dislocations and work hardening, Exercises of Materials science

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(1) Explain stress and strain; (2) Explain Young’s modulus and Poisson’s ratio; (3) Explain storage modulus and loss modulus; (4) The following are given for tantalum: ci = 267 GPa c44 = 82.5 GPa C12 = 161 GPa Determine the Young's moduli in the directions [100], [110], and [111] after calculating the elastic compliances. (1) Explain plasticity and yielding; (2) Explain von Mises yielding criterion; (3) Explain hardness and its relation with yielding strength; (4) Explain ultimate tensile strength, necking and ductility (1) A polycrystalline metal has a plastic stress-strain curve that obeys Hollomon’s equation, o= Ke" Determine n, knowing that the flow stresses of this material at 2% and 10% plastic deformation (offset) are equal lo 175 and 185 MPa, respectively. (2) You are traveling in an airplane. The engineer who designed it is, casually, on your side. | le tells you that the wings were designed using the von Mises criterion. Would you feel safer if he had told you that the Tresca criterion had been used? Why? Consider dislocations blocked in gold. |f the flow stress is controlled by the stress necessary to operate a Frank--Read source, compute the dislocation density ? in the crystal when it is deformed to a point where the resolved shear stress on the slip plane is 45 MPa. Take the shear modulus C! = 27 GPa.