a$)$ Distinguish between low$-$cycle and high$-$cycle fatigue.

$[4$ marks$]$

b$)$ Describe and explain the features you would expect to see on the fracture surface of a metallic rod that has failed by fatigue.

$(6$ marks$)$

c$)$ A group of components have a fatigue life $(N_f)$ of $20{10}^3$ cycles at $+-414$MPa and $1{10}^6$ cycles at $+-276$MPa and the $S-N_f$ relation can be considered a straight line between these two points. A component was subjected to $20{10}^3$ cycles at $+-360$ MPa and then $30{10}^3$ cycles at $+-380$MPa. Estimate the number of cycles to failure if it was further subjected to a stress of $+-310$MPa.

$(10$ Marks$)$

$[$Total $20$ marks$]$