Papers by Keyword: Thermal Behaviour

Abstract: In this study, Natural Rubber Vulcanizates (NRV) reinforced with organomodified kaolin was developed. The NRV were subjected to thermal degradation to ascertain its suitability for high-temperature automotive applications. Kaolin intercalation was achieved using derivatives of Rubber seed oil (Hevea brasiliensis) and Tea seed oil (Camellia sinensis) in the presence of hydrazine hydrate as co-intercalate. The developed Natural Rubber Vulcanizates were characterised using Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM). FTIR spectra obtained for the organomodified natural rubber vulcanizates revealed the presence of carbonyl groups at bands 1564cm^-1 and 1553cm^-1 which is an indication of organomodified kaolin intercalation within the Natural Rubber matrix for kaolin intercalates of Rubber seed oil and Tea seed oil respectively while no value was reported for the Natural Rubber vulcanizates obtained from the pristine kaolin filler. TGA results indicated that NRV developed from kaolin intercalates of Rubber seed oil (RSO) with onset degradation and final degradation temperatures of 354.2°C and 601.3°C were found to be the most thermally stable of the Natural Rubber Vulcanizates investigated. The SEM micrograph revealed that the kaolin nanofillers in Rubber Seed Oil modified Natural Rubber Vulcanizates were well dispersed as compared to that of Tea Seed Oil modified Natural Rubber Vulcanizates.

Abstract: In the process of ceramic stereolithography, the polymerization process of acrylate is exothermic, resulting in changes to temperature of the slurry, which may affect the quality of green parts. In this work, the heat source input in simulation is based on the in-situ measurement of conversion rate and calculated polymerization exotherm. The simulation results showed that the different structures underwent a 1~3°C maximum temperature rise. A thermal infrared detector was used to capture the in-situ temperature changes in entire exposure surface for several structures during the photopolymerization process. The experimental data validated the simulation results and showed that the temperature change and distribution area in the process were related to the exposure structure. The discontinuous structure and the increase of structural boundary length could accelerate the thermal diffusion, thus reducing the heat concentration in the center. Polymerization rate rose marginally with the incident light intensity until at the intensity of 20 milliwatts. Besides, intensity had little effect on the temperature gradient from the center to the boundary of the exposure area. It is inferred that the additional temperature rise after the peak temperature is an indicator of the occurring of secondary photopolymerization during multilayer exposure. And for the same input energy, reducing the exposure intensity and increasing the exposure time to some extent may help improve the degree of secondary photopolymerization. This work provided valuable guidance for the study of the photopolymerization process and structural design of ceramic stereolithography.

Abstract: The research of a failure criterion for concrete under multi-axial stresses is a very important task because of the numerous civil engineering applications. Nowadays several concrete failure tests are available in literature and various criteria have been proposed. A multi-axial failure criterion for the concrete founded on a simple physical basis, has been proposed by one of the authors. In this paper a sharper foundation of this criterion is given. The hardened cement paste (hcp), the binder of all the aggregate particles, is responsible of the concrete strength. Consequently, a preliminary average evaluation of the stresses, occurring, when the concrete is loaded, into the various phases components, and particularly in the hcp, is necessary to analyse the failure. To that end, the paper revolves around the analysis of the thermal behaviour of the concrete at its early stage of setting. It is shown that the heat production during the cement hydration process, is responsible to produce clearances among the various particles and the surrounding hcp that, in turn, the consequent statically determined structure of the concrete. Validation of this result comes out by analysing the elastic moduli and the thermal expansion coefficients. The micro-macro failure condition of Como & Luciano thus receives a sounder physical basis.

Abstract: In the present study, the thermongravimetric analysis (TGA) of laboratory hardwood and softwood particleboard was studied. The TGA showed that both hardwood and softwood have similar thermal behaviour at the same peak temperature. However, softwood is concluded to have higher fire retardancy as more char formation happened in softwood. A further study was carried out to compare the thermal behaviour of laboratory manufactured boards with the commercial grade boards. Superior thermal stability of commercial particleboard had confirmed its effective crosslinking and wood-resin adhesion.

Abstract: The paper is focused on the physical phenomena that occurs during gas atomization process, like fragmentation mechanism of the molten stream, the secondary breakup mechanism, droplets velocities and particles temperature history. The modeling of droplet dynamic and thermal history was achieved by using a software program realized by authors, called MetLAB, using the heat balance equations between the cooling gas and the molten metal droplets.

Abstract: Experimental researches conducted in recent years at the Non Destructive Testing Laboratory of Politecnico di Torino have revealed an unexpected thermal response of concrete subject to short duration cyclic compressive tests: a cooling phenomenon has been observed on medium-quality concrete cores and this contradicts Kelvin’s thermodynamic laws. Such a decrease in temperature is not to be ascribed to the evaporation of absorbed water, while it depends on the applied load intensity, the application frequency and the total number of cycles performed. Moreover, the cooling phenomenon is accompanied by such mechanical effects as performance enhancement and increasing brittleness, observed through static tests performed at the end of cyclic compression: an increase in the failure strength and the elastic modulus of the material as well as a reduction in max. displacement at failure are seen to occur. The present research takes its starting point in the above observations and aims to investigate the relations between thermal and mechanical effects in concrete, in order to check the possibility to use the variation of temperature at the end of a short duration cyclic compressive test as an indicator for the evaluation of damage, the final aim being to develop in the future a methodology for diagnosis of existing structures.

Abstract: Temperature evolution is one of the important parameters of mechanical properties of thin strip products. So the ability of prediction of temperature history before processing is critical to the processing scheme of controlling rolling and controlling cooling. In this paper an integrate model of finite element method is presented for the prediction of the temperature evolution in the finishing rolling during hot strips. The model takes into account the interaction between thermal behavior and mechanical behaviors. By using the second-development method based on the commercial code thermal behavior and temperature distribution of strips through seven-pass finishing rolling are described in detail. A method for computing the mean temperature at the exit of each pass is approached. Using this method the mean temperature can be attained after each pass. In one seven-pass thin strip rolling mills the temperature at the exit after each pass is measured by the pyrometer. The measured results and the simulation results are compared. The validity of the proposed analysis model is examined. The computing results are in agreement with the measured results.

Abstract: Crystallization behavior of gas atomized and spark plasma sintered (SPS) Cu54Ni6Zr22Ti18 amorphous powders were studied using X-ray diffractometer (XRD), differential scanning calorimeter (DSC) and transmission electron microscope (TEM). By heating to the temperatures of 837K and 909K, the amorphous phases in the powders formed particles such as Cu10Zr7 and Cu51Zr14. The size of crystals devitrified is about 20nm and 50nm, respectively. In order to identify the sintering ability of SPS, the compressive strength was measured with the initial powder size and SPS pressure.

Abstract: Thermal behavior and microstructural characterization of the CNTs/Al2O3 nanocomposites with different relative densities were studied by TGA and SEM. The onset temperature for weight loss corresponded to a decomposition of CNTs in TGA increased with an increase of relative density. The activation energy for CNTs decomposition obtained by the Kissinger method increased with increasing relative density. The difference in thermal behavior was explained by the porosity effect on the oxidation and decomposition of CNTs.

Abstract: The effects of BaF2 on thermal behavior and microstructure of melt-processed YBCO superconductors have been investigated. The differential thermal analysis (DTA) results indicated that the peritectic decomposition temperature of YBCO precursor powder was lowered when BaF2 was added (from 1020
to 976
). The peritectic decomposition temperature was lowest at the content of 5 wt.% BaF2, and the variation of melting temperature was not significant above 5 wt.% BaF2. The microstructures of the doped samples have been observed by scanning electron microscopy (SEM). The results showed that the    of BaF2        microstructure  .