A brake drum is a cast iron shaped like a tambourine that is fixed to a tire and rotates at the same speed. Oil pressure is used to push Brake Shoes to touch the inner edge of the Brake drum. The friction force generated by contact restrains the rotation of the tire to achieve the purpose of braking. Brake drum body does not produce hot crack, casting no quality defects, so the general quality of brake drum can be referred to as the "brake do not break" for brake drum is a kind of brittle grey cast iron material and work under the environment of high temperature and high pressure, fatigue crack is from forming on the surface physical properties of cast iron materials, is an irresistible objective laws. With the extension and penetration of cracks in the drum body, the mechanical strength of the drum decreases rapidly, and it is inevitable that the brake will be broken eventually.