Which of the below statement are correct?

Which of the below statement are correct?
A.Impact test is a typical static testing method.
B.Toughness is a measure of a material’s resistance to brittle fracture when a crack is present.
C.A material’s tensile stress tends to gradually increase with the size of the crack increases.
D.Fracture toughness is used in design to find allowable flaw size.
正确答案：Toughness is a measure of a material’s resistance to brittle fracture when a crack is present.；Fracture toughness is used in design to find allowable flaw size.