Andrzej Milenin

Stress-Strain analysis in TiN nanocoating deposited on polymer with respect to Au nanointerlayer

The multiscale analysis in the authors finite element code confirmed possibility of fracture, because of not sufficiently high level of compressive residual stress in the TiN deposited by physical deposition method and varied mechanical properties of the thin film and substrate. The residual stress cannot be identified by X-ray technique for amorphous polymer and layer with domains of crystalline TiN. It is assumed that the buffer biocompatible thin film of Au in the TiN/Bionate II material system will alter the evolution of residual stress and, therefore, will allow to determine the residual stress in profilometry studies, and helps to improve toughness of the connection between TiN and Bionate II. The introduction of Au nanocoating in the material system results in bending of the sample and a compressive residual stress in the TiN coating. Results of finite element simulation show improvement of connection between the polymer and TiN, and an increase of compressive residual stress in the coating by introduction of Au nanointerlayer results in reduction of stress and strain in the substrate (close to the boundary between substrate and coating).

Development of Finite Element Model of Reorientation of Cementite Lamellae in Pearlite Colonies in Wire Drawing Process for Wires Made from High Carbon Steel

Studies of properties of pearlitic steel wires used for production of metal cord or mining hoisting ropes have revealed a relationship between the orientation of cementite lamellas in the material and the mechanical properties of the wire and its resistance to cyclic loads. Influence of technological parameters on the orientation of cementite lamellas in wire was established. Experimental determination of the range of inclination angles of cementite lamellas in a given pearlite colony, at which their advantageous orientation, parallel to the wire axis, occurs, is not feasible in practice. Therefore, the only approach for solving this problem was to develop an appropriate mathematical model. Solution of the formulated problem proceeded in two stages. At first, the DRAWING2d program [3], modified and adapted to the needs of the task, was employed. The software incorporates a model based on the theory of plastic flow of the rigid-plastic medium. The boundary problem of the theory of plasticity is solved in this model considering the flow of heat and material heating due to plastic deformation and friction. Transfer of all strain tensor components data from draw to draw enabled simulation and optimization of the multi-stage drawing processes. Based on the model, strains fields and flow velocities were determined for the whole cross-section of the material being deformed in a particular draw. At the second stage, a program was developed to model the deformation of a single pearlite colony of dimensions corresponding to those of grains occurring in the actual structure of pearlitic steel after patenting. The mechanisms of deformation of the pearlite colony, the boundary conditions related to interaction of adjacent grains, and the rheology of cementite and ferrite were also accounted for.

Digital image correlation of coated and uncoated Religa Heart_Ext ventricular assist device

The digital image correlation is used to estimate influence of deposited heamocompatible coatings (gold and titanium nitride) on mechanical response of ventricular assist device Religa Heart_Ext made of Bionate II (thermoplastic polycarbonate urethane) under working conditions by comparison of the coated Religa Heart_Ext with uncoated Religa Heart_Ext. The DIC is applied for experimental investigation of the strains and displacements distribution on external surface of the blood chamber of ventricular assist device during loading. The experiment was conducted in a hydraulic system with water at operating temperatures of 25 and 37 °C, as well as under static pressures: 80, 120, 180, 220 and 280 mmHg, and static underpressures: -25, -45, -75 mmHg. The subsequent images were taken after stabilization of pressure on a set level. The applied research method shows that the nano-coating of 30 nm in thickness significantly affects deformation of the blood chamber of Religa Heart_Ext in macro scale. The proposed composition of coatings increases strain on external surface of the ventricular assist device.

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.

Determination of heat transfer coefficients for complex spray cooling arrangements

Numerical simulation of quenching by air-water spray cooling requires an accurate knowledge of the spray heat transfer coefficients (HTCs). In this work, a novel method of heat transfer determination is presented that takes lacking aspects of prior determination methods into account. The temperature trends during cooling of a thin-walled tube are used in an optimisation calculation based on a numerical model of the setup to determine the HTCs. It is shown that higher inlet pressures lead to higher heat transfers and that the heat transfer between two spray nozzles increases with decreasing nozzle to nozzle distance. However, for some cases, adjacent sprays can lead to decreasing HTCs. The amount of nozzles in circumferential direction had an overproportioned effect on the heat transfer in the film boiling regime. Verifications generally show a good agreement of measured with computed temperature trends based on the calculated HTCs.

TR Process for Forging Heavy Crankshafts

TR forging process for heavy crankshafts was a breakthrough in forging technology. In the first design connecting rods with joints, which transferred vertical force of the press into two horizontal forces, were applied. The modified process combines upsetting along the shaft axis with bending of the arm. In the former stage of the process a volume of the material satisfactory to form various shapes of arms is gathered. The task of the latter stage of the process was to forge the arm. Therefore, this innovative process allowed efficient forging of a variety of crankshafts. General idea of the process is described in the paper. Numerical simulations were applied to design the best forging technology.