Piotr Kustra

Physical and Numerical Modelling of Wire Drawing Process of Mg Alloys in Heated Dies Accounting for Recrystallization

Magnesium-calcium alloys with increased bio-compatibility are applied in medicine for sake of high compatibility and solubility in human body. Production of surgical threads to integration of tissue may be one of the applications of those types of alloys. A new manufacturing process of thin wires made of biocompatible Mg alloys, including drawing in heated dies, was developed in Authors previous works. Conducting drawing process in conditions, in which recrystallization occurs, is the basis of the process. This allows for multi-pass drawing without intermediate annealing. Control of recrystallization after every pass using experimental method is complex so numerical simulation seems to be a rational method to design the process parameters. The purpose of the paper is developing a mathematical model of recrystallization for MgCa08 alloy, its implementation into the finite element (FE) code that simulates wire drawing and experimental verification of the numerical calculations. The first part of work was focused on the development of mathematical model of wire drawing process of Mg alloys in heated die. Proposed model takes into account thermal phenomena in the wire and in the die, plastic flow of the material, stress-strain state and recrystallization. The fracture criterion was implemented into FE code to eliminate the possibility of damage. The second part of the work was focused on experiments including upsetting and tensile tests for calibration of recrystallization and fracture models. Recrystallization model was calibrated on the basis of flow curves only what is a limitation. Therefore, experimental wire drawing on drawing bench developed by the Authors was the final stage of the work performed to validate the model. Recrystallization during wire drawing was studied. The developed computer program enables prediction of the recrystallization kinetics during wire drawing in heated die for MgCa08 alloy. The model of static and dynamic recrystallization of this alloy and complex model of the drawing process were proposed in this work, as well.

The Multi-Scale FEM Simulation of Wire Fracture during Drawing of Perlitic Steel

The fracture development during wire drawing operation is an important phenomenon governing the productivity as well as the mechanical properties of the drawn wire. The wire drawing processes was investigated in present paper in two separate levels - using the 2-dimensional rigid-plastic finite element method (macro-level) and modelling the microstructure changes (micro-level) by the Representative Volume Elements (RVEs). To predict fracture initiation the phenomenological theory of fracture is used. The influence of initial cementite lamellas orientation on triaxity factor and localization of deformation in micro-level is investigated. Obtained results are helpful for a fundamental understanding of pearlitic deformation during development of high strength steel wires for tire cord applications.

Numerical Optimization and Practical Implementation of the Tube Extrusion Process of Mg Alloys with Micromechanical Analysis of the Final Product

The paper is devoted to the development of a process of tubes extrusion from MgCa08 magnesium alloy. For optimization of extrusion process the Qform software was used. The numerical model of flow stress and fracture criterion for MgCa08 were obtained based on tension/compression measurements performed in a universal testing machine Zwick Z250. Predictions of the flow stress and deformations were modeled as well as the ductility of material. The process was optimized according to the plasticity and temperature criterions. In the optimization process, temperature of the billet and the speed of extrusion were determined. Based on the optimal parameters the extrusion of tubes with external diameter of 5 mm was performed in the laboratory press. On top of the macroscopic testing and calculations, investigations of the material microstructure and the micromechanical behavior of the material after the extrusion were performed by a combination of SEM and nanoindentation analyses. Micromechanical properties of the alloy were detected with the aid of statistical nanoindentation. Samples were characterized in terms of their microstructural defects, distribution of elastic modulus and hardness. Good particle dispersion and homogeneous-like distribution of micromechanical properties was found showing the efficiency of the extrusion process.

Optimization of Profile Extrusion Processes Using the Finite Element Method and Distributed Computing

This paper is dedicated to the development of a FEM model of the extrusion process of tubes and profiles made from Mg alloys. Mg alloys are characterized by low technological plasticity during extrusion. The model is designed to optimize the parameters of extrusion tubes on mandrel and profiles using the ductility of alloy as an objective function and the maximum value of temperature in the deformation zone as a limitation condition. Optimization of extrusion parameters requires a large number of FEM simulations that is why the solution based on distributed computing capabilities was used. The developed software generates a vector of simulation variants and runs them on a computer cluster in parallel mode in the PL-Grid Infrastructure. In this work, an example of optimization process and a procedure for obtaining the needed materials data for simulation using the case of Mg alloy were shown.