$3.$ When a hot ceramic pot is suddenly submerged in very cold water, which part, surface or interior, will be under tensile stress? why? $(2$ pts$)$

$4.$ Astone column is subject to compressive load. What will be the two possible failure modes for the column? $(2$pts$)$

$5.$ Very briefly explain what are principal plane, principal direction and principal stress. $(2$pts$)$

$6.$ When a chalk is under pure torsion, which criterion you are going to use to predict its failure? How will the breaking$/$fracturing surface look like? $(2$pts$)$

$7.$ What are the two yield criteria we discussed in the class? If you break an aluminum rod by torsion, how the final breaking surface looks like? $(3$pts$)$