True or false that the higher the fracture toughness, $$K_C$$  , of a material the less resistance it is to crack propagation.

This is a piece salvaged from the John Thompson pressure vessel failure in 1965. Where do you think is the initiation on the crack?

Steel is the most commonly used metal that shows ductile-to-brittle transition behaviour. Austenitic stainless steels are not generally thought to undergo ductile-to-brittle transitions. Why?

The fracture mode of shaded area is different than the rest. What mode of fracture is this? How can you tell?

Metal A and Metal B both having fracture toughness of $$10\ MPa\ m^{0.5}$$  and $$22\ MPa\ m^{0.5}$$   respectively. If both contain an inside sharp crack with size of $$2a\ =\ 2mm$$  . Which one will propagate when stress of $$175\ MPa$$  is imposed.

A crack having stress intensity factor $$K=\sigma\ \sqrt[]{\pi a}$$  will have which geometry?