10. Two previously undeformed specimens of the same metal are to be plastically deformed by reducing their cross-sectional areas. One has a circular cross section, and the other is rectangular; during deformation the circular cross section is to remain circular, and the rectangular is to remain as such. Their original and deformed dimensions are as follows: Original dimensions Deformed dimensions Circular (diameter, mm) 15.4 12.1 Rectangular (mm) 129 x 175 75 x 164 Which of these specimens will be the hardest after plastic deformation?

Question-8. . A cylindrical metal specimen with a diameter of 16 mm and length of 88 mm is to be subjected to a tensile stress of 80 MPa; at this stress the resulting deformation is elastic. (a) If the elongation is less than 0.058 mm, which of the metals in the table can be considered as candidates? Why ? (b) If the maximum permissible diameter decrease is 0.0012 mm when the tensile stress of 68 MPa is applied, which of the metals satisfy the criterion in question (a) are the suitable candidates? Why ? Metal Shear Modulus / GPa Modulus of Elasticity / GPa 69 Poisson's Ratio Al 25 0.33 Cu 110 46 0.34 Mg 45 17 0.29 Ni 207 76 0.31 Ti 107 6.5 0.34 W 407 23.2 0.28

At operating stress of 420MPa, the number of cycles to fail a specimen is 65 cycles. At operating stress of 360MPa, the number of cycles to fail the specimen is 390 cycles, and at operating stress of 130MPa, the number of cycles to fail the specimen is 11,900 cycles. A test sequence as follows is designed: first, operating stress of 420MPa for 7 cycles, second, operating stress of 360MPa for 65 cycles, and third, operating stress of 130MPa for 325 cycles. Determine at what number of cycle and which operating stress level the specimen would be expected to fail if the above sequence is repeated.

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