Which of the following statements regarding brittle failure and crack propagation is CORRECT? Elastic energy is consumed when a crack propagates, due to unloading of a volume of material O Energy is released when the surface area of a material increases, as a result of crack propagation. The stress at the tip of a crack is less than the nominal stress (force over the cross-sectional area of the component) because the stress flows around the defect. The fracture toughness of a material is its resistance to an increase in the radius of curvature of a crack. O A material will fail in brittle fashion when the stress intensity at the crack tip is greater than the fracture toughness of the material