the factors which determine the rate of sintering. 24.Show how a constitutive relation can be derived from a stress relaxation test.If the test is performed at elevated temperature (0.75 Tm),is it likely that one mechanism will be applicable for the entire test?Why or why not,and what mechanism(s)should apply? 25.Discuss the deformation pattern in a single grain of a polycrystal of a fcc metal being deformed in tension at strains of 0.001,0.01,0.1 and 0.5. 26.Draw a typical deformation map for a pure metal.Indicate how a change in strain rate influences one of the boundary lines in the creep region of the diagram. Present typical constitutive equations for each region of the diagram. 27.Discuss how a large decrease in stacking fault energy would influence the following at room temperature: (a)Stress strain curve for a single phase material. (b)Flow of a dispersion-hardened system. (c)A precipitation hardened system with the effect in the matrix. (d)As in(c)but with the effect in the precipitates. 28.Samples for elevated temperature tensile testing were all made from a single heat of an annealed single phase metal.These samples were tested under controlled true-strain-rate conditions,at three temperatures and three strain rates. In all cases,after a few percent strain,a well-defined,steady-state flow stress was observed.This flow stress as at each temperature and strain rate are shown below. Flow Stress (MPa) Temperature (C) Strain Rate 400 450 500 1E-4 20.3 14.6 11.0 5E-4 34.7 25.0 18.7 1E-3 43.7 31.4 23.6 Based on this data: (a)What is the activation energy for creep in this metal? (b)What can you infer to be the mechanism of deformation?Back up your statements and be as precise as possible. (c)What can you say about the metal based on this? (d)After each of the tests the samples are immediately quenched and examined.In the 450C,1E strain rate,test the dislocation density was measured at 1.0 x 10 cm.What do you expect the dislocation density will be at the same temperature at a strain rate of 1E3? 29.The six major types of porosity in castings are: 1.Macroshrinkage porositythe factors which determine the rate of sintering. 24. Show how a constitutive relation can be derived from a stress relaxation test. If the test is performed at elevated temperature (0.75 Tm), is it likely that one mechanism will be applicable for the entire test? Why or why not, and what mechanism(s) should apply? 25. Discuss the deformation pattern in a single grain of a polycrystal of a fcc metal being deformed in tension at strains of 0.001, 0.01, 0.1 and 0.5. 26. Draw a typical deformation map for a pure metal. Indicate how a change in strain rate influences one of the boundary lines in the creep region of the diagram. Present typical constitutive equations for each region of the diagram. 27. Discuss how a large decrease in stacking fault energy would influence the following at room temperature: (a) Stress strain curve for a single phase material. (b) Flow of a dispersion-hardened system. (c) A precipitation hardened system with the effect in the matrix. (d) As in (c) but with the effect in the precipitates. 28. Samples for elevated temperature tensile testing were all made from a single heat of an annealed single phase metal. These samples were tested under controlled true-strain-rate conditions, at three temperatures and three strain rates. In all cases, after a few percent strain, a well-defined, steady-state flow stress was observed. This flow stress as at each temperature and strain rate are shown below. Flow Stress (MPa) Temperature (°C) Strain Rate 400 450 500 1E-4 20.3 14.6 11.0 5E-4 34.7 25.0 18.7 1E-3 43.7 31.4 23.6 Based on this data: (a) What is the activation energy for creep in this metal? (b) What can you infer to be the mechanism of deformation? Back up your statements and be as precise as possible. (c) What can you say about the metal based on this? (d) After each of the tests the samples are immediately quenched and examined. In the 450°C, 1E-4 strain rate, test the dislocation density was measured at 1.0 x 107 cm -1. What do you expect the dislocation density will be at the same temperature at a strain rate of 1E-3? 29. The six major types of porosity in castings are: 1. Macroshrinkage porosity