Failure Analysis of a Diesel Engine Exhaust Manifold

The diesel engine failed during a 700-h bench test due to the cracking of exhaust manifolds. To investigate the cause of exhaust manifold cracks, material chemical composition, hardness determination, metallographic examination as well as fracture observation were carried out. Besides, the corresponding stress states were calculated using the finite element method. The results show that the material chemical composition, metallurgical morphology and hardness of the exhaust manifolds A and B are in good accordance with the standard. The cracked failure of Part A is due to stress concentration caused by improper structural design. Increasing the fillet radius is a useful way to improve the quality of the exhaust manifold. When the fillet is R6, the stress concentration phenomenon is well resolved. For Part B, the crack is mainly caused by a porosity defects close to the crack initiation area, which has a diameter of 185 mu m.