A bar 200 mm long and having a square cross section 15 mm on an edge
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A bar 200 mm long and having a square cross section 15 mm on an edge

(a) A bar 200 mm long and having a square cross section 15 mm on an edge is pulled in tension with a load of 98,000 N and experiences an elongation of 0.10 mm. Assuming that the deformation is entirely linear elastic, calculate the elastic modulus.

(b) If a metal sample has oy = 148 MPa; 0o = 28 MPa; and Ky = 0.55 MPa m1/2,calculate:

(i) the average grain diameter

(ii) the yield strength of a sample with half the average grain diameter

(c) A sheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200°C and is permitted to achieve a steady-state diffusion condition. The diffusion coefficient for nitrogen in steel at this temperature is 6x10-11 m/s, and the diffusion flux is found to be 1.2x10-7 kg/m2.s. Also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m3. How far into the sheet from this high-pressure side will the concentration be 2.0 kg/m3?

(d) Rank the following materials, gold, polyethylene and alumina in order of increasing thermal conductivity. Justify your answer.

Hint
EngineeringThermal conductivity can be defined as the rate at which heat is transported by conduction through that area. The number of Watts conducted per metre of material thickness per degree of temperature differential between one side and the other (W/mK) is the thermal conductivity of a material. The lower the thermal conductivity, the better, because the material will conduct less heat energ...

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