Temperature Distribution In Specimen Research Articles

Experimental study on self-heating phenomena of CMDB/HTPB propellant under intermediate strain rate compression load

Self-heating behaviour of solid propellants under intermediate strain rate compressive loading have been studied. Effects of two intermediate strain rate (1 s-1 and 150 s-1) of the CMDB/HTPB propellants were investigated. The compression test was conducted using a hydraulic testing machine and the self-heating temperatures were measured by an infrared camera. The results show the following: (1) For CMDB propellant, the surface temperature of specimens rapidly increased at the initial period, then decreased due to the movement of the high temperature region caused by deformation, and then increased again. Finally, the surface temperature slowly decreased due to heat transfer to the surroundings. Infrared thermography showed the formation of a hot spot. Cracks were initiated and gradually expanded to the interior area during compression. (2) For HTPB propellant, the surface temperature of specimens increased slightly. Compared with CMDB specimens, there was no significant damage to HTPB specimens. (3) For both CMDB and HTPB propellants, the temperature distribution of specimens was non-homogeneous. At the centre of the specimen surface, the temperature is the highest. The self-heating temperatures of propellant increased with increasing the strain rate. However, the difference is slight for HTPB propellant, whereas it is considerable for CMDB propellant.

Design and development of a micro-LDH apparatus to determine formability of sheet metal under hot stamping conditions using Gleeble

In the last few years, demand for hot stamped components has increased in the automotive industry. Determination of formability under hot stamping is challenging due to elevated temperature, fast cooling, and high punch velocity. Although there was various strive for formability determination, but there were limitations with experiments like non-uniform heating of specimen, non-uniform strain, and temperature distribution. Therefore, in this work, an experimental apparatus was developed to determine formability at room temperature, high temperature, hot stamping conditions, and any complex process cycle involving heating and cooling. New specimen was designed to produce different strain paths, uniform, and homogenous temperature distribution with the help of FEM software using thermomechanical and thermoelectrical simulation. A micro hemispherical dome-based experimental apparatus was designed using Solidworks. The designed apparatus was used in conjunction with the thermo-mechanical simulator (Gleeble-3800). Thermomechanical analysis was done in PAM STAMP software to optimize specimen size and shape to get uniform strain distribution and different strain paths. A thermoelectric FEM model was developed using Abaqus 6.14 to optimize the temperature distribution in the specimen. The developed model enables choosing the appropriate polarity of the electrical cable connection to achieve uniform temperature distribution in the specimen. Strain path and temperature profiles for experiment and simulation were compared. Further, a forming limit curve was developed using the designed apparatus to verify the feasibility of the apparatus. For feasibility test of apparatus, hot stamping process was selected. This new design apparatus can be used for a range of temperatures up to 1000 °C, hot stamping conditions, and for different materials (aluminum, magnesium alloys, different grade of steel, etc.). It concludes that the connection of different polarities of electrical cable was critical for homogenous and uniform temperature distribution in specimens.

Application of the Trefftz Method for Pool Boiling Heat Transfer on Open Microchannel Surfaces

In the paper, the results of tests on pool boiling heat transfer on open microchannel surfaces were discussed. Nucleate pool boiling from copper microchannel surfaces was examined using ethanol as a working fluid. Parallel microchannels fabricated by machining were about 0.2 to 0.4 mm wide and 0.2 to 0.5 mm deep. In the mathematical model the heat transfer process was in steady state. The heat transfer in copper block was assumed axisymmetric while the specimen temperature distribution was not. The temperature of the copper block and the specimen were assumed to satisfy Laplace’s equations with adequate boundary conditions. The problem was solved by the Trefftz method with two sets of Trefftz functions. Graphs were used to represent the copper block and the specimen temperature distributions, local values of heat transfer coefficients as a function of the heat flux and fin temperature distribution. Uncertainty analysis was presented.

Comparison of Glass-Transition Temperatures for Epoxy Polymers Obtained by Methods of Thermal Analysis

In this review, the characteristic temperatures for epoxy polymers and epoxy matrices of fiber-reinforced composites in the glass-transition ( α-transition) range determined using different methods of thermal analysis (DSC, DMA, and TMA) are compared. The influence of loading frequency in the DMA method and of uniformity of heating and postcuring of specimens in all the methods is revealed. The agreement between the glass-transition temperatures given by different methods is achieved using the same characteristic points in experimental curves and the same time parameters (the frequency of external actions, heating rate, and the uniformity of temperature distribution in specimens in testing chambers).

Strain measurement and error analysis in thermo-mechanical tensile tests of sheet metals for hot stamping applications

In order to conduct uniaxial tensile tests for hot stamping applications, tests are normally performed by using a Gleeble thermo-mechanical materials simulator so that rapid heating and cooling processes can be obtained. However, temperature gradients in a specimen tested on Gleeble are inevitable due to resistance heating principles and heat loss to grips and water-cooled jaws. In this research, a pair of purpose-built grips made of stainless steel with low thermal conductivity and significantly reduced contacting area for clamping, as well as a flat dog-bone specimen with maximised parallel length (80 mm) were designed, for the purpose of improving the temperature uniformity within the concerned gauge section area of the specimen. Uniaxial tensile tests on AA6082 were performed, after controlled heating and cooling processes, at constant deformation temperatures in the range of 400 ℃–500 ℃ and at constant strain rate in the range of 0.1–4/s, to simulate its hot stamping conditions. The digital image correlation system was adopted to enable strain distributions in specimens to be measured. The temperature distributions in specimens were investigated and an effective gauge length of 14 mm was specified accordingly to ensure temperature gradients less than 10 ℃ within it at all tested temperatures. True stress–true strain curves of AA6082 were obtained based on results of strain measurements along the defined effective gauge length and used to calibrate a set of advanced material model. Error analysis was carried out by using thermo-electrical and thermo-mechanical FE models on ABAQUS, in which the calibrated material constitutive equations were implemented via subroutines. The error of stress–strain curves of AA6082 measured based on the specified gauge length was investigated and quantified by analysing the distribution of axial strain and axial stress.

Design principles and testing of internal frost resistance of concrete for road structures - critical review

We present a review of freeze-thaw durability requirements laid down in both European standards and in the national specifications in relation to concrete for road structures. The principles of material selection for concrete mix are presented. We discuss local variations in the severity of the winter season and the extent of frost action in the components of road structures. The characteristic parameters of the test procedure for direct assessment of the resistance of concrete to internal damage are analysed, with particular attention paid to the specimen cooling rate. The temperature distribution in specimens was determined in standard freeze-thaw resistance tests carried out at two accredited laboratories. We discuss the criteria used in indirect assessment of freeze-thaw durability of air-entrained concrete on the basis of air void characteristics. Based on the determined temperature distribution in concrete specimens we postulate an improvement of the standard test procedure to clearly specify the cooling rate. It would be beneficial to distinguish frost impact zones depending on the severity of action of frost and de-icing salts on concrete in road structures.

Thermal property of insulating material at cryogenic temperature

The thermal property of insulation material is essential in developing high temperature superconductor (HTS) devices operating at around liquid nitrogen temperature. Unlike metallic materials, nonmetallic materials have a thermal resistance; therefore, accurate estimate of the heat flow is difficult in the case of nonmetallic materials. In this study, a precise instrument is developed for measuring the thermal property of insulating materials over a temperature range of 30 K to approximately the room temperature by using a cryocooler. The cold head of the cryocooler is thermally anchored to the thermal link and used to cool the apparatus to a desired temperature. The temperature distribution in specimen is measured with respect to the supplied heating power, from which the thermal conductivity is calculated and compared with published data for accuracy confirmation. The effective thermal conductivity of polypropylene laminated paper (PPLP) is presented and the trend in the behavior of conductivity near liquid nitrogen temperature is also discussed.

Investigation of Thermomechanical Properties of Ferromagnetic NiFeGa Shape Memory Alloy Subjected to Pseudoelastic Compression Test

Investigation of Thermomechanical Properties of Ferromagnetic NiFeGa Shape Memory Alloy Subjected to Pseudoelastic Compression TestIn the study stress-induced reversible phase transformation in NiFeGa magnetically controlled shape memory alloy subjected to pseudoelastic compression test was investigated. The specimen's mechanical characteristics and temperature changes related to the exothermic martensite transformation and endothermic reverse transformation were measured in contact-less way by using a fast and sensitive infrared camera (IR). It was found that the stress-induced phase transformation process occurs in this alloy in heterogeneous way, since the observed specimen's temperature distribution was not uniform. Stress-strain curves obtained for the first, as well as for the subsequent six loading-unloading compression cycles and their related temperature changes, elaborated as average from the specimen's surface, were analyzed. It was concluded that the stress and the temperature changes developing in the subsequent cycles depend on the applied test conditions, however the highest discrepancies were observed between the first and the second cycles of the compression loading.

Laboratory investigation into thermal response of asphalt pavements as solar collector by application of small-scale slabs

This paper investigates the thermal response of asphalt pavements as solar collector by application of small-scale asphalt slabs. The copper tubes were embedded in the asphalt slabs for the purpose of water circulation and the thermal sensors were also embedded in different depths for temperature measurement during slab preparation. A laboratory irritation simulation test was performed to heat up the asphalt slabs. The thermal energy stored in the slabs was collected by circulating water. The effects of flow rate, the time for starting collection and the initial temperature distribution of the slabs on the process of heat collection were evaluated. The results show that the asphalt pavement can be cooled down by the solar collection and thus is good for reducing the effect of heat-island in a city, but the temperature gradients between the slabs’ surface and the pipe are noticeable. Furthermore, the efficiency of an asphalt collector can be above 33.3% and the increase of flow rate result in a limited decrease of the surface temperature of asphalt pavement. The steady state temperature distribution in specimens could be used to set the starting collection time. ► Researches into asphalt pavements used as solar collector have been conducted. ► A laboratory irritation simulation test for heat energy collation was performed. ► The characteristics of heat collection in Asphalt Solar Collector were analyzed. ► Various factors may affect the heat collection are taken into account in tests.

Design optimizations of IFMIF High Flux Test Module towards uniform specimen temperature distribution

The test specimen temperature control, together with optimized irradiation and reliability, is the central task of the HFTM design. The temperatures of the specimens should be kept at prescribed levels with acceptable temperature spreads. This paper concerns the design optimizations on HFTM through thermo-hydraulic simulations. Single-parametric studies were carried out for the effects of spacers, cooling channel/insulation gap deformation, multi-channels, insulation gap size, channel-rib contact resistance, etc. It is found that the temperature of the specimens and walls is generally sensitive to the above-mentioned parameters. These parameters therefore need to be considered during the optimization design, accounting also for the manufacture and operation tolerances. Simulation results on latest updated HFTM design are also presented. The results show that the current HFTM design could meet thermal management requirements in general. Further optimizations should be made individually for different target specimen temperatures.

Temperature in high temperature SHPB experiments

As an experimental technique, it’s desired that the temperature in specimen is uniform in high temperature split Hopkinson pressure bar (SHPB) experiments. However, the temperature in specimen decreases and the temperature of bars increases when specimen starts to contact with bars, which induces the nonuniform temperature distribution in specimen, and may result in inaccuracy of experimental results. In this paper, the temperature distributions of specimen and bars in high temperature SHPB experiments were investigated while the specimen was heated alone. Firstly, the temperature history of specimen was measured at different initial temperatures by experiments, then simulation was carried out. Simulation results were consistent with experimental results by adjusting the thermal contact coefficient between specimen and bars. By this way, the thermal contact coefficient and simulation results were validated, and the proper cold contact times of specimen and bars in high temperature SHPB experiments were discussed. Finally, the results were compared with those in references.

Temperature Distribution in Specimen of Belt Type High Pressure Apparatus

Temperature Distribution in Specimen of Belt Type High Pressure Apparatus

The Correction Method of Differential Dilatometer Data and Thermal Expansion Measurement of Carbon Materials

The thermal expansion coefficient (αt) of graphite has been measured as a function of temperature between room temperature and1000°C by using a differential dilatometer for the four grades of specimens;AXF-5Q1 (Poco Graphite Co.), 7477PT (Le Carbone Lorraine Co.), SM1-24 (Anglo Great Lakes Co.) and IG-11 (Toyo Carbon Co.).The measurements have been carried out within an accuracy of1.1×10-5 (ΔL/L0) by taking into account the variation of environmental temperature and the temperature distribution in specimens, revealing that the thermal expansion is isotropic in AXF-5Q1, 7477PT and IG-11, and αt of IG-11 is the lowest among them.

熱疲労試験における高周波加熱コイルの形状と試験片の温度分布

On the high frequency heating apparatus used for thermal fatigue tests, the relation between the shape of heating coils and the temperature distribution of specimens was experimentally examined for SUS 304 stainless steel. This report describes the relation between heating coil dimensions and heating rate, the most ideal coil shape for various specimen types, and the effects of temperature range and specimen shape on temperature distribution.The results obtained are as follows:(1) The heating rate increases with decreasing distance from specimen surface to heating coil and with increasing coil tube diameter.(2) For the general cylindrical and hour glass type specimens, the most ideal coil shapes are a separate type and a parallel type coil, respectively, as judged from the point of temperature distribution.

The Temperature-Distribution of Specimens on Thin Substrates Supported over a Circular Opening in the Electron Microscope

The Temperature-Distribution of Specimens on Thin Substrates Supported over a Circular Opening in the Electron Microscope