Investigation On The Mechanical Modelling And FEM Simulation Of Dynamic Transition From Liquid To Solid In Liquid-solid Forming Under High Pressure

Liquid-solid forming under high pressure is a process that the workpiece staying in liquid-solid state is deformed under high pressure to enhance its performance. This forming process interested the researcher greatly for its low forming load and high performance and so on. The researches on the experiments, performance testing and constitutive modeling have advanced considerably. Unfortunately, investigation on the mechanical modelling and FEM simulation of dynamic transition from liquid to solid is few in the related literatures. So the author conducted the researches from the following four aspects.(1) Mechanical modelling of solid zone at elevated temperaturePure strain rate dependent viscoplastic constitutive model is used to describe the deformation behavior of solid zone against its characteristic of deforming at elevated temperature. A new iterative radial return algorithm is proposed to integrate this con- stitutive model based on the classical radial return algorithm. The new algorithm can improve the convergence of the stiff differential equation compared to the classical radial return algorithm and found the base for the mechanical modelling of liquid-solid forming under high pressure.Identification of constitutive parameters is another important aspect in mechanical modelling. FEM and optimization algorithm are combined to identify the constitutive parameters based on the principle of inverse parameter identification. The errors caused by some assumptions in the analytical parameter identification can be reduced through this combining method.Al₂O_3sf/LY12 composite formed by liquid-solid extruding is compressed at different elevated temperature and different loading speed. The variation of the compressive load is recorded with the height reduction. The constitutive parameters of Al₂O_3sf/LY12 composite is identified based on the selected pure strain rate dependent viscoplastic constitutive model and new proposed integration algorithm by combining FEM and optimization algorithm. (2) Mechanical modelling of liquid zoneMechanical model of liquid zone is established based on the element removal and material constitutive method which can describe the isostatic pressure and incompressive behavior of the liquid zone. The two theoretical model and the key issue on their application are discussed systematically. The two mechanical model are compared through one example. The results show that this two model both can describe the deformation of the liquid zone correctly. The precision of the element removal method is higher than the material constitutive method. While the material constitutive method is implemented through programming and can realize the modelling for dynamic transition from liquid to solid more easily. The established mechanical model of liquid zone overcomes one big difficulties in the mechanical modelling of liquid-solid forming under high pressure.(3) Mechanical modelling of the dynamic transition from liquid to SolidTwo mechanical models of the dynamic transition from liquid to solid are estab lished based on the mechanical models of liquid zone. One is based on the element removing. The dynamic updating of liquid-solid zone, the generation of the fluid element at the interface between liquid and solid and the results transferring are investigated systematically. The other model is based on the material constitutive method. Liquid material model and solid material model are integrated into one material model procedure. The material type is selected based on the element temperature. The liquid material model is selected when the element temperature is higher than liquidus point and vise versa, the solid material model is selected.(4) Investigation on the FEM simulation of liquid-solid extruding forming compositesThe mechanical model of liquid-solid forming under high pressure is used to the FEM simulation of liquid-solid extruding forming composites. The heating of the die, the infiltration of the liquid metal into the preform and the liquid-solid extruding process are simulated successfully and compared to the experimental results. The results show that the deformation state of the workpiece can be reflected more precisely and the more accurate forming load can be got with the proposed mechanical model. The researchâ‘ conducted in this dissertation found the base for FEM simulation of the similar forming process containing liquid phase.