Volume 8, Issue 1 (January 2011)
Lifetime Calculation of Thermo-Mechanically Loaded Materials (Al, Cu, Ni, and Fe Alloys) Based on Empirical Methods
Cyclic loading of metallic engineering components at constant elevated or fluctuating temperatures causes a complex evolution of damage, which cannot be described easily. In many engineering components, thermo-mechanical loading occurs, e.g., cooling components in metallurgy and metal forming, turbine blades, cylinder heads, exhaust systems, etc. At the same time, the thermal expansion is restricted in some regions due to the complex geometry of the components. Therefore, mechanical stresses take place, and the cyclic plastic deformation leads to thermo-mechanical fatigue of the material. A careful analysis and comparison of the experimental results, based on a systematic variation of the relevant influence factors, allow to develop empirical models for computing the fatigue life of thermo-mechanically loaded components made of AlSi cast alloys, Cu alloy, Ni alloy, and cast iron. Based on stress-strain loops from low cycle fatigue tests at different temperatures, a nonlinear combined material model was adopted to describe the cyclic deformation behavior. The simulated loading parameters of stress and strain were the basis for the subsequent lifetime simulation. Different lifetime approaches were tested and analyzed to fulfill the requirements for the fatigue analysis of components made of these alloys. In particular, strain based criteria, damage parameters as well as hysteresis energy criteria were investigated. Also, a new energy based parameter was developed to optimize the scatter band and standard deviation. In order to verify the simulation model for components, numerical results have to be compared, and—if necessary—it also has to be adapted to experimental results from component tests. In addition, the model parameters can be optimized by using these results.