b)What is the structure of lower bainite,how is it formed,and what properties does it produce in a steel? 41 a)What is the Considerate condition for instability in a tensile test? b)Define the Schmidt Factor for resolved shear stress. 42 Describe four methods for increasing the flow stress of metals.In each case, discuss the reasons for the rise in the flow stress. 43.Identically oriented monocrystalline specimens of Cu,Al and Fe are extended in tension at room temperature at a strain rate of 10sec".Sketch possible stress-strain curves,noting carefully any differences among them,and explain the curves you sketch 44 Define (or give an expression for)and explain the following: a.Von Mises criterion for deformation of an arbitrary grain in a polycrystal. b.Resolved shear stress for an arbitrary slip system in a crystal strained in simple tension. c.Relation between tensile strength and tensile strain for a case o=0,other stresses zero,eyw=0,shear strain=-O,ea≠0，E=≠0 d.Mohr circle 45.(a)What is the Portevin-LeShatelier effect and what is the mechanism causing it? (b)Why does an aluminum-copper alloy aged to contain O precipitate have a lower ductility than one aged to contain G-P I zones? (c)What is the influence of grain boundaries on plastic flow?Why does it differ in aluminum and copper? 46 Discuss the phenomena which can lead to serrated stress curves in a tensile test. 47 a)Discuss in detail the process of intersection of two like-sign,perpendicular dislocations.What influence does this process have on metal deformation at high temperature?At low temperature?On recovery processes? b)What is at stacking fault tetrahedron,how does it form,and what effect does it have on mechanical properties? 48. The age hardening of Cu-2%Be alloys develops an exceptionally large increase in yield strength over that of pure copper.As overaging occurs a very fine pearlitic structure develops along the grain boundaries and grow into the grains transforming them to a new structure.b) What is the structure of lower bainite, how is it formed, and what properties does it produce in a steel? 41 a) What is the Considerate condition for instability in a tensile test? b) Define the Schmidt Factor for resolved shear stress. 42 Describe four methods for increasing the flow stress of metals. In each case, discuss the reasons for the rise in the flow stress. 43. Identically oriented monocrystalline specimens of Cu, Al and Fe are extended in tension at room temperature at a strain rate of 10-4sec-1. Sketch possible stress-strain curves, noting carefully any differences among them, and explain the curves you sketch 44 Define (or give an expression for) and explain the following: a. Von Mises criterion for deformation of an arbitrary grain in a polycrystal. b. Resolved shear stress for an arbitrary slip system in a crystal strained in simple tension. c. Relation between tensile strength and tensile strain for a case 0 σ xx = , other stresses zero, , shear strain=0, 0, 0 xx zz ε yy = 0 ε ≠ ε ≠ d. Mohr circle 45. (a) What is the Portevin-LeShatelier effect and what is the mechanism causing it? (b) Why does an aluminum-copper alloy aged to contain O precipitate have a lower ductility than one aged to contain G-P I zones? (c) What is the influence of grain boundaries on plastic flow? Why does it differ in aluminum and copper? 46 Discuss the phenomena which can lead to serrated stress curves in a tensile test. 47 a) Discuss in detail the process of intersection of two like-sign, perpendicular dislocations. What influence does this process have on metal deformation at high temperature? At low temperature? On recovery processes? b) What is at stacking fault tetrahedron, how does it form, and what effect does it have on mechanical properties? 48. The age hardening of Cu-2% Be alloys develops an exceptionally large increase in yield strength over that of pure copper. As overaging occurs a very fine pearlitic structure develops along the grain boundaries and grow into the grains transforming them to a new structure