Through-process simulation has gained increasing significance over the past few years. It spans the entire life of the component, from the manufacturing process including all process steps to the resulting mechanical properties and finally through to material and component failure.
The first part of the project was to develop a material model to calculate the fatigue strength as a function of pore size. It was shown that the lifetime of a specimen can be described in fracture mechanics terms. It is assumed that the crack is initiated at a pore within the first few cycles and that the lifetime is then determined by the velocity of crack growth through the microstructure. A correlation between fatigue strength and pore size was found using the El-Haddad equation. The fracture mechanics parameters required were derived from crack growth curves. The approach was finally verified through fatigue testing and crack growth analysis.
The second part focused on deriving a statistical porosity model to estimate pore distribution in a high-pressure die cast component based on the results of a casting simulation. Aluminium alloy plates of different qualities (different dwell pressures and plunger speeds) were cast to identify the correlations between measured pore distribution and casting simulation parameters. The plates were then cut into pieces to measure pore distribution.
The casting simulations were subsequently compared with the real pore distributions in the cast plates using self-organizing maps. These comparisons revealed a strong correlation between the temperature from the solidification simulation and the porosity. The statistical porosity model thus allows the pore distribution to be computed for a defined temperature range as a function of dwell pressure.
The combination of a fracture mechanics model and a statistical porosity model improves the calculation of cyclic fatigue strength taking into account the results of the casting simulation. A comparison of the results obtained using the new methodology with those from conventional calculations showed a significant increase (approx. by a factor of 2) in calculated safety.
The project was carried out by the Chair of Mechanical Engineering in close cooperation with MAN Nutzfahrzeuge, Georg Fischer and MCL.