniaxial loading axis. The elasto-plastic self-consistent (EPSC) approach was used to model the deformation behavior of the studied material. Comparison between the neutron measurements and the model predictions shows that in most cases the EPSC approach can predict the lattice strain evolution and capture the plastic anisotropy observed in the experiments.

AISI Type 304L austenitic stainless steels are extensively used in industries, and welding is an indispensable tool used for joining these materials. In a multi-pass weld, the development of residual stress to a large extent depends on the response of the weld metal, heat affected zone and parent material to complex thermo-mechanical cycles during welding. Earlier researchers on this area used either mechanical tensioning or heat treatment to modify the residual stress distribution in and around the weld. In this research, microstructural refinement with modification of residual stress state was attempted by using high pressure cold rolling followed by laser processing in 12 mm thick 304L austenitic stainless steels which is a novel technique. The hardening of the weld metal was evaluated after welding, post weld cold rolling, and post weld cold rolling followed by laser processing. The residual stress was determined non-destructively by using neutron diffraction. Residual stress analysis show that post weld cold rolling was effective in modifying the longitudinal residual stress distribution throughout the entire thickness. Post weld cold rolling followed by laser processing performed in this research was to induce recrystallization of the cold rolled grains. However, post weld cold rolling followed by laser processing showed minor grain refinement but was not effective as it reinstated the stress state.

The direct chill casting of rectangular ingots gives rise to large thermally induced strains that lead to several types of casting defects (distortions, cold cracks and hot tearing) and downstream processing issues during sawing especially for high strength alloys and large formats. To reduce stresses, wipers are placed below the mould to eject the falling water from the ingot which gets hotter. As-cast stresses have been determined in AA7050 rectangular ingots cast with and without a wiper using neutron diffraction measurements and a 3D casting model. The stress level is reduced by 33% and the stored elastic energy by 50%.

Residual stresses in welds pose a significant threat to the structural integrity of a component, especially in the presence of defects and are required to be accounted for in assessing component safety. Although the R6 assessment procedure suggests various approximate methods for incorporating these effects in defect assessment, most of them are overly conservative and not very cost-effective. A more reliable approach is to characterise the weld residual stresses around a defect and study how they interact with primary load. The current paper analyses the effects of weld residual stresses on the fracture of a dissimilar weld in the presence of defect. The weld is made between modified 9Cr–1Mo steel and 316LN stainless steel using autogenous electron beam welding. A C(T) specimen was extracted from the centre of the weld and a crack introduced in the fusion zone using electro-discharge machining. The residual stresses around the crack were measured on a grid of measurement points at mid-thickness of the C(T) specimen using neutron diffraction on the strain diffractometer SALSA at ILL, Grenoble. The measured residual stresses around the crack-tip were incorporated into a finite element model and the interaction of these with applied load was predicted under fracture.

The residual stress distributions in oxide dispersion-strengthened steel plates, joined by Friction Stir Welding, have been mapped using neutron diffraction. The measured stress maps were interpreted in terms of the temperature profiles measured for welds using three different tool traverse speeds. The largest peak longitudinal tensile stresses, ∼1200 MPa, were found in the weld produced using the fastest tool traverse speed, and corresponds to relatively high cooling rates. A reduction in tool traverse speed yields a significant decrease in tensile residual stresses in the thermo-mechanically affected zone of the welds, but also causes higher peak temperatures during welding. The transverse residual stresses were not found to be affected by the tool traverse speed and were significantly lower in magnitude than the longitudinal stresses. Additionally, the torque profiles measured during welding increased with the amount of material stirred and therefore correlated with the width of the thermo-mechanically affected zone of the welds.

Tensile armour layers in unbonded flexible pipes are constructed by the parallel helical wrapping of several rectangular wires. Pairs of layers, wound in opposite directions and with different helical shapes are used to provide the necessary axial strength, water depth capacity and torsion balance. The forming of armour wires as supplied by the vendor into a helix shape on the pipe involves significant plastic straining; twisting and repeated bending of the wires in different planes. The wires that are wrapped on the pipe are not unloaded. Therefore the armour wires in flexible pipes are considered to contain residual stress (RS). Knowledge of RS in the wires of the manufactured pipe is essential in making appropriate design decisions with high confidence to meet material utilization requirements and subsequently predict the integrity and fatigue durability of the pipe. This paper describes an investigation performed to examine the evolution of RS in the tensile wires during various stages of the pipe manufacturing process. To this end, different methods including a relatively simple and inexpensive stress relaxation method termed the contour method, as well as diffraction methods were used to evaluate RS in the wire. A finite element (FE) model has been developed to simulate the wire deformation involved in the pipe manufacturing process. The procedure was used to predict the evolution of RS in a tensile wire and change in material response during the pipe manufacturing process. A comparison of FE model predictions and measured data is given. The results show that the RS measured by the contour method give comparable values to those obtained from more advanced methods such as high energy synchrotron X-ray and neutron diffraction. The need for using representative material properties and deformation boundary conditions in FE models to predict RS accurately is highlighted.

Evaluation of residual stress in the weld toe region is of critical importance. In this paper, the residual stress distribution both near the surface and in depth around the weld toe was investigated using neutron diffraction, complemented with X-ray diffraction. Measurements were done on a 1300 MPa yield strength steel welded using a Low Transformation Temperature (LTT) consumable. Near surface residual stresses, as close as 39 µm below the surface, were measured using neutron diffraction and evaluated by applying a near surface data correction technique. Very steep surface stress gradients within 0.5 mm of the surface were found both at the weld toe and 2 mm into the heat affected zone (HAZ). Neutron results showed that the LTT consumable was capable of inducing near surface compressive residual stresses in all directions at the weld toe. It is concluded that there are very steep stress gradients both transverse to the weld toe line and in the depth direction, at the weld toe in LTT welds. Residual stress in the base material a few millimeters from the weld toe can be very different from the stress at the weld toe. Care must, therefore, be exercised when relating the residual stress to fatigue strength in LTT welds.

International audience; Solutionising and quenching are key steps in the fabrication of heat treatable aluminium parts such as AA2618 compressor impellers for turbochargers. Quenching not only dictates the mechanical characteristics of the product but also induces residual stresses that can cause unacceptable distortions during machining and unfavourable stresses in service. Predicting and controlling stress generation during quenching of large AA2618 forgings is therefore of great interest. Since possible precipitation during quenching may affect the local yield strength of the material and thus impact the level of macro-scale residual stresses, consideration of this phenomenon is required. A phenomenological material model accounting for precipitation in a simple way is used instead of modelling in detail precipitation that occurs during quenching. The required model parameters are identified using a limited number of tensile tests achieved after representative interrupted cooling paths in a Gleeble machine. This model is used in FE computations of stress generation during quenching of large massive AA2618 forgings for compressor impellers. The residual strain and stress profiles are compared with neutron diffraction measurements carried out at SALSA and STRESS-SPEC diffractometers in as-quenched and in T6 conditions. It turned out that the residual stress predictions by FE modelling might be wrong if precipitation is not taken into account properly in the material model.

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.

Spatially-resolved neutron diffraction has been applied to probe the lithium distribution in radial direction of a commercial Li-ion cell of 18650-type. The spatial evolution of selected Bragg reflections for LiCoO2 (positive electrode, “cathode”) and graphite and lithium intercalated graphite (negative electrode, “anode”) was observed and evaluated by taking beam attenuation and cell geometry effects into account. No evidences for lithium inhomogeneities have been found for the investigated set of cells. Computed neutron tomography using a monochromatic neutron beam confirmed the homogeneous lithium distribution. The relevance of the monochromatic beam to neutron imaging studies of Li-ion cells is discussed.

To improve the fatigue life of components subject to loads with high surface strain gradients, it is possible to coat them with an alloy of higher durability. The present study focuses on the effect of cladding high value track components, made of a standard rail steel UIC 900A/grade 260, with a layer of a premium martensitic stainless steel to reduce wear and fatigue. The laser cladding process inevitably generates residual stresses in the clad and parent metal, which could be detrimental to the integrity of the component. Therefore, measurements to determine the residual stress state of cladded rail were performed using semi-destructive centre-hole and deep hole drilling and non-destructive neutron diffraction techniques. Subsequently, the effects of cycling loading and wear, representative of typical service loads, on the redistribution of the residual stress field were investigated. It was observed that laser cladding causes a triaxial compressive residual stress field in the clad and near the interface and a tensile stress field in the parent material. The stress field is shown to change when the first cycle of load is applied but reaches a steady state after only 10 cycles: After the 10th cycle there is no evidence that the clad continues accumulating strain which could indicate that there is low risk of ratcheting. Wear effect on residual stress redistribution was found to be local on the surface of the specimen only.

The post-welding rolling technique was used to modify the welding residual stress profile of butt joints of S355 structural steel. Two different residual stress measurement techniques were used: contour method and neutron diffraction. A good agreement between the results of both measurement techniques was found, illustrating the capability of the contour method to provide data otherwise available only using costly neutron and synchrotron radiation. The effect of post-weld roller tensioning on residual stress consisted in a substantial change in residual stress profile, with the large tensile stresses along the weld seam becoming compressive

Cold drawing is widely applied in the industrial production of seamless tubes, employed for various mechanical applications. During pre-processing, deviations in tools and their adjustment lead to inhomogeneities in the geometry of the tubes and cause a gradient in residuals. In this paper a three dimensional finite element (3D-FE)-model is presented which was developed to calculate the change in wall thickness, eccentricity, ovality and residual macro-stress state of the tubes, produced by cold drawing. The model simulates the drawing process of tubes, drawn with and without a plug. For finite element modelling, the commercial software package Abaqus was used. To validate the model, neutron strain imaging measurements were performed on the strain imaging instrument SALSA at the Institute Laue Langevin (ILL, Grenoble, France) on a series of SF-copper tubes, drawn under controlled laboratory conditions, varying the drawing angle and the plug geometry. It can be stated that there is sufficient agreement between the finite element method (FEM)-calculation and the neutron stress determination. © 2013 by the authors.

In this paper the microstructural and residual-stress analysis of an induction hardened plate of medium carbon steel is described. The stress gradient was determined using laboratory X-ray diffraction (IWT, Bremen, Germany) and neutron strain scanning (ILL, Grenoble, France). Due to slight variations of chemical composition in the depth, matchstick like (cross section 2×2mm²) d0-reference samples were prepared from a similarly treated sample. The d0shift induced by variation of chemical composition was measured by neutron and by X-ray diffraction along the strain free direction (sin²ψ*) and used for the evaluation of the neutron stress calculation. The d0distribution obtained from the neutron measurement did not appear reliable while the method using X-ray diffraction seems to be an efficient and reliable method to determine d0profiles in small samples. The evaluation of neutron measurements was then done using the X-ray diffraction d0distribution. High compressive residual stresses were measured in the hardened layer followed by high tensile residual stresses in the core. A comparison of the neutron measurements with X-ray diffraction (XRD) depth profiles obtained after successive layer removal showed that both methods give similar results. However, these investigations opened the question about the direct comparison of the residual stresses obtained by neutron and XRD. Indeed, a correction of the neutron data regarding the residual stresses in thickness direction might be necessary as these are released in the case of X-ray diffraction measurements after layer removal.

Two-dimensional neutron diffraction measurements of superlattice and fundamental lattice reflections from a single-crystal superalloy confirm the existence of angular distortion and shear stress in the γ′ phase, and reveal its correlation with the morphology and deformation of the γ′ phase during heat treatment. The tetragonal distortions with c/a > 1 are developed and retained during subsequent heat treatments, whereas the angular distortions are enhanced for the γ′ phase during the aging treatments. The evolution of the lattice mismatch and anisotropy during the subsequent heat treatments are consistent with the transformation of certain macroscopic anisotropic compositional and stress distributions in the as-cast sample to the microscopic level at the γ/γ′-interface upon reprecipitation and the growth of the γ′ from the supersaturated γ-matrix. The high negative γ/γ′ lattice mismatch of the alloy is consistent with the high levels of refractory elements, in particular Cr, in the alloy. Comparison between superlattice and fundamental lattice reflections is revealing. Firstly, the existence of lattice misorientation at the γ/γ′-interface and the discrete misorientations from the splitting of coherently aligned aggregates of γ′-precipitates on the smoothly distributed γ -matrix is shown. Secondly, the measured lattice misorientation correlates with the spacing of dislocations at the γ/γ′-interface and evidenced by the transmission electron microscopy observation. Furthermore, it indicates the anisotropic distribution of dendrites along crystal growth axis and the presence of small misoriented higher-order dendrite arms in variously heat-treated samples.

The residual stress state and the texture in Cu-tubes, drawn without a plug under controlled laboratory conditions, are presented. Neutron stress determination confirms a stress gradient from the outer to the inner surface of the tube walls. High energy X-rays were used to analyze the texture gradient around the perimeter of the tubes as well as over the wall thickness. Anisotropic flow during tube processing results in texture variations described by ODF-analysis.

Residual stress measurements have been made in a range of electron beam welded samples to study how the weld induced residual stresses redistributed during fabrication of compact tension, C(T), specimens. The samples were manufactured from Type 316H stainless steel in the ex-service material condition and in material which had been preconditioned by inducing 8% plastic strain. Measurements made using neutron diffraction, slitting and the contour method were generally in good agreement and showed residual stress components of up to three times the base material's yield strength existed in the samples. When sectioning a sample to perform the contour method, large elastic deformations occurred at the cut tip due to the large residual stresses present. A correction was applied to the measured surface displacements to account for this deformation. Neutron diffraction measurements were made at various stages of the fabrication process, which showed significant stress redistribution occurred as the welded samples were machined into C(T) specimens. However the tensile stresses near the crack tip of the C(T) specimens remained large and could significantly influence subsequent crack growth tests.

The formation of large residual stresses continues to be a problematic side effect of all common welding processes. In this work, localised high pressure rolling of gas metal arc welds to relieve these residual stresses has been investigated using strain gauging and neutron diffraction. Rolling was found to remove undesirable tensile stresses and even induce large compressive ones, though only when applied after rather than during welding. Strain measurements taken during combined welding and rolling operations show that this is because material at the weld line continues to yield as it cools. This erases any beneficial effect on the stress distribution of rolling at high temperature. A method of rolling using an oscillating force is also presented and found to be just as effective as the equivalent static force process.

Using penetrating high-energy synchrotron X-ray radiation and thermal neutrons, the residual strains and stresses associated with the high-velocity oxygen-fuel (HVOF) thermal spray coating of WC–Co on two different substrate materials with significantly different coefficients of thermal expansion (CTE) to that of the coating material, have been investigated in a systematic approach. This approach enabled quantification of the residual strain and stress contributions that emanate from the different processing steps associated with the coating process. An eigenstrain approach enabled direct comparison of the contributions of the different processing steps to the plastic strains. It is shown that the dominant contribution originates from the grit-blast surface preparation step. Contributions purely from the coating process are not distinguishable from that of the grit blasting process within the measurement accuracy. For the as-coated samples no obvious contributions ascribable to the differences in the CTEs of the substrates, or impact related effects are observed.

Anode and cathode materials, graphite and LiCoO2, are studied by neutron diffraction under “in operando” conditions in commercial batteries (ICR 18650-type). The evolution of their crystal structure versus state of charge (SOC) and fatigue (state of health, SOH) has been analyzed using the Rietveld refinement technique. Neutron radiography data and their tomography reconstruction revealed the local neutron absorption density, which reflects mainly the Li-distribution density, but also further details of the battery design. Changes in the neutron absorption contrast have also been evaluated in dependence on SOC and SOH.

A deep rolling process was applied on 4140H steel specimens with a self-built loading frame and investigated in situ with neutron radiation using the SALSA instrument at the Institut Laue-Langevin (ILL). A neutron diffraction stress imaging approach was developed and used to determine material changes from the surface up to several millimeters inside the material by single expositions. The strains could be evaluated as deviations of the diffraction signal along the height of an area detector, and the theoretical maximum depth resolution was given by geometrical magnification together with the detector pixel size. The results of these experiments together with complementary post-process investigations could be used to link the internal load during the process with resulting material modifications such as the generated residual strains.