E3: Residual Stress Neutron Diffractometer at BER II

The E3 residual stress neutron diffractometer operated at Helmholtz-Zentrum Berlin (HZB) is designed for studies in material science and engineering applications. Recent upgrade activities have made the instrument faster and more adaptable to different types of measurement. Thus, E3 has become more attractive to a broad user community, including industry, and increased substantially its scientific output

Geant4 based simulations for novel neutron detector development

A Geant4-based Python/C++ simulation and coding framework, which has been developed and used in order to aid the R&D efforts for thermal neutron detectors at neutron scattering facilities, is described. Built upon configurable geometry and generator modules, it integrates a general purpose object oriented output file format with meta-data, developed in order to facilitate a faster turn-around time when setting up and analysing simulations. Also discussed are the extensions to Geant4 which have been implemented in order to include the effects of low-energy phenomena such as Bragg diffraction in the polycrystalline support materials of the detector. Finally, an example application of the framework is briefly shown.Comment: Proceedings for the 20th International Conference on Computing in High Energy and Nuclear Physics (CHEP

EDDIDAT: A graphical user interface for the analysis of energy-dispersive diffraction data

EDDIDAT is a MATLAB-based graphical user interface for the convenient and versatile analysis of energy-dispersive diffraction data obtained at laboratory and synchrotron sources. The main focus of EDDIDAT up to now has been on the analysis of residual stresses, but it can also be used to prepare measurement data for subsequent phase analysis or analysis of preferred orientation. The program provides access to the depth-resolved analysis of residual stresses at different levels of approximation. Furthermore, the graphic representation of the results also serves for the consideration of microstructural and texture-related properties. The included material database allows for the quick analysis of the most common materials and is easily extendable. The plots and results produced with EDDIDAT can be exported to graphics and text files. EDDIDAT is designed to analyze diffraction data from various energy-dispersive X-ray sources. Hence it is possible to add new sources and implement the device-specific properties into EDDIDAT. The program is freely available to academic users

Minimizing and Characterizing Uncertainties in Neutron Strain Measurements with Special Attention to Grain Size Effects

The accurate determination of strain during measurement using neutron diffraction depends on many factors. The statistical uncertainty of the diffraction data is not always the most important contributor to the total uncertainty in the measured strain. Other contributors, such as sample positioning, size and shape of the sampling (gauge) volume and the size and distribution of grains within the sampling volume, often play an important role as well. Grain size issues have been the least studied and their impact is often ignored even though the potential uncertainty contribution can be large. Certain methods such as oscillating the sample during measurement can help in reducing the magnitude of the grain size effect and hence also that of the related uncertainty contribution. A thorough characterization of uncertainties due to grain size effects however, in terms of absolute values that should be added to the uncertainties propagated from the Bragg peak fits, have not yet been implemented. This paper will present an improved method to characterize and estimate absolute uncertainty values due to grain size effects.JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes

Numerical Simulation of Residual Stresses in Hardmetals Using an Elastic-Viscoplastic Material Description

Based on five mesoscopic 2,5D representative volume elements RVE representing a WC6wt. Co hard metal grade, the temperature dependent internal and final residual stress state is predicted by FEM using an elasto viscoplastic modelling approach. The utilized models are semi automatically derived from backscatter electron micrographs and extruded in the third dimension get a more realistic deformation pattern compared to plane strain or plane stress assumptions. For the isotropic visco plastic material description of the binder alloy Co , Voce hardening law in combination with the Nor ton Bailey law is used for modelling the creep and relaxation behaviour. The mechanical behaviour of the carbides WC is assumed to be in the isotropic elastic region. The internal stresses are predicted in a temperature range between 900 C and room temperature RT . The temperature dependent in ternal stresses are compared to neutron diffraction results for the same hard metal grad

Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting

Residual stress/strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting (EBM) of Ti-6Al-4V with resulting phase distributions and residual stress/strains, extensive experimental work has been performed. A large number of polycrystalline Ti-6Al-4V specimens were produced with different optimized EBM process parameter combinations. These specimens were post-sequentially studied by using high-energy X-ray and neutron diffraction. In addition, visible light microscopy, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) studies were performed and linked to the other findings. Results show that the influence of scan speed and offset focus on resulting residual strain in a fully dense sample was not significant. In contrast to some previous literature, a uniform α- and β-Ti phase distribution was found in all investigated specimens. Furthermore, no strong strain variations along the build direction with respect to the deposition were found. The magnitude of strain in α and β phase show some variations both in the build plane and along the build direction, which seemed to correlate with the size of the primary β grains. However, no relation was found between measured residual strains in α and β phase. Large primary β grains and texture appear to have a strong effect on X-ray based stress results with relatively small beam size, therefore it is suggested to use a large beam for representative bulk measurements and also to consider the prior β grain size in experimental planning, as well as for mathematical modelling.Funders: InterReg ESS &amp; MaxIV [MAH-003]; “Nationellt rymdtekniskt forskningsprogram” (NRFP); European Spallation Source–participation of the Czech Republic—OP”, [CZ.02.1.01/0.0/0.0/16 013/0001794]</p

Tem­per­ature dependence in Bragg edge neutron transmission measurements

A systematic study has been carried out to investigate the neutron transmission signal as a function of sample tem per ature. In particular, the experimentally de ter mined wavelength dependent neutron attenuation spectra for a martensitic steel at tem per atures ranging from 21 to 700 C are com pared with simulated data. A theoretical description that includes the Debye Waller factor in order to describe the tem per ature influence on the neutron cross sections was im plemented in the nxsPlotter software and used for the simulations. The analysis of the attenuation coefficients at varying tem per atures shows that the missing contributions due to elastic and inelastic scattering can be clearly distinguished while the elastically scattered intensities decrease with higher tem per atures, the inelastically scattered intensities increase, and the two can be separated from each other by analysing unique sharp features in the form of Bragg edges. This study presents the first systematic approach to qu antify this effect and can serve as a basis , for example, to correct measurements taken during in situ heat treatments, in many cases being a prerequisite for obtaining qu anti fiable result