Papers by Keyword: Temperature

Abstract: This paper presents a method for acquiring true stress–strain curves using engineering strain curves obtained from upset forging of cylindrical specimens. The main problem deals with determination the true strain in upset hot forging on hummers when the values of strain rates are differ in the range from 0 to 10^-3s. At such strain rates due to wave processes strain distribution in cylindrical specimen will be uneven. The purpose of this publication is to analytically determine the strain distribution in compressed cylindrical specimen.

Abstract: Magnesium and its alloys have high potential for lightweight applications in the automotive and aerospace industries. In order to design parts for new applications with optimized mechanical properties and higher, more economic production rates, the forming limit behaviour of thin sheets (t < 1.0 mm) has to be known for different temperatures and loading rates. In this study, forming limit curves of 0.8 mm thick AZ31 sheet were measured for deformation at 200 °C and 250 °C and at loading rates of 1 mm/s and 10 mm/s with the Nakajima test. The investigations showed that an increase in temperature from 200 °C to 250 °C tends toward higher forming limit values for all stress states. In contrast, an increase in the loading rate from 1 mm/s to 10 mm/s induces a reduction in formability. It can be seen that the temperature, loading rate, and stress state influence the force-distance curves, the distribution of the local major strains, and the sheet thickness reduction.

Abstract: The influence of temperature, strain rate, and sheet thickness on the mechanical properties of twin-roll cast, rolled and heat-treated AZ31 was investigated under tensile loading from different directions (0°, 90°). To assess the forming behaviour of different sheet thicknesses (0.6 mm, 1 mm), tensile tests were performed with an electromechanical testing device between 20 °C and 300 °C at strain rates of 10⁻⁴ s⁻¹ and 10⁻² s⁻¹. With rising temperature, the flow stress decreased while the elongation to failure (A₈₀) increased, which may be related to the enhanced dislocation motion and the activation of additional nonbasal slip systems at T > 200 °C. It can be seen that the anisotropy of flow stress and elongation to failure was influenced by the temperature, the strain rate, and the sheet thickness.

Abstract: The article presents data on dependence of the myocardial electrical impedance on the temperature. These data have high clinical relevance because radio frequency energy-induced destruction of the myocardium in the course of surgical treatment of cardiac arrhythmias should be performed transmurally. Insufficient transmural myocardial damage results in recurrence of cardiac arrhythmias. Therefore, achieving transmural treatments of the myocardium is of high significance.Studies were performed by using 20 isolated hearts. To evaluate the effectiveness of radio frequency exposure, we studied two temperature settings: myocardial normothermia (36.6 °C) and myocardial hypothermia (20 °C). The depth of destruction as well as the temperatures of the epicardial, endocardial, and intramural myocardium at the points of impact were estimated. Data showed that lower temperature decreases tissue electrical impedance and results in a greater depth of damage.

Abstract: The paper presents the software and data transfer method between ProCAST and Deform-3D, which allow to take into account the geometry, temperature, residual stresses and microstructure of semi-finished product in the “casting – forming” processes.

Abstract: Temperature and humidity cycles test of photovoltaic glass modules are carried out by different cycling time. The change of transmittance, interface and strength of photovoltaic glass modules are compared by different experiment time. With the increasing of temperature humidity cycle time of photovoltaic glass modules, the light transmittance of influence is more serious, and stress strength of the longest cycle is weakened 32.84% than one cycle. Therefore, the influence of photovoltaic glass modules under different temperatures and humidity conditions is more serious. So it is very necessary to study durability and safety under temperature and humidity cycles of photovoltaic glass, related to power generation efficiency of the photovoltaic glass modules.

Abstract: Silicon carbide (SiC) is widely used in terrestrial and space applications because of its good mechanical, thermal and optical properties. Nevertheless, traditional grinding and polishing technologies cannot meet the machining requirements due to the high hardness and brittleness. In this paper, Inductively Coupled Plasma (ICP) is utilized to process the SiC optics. The effects of different processing recipes on the removal rate and temperature are investigated. The results show that the removal rate almost keeps stable with processing time and changes with the flow rate of plasma gas, reaction gas, the ratio of CF₄/O₂ and the power. The input power and processing time are the two main influence factors on the processing temperature.

Abstract: The contact thermal insulation system is a major trend in building construction in the Czech Republic. In this way both for new buildings and for renovations to improve thermal and technical parameters of buildings. Effort of an extension of the construction season, however, causes frequent visits of the application of this system in unsuitable weather conditions. One of the important layers in the systems ETICS (which is the contact thermal insulation of the building) is the basic layer with glass-fibre reinforcing mesh. Such a cover layer of thermal insulation and at the same time a basis for the final outer layer - plaster. Climatic conditions during application are given by the manufacturer. Normal temperature is indicated by + 5°C to +30°C. The lower boundary is not often observed. That's why I have my research and thesis focused on testing the parameters of the base layer made outside the ideal conditions. I thus produced samples underwent laboratory tests and watching the resulting parameters. This article provides a brief description of the testing methods and their advantages and disadvantages. The methods used were, for example, tests in flexural strength, pressure, water absorption test or tests of beginning and end of solidification. The most important findings of my research were the facts that significantly limit the applicability of standardized tests to determine the beginning and end of solidification. For the base layer samples of 4mm even these methods give very distorted information. Another effort of my research will be to verify these results and determine how it will be necessary to modify the methodology of testing, we received the relevant data. Preliminary hypothesis is at least the size of a substitute specimens - especially reducing the sample thickness from 40 mm to 4-6 mm, which corresponds to the reality of practical implementation. The data obtained would subsequently be used to adjust the rules for testing insulation systems. Data were obtained primarily from my research within VUT FAST brand FAST‑J‑10‑50

Abstract: The temperature and relative humidity measurement in building physics needs special equipment which is often expensive and not available for young researchers. Several programmable platforms are available. This article describes the low-cost solution of temperature and relative humidity measurement using combined Digital Humidity/Temperature sensors and Raspberry Pi as the datalogger. Five lightweight timber frame wall fragments with various thermal insulations and outdoor coating colors were exposed to the real outdoor boundary climate conditions. The indoor boundary conditions were secured as constant. The results of measurement using low cost sensors were compared to values obtained by commercially available thermocouples for scientific use and non-steady HAM simulation in WUFI software.

Abstract: Knowing temperatures at the tool-chip interface is extremely important to optimize the machining condition and to improve the machining performance, furthermore to design high performance materials. In order to grasp the temperature distribution at the tool-chip interface, this study has devised an indexable insert with seven pairs of built-in micro Cu/Ni thermocouples on the rake face near the cutting edge. This paper shows the performance of the indexable insert with built-in micro thermocouples developed. The thickness of each element of the micro thermocouple is approximately 15 μm. The result of unsteady heat conduction analysis employing FEM shows that the temperature difference by installing the micro thermocouples is less than 10 K or 1.2 %. The temperature measurement experiments by cutting of aluminum alloy were carried out by changing the cutting speed. The results provided the evidence that the temperature distribution at the tool-chip interface can be grasped with the indexable insert with built-in micro thermocouples developed.