Radim Kocich

Twist channel angular pressing (TCAP) as a method for increasing the efficiency of SPD

The paper proposes a new variation for the application of SPD methods. Suggested TCAP (twisted channel angular pressing) technology obtains the larger imposed strain more effectively while increasing homogeneity of material. The number of passes needed to obtain the ultra-fine to nano-scale grains in bulk materials can be significantly reduced. Commercially pure copper (99.97%) was used for the experimental verification of the suggested process. The thermal stability of extruded copper was studied after the application of two modes of heat treatment. The deformation parameters of the process were also described using the numerical simulation based on FEM analysis. Predicted value of imposed strain, after a single pass, reached approximately 2.3. Measured strength, determined after four passes, achieved values around 440 MPa homogeneously along the cross-section of the extruded material. The grain size, determined after four passes, averaged out 1.2 μm. Homogeneity of deformation was also confirmed by micro-hardness tests.

Design, analysis and verification of a knee joint oncological prosthesis finite element model

BACKGROUND The aim of this paper was to design a finite element model for a hinged PROSPON oncological knee endoprosthesis and to verify the model by comparison with ankle flexion angle using knee-bending experimental data obtained previously. METHOD Visible Human Project CT scans were used to create a general lower extremity bones model and to compose a 3D CAD knee joint model to which muscles and ligaments were added. Into the assembly the designed finite element PROSPON prosthesis model was integrated and an analysis focused on the PEEK-OPTIMA hinge pin bushing stress state was carried out. To confirm the stress state analysis results, contact pressure was investigated. The analysis was performed in the knee-bending position within 15.4-69.4° hip joint flexion range. RESULTS The results showed that the maximum stress achieved during the analysis (46.6 MPa) did not exceed the yield strength of the material (90 MPa); the condition of plastic stability was therefore met. The stress state analysis results were confirmed by the distribution of contact pressure during knee-bending. CONCLUSION The applicability of our designed finite element model for the real implant behaviour prediction was proven on the basis of good correlation of the analytical and experimental ankle flexion angle data.

The Methods of Preparation of Ti-Ni-X Alloys and Their Forming

The continuous development of science and technology in all industrial sectors means connecting and usage of a wide range of new knowledge together with implementation of new modern technologies for production of materials with high functional, specific and special properties. Intermetallic compounds TiNi with shape-memory effect are an interesting group of materials. These materials are used in a wide range of industry, such as electronics, robotics, tele-communication and also in medicine and optics. Shape-memory alloys (SMA) are a group of materials characterized by shape-memory effect (SME) and superelasticity (SE), also called pseudoelasticity.

FEM simulation of extrusion by ECAP method on magnesium alloy AZ91

The simulation of extrusion process by (ECAP) technique, which involves a simple large shear deformation during passage through two intersecting channels, was applied to the AZ91 Mg alloy to obtain an ultrafine-grained microstructure. For the stress and strain intensity investigation, computer simulation was used. Temperature dependences of extrusion process have been detected along with others. Four pressings were conducted at 250?C, while the fifth pressing was conducted at 180?C. The grain refinement and homogeneity of grain-size distribution increased with pass number. Temperature of process was measured during pass and decreased with respect to the number of pass along with obtaining finer grains. Finite Element Method (FEM) simulation was examined on AZ 91 alloy by practical tests. The experimental result agreed well with that obtained from numerical analyses carried out based on the FEM. Presented paper shows evidences that this forming method is an efficient tool for improving the mechanical properties. [Received 15 March 2006; Accepted 9 March 2007]

CFD analysis of the plate heat exchanger – Mathematical modelling of mass and heat transfer in serial connection with tubular heat exchanger

Application of numerical simulations based on the CFD calculation when the mass and heat transfer between the fluid flows is essential component of thermal calculation. In this article the mathematical model of the heat exchanger is defined, which is subsequently applied to the plate heat exchanger, which is connected in series with the other heat exchanger (tubular heat exchanger). The present contribution deals with the possibility to use the waste heat of the flue gas produced by small micro turbine. Inlet boundary conditions to the mathematical model of the plate heat exchanger are obtained from the results of numerical simulation of the tubular heat exchanger. Required parameters such for example inlet temperature was evaluated from temperature field, which was subsequently imported to the inlet boundary condition to the simulation of plate heat exchanger. From the results of 3D numerical simulations are evaluated basic flow variables including the evaluation of dimensionless parameters such as Colburn j-factor and friction ft factor. Numerical simulation is realized by software ANSYS Fluent15.0.

Investigation of Mechanical Properties and Microstructure Development of AZ61 Alloy during Rolling, Forging and ECAP

Results of experiments, focused on development of modified AZ61 alloy structure after hot forming, are summarized in this paper. Microstructure changes of the alloy after rolling and forging at temperatures of 380°C and after ECAP processed at 250°C were observed. After forging, the original grain size was reduced almost 14 times down to a value around 9 μm. After ECAP the grain size reduction was even better, almost 60 times. Important role of the ß-phase (Mg17Al12) in this alloy, during plastic forming, was confirmed. Independently of processing technology, the best final properties of the AZ61 alloy were supported with very fine particles distributed in the Mg matrix. The experiment succeeded in proving the influence of precipitates on restoration processes too.

Mathematical modeling of gas flow including heat transfer in spiral heat exchanger

Přispěvek prezentuje numericke řeseni prouděni spalin ve spiralovem výměniku tepla, kterým se ohřiva proudici voda. Plynne spaliny jsou ziskany ze spalovani zemniho plynu V mikroturbině, ktera dosahuje výkonu řadově desitky [kW]. V přispěvku je definovan matematický model prouděni spalin ve výměniku vcetně uvažovani přestupu tepla skrz vodive oblasti spiraloveho výměniku. Vodivými oblastmi výměniku tepla jsou jednotlive stěny a vrstva izolace, ktera obklopuje samotný výměnik. Vstupni okrajove podminky pro spaliny a vodu byly ziskany na zakladě experimentalniho měřeni. Definovaný matematický model byl nasledně řesen numericky V programovem prostředi ANSYS Fluent13. Výsledky numericke simulace jsou prezentovany rozloženim zakladnich proudových velicin V jednotlivých řezech výměnikem. Nasledně jsou vyhodnoceny veliciny K stanoveni energeticke analýze výměniku tepla.