Work Hardening Of Metals Research Articles

Attractive dislocation intersections and work hardening in metals

The behaviour of two intersecting dislocations in a stressed crystal is discussed in relation to the problem of work hardening. It is assumed that the crystal is elastically isotropic and the effects of changing the applied stress and the Burgers vectors of the dislocations are examined in detail. Quantitative estimates of the yield stress as a function of the dislocation distribution are made and compared with experimental results. It is deduced, qualitatively, that the mechanism is probably an important factor in describing the temperature dependance of the flow stress, the orientation dependence of work hardening, the Bauschinger effect and the formation of cell walls.

The effect of work-hardening on the mechanics of cutting in simulated abrasive processes

The mechanics of abrasive cutting, derived from a force analysis at the abrasive particle/workpiece interface for lead workpieces, has been extended to include fully work-hardened metals and alloys. The results obtained using annealed materials are also discussed. It is shown that the critical attack angle of the cutting face at which a chip is first cut is determined primarily by the coefficient of friction between the contacting surfaces, whilst the increase in the force opposing the motion of an abrasive particle due to prior deformation of the workpiece is primarily due to the increase in hardness.

Variation of steel properties during hardness tests by ball indentation

1. A departure from geometric similarity, associated with the variation of the ball's angle of impression with increasing load, leads to a drop in the numerical hardness value, while a departure from structural similarity (work hardening of metal) causes the hardness to increase. 2. In metals not responsive to cold working the hardness value at the initial moment may remain unchanged, or it may even decline, but ultimately the effect of cold work is greater than that of the geometric factor, and the numerical hardness value increases as greater loads are applied to the ball. 3. With increasing load on the ball, the hardness of the ductile metals increases more rapidly and becomes higher than the hardness value of a number of harder metals. The difference in the hardness of steels diminishes as the load applied to the ball continues to increase. 4. The tendency of the soft steels to work harden in the process of testing is higher, and in order of their susceptibility to cold working the investigated metals range in a succession inversely propertional to their hardness value.

Deformation twinning in face-centred cubic metals

Abstract The principal features of the experimental results of Blewitt et al. (1957) and of Suzuki and Barrett (1958) on deformation twinning in face-centred cubic metals are explained in terms of an extension of the ‘prismatic’ source mechanism of Cottrell and Bilby (1951). Suitable prismatic dislocation sources are thought to be long jogs in the dislocations of the two conjugate slip systems in a work-hardened metal and prismatic dislocation loops produced by vacancy condensation in a neutron-irradiated metal. The dissociation of slip dislocations is also considered and is found to be an unlikely mechanism for the production of deformation twins in copper, silver or gold.

Work hardening of metals

Work hardening of metals

The coefficient of friction of metals

To explain the increase in the area of contact, and hence in the adhesion, of a steel ball sliding on indium, McFarlane and Tabor produced an analysis based on the interaction of the normal and tangential stresses applied during sliding. In their work, McFarlane and Tabor showed experimentally that in the load range 0–100 g the coefficient of friction of a 1 8 ′' steel ball sliding on indium is strongly dependent on the load, the coefficient of friction reaching very high values at light loads. In the present work, their analysis is shown to apply only to a fully work-hardened metal and experimental evidence is given which shows that indium work-hardens in the range of strains set up when a flat indium surface is indented by a 1 8 ′' steel ball with loads up to 100 g. Using the empirically determined relation between load and area of indentation and adopting a similar treatment to that of McFarlane and Tabor, the experimentally observed friction-load behaviour of indium is explained in terms of the incomplete work-hardening of the contact region material when relative motion of the surfaces begins. The treatment is extended to the case of a fully work-hardened metal, when it is shown that the coefficient of friction becomes independent of the load, and criteria for the occurrence of slip and of seizure are obtained. Finally, the argument is extended to give a qualitative explanation of the breakdown of Amontons's law with harder metals in the presence of thin film lubrication.

Anisotoropy Produced by Plastic Deformation (Part 1)

From the experimental facts reported in Part 1, the author anticipated that if the metals previously over-strained by shear in one direction are tested by shear in various directions, some properties of anisotropy produced by plastic deformation will be more evident than the results of the experiments in Part 1. When a thin-walled tube is subjected to the combined loading of external hydraulic pressure and axial tension, if the absolute value of circumferential stress equals to axial stress, the tube is under the pure shear in the direction of 45 degrees to its axis. Using this stress-condition and the stress-condition of torsion the author tested the anisotropic properties for shear of the metals over-strained by shear. The results of these tests confirmed the author's anticipation, and made his idea as to anisotropy of work-hardened metals more reliable.

Anisotoropy Produced by Plastic Deformation (Part 2)

From the experimental facts reported in Part 1, the author anticipated that if the metals previously over-strained by shear in one direction are tested by shear in various directions, some properties of anisotropy produced by plastic deformation will be more evident than the results of the experiments in Part 1. When a thin-walled tube is subjected to the combined loading of external hydraulic pressure and axial tension, if the absolute value of circumferential stress equals to axial stress, the tube is under the pure shear in the direction of 45 degrees to its axis. Using this stress-condition and the stress-condition of torsion the author tested the anisotropic properties for shear of the metals over-strained by shear. The results of these tests confirmed the author's anticipation, and made his idea as to anisotropy of work-hardened metals more reliable.

Die pressure in plane strain drawing: Comparison of experiment with theory†

The problem of drawing the ideal solid of the mathematical theory of plasticity through a wedgeshaped die in plane strain has been solved by Hill and Tupper. and by Green. Different solutions have been proposed earlier, by Sachs and others, based on a more elementary theory of plastic deformation. Cook and Wistreich have measured the pressure on the die fare during the plane-strain drawing of solder. In this paper, Cook and Wistreich's measurements and those obtained in two further experiments are interpreted in terms of the Sachs and Hill theories. The Sachs theory is rejected. Significant similarities are found between the experimental and theoretical patterns of pressure according to the other authors mentioned above. It seems likely that patterns of deformation characteristic of the ideal solid are substantially preserved in a work-hardening metal. The quantitative comparison of mean die pressures is inconclusive on account of short-comings of the experimental data. In particular, the question of the validity or otherwise of Hill and Tupper's correction for work-hardening remains open.

On the Plastic Deformation of Copper Single Crystals. Part 1. Two Stages in the Progress of Deformation

The stress-strain curves of copper single crystals have been obtained at room temperature. When the resolved shear strain reaches about 20 percent, the stress increases rather rapidly with increasing strain and thus the progress of deformation is found to be made of two stages. This change in the nature of work-hardening may be explained from the view of the presence of two types of strains inside work-hardened metals that has been discussed in the previous paper (J. Phys. Soc. Japan 6 (1951) 90). If this view is correct, the number of stopped dislocations is expected to show rapid increase in the second stage of deformation.

Workhardening of metals—a general theory

Workhardening of metals—a general theory