Cracking failure analysis of an engine exhaust manifold at high temperatures based on critical fracture toughness and FE simulation approach

D5S is an alloy used in the manufacture of exhaust manifold of the internal combustion (IC) engines. Considering that exhaust manifold is one of the engine components that are under intense thermal and mechanical loads, fracture failure analysis should be regarded for this engine part. Fracture toughness determination is the main criterion for structural fracture analysis. In this research, crack failure was analyzed based on the finite element method (FEM), upon which critical fracture toughness was determined. Using the FEM analysis, a crack was assigned on the exhaust manifold model in order to obtain its fracture toughness at the first mode (K-I) under thermo-mechanical loads. According to the ASTM standard, four compact tension (CT) specimens with different notch lengths of 4 mm, 5 mm, 9 mm, and 12 mm were prepared. Then, using the tension test at a high temperature, critical fracture force was determined. CT specimens were simulated by the finite element ABAQUS software. Fracture force obtained from the tension test was exerted on the CT specimen in the simulation software. Then, critical fracture toughness (K-IC) was gained by using the fracture analysis in FE simulation. Finally, K-I was compared with K-IC and crack propagation was discussed.