Petr Jonšta

Wrought aluminium–magnesium alloys subjected to SPD processing

Abstract The article presents the influence of stationary plastic deformation, using the equal channel angular pressing (ECAP) method, on the structure and properties of an aluminium alloy with 3 % magnesium content. In order to investigate changes in the structure and substructure, light microscopy and transmission electron microscopy were used. The influence of plastic deformation was determined by hardness measurement using the Vickers method. The results of the investigation show that, even after one ECAP, it is possible to decrease grain size to a range of 30 – 70 nm, and increase the mechanical properties by nearly 90 %. It was also found that the additional twist angle of the die has a minor effect on the properties and structure of the investigated alloy.

Advanced Fillers Enhancing Thermal and Mechanical Properties of Rubber Blends

In the paper we present measurements of transport physical parameters such as thermal conductivity, diffusivity and specific heat capacity and dc electrical conductivity as well as the mechanical values E*, tg δ for rubber compounds filled by different ratio of silica - carbon black fillers. From presented results it is possible to see that proper filler concentration (rubber blend - silica - carbon black) rising all thermal parameters as well as mechanical properties represented by complex Young’s modulus and so, maintains the good mechanical parameters of the blend and finally it also lowers the electrical resistance. All trends are favourable for the improvement of useful rubber blends properties.

Abrasive Water Jet Cutting of the Steels Samples Cooled by Liquid Nitrogen

The paper is aimed at abrasive water jetting of non-corroding steels treated by cryogenic temperatures in liquid nitrogen. The investigation of cut walls shows that cryogenic temperatures influence material structure and respective properties. This research is focused on improvement of material reliability in various states of production systems and operation conditions.

Artificial Neural Network Modelling of Glass Laminate Sample Shape Influence on the ESPI Modes

The present work is devoted to the applications of artificial neural networks (ANN) for material design prediction. We have investigated the dependence of the generated mode frequency as a function of a sample thickness and a sample shape of glass laminate samples by electronic speckle interferometry (ESPI). The obtained experimental results for differently shaped (thickness, canting and rounding) glass laminate samples are compared with those of ANN. The coincidence of both experimental and simulated results is very good.

The Influence of Rubber Blend Aging and Sample Homogeneity on Heat Transport Phenomena

This paper is devoted to the study of thermal transport phenomena changes caused by natural aging of rubber blends. Thermal conductivity, diffusivity and heat capacity of rubber blends were measured and compared for the same samples before and after half of a year. Samples were stored at room temperature and daily light. In the frame of our investigations there has been observed the decrease of the thermal diffusivity as well as the thermal conductivity in the interval approximately 40-50 %. The changes of specific heat capacity after sample aging were negligible. The explanation of such behaviour we can see in the sample structure degradation caused by the environmental influence.

Influence of Gama Prime Changes on the Heat Transport Phenomena of a Nickel Super Alloy

The paper deals with the influence of microstructural changes of the nickel superalloy (NiS) on heat transport changes in MAR-M247. The dissolving annealing within the temperature interval of 900 – 1240°C and cooling in water has been applied to enhance structural changes. It has been shown that the narrow connection between the γ’ phase morphology changes, as well as values of density, thermal conductivity and specific heat capacity. In the dissolving annealing process, the γ’ particles change in certain cycles from fine to rough and back to fine one. Obtained results of changes of thermal conductivity, density and specific heat capacity correlate with image analysis and electron microscopy observation.

Materialographic Analysis of MAR M-247 Superalloy

This paper presents the results of structural phase analysis of MAR-M247 superalloy. Analysis was performed at initial and in as casted state after various type of solution annealing in the range 900 °C to 1240 °C with cooling in water. Presented polycrystalline alloy is heat resisting nickel superalloy, especially usable for highly strained components in the industry producing stationary gas turbines and aircraft engines. Analysis was performed using of a Quanta FEG 450 scanning electron microscope with micro-analytic system Trident APEX-4 which have identified presented minor phase. Attention was also paid to its eventual changes after different type of solution annealing.

Evaluation of Degradation Causes of the Forged Rotors Made of NiCrMo Steel Grade

Contamination of steel by excessive amount of non metallic inclusions leads tosignificant deterioration of its quality and consequent degradation. Cause of degradation of forgedrotors for steam turbines made of NiCrMoV steel grade is examined in this paper. Metallographicand electron-microscopic analyses were performed, including X-ray microanalysis for detecting thepurity of the forging being examinated. Concurrently, the consequence of failed technologicalproduction process, namely the influence of broken brick for argon blowing at the casting ladle, wasalso examined.

Influence of Spur Gears Hardened Method to Allowable Stress Numbers for Bending

The presented paper deals with comparison of spur gears classical and modern hardening process of the bending fatigue properties. It concerned particularly the hardened surface of the tooth flank using optical source of electromagnetic radiation. The results of fatigue tests were obtained on a servo-hydraulic testing machine LFV 100 kN made by walter+bai ag. These tests were defined by the standard ISO 6336 as method B, when testing is carried out under reference conditions close to the real operation. Comparison of test samples is also carried out on the basic of the achieved local hardness and hardened layer thickness in the tooth root, which is an initiation of fatigue crack.

Influence of the Filler Root Surface Treatment on Bending Fatigue Test Results of the Hardened Gears

This article deals with testing of fatigue properties of hardened gears at bending. These tests are defined by the standard ISO 6336 - method B, when testing is carried out under reference conditions close to the real operation. This type of testing may be helpful to evaluate the influence of new materials, design parameters, production technology, or the effects of surface finishing. The first part of this article deals with the theory of fatigue testing methodology using modified stair-case method and characteristics of the testing machine. The second part of the paper is devoted to the characteristics of the experimental material and the results achieved. The case hardened steel gears alloyed by Cr-Ni-Mo were selected for the experiment. Hardened gears were subjected to local hardness measurement and subsequently the bending fatigue tests were performed. Ruptured samples were analyzed using a scanning electron microscope. The local bending stress was determined using the modified computational model based on the ISO 6336 standard methodology. The focus of this work consisted in evaluation of the influence of the filler root surface treatment on fatigue limit at bending on the basis of the realized experiments and their confrontation with the equivalents specified in the standards ISO 6336 and ČSN 01 4686.