Degree Of Work Hardening Research Articles

Isochronal recovery of work hardening in aluminium-alumina alloys

The isochronal recovery of work hardening in Al-Al 2O 3 SAP type alloys has been studied by combining several techniques, mainly electrical resistivity and metallographic observations. The effects of the oxide content on the amount of defects produced by cold work and on the way they anneal out have been observed. The influence of impurities has also been considered. It is noticed that work-hardening gives rise to a high lattice strain increasing with oxide content and depending on particle spacing too. Annealing takes place in stages. The last corresponds to recrystallization and is preceded by a recovery process giving rise to polygonization and growth of the grains. This is characterized by the presence of substages: three peaks are observed in less pure alloys, a single peak, centered at ≈ 200° C, in the samples prepared from pure aluminium. This substage seems connected with annealing of vacancies. For a given degree of work-hardening, recrystallization takes place at temperatures rapidly rising with the oxide content. Probably this behaviour results from competition between recovery and recrystallization increasing with the dispersed phase.

Effect of Yield on the Interference between a Pin and a Plate

The optically sensitive coating technique is used to determine the post-elastic behaviour of a large plate with an interference fit pin. An aluminium alloy exhibiting a small degree of work-hardening was chosen and this is thought to be similar in behaviour to a lightly cold-worked mild steel. Theoretical analysis of an idealized material indicates that work-hardening has a significant effect on the spread of plastic regions.

Correlation between fatigue limit, ultimate strength and other mechanical characteristics of steels and alloys

1. The fatigue limit σ−1 correlates more closely with the ultimate strength than with other strength characteristic 2. In a number of very important cases (variation in temperature of the medium, tempering temperature, degree of work hardening, etc.) there is a linear relationship between σ−1 and σb. Evaluation of σ−1 on the basis of this realationship leads to fever than when assuming the ratio σ−1]σb to be constant, or when using the Striebeck, Maylinder, Junger and Zhukov equations. 3. If there is an abnormal relationship between σb and temperature, degree of work hardening, aging or variation in the direction of cut of the specimens, there is no correlation between σ−1 and σb.

Thermal Stresses in an Elastic, Work-Hardening Sphere

In this paper, a method is presented for obtaining the transient thermal-stress distribution and the residual stresses in a spherical body where the time-dependent temperature distribution is symmetrical with respect to the center of the sphere. The material is assumed to be elastoplastic, while in the plastic range it work-hardens isotropically. The von Mises yield condition is used. The thermal and mechanical properties of the material are assumed to be temperature independent. The problem is reduced to a single nonlinear differential equation which is solved numerically on the NCR 304 digital computer. Several sets of numerical data representing various degrees of work-hardening in the spherical bodies during a cooling process are presented.

Hardness Plateaus and Twinning in Explosively Loaded Mild Steel

Hardness measurements were made along radii of circular cross sections of an annealed thick-walled low-carbon steel cylinder internally loaded with an explosive charge. The degree of work-hardening in the cylinder wall was found to decrease nonuniformly with an increase in distance from the surface in contact with the explosive. Each hardness versus distance curve exhibited a series of plateaus along which the hardness remained constant. The plateaus appear to be related to Neumann bands which are present in the steel. The maximum number of twin directions in a single grain increases with the magnitude of the stress. The presence of the hardness plateaus and the increase in the number of twin directions with hardness and stress level point to the existence of critical stresses for twinning.

Effect of Surface Condition on Creep of Some Commercial Metals

Abstract The relative creep rate of specimens of 2S aluminum and commercial drawn copper were investigated with the oxide surface layers removed and then, under the same conditions, after the oxide was permitted to form. The oxide was removed mechanically by stripping the test specimens in an inert atmosphere furnace so equipped that an axial stress could be applied and the creep rate determined without disturbing the atmosphere. After the oxide-free specimen was observed to be creeping essentially linearly with time (i.e., the quasiviscous, secondary creep range was established), air was admitted to the furnace. The extension versus time plot was continued after admission of air and the temperature held constant. Since all of the known parameters affecting creep rate (temperature, grain size, degree of work hardening, stress, and so on) except the gaseous environment were the same before and after admitting air, the effect of this change could be isolated. A decrease in creep rate was observed after air had been admitted to the furnace. These experimental results indicate that the presence of an oxide surface layer on the commercial grades of pure copper and aluminum increases the creep strength of these metals. The manner in which this relatively thin surface layer contributes to the strength of the parent metal is not clear, but the phenomenon is consistent with the theory of dislocations as presented by G. I. Taylor if it is assumed that the oxide inhibits the generation and/or migration of dislocations.