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Unformatted text preview: Bonus Homework Assignment 5 points Metal Forming 18.11 A tensile test is carried out to determine the strength constant C and strain -rate sensitivity exponent m for a certain metal at 1000 F. At a strain rate = 10/sec, the stress is measured at 23,000 lb/in 2 ; and at a strain rate = 300/sec, the stress = 45,000 lb/in 2 . (a) Determine C and m . (b) If the temperature were 900 F, what changes would you expect in the values of C and m ? Solution : (a) Two equations: (1) 23,000 = C (10) m and (2) 45,000 = C (300) m 45,000/23,000 = 1.9565 = (300/10) m = (30) m ln 1.9656 = m ln 30 0.67117 = 3.4012 m m = 0.1973 (1) C = 23000/10 0.1973 = 23000/1.5752 = 14,601.4 (2) C = 45000/300 0.1973 = 45000/3.0819 = 14,601.4 C = 14,601.4 (b) If temperature were decreased to 900 F, the strength constant C would increase and the strain-rate sensitivity exponent m would decrease. 18.13 A workpart with starting height h = 100 mm is compressed to a final height of 50 mm. During the deformation, the relative speed of the plattens compressing the part = 200 mm/s. Determine the strain rate at (a) h = 100 mm, (b) h = 75 mm, and (c) h = 51 mm. Solution : (a) strain rate = 200/100 = 2.0 s-1 (b) strain rate = 200/75 = 2.667 s-1 (c) strain rate = 200/51 = 3.922 s-1 Bulk Deformation 19.20 A hydraulic forging press is capable of exerting a maximum force = 1,000,000 N. A cylindrical workpart is to be cold upset forged. The starting part has diameter = 30 mm and height = 30 mm. The flow curve of the metal is defined by K = 400 MPa and n = 0.2. Determine the maximum reduction in height to which the part can be compressed with this forging press, if the coefficient of friction = 0.1. Use of a spreadsheet with this forging press, if the coefficient of friction = 0....
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- Fall '08