(Multiple choice) Which one of the following statements is true? EXPLAIN ANSWER

Question

(Multiple choice)

             Which one of the following statements is true? EXPLAIN ANSWER

             (a) The length of dislocation line per unit volume in a material equals the number of dislocations per unit area.

             (b) Metals are hardened by cold working because many of the dislocations have passed right through the grains and are no longer available to facilitate slip.

             (c)   Plastic deformation of a polycrystalline metal does not increase the density of the metal.

             (d) To avoid breaking a material when it is being cold worked, it is sufficient to perform the cold work in compression.

             (e)   To avoid breaking a material when it is being cold worked, it is necessary to perform the cold work in compression.

Explanation / Answer

a) TRUE ( both give dislocation density)

b) FALSE (Cold working or work hardening generates many dislocations which pile up and entangle this will prevent the further movement of dislocations)

c) False (Plastic deformation increases the dislocation density(single and polycrystalline materials) and changes
grain size distributions (polycrystalline materials).

d) False

e) False

Reason for d) and e) to be false are

cold working is done by shaping the workpiece at a temperature below its recrystallization temperature, usually at the ambient temperature.

Cold forming techniques are usually classified into four major groups: squeezing, bending, drawing, and shearing

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