Yield strength of metals

All real metals contain dislocations even a well-annealed metal would typically contain 10 dislocations per square millimetre, while a heavily cold-worked metal could contain up to lO Vmm. At first sight this is an anomaly dislocations were postulated to account for the low yield strength of metals, and whereas an annealed material with a low dislocation density is weak, a cold-worked metal with a high dislocation density is strong. The answer lies in the fact that when the dislocation density is low, the dislocations are generally too far apart to interact with each other very often and are more free to move under the influence of a low applied stress. On the... 

Strength-weight ratio determined by dividing tensile yield strength of metals and ultimate tensile strength of nonmetallics by density. 

Cemented carbides possess high compressive strength but low ductihty at room temperature, but at temperatures associated with metal-cuttiag these materials exhibit a small but finite amouat of ductihty. Measuremeat of yield strength is therefore more appropriate at higher temperatures. Like hardness, the compressive yield strength of cemented carbide decreases monotonicaHy with increa sing temperatures. 

The level of stress may be, and generally is, much less than the yield strength of the metal. However, in general, higher stresses increase crack growth rate and the number of cracks initiated. 

In this chapter we show that k = Oy/2, and use k to relate the hardness to the yield strength of a solid. We then examine tensile instabilities which appear in the drawing of metals and polymers. 

Stecl a was quenched and tempered to a tensile, strength of 830 N/min and a yield strength of 670 N/inin, and steel b to 620 and 450 N/mm, respectively. It was considered that the maximum thickness of metal that could be welded onsite was 38 mm. 

Yield Strength of Candidate Metals. To avoid yield of the tank, the hoop stress must be less than the yield stress of the material used, Oy ... 

Below yield strength of the metal, coating of liquid metal has no effect whatsoever on the mechanical properties of the metal. 

A typical stress-strain diagram for a metal is shown in Fig. 11. This metal follows Hook s law up to a proportional limit ox yield strength) of 2 x 109 Pa. The elastic limit, above which the metal undergoes plastic deformation, which is not recoverable when the stress is removed, is close to the proportional limit. The maximum stress that the metal can support is the ultimate strength (or tensile strength) of the metal, which occurs at the maximum extension of the material. 

For this analysis, symmetrical parts have been considered Figure 7 shows the contour plot of Oy stress. As expected the Ni-rich layers at the surfaces are under compression and the Copper -rich layers in the central part under tension. The peak values varies between 100 and -100 MPa. From the contour plot of the plastic deformation shown in figure 10, we can see that all of them occur in the pure metal layers in both Ni and Cu. This is explained by the low yield strength of pure Cu and Ni which are soft metals as compared to the solid solutions hardened CuNi alloys. 

As the hquid metal in a weld solidihes, it becomes at least partially constrained by the surrounding parent metal. When the weld metal cools to ambient temperature, the resulting residual stress in the weld is approximately equal to the ambient temperature yield strength of the parent metal. Stress relief heat treatment for welds is called postweld heat treatment. An additional benefit of such treatment is a reduction of the hardnesses of the weld metal and heat-affected zone (HAZ), thns reducing the risk of stress corrosion cracking. 

---