Masanobu Ohmori

Effect of strain rate on Lüders band propagating velocity and Lüders strain for annealed mild steel under uniaxial tension

For annealed mild steel that exhibits yield-point phenomena under uniaxial tension, physical equations expressing the strain-rate dependencies of the strain and the Luders-band velocity have been proposed in this work. In these expressions, both the Luders strain and the Luders-band velocity increase with gauge-length strain rate in the form of exponent functions. The proposed equations have been verified by our experimental data of uniaxial tension on mild steels, as well as by those reported by some other researchers. The proposed equations may provide a simple method to determine the stress-rate sensitivity exponent, in the equation of stress-dependent dislocation velocity, which is usually difficult to be measured by experiments.

Finite element simulation on the propagation of Lüders band and effect of stress concentration

Finite element method (FEM), using a viscoplastic constitutive model proposed by Yoshida [Int. J. Plasticity 16 (2000) 359], has been applied to simulate the propagation of Luders band for an annealed low-carbon steel strip under uniaxial tension test. By reducing the thickness of corresponding element, additional stress concentration is introduced into the FEM model. Calculated results show that the formation and propagation of Luders band are affected by the level of stress concentration existing at the ends of the specimen.

Improvement of mechanical properties of chromium-nickel sintered compacts by multiple rolling

Abstract The present paper provides details on the thermomechanical treatment of chromium–nickel alloys with high content of chromium, which leads to considerable improvement of their mechanical properties. The investigated alloys were prepared from Cr–Ni powder mixtures containing 50% and 80% of chromium in mass. They were formed by a particular sequence of cold and hot isostatic pressing. The as-sintered compacts were essentially brittle at room temperature, while they have exhibited considerable ductility after the special thermomechanical treatments. The treatment consisted of a sequence of repeated rolling and annealing operations, which is relatively simple and applicable in the industrial production. It is found that the treatments led to a more homogeneous, better alloyed structure and enhanced interdiffusion of the component metals.

The effect of shock pressure on the mechanical properties of some b.c.c. metals

Abstract This paper firstly presents the effect of carbon content (0.06–0.85 wt.%C) on the mechanical properties of steels exposed to weak shock pressure and the effect of grain size (9–80 μm) on the mechanical properties of 0.06 wt.%C steel with the shock pressure treatment. Secondly, the effect of shock pressure on the tensile properties including the ductile-to-brittle transition behavior for sintered chromium (99.8 mass% purity) is investigated. The experimental results confirm that the mechanical properties of some b.c.c. metals are markedly influenced by the shock pressure treatment.

Bendability of aluminiumand steel-clad chromium plates

The present paper describes how the cladding of chromium plate with dissimilar metals improves the plastic bendability of the chromium. Three-point bending tests at various temperatures were performed for three types of chromium specimens: a monolithic chromium plate, aluminium- and steel-clad chromium plate. The aluminium-clad chromium plate was bent at 343 K up to a bent angle of 90 degrees without failure, even when the chromium layer was located outside of the plate (tension side), while the monolithic chromium plate could be bent exclusively at temperatures above 403 K. When the chromium layer was located inside of the steel-clad chromium plate (compression side), the plate was successfully bent at 307 K. The FE stress analysis of bending proved that the cladding of chromium plates with proper metals of different kinds is effective to reduce the tensile stress in chromium induced during bending and also the residual stress existing after bending operation.

Mechanical properties of a low carbon steel shock loaded by an explosive.

焼きなました低炭素鋼に水中で爆薬による衝撃圧力psを与えたのちの応力-ひずみ挙動と延性-ぜい性遷移温度Tcを調べた.降伏応力σsはpsの増大とともに減少しps=1400MPaで最小(焼きなまし材のσsの62%)になった.時効特性からこの軟化は自由転移の形成によると考えられた.p>1400MPaではσsの減少量は少なくなるが,それは双晶の増加による.1400MPa衝撃圧力負荷材のTcは焼きなまし材より15K低く,σsの単位現象当りのTcの低下は0.21K/MPaであった.

Deformation Characteristics of Some Metals under Hydrostatic Pressure

Hereunder is presented a report of an experimental study in which tests were made, under hydrostatic pressure up to 3000kg/cm2, of three polycrystalline metals, mild steel, 70-30 brass and pure industrial aluminium, with respect both to their tension and torsion, with a view to finding the characteristics in their increase in ductility due to the pressure superimposed on them. Besides these tests a tension test of aluminium crystals of high purity was also carried out under various pressures. The main results of the study are summarized as follows.(1) The increase in ductility due to the superimposed pressure is meant, concerning the tensile deformation, by the increase not in uniform elongation but local elongation or in fracture strain, and, concerning the torsional deformation, by the increase in uniform shear strain, leading to the failure along the axis of the specimen.(2) When two specimens of one metal were subjected to incipient strain under certain pressure, to be more precise, when one of the specimens was subjected to as large strain as the other, but while the one was processed under atmospheric pressure, the other was processed under high hydrostatic pressure, and when the strain has since been kept on both the specimens under as high pressure as at the beginning until the failure has begun to occur, the larger residual strain has been being presented up to the failure in that specimen which was subjected to the incipient strain under high hydrostatic pressure, than in the other that was processed under atmospheric pressure. These different effects from each other given on the specimens can be considered as suggestive of their origin intrinsically impressed in the structure of these specimens which were differently affected incipiently from each other, i. e. one under atmospheric pressure and the other under hydrostatic pressure. It is noteworthy, on the other hand, however, that there is no such intrinsic difference effected on the specimens in evidence as has been suggested above in the microscopic examination which was conducted for comparative studies of dislocation cell structure of mild steel and of slip line patterns in single crystalline high purity aluminium. These metals were stretched or twisted, each under the respective kind of pressure either atmospheric or hydrostatic. Neither of the specimens presented any difference in the result of its treatment.(3) In mild steel its fracture strain increases to the failure due to tension under high hydrostatic pressure. In pure industrial aluminium its shear strain increases to the failure due to torsion under high hydrostatic pressure. It is noteworthy in this connection that the lower the speed of deformation in these metals drops, the higher the rate of increase in the strain in them rises, though it is not known yet how the phenomena are to be accounted for.