Papers by Keyword: Elastic Anisotropy

Abstract: The structural, mechanical, and thermodynamic properties of refractory metals Rh, Ir, W, Ta, Nb, Mo, Re, and Os have been systematically investigated by first-principles calculations based on density functional theory. Comparative studies reveal that Young's modulus (E = 636.42 GPa), shear modulus (G = 256.81 GPa), bulk modulus (B = 406.55 GPa), and microhardness (H = 44.69 GPa) of hexagonal Os are the highest, which reveals Os has the best overall mechanical properties. The body-centered cubic Nb has the smallest Young's modulus (E = 94.76 GPa), shear modulus (G = 33.62 GPa), bulk modulus (B = 174.50 GPa), and hardness (H = 2.04 GPa). Based on the ratio of bulk to shear modulus, it is judged that Rh, Ir, and Os are brittle materials (B/G < 1.75), and Nb, Ta, Mo, W, and Re exhibit ductile (B/G > 1.75). The elastic anisotropy has also been discussed by plotting both the 3D contours and the 2D planar projections of Young's modulus. For the face-centered cubic metals Rh and Ir and hexagonal close-packed metals Re and Os, the 3D contours of the Young's modulus are very similar, whereas body-centered cubic metals Ta, W, Nb, and Mo exhibit significant difference in elastic anisotropy. The thermodynamic calculations show that Debye temperature and minimum thermal conductivity decreases along Rh, Os, Mo, Ir, Re, W, Ta, Nb sequence. Furthermore, the results can be used as a general guidance for the design and development of high temperature refractory alloy system.

Abstract: The paper analyzes Poisson’s ratios μ₀=μ_100,001=-s₁₂/s₁₁ and elastic anisotropy factor A'=s/s₁₁ (s=s₁₁-s₁₂-s₄₄/2) for single crystal materials of binary and three-component TiNi-TiFe alloys with gradually deteriorating resistance first to one B2-R and further to two martensite transformations B2-R-B19'. The study discusses a ratio H/E of TiNi-TiFe alloys both subject and not exposed to martensite transformations. Surprisingly, this ratio exceeds 0.035 for alloys with martensite transformations, being far higher than in the majority of metals and alloys.

Abstract: Fe-Ga alloys show large magnetostriction, which strongly depends on crystal orientation. This phenomenon is associated to some degree with large elastic anisotropy. In this study, white X-ray diffraction with micro-beam synchrotron radiation was used to evaluate the microscopic stresses evolved in a polycrystalline Fe-Ga alloy under tensile loading. In the analysis, the large elastic anisotropy of the Fe-Ga alloy was focused. The stress distribution in the alloy microstructure under tensile loading was estimated using a finite element method (FEM) simulation that considered the dependence of the elasticity on the crystal orientation. The crystal orientation of grains in the polycrystalline Fe-Ga alloy was measured using electron backscatter diffraction. The FEM simulation showed that the stress distribution in the microstructure depended on the crystal orientation. The X-ray diffraction stress analysis indicated that under tensile loading, the stresses in the alloy depended on the crystal orientation. This finding is similar to the results obtained from the FEM simulation, although the absolute values of the stresses may have reflected the effects of heterogeneous deformation on the stress distribution.

Abstract: Metal forming processes often involve large strain gradients which results in heterogeneous deformation and consequently residual stresses. Furthermore the strain gradients also generate variations in the deformation texture and related properties. For materials with a significant crystallographic elastic anisotropy such as ferritic steel, these textures may have a substantial effect on the reliability of the determination of residual stresses. In the present investigation this influence is examined for the hole drilling method by a combination of experiments and finite element simulations.

Abstract: A novel method has been discovered for controlling the crystallographic orientation of pure iron using the γ to α phase transformation. When pure iron with clean metal surfaces undergoes the γ to α phase transformation, it develops a strong cube-on-face texture ({100}<0vw>) with the grain size being larger than the sheet thickness. The mechanism controlling the <100> orientation obtained is associated with the fact that the {100} faces are elastically compliant so that the <100> texture can develop in a manner consistent with minimization of strain energy. However, in commercial steels, although so many texture analyses have been conducted, the cube-on-face texture has been rarely observed. According to thermodynamic analysis, surface oxidation in commercial steels appears to be responsible for the deterioration of the <100> texture. This phenomenon can be explained in terms of the modification of the inherent elastic anisotropy of metal surface by the surface oxidation.

Abstract: The paper analyzes the depth and spacing of cracks in a tensile strained In0.25Ga0.75As epitaxial layer on a InP substrate using the minimum energy theorem. The elastic anisotropy of both the layer and the substrate is considered. The concept of weight function obtained numerically by means of detailed FEM is employed.

Abstract: Material of the specimen was austenitic stainless steel (SUS316L). The specimens were given tensile plastic strains from 0% to 55%. The Vickers hardness of the specimen corresponded to the plastic strain. The residual macrostress was measured by Mn-Kα radiations. The residual macrostress of the annealed specimen had a small compression and changed into a tension after ten- sile plastic deformation. The specimen with 1% plastic strain showed the maximum tensile residual stress. To examine the dependency of the residual stress on the lattice plane, the residual microstress for each lattice plane was measured by hard synchrotron X-rays. The residual microstress was related with Young’s modulus which was calculated by Kro¨ ner model. A new method, 2θ-cos2 χ method, was proposed to solve the problem of coarse grains and it was excellent in comparison with the sin2 ψ method.

Abstract: Current analytical techniques for simulating the generation of residual stresses within welded structures make approximations and simplifications relating to the mechanical properties of the weld metal. This is due to the paucity of knowledge on the anisotropic nature of weld metal. Consequently, the study of elastic and plastic anisotropy, within metals has been a subject of considerable interest to both experimentalists and modellers alike. This study investigates the elastic and plastic response of crystal lattice planes within single-pass and multi-pass austenitic steel weld metal using time-of -flight (TOF) neutron diffraction. As this material is often used for the fabrication of high temperature, pressure vessel components, it is important to understand the evolution of lattice strains within each set of planes during elastic and plastic loading. Neutron diffraction measurements were carried out for both single and multi-pass weld metal subjected to in-situ uni-axial tensile loading. The elastic response of individual reflections was recorded by diffraction measurements. All measurements were carried out at the ENGIN-X facility at ISIS, UK. The objective of the measurements was to determine the Young's modulus and characterise the elastic and plastic anisotropy of the weld metal. Measurements indicate a significant variation between the Young's modulus for the two materials, with values close to 210 GPa for the singlepass weld metal and 90-130 GPa for the multi-pass welds. These results are explained in terms of the texture of the welds.

Abstract: A novel procedure, based on the Resonant Beam Technique, and its application to anisotropic composites is presented. The evaluation of the elastic modules of anisotropic materials from the measurement of the transverse eigenfrequency spectra of resonant beams is performed by a two step process: firstly the beams cut out from the test material in different directions are evaluated in-dependently of each other under the assumption, that they are isotropic, solving Timoshenko´s equations using an isotropic correction factor for shear. Secondly the beams are evaluated together as representatives of one anisotropic material, using an anisotropic correction factor for shear. The equipment, developed for such measurements is presented. Finally, the procedure is applied to a transversely isotropic carbon fibre-reinforced carbon composite and the relevance of the results is discussed.