Low cycle fatigue prediction for cylinder heads considering stress gradient and local yielding

Abstract

Due to the complex geometry and thermo-mechanical loading, cylinder heads is the most challenging parts among all parts engines. It must endure cyclic thermo-mechanical stresses throughout their lifetime. In this paper, the low cycle fatigue (LCF) life analysis of the cylinder heads considering the stress gradient and local yielding, is performed using the finite element method and ANSYS software to predict the temperature and stresses, and then, LCF life using Morrow theory and nCode Design Life software. Elastic and plastic properties of cylinder heads obtained by LCF tests at different temperatures. The results of finite element analysis (FEA) showed that the maximum temperature and stress values in the cylinder heads are 220.29°C and 89.868 MPa and the position is at the valve bridge between exhaust valves. The numerical results showed that bridge between exhaust valves and valve seats are areas susceptible to fatigue cracks. The LCF life results showed that 1073 cycles is the minimum fatigue life and occurs between exhaust valves. 400-h durability test showed no rupture in different parts of the cylinder heads.