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  • Print publication year: 2008
  • Online publication date: June 2012

Chapter 3 - Plasticity

Summary

Introduction

Upon being mechanically stressed, a material will, in general, exhibit the following sequence of responses: elastic deformation, plastic deformation, and fracture. This chapter addresses the second response: plastic deformation. A sound knowledge of plasticity is of great importance for the following reasons.

Many projects are executed in which small plastic deformations of the structure are accepted. The “theory of limit design” is used in applications where the weight factor is critical, such as space vehicles and rockets. The rationale for accepting a limited plastic deformation is that the material will work-harden at that region, and plastic deformation will cease once the flow stress (due to work-hardening) reaches the applied stress.

It is very important to know the stresses and strains involved in deformation processing, such as rolling, forging, extrusion, drawing, and so on. All these processes involve substantial plastic deformation, and the response of the material will depend on its plastic behavior during the processes. The application of plasticity theory to such processes is presented later in this chapter.

The mechanism of fracture can involve plastic deformation at the tip of a crack. The way in which the high stresses that develop at the crack can be accommodated by the surrounding material is of utmost importance in the propagation of the crack. A material in which plastic deformation can take place at the crack is “tough,” while one in which there is no such deformation is “brittle.”

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Suggested reading
Plasticity
Gordon, J. E., The New Science of Strong Materials, or Why You Don't Fall Through the Floor. Princeton, NJ: Princeton University Press, 1976.
Popov, E. P., Engineering Mechanics of Solids. Englewood Cliffs, NJ: Prentice Hall, 1990.
Roylance, D., Mechanics of Materials. New York, NY: J. Wiley, 1996.
Wachtman, J. B., Mechanical Properties of Ceramics. New York, NY: J. Wiley, 1996.
Wagoner, R. H. and Chenot, J. L., Fundamentals of Metal Forming. New York, NY: J. Wiley, 1996.
Hardness
Boyer, H. E., ed. Hardness Testing. Metals Park, OH: ASM Intl., 1987. Metals Handbook, Vol. 8: Mechanical Testing. Metals Park, OH: ASM Int., 1985.
Fischer-Cripps, A. C., Nanoindentation. New York, NY: Springer, 2002.
M. C. Shaw, Mechanical Behavior of Materials. McClintock, F. A. and Argon, A. S., eds. Reading, MA: Addison-Wesley, 1966, p. 443.
Tabor, D., The Hardness of Metals. London: Oxford University Press, 1951.
Westbrook, J. H. and Conrad, H., eds., The Science of Hardness Testing and Its Research Applications. Metals Park, OH: ASM Intl., 1973.
Formability
Brazier, W., Closed Loop (MTS Journal), 15, No. 1 (1986) 3.
Chan, K. S., J. Met., Feb. (1990) 6.
Hecker, S. S., in Constitutive Equations in Viscoplasticity: Computational and Engineering Aspects. New York, NY: ASME, 1976, p. 1.
Hecker, S. S. and Ghosh, A. K., Sci. Am., Nov. (1976), 100.
Hecker, S. S., Ghosh, A. K., and Gegel, H. L., eds. Formability: Analysis, Modeling, and Experimentation. New York, NY: TMS-AIME, 1978.
Hosford, W. F. and Caddell, R. M., Metal Forming—Mechanics and Metallurgy. Englewood Cliffs, NJ: Prentice-Hall, 1983.