$($a$)$ Describe how imperfections in metal structures give rise to plastic deformation.

Your answer should include $1)$ detail on the relevant defect $/$ imperfection,

$2)$ description of $$slip$$ and $$plastic deformation$,$ and $3)$ a discussion of how the

application of stress impacts atomic motion, in comparison to a defect free system.

$6$ marks

$($b$)$ Calculate if a single crystal metal sample will yield when stressed at $80$ MPa in

tension, if the angle normal to the slip plane and the angle of slip direction are at

$44\backslash$deg and $56\backslash$deg to the tensile axis, respectively. If not, what stress is required to

reach the yield point? Consider the critical resolved shear stress to be $0\mathrm{.}040$ GPa.

Given:

$\backslash$tau R $=\backslash$sigma cos $\backslash$lambda cos$\backslash$phi $\backslash$tau R $=$ Resolved sheer stress $\backslash$sigma $=$ Tensile stress

$5$ marks

$($c$)$ Using the micrographs below, taken $$before$$ and $$after$$ processing a steel

sample, describe the grain structure within each image. State the process used

and predict how the mechanical properties will have been influenced by the

process.