Gray Cast Iron Cylinder Head Thermal Mechanical Fatigue Analysis

Abstract

Heavy duty diesel engine cylinder head crack is one of the main problems which affects engine durability. With the increasing requirements for better engine performance, less exhaust emission and lower fuel consumption, increased combustion pressure and elevated temperature make the engine cylinder head to be the most complicated and critical part for the engine design. The objective of this study was to apply cylinder head TMF simulation method to improving cylinder head structure and increasing its TMF life. Machined samples of gray cast iron (GJL 250) taken from cylinder head were used in material tests and material properties under different temperature were obtained from the tests. The finite element model of the whole assembled engine cylinder head/block was built and stress–strain curve were gained by cylinder head cold-hot cycle simulation. Then, cylinder head TMF life was calculated and different life prediction approaches were compared with each other and also with test results. Simulation and test results were generally in good agreement. The position of minimum TMF life from Ostergren approach, which considers mean stress effect, agree quite well with the early crack position of the cylinder head. By optimizing the cylinder head structure, TMF life of the cylinder head was greatly increased. Design standards, the best ratio between valve diameter and the distance of valve centers, maximum valve angle and optimized cylinder head wall, were set for the design of cylinder head of gray cast iron. Based on the creation of the whole assembled FE model of engine cylinder head/block and the application of the cold and hot cycle analysis and life prediction, TMF life of gray cast iron cylinder head were guaranteed at engine early development stage, and time and cost were saved.