8-8 Define the terms: strain-hardening expo- nent (n) and strain-rate sensitivity (m). Use appropriate equations. 8-9 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?

Question-7. Steady-state creep data taken for an alloy at a stress level of 160 MPa are given below. The stress exponent n for the alloy is 6.8. R is 8.3145 J/mol-K. Compute the steady-state creep rate at 1000 °C and a stress level of 68 MPa. Es (h-1) 6.8 × 10-5 T (°C) 800 8.6 x 10-3 900

296 8-10 A 0.505-in.-diameter metal bar with a 2-in. gage length o is subjected to a tensile test. The following measurements are made in the plastic region: 8-13 Chapter 8 Strain Hardening and Annealing Figure 8-23 shows a plot of the natural log- arithm of the true stress versus the natural logarithm of the true strain for a Cu-30% Zn sample tested in tension. Only the plastic portion of the stress strain curve is shown. Determine the strength coefficient K and the work-hardening exponent n. Change in Force Gage length Diameter (lb) (in.) (Al) (in.) 21 27,500 0.2103 0.4800 27,000 0.4428 0.4566 20 25,700 0.6997 0.4343 8-11 Determine the strain-hardening exponent for the metal. Is the metal most likely to be FCC, BCC, or HCP? Explain. A 1.33-cm-diameter metal bar with a 3-cm gage length (10) is subjected to a ten- sile test. The following measurements are made in the plastic region: In [True stress (Pa)] 18 16 -2.5 -2.0 -1.5 -1.0 -0.5 -0.0 In (True strain) Figure 8-23 The natural…

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