Vladimir Luzin

The Strain-Scanning Diffractometer Kowari

Residual stress has a crucial significance, especially for critical applications such as structural components of airplanes, in the pipeline industry, for welding technology, etc. Stress is introduced during the manufacturing of components or during their service life and can be beneficial or can have a negative impact on the mechanical integrity of components. When it comes to control or experimental assessment of these components, the neutron residual-stress diffractometer is an indispensable tool for non-destructive examination. Using the high penetration of thermal neutrons and a special design the stress instruments can measure distortions of the crystal lattice as accurate as ∼10−5 Å for d∼1 Å.

Through-Thickness Residual Stress Measurement in Metal and Ceramic Spray Coatings by Neutron Diffraction

Thermal and cold spraying encompasses a great variety of techniques for deposition of fully or partially molten or cold particles of material to produce coatings with a specific microstructure and properties for the purpose of surface enhancement. Among the many factors influencing sprayed coating integrity, residual stress is very important since it will be the driving force for possible crack propagation and consequent coating failure. The very complex physical processes occurring during coating deposition make first principles treatment difficult. A number of empirical models have been proposed to predict and describe quantitatively the stress distribution in the coating/substrate system. However, there are a limited number of experimental measurements on through-thickness stress distribution and for only a few materials and few spraying techniques, to validate any model and to define its area of applicability. Several metal and ceramic coatings produced by different spraying techniques were measured by means of neutron diffraction. Through-thickness stress profiles were obtained and treated in the frame of the empirical progressive coating deposition model. The comparison between experimental and simulated results is discussed.

In-situ neutron diffraction study of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals under uniaxial mechanical stress

Q.L., Y.L., and R.L.W. acknowledge financial support from the Australian Research Council (ARC) in the form of an ARC Discovery Grant. Y.L. also acknowledges support from the ARC Future Fellowships program. The authors also thank the Australian Institute of Nuclear Science and Engineering (ANSIE) for financial support to access the national neutron facilities at ANSTO.

Bragg-edge elastic strain tomography for in situ systems from energy-resolved neutron transmission imaging

Technological developments in high resolution time-of-flight neutron detectors have raised the prospect of tomographic reconstruction of elastic strain fields from Bragg-edge strain images. This approach holds the potential to provide a unique window into the full triaxial stress field within solid samples. While general tomographic reconstruction from these images has been shown to be ill-posed, an injective link between measurements and boundary deformations exists for systems subject to in situ applied loads in the absence of residual stress. Recent work has provided an algorithm to achieve tomographic reconstruction for this class of mechanical system. This letter details an experimental proof-of-concept for this algorithm involving the full reconstruction of a biaxial strain field within a non-trivial steel sample. This work was carried out on the RADEN energy resolved neutron imaging instrument within the Japan Proton Accelerator Research Complex, with validation through Digital Image Correlation and constant wavelength neutron strain scans.

Kowari : The residual-stress diffractometer for engineering applications at OPAL

Since the first residual-stress experiments were done using neutron diffraction the demand for dedicated instruments increased constantly. Nowadays, it is a well established technique suitable to determine precisely and reliably sub-surface stresses in engineering components. Kowari is a dedicated residual stress diffractometer and part of the first suite of instruments of Australia’s new research reactor OPAL. In June 2007 Kowari detected the first neutrons which allowed doing some preliminary checks with Monte Carlo simulations. To further check the simulations experimental resolution curves are compared with results from FRM-II. We would like to give an update on the progress of the instrument’s installation and commissioning. A schematic view of the instrument is shown in Fig. 1 and the main components are described in the following sections.

High-pH inclined stress corrosion cracking in Australian and Canadian gas pipeline X65 steels

High-pH stress corrosion cracking is a form of environmental degradation of gas pipeline steels. The crack path is intergranular by nature and typically perpendicular to the maximum applied (hoop) stress (i.e. perpendicular to the pipe outer surface). Some unusual instances of cracks have been observed in Canadian and Australian X65 pipes, where cracks grow away from the perpendicular for considerable distances. This paper presents a comparative study in terms of crack morphology, mechanical properties and crystallographic texture for these Australian and Canadian pipe steels. It is shown that the crack morphologies are quite similar, the main difference being the angle at which the cracks propagate into the material. This difference could be explained by the different through-wall texture and grain aspect ratio measured in the two materials. The interdependency of crack tip plasticity, crack tip electrochemistry and anisotropy in microstructural texture seems to heavily affect the resulting inclined crack path.

The role of metallurgical solid state phase transformations on the formation of residual stress in laser cladding and heating

There are two major types of solid state phase transformations in metallic materials; the formation of second phase particles during heat treatments, and the transformation of the matrix from one crystalline packing arrangement to another during either heating or cooling. These transformations change the spacing between adjacent atoms and can thus influence the residual stress levels formed. The heating and cooling cycles of materials processing operations using lasers such as cladding and melting/heating, can induce phase transformations depending on the character of the material being processed. This paper compares the effects of the different phase transformations and also the influence of the type of laser processing on the final residual stress formed. The comparisons are made between laser clad AA7075, laser clad Ti-6Al-4V and laser melted nickel-aluminium bronze using neutron diffraction and the contour method of measuring residual stress.

Measurement and Calculation of Elastic Properties in Low Carbon Steel Sheet

Low carbon steel (usually in sheet form) has found a wide range of applications in industry due to its high formability. The inner and outer panels of a car body are good examples of such an implementation. While low carbon steel has been used in this application for many decades, a reliable predictive capability of the forming process and “springback” has still not been achieved. NIST has been involved in addressing this and other formability problems for several years. In this paper, texture produced by the in-plane straining and its relationship to springback is reported. Low carbon steel sheet was examined in the as-received condition and after balanced biaxial straining to 25%. This was performed using the Marciniak in-plane stretching test. Both experimental measurements and numerical calculations have been utilized to evaluate anisotropy and evolution of the elastic properties during forming. We employ several techniques for elastic property measurements (dynamic mechanical analysis, static four point bending, mechanical resonance frequency measurements), and several calculation schemes (orientation distribution function averaging, finite element analysis) which are based on texture measurements (neutron diffraction, electron back scattering diffraction). The following objectives are pursued: a) To test a range of different experimental techniques for elastic property measurements in sheet metals; b) To validate numerical calculation methods of the elastic properties by experiments; c) To evaluate elastic property changes (and texture development) during biaxial straining. On the basis of the investigation, recommendations are made for the evaluation of elastic properties in textured sheet metal.

Experimental deformation of deuterated ice in 3D and 2D: identification of grain-scale processes

Major polar ice sheets and ice caps experience cycles of variable flow during different glacial periods and as a response to past warming. The rate and localisation of deformation inside an ice body controls the evolution of ice microstructure and crystallographic fabric. This is critical for interpreting proxy signals for climate change, with deformation overprinting and disrupting stratigraphy deep under ice caps due to the nature of the flow. The final crystallographic fabric in polar ice sheets provides a record of deformation history, which in turn controls the flow properties of ice during further deformation and affects geophysical sensing of ice sheets. For example, identification of layering in ice sheets, using seismic or ice radar techniques, is attributed to grain size changes and fabric variations. Such information has been used to provide information on climate state and its changes over time, and as the Fourth Intergovernmental Panel on Climate Change (IPCC) Report (Solomon et al. 2007) points out there is currently still a lack of understanding of internal ice-sheet dynamics. To answer this we have recently conducted experiments at the Australian Nuclear Science and Technology Organisation (ANSTO) to collect fully quantitative microstructural data from polycrystalline heavy water (D2O) ice deformed in a dynamic regime. The ice and temperature (–7°C) chosen for this study is used as a direct analogue for deforming natural-water ice as it offers a unique opportunity to link grain size and texture evolution in natural ice at –10°C. Results show a dynamic system where steady-state rheology is not necessarily coupled to microstructural and crystallographic fabric stability. This link needs to be taken into account to improve ice-mass-deformation modelling critical for climate change predictions.

Kowari - OPAL's New Stress Diffractometer for the Engineering Community: Capabilities and First Results

Kowari is a neutron diffractometer at ANSTO’s research reactor OPAL. The instrument is dedicated to investigate residual strains and stresses in engineering samples or new materials. Besides its usage in engineering/strain-scanning it is more and more frequently being used for obtaining texture information related to materials science applications. In particular the possibility of using the gauge volume defining slit systems allows extracting local information from the diffraction peak, i.e. position, intensity, and width, without the need to cut the sample specimen. The instrument obtained its operating license in August 2008 to briefly describe the instruments parameters and capabilities, and give examples of two typical applications since it went from commissioning into user mode.