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In the present work, ring-shaped samples made from steel 20MnCr5 were low-pressure carburized (LPC) and subsequently hardened by gas quenching (case-hardened). This results in a near-surface gradient in chemical composition, microstructure- and hardness distribution, as well as a three-dimensional residual stress (RS) distribution, which was investigated by neutron diffraction. Near-surface RSs in the ferrite-/martensite- and austenite phase are additionally determined by X-ray diffraction. It is shown that the chemical gradient has an influence on the chosen d 0 strategy and how such a reference sample should be extracted. If near-surface RS values are to be determined by neutron diffraction, the pseudo-strain effect must be taken into account. For this purpose, a suitable approach using the "open source" software SIMRES and STRESSFIT is also presented. By combining neutron and X-ray diffraction data, a complete RS distribution over the whole sample can be obtained. [ABSTRACT FROM AUTHOR]

The residual stresses in multiphase metal matrix composites with both random planar-oriented short fibers and particles were studied by neutron diffraction and by a model based on the reformulation of classic Maxwell's homogenization method. Contrary to common understanding and state-of-the-art models, we experimentally observed that randomly oriented phases possess non-hydrostatic residual stress. The recently developed modeling approach allows calculating the residual stress in all phases of the composites. It rationalizes the presence of deviatoric stresses accounting for the interaction of random oriented phases with fibers having preferential orientation. [ABSTRACT FROM AUTHOR]

To know the residual stress state within a component is essential for predicting its service life time. Neutron diffraction is a reliable tool for non-destructive determination of macroscopic residual stresses, even deep inside a component. One standard procedure in neutron residual stress analysis is to cut out small macrostress free coupons from the strained component, which serve as reference samples. Redistribution of intergranular stresses due to relaxation when the coupon is cut out, however, may lead to spurious macroscopic stresses. A quantitative study of the change of intergranular stresses shows that, contrary to conventional thought, even the {311} Bragg reflection is affected strongly by this phenomenon. In this case, the use of reference values calculated using boundary conditions of mechanical equilibrium enables to extract reliable macroscopic residual stress values. [ABSTRACT FROM AUTHOR]

A combined study of neutron diffraction and difference dilatometry on submicrocrystalline Ni prepared by high pressure torsion aims at studying the anisotropic behaviour during dilatometry and its relation to internal stress and structural anisotropy. Macroscopic stresses were undetectable in the dilatometer samples. Along with specific tests such as post cold-rolling, this shows that an observed anisotropic length change upon annealing is not caused by internal stress, but can be explained by the inherent microstructure, i.e. the anisotropic annealing of relaxed vacancies at grain boundaries of shape-anisotropic crystallites. [ABSTRACT FROM AUTHOR]

In this paper we report about the formation of intergranular strains in superalloy Haynes 282 studied by neutron diffraction during uniaxial tensile testing. The results gained from the initial bar material are compared to results of a peak-aged sample state at ambient temperature. A comparison of the results with data from a fully aged IN 718 alloy sample shows that intergranular strains are much lower in Haynes 282 than in the conventional nickel based superalloy. In contrast to IN 718 the formation of intergranular residual strains between bar material and heat treated sample state shows no significant differences. The relevance of the results to the macroscopic residual stress analysis by neutron diffraction on both continuous wavelength and spallation neutron sources is discussed in detail. [ABSTRACT FROM AUTHOR]

Knowledge of the macroscopic residual stresses in components of complex high performance alloys is crucial when it comes to considering the safety and manufacturing aspects of components. Diffraction experiments are one of the key methods for studying residual stresses. However a component of the residual strain determined by diffraction experiments, known as microstrain or intergranular residual strain, occurs over the length scale of the grains and thus plays only a minor role for the life time of such components. For the reliable determination of macroscopic strains (with the minimum influence of these intergranular residual strains), the ISO standard recommends the use of particular Bragg reflections. Here we compare the build-up of intergranular strain of two different precipitation hardened IN 718 (INCONEL 718) samples, with identical chemical composition. Since intergranular strains are also affected by temperature, results from room temperature measurement are compared to results at T =550 °C. It turned out that microstructural parameters, such as grain size or type of precipitates, have a larger effect on the intergranular strain evolution than the influence of temperature at the measurement temperature of T =550 °C. The results also show that the choice of Bragg reflections for the diffractometric residual stress analysis is dependent not only on its chemical composition, but also on the microstructure of the sample. In addition diffraction elastic constants (DECs) for all measured Bragg reflections are given. [ABSTRACT FROM AUTHOR]

Abstract: Metal-based additive processes are characterized by numerous transient physical effects, which exhibit an adverse influence on the production result. Hence, various research approaches for the optimization of e. g. the structural part behavior exist for layered manufacturing. Increasingly, these approaches are based on the finite element analysis to be able to understand the complexity. Hereby it should be considered that the significance of the calculation results depends on the quality of modeling the process in the simulation environment. Based on a selected specimen, the current work demonstrates in which way the numerical accuracy of the residual stress state can be analyzed by utilizing the neutron diffraction. Thereby, different process parameter settings were examined. [Copyright &y& Elsevier]

Material fracture toughness data are required to undertake fitness-for-service assessments of engineering components containing cracks. Calculations of crack driving force in the component are compared with material fracture toughness values to assess the likelihood of subsequent failure. Experimental measurements of fracture toughness are usually made on small specimens extracted from a larger 'parent' component following strict experimental guidelines, formulated to ensure measured toughness values in the fracture specimens are appropriate for use in the full-size component. Implicit in this procedure is the assumption that the extracted fracture specimens contain no residual stresses, with any residual stresses in the full-size component being accounted for in the crack driving force calculation. This paper considers a recent conjecture within the structural integrity community that the extracted fracture specimens may themselves contain a residual stress field which may influence measurements of fracture toughness. This could potentially lead to a degree of 'double accounting', i.e. the effect of residual stresses may be included in both the material toughness and the crack driving force. This, in turn, could lead to unnecessary conservatism in safety assessments. To explore this conjecture, the results of numerical modelling and neutron diffraction measurements of residual stresses in fracture specimens extracted from two different welded parent components are presented. One of the components is significantly larger than the extracted specimens, with the other being marginally larger than the extracted specimens. Results confirm the intuitive expectation that the residual stresses in specimens extracted from much larger components are negligible, whereas if the dimensions of the extracted specimens are comparable with the larger component then significant residual stresses may remain. [ABSTRACT FROM AUTHOR]

Abstract: In laser beam welding, a serious challenge is to control the distortion during the process. Understanding the whole process chain in view of different distortion potentials applied in each processing step provides the ability to control the distortion of the welded components. Every manufacturing step induces residual stresses in the component which can be released by the heat of the welding process, while further residual stresses are introduced into the welded parts upon cooling. The laser beam sources of the new generation permit a high power welding process and high beam quality at the same time. These laser beams are capable of producing deep and narrow seams. Thus the thermal strains of the joined parts are expected to be minimized. Especially axial welded shaft-hub joints show an irregular distribution of bending deformation, which is caused by the self-influencing welding gap. This work deals with the investigation of different laser beam sources and their effect on the welding distortion in axial welded shafthub joints made of steel (20MnCr5). The aim of the work done was to achieve minimal distortion after the welding process. To characterize the influences on the distortion behaviour of the welded parts, residual stresses have been determined by neutron diffraction. [Copyright &y& Elsevier]

Accumulation of residual stresses in rails during service can contribute to crack initiation and fracture and may result in serious accidents. It is therefore necessary and important to quantify the residual stresses that evolve under repeated rolling contact between wheel and rail. In the present study, triaxial residual strain measurements were performed in a worn British railway rail using neutron diffraction. Localized stress is observed close to the region of contact, showing the asymmetry and complexity of distributions that arise from the non-uniform plastic deformation. Contact-induced plasticity is revealed by the broadening (increase in the full width at half-maximum (FWHM)) of the diffraction peaks. [ABSTRACT FROM AUTHOR]

Abstract: Non-destructive analysis of phase specific residual stresses and textures is only possible by diffraction methods. The new neutron diffractometer STRESS-SPEC was installed at FRM-II in Munich, Germany, for this purpose. It is designed to be equally applied to texture and residual stress analyses by virtue of its flexible configuration. The results of measurements on a single bead on plate weld within the framework of the European Network on Neutron Techniques Standardisation for Structural Integrity (NET) are presented here, in order to demonstrate the reliability and accuracy of the instrument by comparing previous results from other neutron diffraction facilities by using a Bayesian statistical approach. [Copyright &y& Elsevier]

Abstract: The composite casting process is mainly used to produce composite engine blocks with in-cast liners. Due to different thermal expansion of the casting material and the material of the insert residual stresses occur during solidification. These residual stresses can reduce fatigue strength and lead to distortions of the part. They can be minimised by constructive measures. Casting simulation is a suitable method to predict residual stresses and distortions and thus to optimise design of parts. To improve the accuracy of stress simulation composite castings were designed and characterised using conventional and modern test methods such as neutron tomography and neutron diffraction. Neutron diffraction enables to measure, non-destructively, stress distributions within the bulk of the specimen. The results are used to verify and optimise the residual stress simulation. In the end this enables an optimised construction of composite castings. [Copyright &y& Elsevier]

Abstract: Carbon fibre ceramic matrix composite materials, C/SiC, are excellent candidates as lightweight structural materials for high performance hot structures such as in aerospace applications. Satellite nozzles are manufactured from C/SiC, using, for instance, the Liquid Polymer Infiltration (LPI) process. In this article the applicability of different non-destructive analysis methods for the characterisation of C/SiC components will be discussed. By using synchrotron and neutron tomography it is possible to characterise the C/SiC material in each desired location or orientation. Synchrotron radiation using tomography on small samples with a resolution of 1.4 μm, i.e. the fibre scale, was used to characterise three dimensionally fibre orientation and integrity, matrix homogeneity and dimensions and distributions of micro pores. Neutron radiation tomography with a resolution of about 300 μm was used to analyse the over-all C/SiC satellite nozzle component with respect to the fibre content. The special solder connection of a C/SiC satellite nozzle to a metallic ring was also successfully analysed by neutron tomography. In addition, the residual stress state of a temperature tested satellite nozzle was analysed non-destructively in depth by neutron diffraction. The results revealed almost zero stress for the principal directions, radial, axial and tangential, which can be considered to be the principal directions. [Copyright &y& Elsevier]

The measurement and analysis of residual stresses has gained significant importance over the past couple of years due to the increasing demands in improving the properties of new engineering materials and components. The ability to measure these residual stresses accurately will thus lead to the manufacture of stronger, lighter, and cheaper components by industry. The drive to optimize material performance whilst minimizing component weight will ensure that this field continues to grow. Experimentally, non-destructive analysis of phase-specific residual stresses is only possible by means of diffraction methods. While X-ray scattering is essentially a surface method, the high penetration depth of neutrons into the bulk material (e.g., 20 mm into steel or 100 mm into aluminium) allows extracting reliable information from the inside of components. [ABSTRACT FROM AUTHOR]

Neutron diffraction strain measurements with high spatial resolution were carried out on a dissimilar metal weld (DMW). Residual stress were calculated and compared using three different approaches for reference value (d 0). The results underline the sensitivity of the resulting residual stress profiles on the d 0 used, particularly in the welded region. [ABSTRACT FROM AUTHOR]

Abstract: In response to the development of new materials and the application of materials and components in new technologies the direct measurement, calculation and evaluation of textures and residual stresses has gained worldwide significance in recent years. In order to cater for the development of these analytical techniques the Materials Science Diffractometer STRESS-SPEC at FRM-II is designed to be equally applied to texture or residual stress analysis by virtue of its flexible configuration and the high neutron flux at the sample position. The instrument is now available for routine operation and here we present details of first experiments and instrument performance. [Copyright &y& Elsevier]

Abstract: Mechanical surface treatments such as shot peening (SP) or ball-burnishing (BB) induce plastic deformation close to the surface resulting in work-hardening and compressive residual stresses. It enhances the fatigue performance by retarding or even suppressing micro-crack growth from the surface into the interior. SP and BB were carried out on a solution heat treated (SHT) Ti-2.5Cu. The investigations of compressive and balancing tensile residual stresses need a combination of energy-dispersive synchrotron (ED) and neutron diffraction. Essential for the stress distribution is the stress state before surface treatments which was determined by neutron diffraction. Results show that the maximum compressive stress and its depth play an important role to improve the fatigue performance. [ABSTRACT FROM AUTHOR]

Abstract: Within Task Group 1 (TG1) of the European Network on Neutron Techniques standardization for Structural Integrity (NeT), residual stress determinations by neutron diffraction were performed on a single weld bead on a plate (BoP) specimen by several laboratories. By following a pre-defined protocol, residual stress distributions have been estimated in the plate. Each residual strain/stress instrument at each institute have their own characteristics and their own methods by which the data is analyzed; however, the final estimate of the stress distributions are expected to be ‘the same’ to within the quoted uncertainty. This implies that this quoted uncertainty for each stress determination should be realistic. For specific measurement locations in the BoP specimen a modified Bayesian approach was used to obtain an average stress. This special approach is less affected by outliers, although care must be taken as it has been observed that in the case where there are few data points in the average, a strong bias can occur towards data points with a relatively small quoted uncertainty. In the data analyses used here, a ‘fairer average’ less influenced by such bias is implemented. Presented here is an overview of the main features that influence the stress and associated uncertainty determination, such as reference values, choice of moduli values, grain size effects and positioning etc. [Copyright &y& Elsevier]

Neutron diffraction measurements have been carried out for non-destructive characterization and numerical predictions validation of the residual stresses in a mock-up of the ITER-like divertor target plasma-facing component, made by hot radial pressing of 4 tungsten blocks to a CuCrZr cooling pipe via a soft copper interlayer. The neutron diffraction measurements were carried out, at room temperature, at FRM II reactor in Garching. Stress-relieved W and CuCrZr were examined as reference state before joining. The 3D stress tensor was determined in one of the two external W-blocks and CuCrZr pipe segments, scanning the mock-up from the outer surface of the W block towards the inner wall of the CuCrZr pipe with the interval of 0.4–0.5 mm. A residual stress distribution from tension to compression through the bonding line is detected, as expected from the requirement of force balance. Except at the interlayer, stresses well below 100 MPa are found, confirming the good fabrication quality of the investigated monoblock. These experimental results are comparable with the FEM-based numerical prediction, but at the interlayer and inside the pipe a sharper spatial resolution is needed for the neutron diffraction measurements to catch the hoop and axial stress gradient profile. [ABSTRACT FROM AUTHOR]

A study of the residual stress distribution and texture evolution in stationary shoulder friction stir welded (SSFSW) AA7050 plate through non-destructive energy-resolved neutron imaging (NI), monochromatic neutron diffraction (ND) and destructive contour method (CM) is described in this paper. The presence of Bragg edges in the neutron transmission spectra are shown to be effective in determining the longitudinal residual stress and compare well with results obtained by ND and CM. The texture in the weld zone and base metal has been mapped by contrast in the narrow-energy transmission image combined with an analysis of the Bragg edges in the transmission spectra at each pixel showing agreement with the results obtained by electron backscatter diffraction (EBSD) mapping. The ND results were complicated by plastic anisotropy effects in the rolled plate which meant that different reference stress-free lattice spacings were required at each point in the 3 principal directions for this material. NI and CM were unaffected by texture effects in determining residual stress. Compared to conventional techniques, NI is shown to be an effective way of quantifying both texture and residual stress in one shot. [ABSTRACT FROM AUTHOR]

After several decades, it is still difficult to predict “macroscopic and microscopic (M-m)” residual stresses (RSes) in metal matrix composites (MMCs) after welding. In this work, an enhanced multiscale model is developed to predict the evolution of M-m RSes in MMCs during several thermo-mechanical processes including welding. This multiscale model is capable of handling non-zero initial M-m RSes and integrates the temperature history dependent constitutive model (THDCM) at both macroscale and microscale. Meanwhile, thermal source model of friction stir welding (FSW) is integrated. The extension to other welding thermal source is straightforward. This multiscale model is used to study the generation, inheritance, and evolution of M-m RSes in a SiC/Al composite during quenching, FSW and post-welding heat treatment (PWHT). The effects of initial M-m RSes and material constitutive models on the prediction of M-m RSes are systematically assessed. It is found that using the THDCM and taking into account the initial RSes, this multiscale model shows the best predictions of RSes in the FSW joint of MMCs. The predictions agree with the neutron diffraction measurements reasonably well. It is found that the reduction of RSes during PWHT is mainly caused by the stress relaxation during the solution treatment stage. [ABSTRACT FROM AUTHOR]

The materials science neutron diffractometer STRESS-SPEC located at FRM II is a dedicated instrument for strain and pole figure measurements. Both methods make complementary demands on sample handling. On one hand pole figure measurements need a high degree of freedom to orient small samples and on the other hand in strain investigations it is often necessary to handle large and heavy components. Therefore a robot based sample positioning system was developed, which has the capability to provide both possibilities. Based on this new robot system further developments like a full automated sample changer system for texture measurements were accomplished. Moreover this system opens the door for combined strain and texture analysis at STRESS-SPEC. [ABSTRACT FROM AUTHOR]

This study presents a new method to determine both the macroscopic and microscopic (including elastic mismatch, thermal misfit and plastic misfit) residual stresses in metal matrix composite (MMC) welds via neutron diffraction. As an illustration, friction stir welded 17 vol.% SiCp/2009Al-T4 plates were investigated. It is shown that the calculation of the thermal misfit plus plastic misfit residual stresses in the metal matrix of the MMC welds is much more accurate by using the absolute unstrained lattice parameter of the SiC powder sample based on the stress equilibrium condition compared with using that of the unreinforced alloy sample. The profiles of the longitudinal ( L ), transverse ( T ) and normal ( N ) components of the total residual stress in the reinforcement are entirely different from those in the matrix. It was found that the profiles and total variations of the L , T and N components of the total residual stress are dominated by those of the macroscopic residual stress in the matrix, and by those of the elastic mismatch residual stress in the reinforcement, revealing a significant load transfer from the matrix to the reinforcement. The maximum total residual stress in the metal matrix of the FSW 17 vol.% SiCp/2009Al-T4 weld could reach up to ∼69% of the yield strength of the 2009Al-T4 alloy. Increasing the rotation rate has small effects on the basic profiles of the total residual stress, apart from increasing the width of the profiles. [ABSTRACT FROM AUTHOR]

Abstract: Residual stress evaluation is an important stage to interpret the fatigue behavior of many engineering materials. The present research aimed at evaluating non-destructively the macroscopic compressive and balancing tensile residual stresses generated in the surface layer and in the core region, respectively, in mechanically surface treated alpha titanium alloy Ti–2.5Cu. In order to achieve that purpose, a combination of energy-dispersive X-ray and neutron diffraction was used. Results revealed that the zero-crossing depths (where the residual stress value of zero is reached) and balancing tensile residual stress distributions in the core region were well defined. [Copyright &y& Elsevier]

Abstract: We discuss the stability of weld residual strain under static and quasi cyclic transverse tensile loading in the elastic and elastic–plastic region. The test welds were joined with low transformation temperature weld filler materials with 10wt% Cr and varying Ni-content from 8 to 12wt%. Using neutron diffraction the residual lattice strain in the martensitic α′- and austenitic γ-phase in the fusion zone as well as the ferritic α-phase in the heat affected zone and base metal as (1) induced by welding, (2) superimposed by stepwise tensile loading and (3) after unloading was measured. The amount of retained austenite in the fusion zone increases with increasing Ni-content, but it decreases with increasing load level due to stress induced martensite formation. In the as-welded condition the transverse macroscopic residual lattice strain was found to be in low compression in the fusion zone in each weld, while the heat affected zone was in tension. Local plastic deformation of the γ-phase as a result of yielding during tensile loading in combination with the change in phase fraction resulted in increased macroscopic compression in the fusion zone. The reduced yield strength in the heat affected zone resulted in plastic deformation and a considerable shift into compression. Comparison with the cross weld distribution of the hardness and FWHM of the neutron diffraction interference lines supported the assumption of plastic deformation of the γ- and α-phase in the fusion and heat affected zone, respectively, while the α′-phase in the fusion zone was stressed within the elastic regime only. Microstructural observations as well as measurement of the local γ-phase fraction by means of laboratory X-ray diffraction in the fusion zone strengthen these observations. [Copyright &y& Elsevier]

Abstract: In response to the development of new materials and the application of materials and components in advanced technologies, non-destructive measurement methods of textures and residual stresses have gained worldwide significance in recent years. The materials science neutron diffractometer STRESS-SPEC at FRM II (Garching, Germany) is designed to be applied equally to texture and residual stress analyses by virtue of its very flexible configuration. Due to the high penetration capabilities of neutrons and the high neutron flux of STRESS-SPEC it allows a combined analysis of global texture, local texture, strain pole figure and FWHM pole figure in a wide variety of materials including metals, alloys, composites, ceramics and geological materials. Especially, the analysis of texture gradients in bulk materials using neutron diffraction has advantages over laboratory X-rays and EBSD for many scientific cases. Moreover, neutron diffraction is favourable for coarse-grained materials, where bulk information averaged over texture inhomogeneities is needed, and also stands out due to easy sample preparation. In future, the newly developed robot system for STRESS-SPEC will allow much more flexibility than an Eulerian cradle as on standard instruments. Five recent measurements are shown to demonstrate the wide range of possible texture applications at STRESS-SPEC diffractometer. [Copyright &y& Elsevier]

Positional accuracy is an important parameter in residual stress investigations with neutron diffraction, considering that precise measurements of strains at the same localised position along a number of sample orientations are required, including investigations of complete complex shaped engineering components. This study reports the development of a standardised approach for quantitative analysis of positional accuracy on neutron strain scanners that builds on previous campaigns. The approach uses standardised sample sets with specific geometries that enable quantitative assessment of instrumental and sample alignment procedures and associated accuracies. This method has been implemented on four participating instruments: ENGIN-X (United Kingdom), MPISI (South Africa), SALSA (France) and STRESS-SPEC (Germany), to render results representative of monochromatic and time-of-flight strain scanners. The benchmarking results show comparable performance between the instruments with positional accuracies around 100 μ m readily achieved. This standardised approach confirms the high positional precision attainable for non-destructive stress determination, to unequivocally benefit utilisation by academia and industry alike. It is envisaged that this common calibration protocol and reporting template that conforms to the newly developed Neutron Quality Label for Internal Stress Characterisation be adopted by other facilities to facilitate expansion of the supportive network. [ABSTRACT FROM AUTHOR]