Papers by Keyword: Thermal Shock

Abstract: The work is devoted to processes during melting of thin aluminium film on silicon surface in pulse current mode. An experiment was conducted to study the dynamics during the onset of the liquid phase on a metal film. Besides, the process of formation droplet localization zones is considered. The experimental part revealed critical current values ​ during an electrical explosion of thin metal films near the thermal shock source. Using the oscillographic method, the temperature profile of the metallization track is calculated.

Abstract: The purpose of this work is to experimentally prove the possibility of modifying the surface of a material by exposure to a long-lived plasma formation (DPO). Under this action, the surface of the material experiences heat shock, since the contact time is about 100 ms. The paper deals with the usage of autonomous long-lasting plasm formations (DPO). The tasks of thermal processing, coating, thermal shock tests metallic and non-metallic materials are introduced in the given paper. Large stored energy (till 10 kJ) and high brightness temperature (4 500 K) at sufficient time of influence can determine the range of technological problems, where long-lasting plasma formations have advantages in comparison with plasmatrons. This paper presents the results of the tests of the thermal shock by the concentrated flow of electromagnetic energy, saved by long-lasting plasm formation.

Abstract: Fiber reinforced polymeric (FRP) composite materials are currently used in numerous structural and materials related applications. But, during their in-service period these composites were exposed to different changing environmental conditions. Present investigation is planned to explore the effect of thermal shock exposure on the mechanical properties of nanoTiO₂ enhanced glass fiber reinforced polymeric (GFRP) composites. The samples were conditioned at +70°C temperature for 36 h followed by further conditioning at – 60°C temperature for the similar interval of time. In order to estimate the thermal shock influence on the mechanical properties, tensile tests of the conditioned samples were carried out at 1 mm/min loading rate. The polymer phase i.e. epoxy was modified with different nanoTiO₂ content (i.e. 0.1, 0.3 and 0.5 wt. %). The tensile strength of 0.1 wt.% nanoTiO₂ GFRP filled composites exhibited higher ultimate tensile strength (UTS) among all other composites. The possible reason may be attributed to the good dispersion of nanoparticles in polymer matrix corresponds to proper stress transfer during thermal shock conditioning. In order to access the variations in the viscoelastic behavior and glass transition temperature due to the addition of nanoTiO₂ in GFRP composite and also due to the thermal shock conditioning, dynamic mechanical thermal analysis (DMTA) measurements were carried out. Different modes of failures and strengthening morphology in the composites were analyzed under scanning electron microscope (SEM).

Abstract: This paper deals with a mathematical model of thermoelastic rectangular nano-beam, which is thermally loaded by thermal shock and subjected to moving heat source with constant speed. The nano-beam has been clamped-clamped and its length along the x-axis. The governing equations have been written by using the Euler–Bernoulli equation of nano-beams and the non-Fourier heat conduction with one-relaxation time. Laplace transform has been applied with respect to the time variable, and the solutions have been derived in its domain. The numerical solutions for the Silicon material have been done by using Tzou method. The results have been shown in figures for the temperature increment and the lateral deflection with various values of heat source speed to stand on its effects. Moreover, the effects of the ratio between the length and the width of the beam have been discussed. The speed of the heat source and the dimensions of the beam have significant effects on the temperature increment and the lateral deflection of the beam.

Abstract: This paper reports a comparative study on characterization and thermal shock behavior of air plasma sprayed Al₂O₃-13wt.%TiO₂ coatings using two kinds of raw materials, i.e. nanostructural and micro-structural (traditional) feedstock powders. The characterization, before and after thermal shock test, was carried out using micro-Vickers hardness tester, XRD and SEM. The thermal shock test was carried out using a water quenching method by employing cyclic heat treatment between ambient temperature and 650°C in air. The results showed that in spite of having denser structure, the nanostructural coating showed hardness a little lower than the traditional one at both conditions of before and after thermal shock tests. However, the nanostructural coating showed very good thermal shock behaviour.

Abstract: Mechanical fatigue due to repeated thermal shock cycling is of great importance for most materials intended for refractory applications. This work explores thermal shock resistance and cyclic thermal shock effects of cordierite ceramic made from clay-containing mixtures. Different means of detection of change in modulus of elasticity have been employed including impulse excitation and dynamic-mechanic tests (DMA). Results have shown that the elastic modulus of cordierite ceramic gradually decreases over thermal shock cycles, the sharpest change being observed after the first cycle. Unlike synthetic cordierite ceramic material, clay-substituted cordierite composites show "self-healing" effect, which can be explained by the gradual filling of cracks with glassy phase that leads to the strengthening of the whole structure of material. This effect is directly dependent upon the composition of the sample and the material with lesser amount of glassy phase can be characterized with the largest inertia of this effect.

Abstract: The aim of this study was to evaluate the effect of Y₂O₃:Al₂O₃ additives and sintering temperature on thermal shock resistance of silicon carbide sintered via liquid phase. Silicon carbide samples containing 10 mol% Y₂O₃:Al₂O₃ (1:3 and 1:4) were prepared, compacted and sintered at 1750, 1850 and 1950 °C in a graphite resistive furnace. Thermal shock resistance was evaluated after each thermal cycle performed at 600, 750 and 900 °C followed by abrupt cooling in water. Samples with two Y₂O₃:Al₂O₃ proportions did not show major differences when sintered at the same temperature, though, rising the sintering temperature improves Y₂O₃:Al₂O₃ modified-SiC thermal shock resistance.

Abstract: This paper presents research into analysing the volume stability of composite materials based on a polymer-cement matrix. The attention was paid to the influence of extreme temperatures shocks. Materials of modified composition were gradually exposed to extreme temperatures and then cooled in furnaces. Cooling was carried out by two different ways, i.e. slow and rapid. Emphasis was placed on the aggregate type used – fine lightweight and dense. Also available materials from alternative resources which have positive effect on thermal stability of composites based on silicate matrix were considered.

Abstract: Selective laser melting is a layer-by-layer technique to form a solid part from powder. The thermal cycle of this process can be as short as one millisecond and less. This is why it is favorable to obtain nanostructured materials with advanced properties. Metal matrix composite WC-Co is studied. Micron-sized Co powder was mixed with WC nanopowder in a planetary ball mill to prepare uniform composite powder. Single remelted beads and monolayers were obtained from the composite powder on the substrates of sintered WC-Co. No cracks and good adhesion to the substrate are observed. The high cooling rate up to 10⁶ K/s explains the fine microstructures. Increasing the scanning velocity is favourable because of refining the microstructure and decreasing the balling-effect. The attained values of surface roughness are as low as 1-2 μm.

Abstract: It is well known that a series of cracks running perpendicular to the cutting edge are sometimes formed on the rake face of brittle cutting tools during intermittent cutting. The cutting tool is exposed to elevated temperatures during the periods of cutting and is cooled quickly during noncutting times. It has been suggested that repeated thermal shocks to the tool during intermittent cutting generate thermal fatigue and result in the observed thermal cracks. Recently, a high speed machining technique has attracted attention. The tool temperature during the period of cutting corresponds to the cutting speed. In addition, the cooling and lubricating conditions affect the tool temperature during noncutting times. The thermal shock applied to the tool increases with increasing cutting speed and cooling conditions. Therefore, to achieve high-speed cutting, the evaluation of the thermal shock and thermal crack resistance of the cutting tool is important. In this study, as a basis for improving the thermal shock resistance of brittle cutting tools during high-speed intermittent cutting from the viewpoint of cutting conditions, we focused on the cooling conditions of the cutting operation. An experimental study was conducted to examine the effects of noncutting time on thermal crack initiation. Thermal crack initiation was found to be restrained by reducing the noncutting time. In the turning experiments, when the noncutting time was less than 10 ms, thermal crack initiation was remarkably decreased even for a cutting speed of 500 m/min. In the milling operation, the number of cutting cycles before thermal crack initiation decreased with increasing cutting speed under conditions where the cutting speed was less than 500 m/min. However, when the cutting speed was greater than 600 m/min, thermal crack initiation was restrained. We applied the minimal quantity lubrication (MQL) coolant supply to the intermittent cutting operation. The experimental results showed that the MQL diminished tool wear compared with that under the dry cutting condition and inhibited thermal crack initiation compared with that under the wet cutting condition.