Question

Why are materials whose yield stresses are highly strain rate dependent more likely to fail by brittle fracture. Please consider microstrucural effects in your answer and not copy from another incorrecly answered question copied from the internet.   

Answer 1

Ductilty means the ability of a material to undergo PLASTIC DEFORMATION. Fracture occurs by the enlargement of voids and further coalescence to form a crack. A brittle material is one, in which cracks are propagated quickly and and us perpendicular to applied stress direction.

Brittle material lacks plasticity, means that it has greater strength, but it's ability to absorb energy us less. So it's yield strength are highly strain rate dependent.

Brittle fracture can be intergranular and transgranular fracture depending on the direction of crack propagation with respect to grains.