What caused the failure of the truck brake drum

Brake drum is an important part of trucks and the primary inspection part in the daily maintenance of trucks. Brake drum failure mainly comes in five forms: cracking, cracking, bottom falling, excessive wear and abnormal wear.

The failure of casting is mainly considered from two aspects: one is the material composition and strength of casting; the other is the change of mechanical properties caused by the change of material structure under certain working conditions. Generally speaking, the mechanical properties of casting parts mainly depend on the material composition and the external environment (temperature, cooling rate, etc.).

When the brake drum is working, the friction between brake drum and brake pad generates a large amount of heat energy, which leads to the increase of brake drum temperature. However, the friction between brake pad and brake drum is mostly speckle contact. The heat generated by friction on the contact surface makes the tissue undergo phase transition and produces phase transition stress, which reduces the thermal fatigue resistance capacity of the brake drum. At the same time, due to the uneven heating, the parts with high temperature have changed, while the parts with low temperature have not changed, and some parts have not even been affected by heat. Phase transformation stress, uneven heating will also produce stress, the existence of residual stress, makes the mechanical properties of the non-uniform, under the frequent braking load, (see below) has certain rules of cracks, the crack in the axial distribution of intermittent or continuous state, from the crack distribution analysis, the crack is mainly affected by tangential force. The tangential force ACTS on the brake surface and tears the matrix, causing internal stress on the matrix and reducing the thermal fatigue strength of the material, then continuous or discontinuous cracks are generated, seriously causing fracture.

On the other hand, the brake drum produces phase transitions. The internal tissue phase transition is mainly affected by temperature. The temperature generated by the brake drum during operation can be as high as enough to cause the tissue phase transition. The main phase transitions occurring at this temperature include: 850° C--900° C, 1. Eutectic carbide is decomposed into graphite and ferrite at or below 800℃. 2. Pearlite and ferrite convert to austenite above 800℃; 3. Austenite converts to martensite during rapid cooling. On the brake drum cracking problem, this should be analyzed from two aspects, one is in the braking state, due to the strength of the material itself and the stress of fracture; Second, after the emergence of cracking, the brake drum is finally cracked under the interaction of thermal stress and phase transition stress, and due to the reduction of local strength of structural phase transition, under the frequent action of external braking forces. For the bottom and no cracking on the formation of cracking, also from two aspects of analysis, one is the strength of the brake drum material itself; Second, the brake drum cracking is caused by unreasonable abnormal external forces.