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HW4 Sol

# HW4 Sol - UCLA MAE 183 HW#4 Solutions Fall 2010 Review Q...

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1 UCLA MAE 183 HW#4 Solutions – Fall 2010 Review Q 18.6: How does increasing temperature affect the parameters in the flow curve equation? Answer . Increasing temperature decreases both K and n in the flow curve equation. Review Q 18.7: Indicate some of the advantages of cold working relative to warm and hot working. Answer . Advantages of cold working are (1) better accuracy, (2) better surface finish, (3) increased strength due to work hardening, (4) possible directional properties due to grain flow, and (5) no heating of work required. Review Q 18.10: Why is friction generally undesirable in metal forming operations? Answer . Reasons why friction is undesirable in metal forming include the following: (1) it inhibits metal flow during deformation, causing residual stresses and product defects; (2) it increases forces and power required; and (3) it increases wearing of the tools. Multiple Choice Q 18.5: Hot working of metals refers to which one of the following temperature regions relative to the melting point of the given metal on an absolute temperature scale: (a) room temperature, (b) 0.2 T m , (c) 0.4 T m , or (d) 0.6 T m ? Answer . (d). Prob. 18.2: A metal has a flow curve with parameters: strength coefficient = 850 MPa and strain- hardening exponent = 0.30. A tensile specimen of the metal with gage length = 100 mm is stretched to a length = 157 mm. Determine the flow stress at the new length and the average flow stress that the metal has been subjected to during the deformation. Solution : ε = ln (157/100) = ln 1.57 = 0.451 Flow stress Y f = 850(0.451) 0.30 = 669.4 MPa Average flow stress = 850(0.451) 0.30 /1.30 = 514.9 MPa. Prob. 18.6: For a certain metal, the strength coefficient = 700 MPa and strain-hardening exponent = 0.27. Determine the average flow stress that the metal experiences if it is subjected to a stress that is equal to its strength coefficient K . Solution: Y f = K = 700 = K n = 700 0. 27 must be equal to 1.0. = 700(1.0) .27 /1.27 = 700/1.27 = 551.2 MPa Review Q 19.2: Name the four basic bulk deformation processes. Answer

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HW4 Sol - UCLA MAE 183 HW#4 Solutions Fall 2010 Review Q...

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