서강대학교

초록/요약

This research work aims at describing the flow behaviour and formality of aluminium - alumina metal matrix composite used in piston forging process. A Piston head which used in an internal combustion engine works under high pressure and thermal loads. Therefore, the material used for pistons should have low thermal expansion coefficient and enhanced mechanical properties compared to the conventional materials. To attain improvement in the mechanical and thermal properties aluminium metal matrix composite are substituted instead of aluminium piston alloy. Since the material undergoes complex process of large plastic deformation during piston forging process, the material characterization as well as the damage model to predict the crack occurrence during forging process has to be done properly and accurately. Compression tests data under various temperatures and strain rates are utilized to identify the constants of Arrhenius constitutive model equations and enhanced Lemaitre damage model. A 2-step piston head forging process is adopted, and numerical analyses were carried out with the Arrhenius flow stress and enhanced Lemaitre damage model in DEFORM 3D software. Numerical simulation and experimental flow line in the piston cross section has been compared to validate the material characterization implemented in numerical simulation. Verification of the damage model is carried out by comparing the crack location between the experiment and simulation results. Furthermore, to prevent the formation of crack, preform design has been changed based on the piston forging results and the developed preform is checked for reduction of damage value using numerical simulation.