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In a deforming object, different states of stress would exist depending on the loading conditions and boundary constraints. This chapter begins with a section on yield criterion, discussing two major yield criteria that have been used extensively in the analysis of metal forming and forging: Tresca or shear stress criterion of yield or plastic flow and von Mises or distortion energy criterion of yield or plastic flow. The relation between the stresses and strain rates is then provided, followed by a discussion of flow rules that guide the flow of stresses at a given point in a metal. The chapter also provides information on transformation of power and energy of plastic deformation processes. It ends by showing how to calculate effective strain and effective strain rates.

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Gracious Ngaile, Plastic Deformation: Complex State of Stress and Flow Rules, Cold and Hot Forging: Fundamentals and Applications, Edited By Taylan Altan, Gracious Ngaile, Gangshu Shen, ASM International, 2005, p 51–57,

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