Section 8-1 Relationship of Cold Working to the Stress Strain Curve 8-1 8-2 8-3 8-4 8-5 8-6 Using a stress strain diagram, explain what the term "strain hardening" means. What is meant by the term "springback"? What is the significance of this term from a manufacturing viewpoint? What does the term "Bauschinger effect" mean? What manufacturing techniques make use of the cold-working process? What is the difference between extrusion and drawing? Consider the tensile stress strain curves in Figure 8-20 labeled 1 and 2 and answer the following questions. These curves are typical of metals. Consider each part as a separate question that has no relationship to previous parts of the question. 2 True stress (MPa) 8-7 600 500 400 300 200 (c) Assume that the two stress strain curves represent successive tests of the same sample. The sample was loaded, then unloaded before necking began, and then the sample was reloaded. Which sample represents the first test: 1 or 2? How do you know? Figure 8-21 is a plot of true stress versus true strain for a metal. For total imposed strains of = 0.1, 0.2, 0.3 and 0.4, determine the elastic and plastic components of the strain. The modulus of elasticity of the metal is 100 GPa. Stress 100 0 0 0.1 0.2 0.3 0.4 0.5 True strain Strain Figure 8-20 Stress strain curves (for Problem 8-6). (a) Which material has the larger work- hardening exponent? How do you know? (b) Samples 1 and 2 are identical except that they were tested at different strain rates. Which sample was tested at the higher strain rate? How do you know? Figure 8-21 A true stress versus true strain curve for a metal (for Problem 8-7). 8-8 8-9 Define the terms: strain-hardening expo- nent (n) and strain-rate sensitivity (m). Use appropriate equations. An annealed copper sample experiences a true strain of 0.07 caused by a true stress of 164 MPa. If this is in the plastic deformation region and the strain- hardening exponent is 0.44, what is the strength coefficient?