00035___d5527b3b63f287dd3888976f41a82b83

00035___d5527b3b63f287dd3888976f41a82b83 - 1.4. PLASTICITY...

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14 INTRODUCTION Chap. 1 Frequency Fig. 1.3:2. A typical relaxation spectrum. (After C. M. Zener, Elasticity and Anelas- ticity of Metals, The University of Chicago Press, 1948.) oscillations of metal wires at various temperatures, reduced to room tem- perature according to certain thermodynamic formula, yield a typical “relaxation spectrum” as shown in Fig. 1.3.2. Many peaks are seen in the internal-friction-versus-frequency curve. It has been suggested that each peak should be regarded as representing an elementary process as de- scribed above, with a particular set of relaxation times T,, rE. Each set of relaxation times T,, T~ can be attributed to some process in the atomic or microscopic level. A detailed study of such a relaxation spectrum tells a great deal about the structures of metals; and the study of internal friction has provided a very effective key to metal physics.
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Unformatted text preview: 1.4. PLASTICITY Take a small steel rod. Bend it. When the deflection is small, the rod will spring back to its original shape when you release the load. This is elas- ticity. When the deflection is sufficiently large, a permanent deformation will remain when the load is released. That is plasticity. The load-deflection relationship of an ideal plastic material is shown in Fig. 1.4:1(a). For an ideal plastic material, the deflection is zero when the load is smaller than a critical value. Then, when the load reaches a critical value, the de- flection continues to increase (the material flows) as long as the same load remains. If, at a given deflection, the load becomes smaller than the criti- cal value, then the flow stops. There is no way the load can be increased beyond the critical value....
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