Papers by Author: Vladimir Luzin

Abstract: A synergic combination of neutron techniques was applied to characterize non-invasively the laminated structure of a set of ancient katana, part of the East Asian Collection of the Museum of Applied Arts and Sciences (MAAS) in Sydney. Neutron tomography, diffraction, residual stress and Bragg-edge transmission analyses were undertaken on samples of well-known origin, time period and authorship to create a reference database on the main manufacturing methods developed by Japanese swordsmiths. In the attempt to attribute mumei (no-signature) blades basing on a scientific analytical method rather than a stylistic analysis, data from the reference samples were benchmarked against the results obtained from the unknown blade to identify differences and commonalities in the production process.

Abstract: Granular materials demonstrate unique mechanical properties stemming from their discrete nature. At large length scales granular assemblies are often viewed from the perspective of continuum theory where they show complex behaviour such as elastic and plastic anisotropy related to the load and deformation history. This complex behaviour is inextricably linked to the micromechanics of load sharing and force transmission at the particle level. At these scales, bulk stress is not shared homogeneously between particles, but rather by a network of `force chains' that form a skeleton supporting the vast majority of the applied load. The formation and failure of these structures govern much of the bulk behaviour of these materials. Neutron diffraction techniques are now providing a window into the mechanics of granular materials at both bulk and particle scales. Through a combination of tomographic neutron imaging and diffraction based strain measurement it is now possible to directly examine the stress within individual particles in granular assemblies. Results of these experiments in two and three dimensions are presented and the outlook for this approach to studying the mechanics of granular materials is discussed.

Abstract: A great variety of techniques are nowadays used to spray coatings with different functionality and properties for the purpose of surface enhancement. Depending on application and design, these can be thermal (plasma or high-velocity oxy-fuel are the most widely used) and warm or cold spraying, which are known to generate considerable residual stresses. This stress is a function of the spaying process as well as the material and thickness of the coating-substrate system. The mechanical integrity of coatings is critical for certain applications, e.g. wear resistant and thermal-barrier coatings, hence residual stress control and mitigation are essential in preventing the coating’s mechanical failure, improving the coating’s performance and the its operational lifetime. Although hole drilling technique or x-ray diffraction combined with layer removal method can be applicable for stress measurements in coatings, the neutron diffraction stress analysis also provides an effective and efficient tool for non-destructive through-thickness stress measurements with a commensurately high resolution, down to 0.1-0.2 mm. The most recent results of neutron diffraction stress measurements in coating systems are presented herein.

Abstract: Three natural polycrystalline diamond samples have been investigated non-destructively in their raw as-discovered forms. The samples originate from different locations in the world and possibly have different mechanisms of formation. The study reveals that the stones are primarily composed of cubic diamond with varying amounts of impurities that emanate from their excessive porosities and entrapped environmental contamination from the areas they were formed and subsequently discovered. Residual stress analyses with X-ray and neutron diffraction techniques of the diamond phase in the interior regions of the diamonds revealed low stress values.

Abstract: The unique and unusual state of matter represented by granular materials has historically made it very difficult to develop models of stress distributions and was previously not able to be explored experimentally in the required detail. This paper reports the application of the neutron diffraction strain scanning method, originally developed for residual stress measurements within engineering components, to the problem of the stress distribution in granular Fe under a consolidating pressure. Strains were measured in axial, radial, circumferential and an oblique direction using the neutron strain scanning diffractometer KOWARI at ANSTO (Sydney). The full stress tensor as a function of position was able to be extracted for both straight walled, converging and stepped dies.

Abstract: Insulated rail joints (IRJs) are a primary component of the rail track safety and signalling systems. Rails are supported by two fishplates which are fastened by bolts and nuts and, with the support of sleepers and track ballast, form an integrated assembly. IRJ failure can result from progressive defects, the propagation of which is influenced by residual stresses in the rail. Residual stresses change significantly during service due to the complex deformation and damage effects associated with wheel rolling, sliding and impact. IRJ failures can occur when metal flows over the insulated rail gap (typically 6-8 mm width), breaks the electrically isolated section of track and results in malfunction of the track signalling system. In this investigation, residual stress measurements were obtained from rail-ends which had undergone controlled amounts of surface plastic deformation using a full scale wheel-on-track simulation test rig. Results were compared with those obtained from similar investigations performed on rail ends associated with ex-service IRJs. Residual stresses were measured by neutron diffraction at the Australian Nuclear Science and Technology Organisation (ANSTO). Measurements with constant gauge volume 3x3x3 mm³ were carried in the central vertical plane on 5mm thick sliced rail samples cut by an electric discharge machine (EDM). Stress evolution at the rail ends was found to exhibit characteristics similar to those of the ex-service rails, with a compressive zone of 5mm deep that is counterbalanced by a tension zone beneath, extending to a depth of around 15mm. However, in contrast to the ex-service rails, the type of stress distribution in the test-rig deformed samples was apparently different due to the localization of load under the particular test conditions. In the latter, in contrast with clear stress evolution, there was no obvious evolution of d₀. Since d₀ reflects rather long-term accumulation of crystal lattice damage and microstructural changes due to service load, the loading history of the test rig samples has not reached the same level as the ex-service rails. It is concluded that the wheel-on-rail simulation rig provides the potential capability for testing the wheel-rail rolling contact conditions in rails, rail ends and insulated rail joints.

Abstract: Stress Corrosion Cracking (SCC) may be a serious problem in gas pipelines. This work studies the hardness and residual stress profiles in two nominally identical sections of adjacent pipe with similar environment and coating, one of which was affected by detectable SCC and the other that was not. The results show changes in texture, residual stress, plastic strain, and hardness at the pipe surface which may be responsible for the altered susceptibility to SCC.

Abstract: Zirconium alloys are widely used in the nuclear industry because of their relative high strength, neutron transparency, resistance to high neutron-irradiation environment and corrosion resistance. One application for Zirconium alloy Zr-2.5Nb is the vacuum confinement vessel utilised in the cold neutron source of the OPAL research reactor at ANSTO. Having a total length of more the 3 meters, it is made of two sections joined using electron beam welding. The weld and the nearby regions are critical for the performance and integrity of the component and therefore understanding of the residual stresses development within the weld is important in connection to (i) evolution of fine dual phase α/b microstructure and crystallographic texture (ii) and stress-related radiation induced phenomena, such as grain growth, creep and sub-critical crack growth by delayed hydride cracking. The stresses were measured in and around an electron beam weld produced during the development of this component of the OPAL Cold Neutron Source. The effects of a large grain size in the weld were reduced by taking advantage of rotational symmetry and rotating the sample to increase the swept volume. Due to the heat-treatment after welding, the stresses were very low, less than 10% of the yield strength of the material, in both the hoop and axial directions. As a result of phase transformation effects during the welding process the final stresses are compressive in the weld, which reduces the likelihood of fracture or of hydride formation in this region. The highest stresses are in the parent material adjacent to the weld where the toughness is expected to be higher than in the weld material.

Abstract: Cold coiling of high tensile steel rod into helical coil springs for the automotive industry is a new technique being implemented amongst spring manufacturers worldwide. To characterise this coil production process, the neutron strain scanning technique has been employed to non-destructively elucidate the influence production stages have on the tri-axial residual stress state. Samples investigated represented key production steps in the cold-coil forming process: Cold coiling; Tempering; Hot setting; Hot peening; Shot peening. Investigations revealed that the stress field was axi-symmetrical, that the dominant variation in all samples occurred along the hoop direction (helical circumference), whilst the radial and axial stresses are substantially lower. Accurate two-dimensional stress maps of the rod cross section have been compiled revealing key features associated with the cold coiling step. Comparison of the stress fields after each production step revealed altered stress values. The final shot peening process stage not only reduced stress concentrations at the internal bore, but contributed to the establishment of favourable surface residual stress conditions that enhance the fatigue life of the final product.

Abstract: Investigations of interaction residual stresses between thin WC-Co surface coated layers on thick mild steel substrates have successfully been performed with neutron diffraction. This systematic approach was conducted on the reference grit-blasted substrates and their HVOF coated WC-Co products. Using a sub-millimeter gauge volume, precisely positioned, the stress gradient through the coated and non-coated substrates were determined and used to derive the coating stress condition prevailing in the thin coating by applying the stress balance (Stoney) approach. In addition, the average stress in each 200 μm thick coating was measured directly with very good agreement obtained between the calculated and measured stress values. Investigations were extended to determine the thermal nature of the residual stresses by studying the annealed counterpart samples as well to follow the evolution of the residual stress upon annealing.