How fracture toughness is defferent from strenght?

Materials can have high strength but be brittle. (For instance, gl, which has considerable tensile strength but is easily shattered.) Brittle materials are prone to breaking due to stress concentration, which can result in cracking. Once a crack starts it propagates easily through brittle materials. Also, it takes less impact energy to break a brittle material because it doesn't yield (deform) the way ductile materials do. Yielding absorbs some of the impact energy. (See the ref.).