Showing papers on "Thermal shock published in 1986"
TL;DR: The heat shock response is now known to occur in bacteria and in plants as well as in animals, and is a rapid but transient reprogramming of cellular activities to ensure survival during the stress period, to protect essential cell components against heat damage and to permit a rapid resumption of normal cellular activities during the recovery period.
Abstract: As all biologists appreciate, there is constant interaction between life and the environment, and temperature plays a critical role. It establishes distribution limits, it affects rates of function as well as the survival of organisms. Notoriously sensitive to temperature is plant growth. Critical steps in plant life such as germination, flowering and breaking of dormancy can be manipulated by the application of certain temperature treatments. Animal life is mainly limited to a narrow range of temperatures, from a few degrees below the freezing point of water to approximately 50 'C. Animals nevertheless differ in the range of temperatures that they can tolerate. Temperature tolerance may however change with time and a certain degree of adaptation is possible. The limits of temperature tolerance for a given animal are not fixed. Indeed, it has been known for some time that exposure to a near lethal temperature often leads to a degree of adaptation so that a previously lethal temperature is tolerated. This particular response to heat shock has attracted considerable attention from molecular biologists over the last decade, which has resulted in a rapid accumulation of data providing considerable insights, not only into the molecular basis of acquired thermotolerance, but into stress physiology in general. The heat shock response is now known to occur in bacteria and in plants as well as in animals, and is a rapid but transient reprogramming of cellular activities to ensure survival during the stress period, to protect essential cell components against heat damage and to permit a rapid resumption of normal cellular activities during the recovery period.
336 citations
TL;DR: The phenomenon of thermal-shock cracking in ceramics is approached theoretically and experimentally in this article, where sintered slabs made from a glass-quartz powder mix were quenched in water in order to generate crack patterns of various types, depending on the severity of the shock.
Abstract: The phenomenon of thermal-shock cracking in ceramics is approached theoretically and experimentally. Sintered slabs made from a glass-quartz powder mix were quenched in water in order to generate crack patterns of various types, depending on the severity of the shock. The patterns serve as evidence for a scheme set up with the aim of explaining the variety of ways in which materials respond to thermal shock. The fracture-mechanical explanations are based on the time-dependent thermal load and on the concept of an energy release rate, with single and multiple crack propagation starting from randomly distributed initial flaws on the surface.
134 citations
TL;DR: In this article, compacts formed from high-purity fused submicrometer mullite powders, both pure and with the additions of 5 to 25 vol% ZrO2 of particle size 1, 2, or 4 μm (average), were sintered in air at 1610°C for 6 h to form dense ceramic bodies.
Abstract: Compacts formed from high-purity fused submicrometer mullite powders, both pure and with the additions of 5 to 25 vol% ZrO2 of particle size 1, 2, or 4 μm (average), were sintered in air at 1610°C for 6 h to form dense ceramic bodies. Mechanical properties (flexural strength, Kic, and Young's modulus) were measured both before and after thermal shock. The strength after thermal shock increased considerably in systems containing additions of 10 to 20 vol% ZrO2; Kic also increased, but not so markedly. The low fraction of tetragonal ZrO2 (0.1 to 0.2) in the as-fired samples and the increase in Young's modulus after thermal shock for some strengthened samples supported the view that the interaction of residual internal stresses induced by quenching and the accompanying martensitic transformation of ZrO2 result in potential nucleation sites for microcracking. Thus, microcracking may be the predominant energy-absorbing mechanism responsible for strengthening and toughening the quenched ceramic bodies.
55 citations
Patent•
17 Oct 1986TL;DR: In this paper, a thermal spray coating composition applied to a substrate by thermal spray process is characterized by improved wear, thermal shock resistance and chemical resistance at elevated temperatures, the coating composition containing greater than about 60 volume percent refractory oxide with the balance comprising a cobalt and or nickel and/or iron base metal matrix.
Abstract: A coating composition applied to a substrate by thermal spray process, characterized by improved wear, thermal shock resistance and chemical resistance at elevated temperatures, the coating composition containing greater than about 60 volume percent refractory oxide with the balance comprising a cobalt and/or nickel and/or iron base metal matrix containing chromium, aluminum and tantalum.
46 citations
TL;DR: In this article, multiple cracking caused by thermal shock of smooth specimens is predicted qualitatively by invoking time dependent energy release rates, and the experimentally observed final crack pattern may have developed stably from an intermediate transient state of unstable crack growth initiated from preexisting flaws.
35 citations
TL;DR: In this article, the fracture of alumina disks subjected to thermal shock is predicted from Weibull parameters derived from isothermal three-point-bend tests using the principle of independent action model and the shear-insensitive Batdorf model.
Abstract: The fracture-of alumina disks subjected to thermal shock is predicted from Weibull parameters derived from isothermal three-point-bend tests. Both the shear-insensitive Batdorf model and the principle of independent action model are used to compare results from three-point-benr1 and isothermal biaxial strength tests to results from thermal fracture tests. It is found that the shear-insensitive Batdorf model gives good agreement between mechanical tests and fracture of the thermally shocked disks.
27 citations
TL;DR: In this paper, the thermal shock disk testing method developed by Sato has been modified to use a moving electron beam as a heat source, which yields results on thermal shock damage characterized by the final crack length in addition to thermal shock resistance and thermal shock fracture toughness.
26 citations
TL;DR: In this article, the thermal properties of aluminum titanate-mullite composites were studied for a wide composition range to develop material having high thermal shock resistance, which tended to increase with increasing aluminum titanates content.
Abstract: Thermomechanical properties of aluminum titanate-mullite composites were studied for a wide composition range to develop material having high thermal shock resistance. The thermal shock resistance tended to increase with increasing aluminum titanate content. Composite having 82 vol% aluminum titanate can withstand water quench from above 1200°C and has a room-temperature strength of 60 MPa. Composite with less aluminum titanate has lower thermal shock resistance but has higher strength. The relation between thermal shock resistance and strength, Young's modulus, and thermal expansion coefficient is discussed.
25 citations
TL;DR: An elementary model was developed to predict the strength and modulus based on the powder particle heating and acceleration as well as the residual stress of the substrate and the thermal shock induced during spraying.
Abstract: Thirty three plasma spray runs of ZrO2 (with 20% Y2O3) were made in which processing parameters were intentionally varied. Strength and modulus were measured using four-point bend testing. Strength values ranging from 2110 to 7690 lbf in-2 and modulus values ranging from 2.88 to 6.80 Mlbf in-2 were observed. An elementary model was developed to predict the strength and modulus based on the powder particle heating and acceleration as well as the residual stress of the substrate and the thermal shock induced during spraying. The model explains 88% of the variation in strength values and 72% of the variation in modulus values.
19 citations
TL;DR: In this paper, two tool materials, CC 620 and CC650, were used for evaluating thermal shock resistance, both by quenching from elevated temperature into cold water and by steel machining tests.
Abstract: Most ceramic materials are unsuited to conditions involving non-uniform temperature distributions because of their inherent brittleness. Ceramic cutting tools operate in conditions of rapid temperature variation and consequently thermal cracking is frequently observed. Under certain cutting conditions, these cracks are the major cause of tool failure. Thus, establishing the conditions under which thermal cracking occurs and identifying material parameters governing thermal shock resistance should lead to clearer ideas about how to develop thermal shock resistant ceramic cutting tool materials. Two tool materials, CC 620 (a pure ceramic containing Al2O3 and ZrO2) and CC650 (a mixed ceramic containing Al2O3 and Ti(N, C)), were used for evaluating thermal shock resistance, both by quenching from elevated temperature into cold water and by steel machining tests (SS 2541). It is shown that material parameters quantifying thermal shock resistance developed from simple quenching experiments, although fre...
18 citations
TL;DR: In this article, the authors used the finite element method to solve the problem of a strip containing a crack and subjected to a thermal shock on one edge, which was compared to the exact solution and it was shown that the FEM yields results with less than 1% error.
TL;DR: In this paper, the authors analyzed the difference between using temperature-dependent material properties and constant ones and showed that in general, using constant material properties over large temperature ranges can lead to considerable underestimation of the maximum stress intensity factors.
Patent•
04 Aug 1986
TL;DR: A silicon nitride sintered body containing compounds of Mg, Sr and Ce in amounts of weight of from 0.5 to 5% calculated as MgO, from 0., 5 to 5 % calculated as SrO and from 1 to 10% calculated As CeO₂, the balance being silicon Nitride further contains an Al compound in the amount of from 1, 20% calculated AlO⁂O ⁃ as mentioned in this paper.
Abstract: A silicon nitride sintered body containing compounds of Mg, Sr and Ce in amounts of weight of from 0.5 to 5% calculated as MgO, from 0.5 to 5% calculated as SrO and from 1 to 10% calculated as CeO₂, the balance being silicon nitride further contains an Al compound in the amount of from 1 to 20% calculated Al₂O₃. The addition of the Al compound gives the silicon nitride sintered body a low thermal conductivity while high mechanical strength and high thermal shock resistance are maintained.
TL;DR: ZrO2-7wt% Y2O3 as discussed by the authors was the first one to use a 7-weighted team and achieved a 4-17-wt performance.
Abstract: Y2O3含有量を4-17wt%と変化させた安定化ZrO2の耐熱衝撃性について検討した. 円板試料を1100℃に急熱後, 室温まで約500℃/minで急冷するサイクルを繰り返して熱衝撃試験を行った.ZrO2-4wt% Y2O3は単斜晶ZrO2の割合が多いため, 単斜晶→←正方晶のマルテンサイト変態に伴う寸法変化が著しく, 耐熱衝撃性が劣る. 一方, 立方晶単相のZrO2-12及び17wt% Y2O3では相変態は見られないが, 破壊靱性値が低いためにやはり耐熱衝撃性は劣る. ZrO2-7wt% Y2O3では, 変態に伴う寸法変化が比較的小さく, また破壊靱性値も比較的高いために良好な耐熱衝撃性を示す.ZrO2-7wt% Y2O3に, 更に0.5-4wt%のAl2O3を添加すると気孔率が低下し, 硬さ及び破壊靱性値が向上して耐熱衝撃性が改善される. また, ZrO2-7wt% Y2O3では, 単斜晶ZrO2粒同士が結合して大きな集合体となっているのに対して, Al2O3添加材では球状の単斜晶ZrO2粒が比較的孤立して存在している. 熱衝撃試験において, クラックは主に単斜晶ZrO2から発生すると考えられ, 単斜晶ZrO2の形態の違いも耐熱衝撃性改善の原因の一つと考えられる. なお, SiO2を添加しても耐熱衝撃性の改善は認められない.
TL;DR: Results show that for αm(metal) αp, the surface stress is lower, and the interface stress is higher than αm=αp, when αp-αm>2×10-6°C-1, cracks are more easily initiated in the porcelain surface rather than the interface.
Abstract: Computer calculations were used to simulate the effects of thermal shock on the stresses developed in porcelain-fused-to-metal (PFM) systems. A three-dimensional-finite-element model was employed to first calculate time-dependent temperature distribution in a beam shaped specimen 1.25-2.5×8×20mm. These were then used in a two-dimensional analysis of stresses in a beam consisting of 50 elements. Transient stresses in a beam consisting of 50 elements were calculated for porcelain, porcelain with an opaque layer, and porcelain-opaque-alloy system; the effects of porcelain thickness, thermal expansion coefficients, and quenching temperatures were evaluated. Experimental tests were also conducted for correlation with the theoretical calculations.Results show that for αm(metal) αp, the surface stress is lower, and the interface stress is higher than αm=αp. When αp-αm>2×10-6°C-1, cracks are more easily initiated in the porcelain surface rather than the interface. Theory and experiment are in general agreement.
TL;DR: In this article, the depression at the nozzle corner caused by the trepan removal has been repaired by "temper bead" welding without stress relief heat treatment, similar to the half bead technique of the ASME Boiler and Pressure Vessel Code.
Patent•
22 Jan 1986
TL;DR: In this paper, the authors describe the structure, the composition and the manufacture of ceramic materials for special applications such as, for example, adiabatically operating engines, transmissions and other combustion machines and also every type of machine element.
Abstract: The present invention describes the structure, the composition and the manufacture of ceramic materials for special applications such as, for example, adiabatically operating engines, transmissions and other combustion machines and also every type of machine element. The composition allows matching of the thermal conductivity, the strength, the thermal shock resistance, the precision machinability and thus the performance in exactly defined application areas of such units. The composition and the low thermal expansion of the material allow precision machining of its surfaces and the lubricant-free movement of the surfaces of this material on one another at high temperature with high precision.
Patent•
07 May 1986
TL;DR: In this paper, a method of producing cordierite ceramics by molding and firing a batch material containing a -alumina, which comprises adjusting the particle size distribution of a-Alumina so that the amount of particles having a particle size of not more than 3 µm is not more more than 17 wt% and a particle sizes of 50 % by cumulative weight is 4-15 µm.
Abstract: A method of producing cordierite ceramics by molding and firing a batch material containing a -alumina, which comprises adjusting the particle size distribution of a-alumina so that the amount of particles having a particle size of not more than 3 µm is not more than 17 wt% and a particle size of 50 % by cumulative weight is 4-15 µm. In this way consistent production of ceramics of low thermal expansion and high thermal shock resistance is achieved.
TL;DR: In this article, the improved thermal shock resistance of PDZ with the phase inversion of the free zirconia, generated as a consequence of destabilisation, was investigated and compared.
TL;DR: In this article, the distribution of stresses in the cylindrical section of a reactor pressure vessel is evaluated for transient temperature and pressure loads, taking particularly into account the thermoplastic stresses of the cladding and the transition zone to the base material.
Patent•
08 May 1986
TL;DR: In this article, a closed gas-cell cellular material is formed by heat treating a hydrosilicate, especially perlite, at a low temperature and then in the form of grains of a grain size of 5 to 8000 micrometers, feeding these grains through a space at a temperature of 800° C. to 2000° C for a short residence time at a uniform space load of 0.1 to 500 kg/h.
Abstract: A closed gas-cell cellular material is formed by heat treating a hydrosilicate, especially perlite, at a low temperature and then in the form of grains of a grain size of 5 to 8000 micrometers, feeding these grains through a space at a temperature of 800° C. to 2000° C. for a short residence time at a uniform space load of 0.1 to 500 kg/h. Then the grains are subjected to thermal shock in a thermal shock space connector directly to the feed spacing and heated to 1,000° C. to 3,500° C. The density of the granular material thus produced is 0.12 to 27 g/cm 3 and the weight per volume thereof at 0.01 to 1 kg/liter.
TL;DR: In this article, the applicability of ductile fracture mechanical J-integral concept on mechanical and thermal shock loaded structures with flaws is investigated, by that the behaviour of possible flaws in components of power plants during accidents can be described (e.g. reactor pressure vessel and piping during emergency cooling).
01 Jan 1986
TL;DR: In this paper, expressions for the temperature response across a thin large space structure during and immediately following the onset of thermal shock are obtained as a function of the properties of the material and the solar incidence angle.
Abstract: Expressions for the temperature response across a thin large space structure during and immediately following the onset of thermal shock are obtained as a function of the properties of the material and the solar incidence angle. The thermal gradients induced due to solar radiation heating result in thermal deformation. From the temperature gradient information, expressions are developed for the time history of the thermally induced deflections based on the thermoelastic relationships. The effect of the variation of the solar incidence angle and the variation of the emissivity of the surface is considered. From the deflection time history, a model of the disturbance moments is developed and evaluated for different solar incidence angles.
TL;DR: In this article, the authors proposed a method to solve the problem of the lack of knowledge about the environment in the context of IoT devices, which is the first step in the development of IoT applications.
Patent•
25 Jun 1986
TL;DR: In this paper, a thermal shock treatment comprising a brief exposure of said products simultaneously to high intensity radiant heat from a vessel and high temperature, low pressure superheated steam or other fluid or gaseous medium inside the vessel is described.
Abstract: A method for the rapid removal of the peelings or outer coverings from certain food products with minimal loss of or damage to the other portions thereof, by a thermal shock treatment comprising a brief exposure of said products simultaneously to high intensity radiant heat from a vessel and high temperature, low pressure superheated steam or other fluid or gaseous medium inside the vessel.
TL;DR: Considering theoretical porosity-property-correlations, a porosity dependance of the thermal shock resistance of ceramics is discussed in this paper, where the treatment demonstrates that low porosity may lead to an increase in thermal shock resilience.
Abstract: Es wird die Porositatsabhangigkeit der Thermoschockbestandigkeit aus theoretischen Ansatzen hergeleitet und begrundet, warum unter gegebenen Bedingungen geringe Porositaten zu einer erhohten Thermoschockbestandigkeit fuhren.
Porosity and Thermal Shock Behaviour of Ceramic Materials
Considering theoretical porosity-property-correlations a porosity dependance of the thermal shock resistance of ceramics is discussed. The treatment demonstrates, that low porosity may lead to an increase in the thermal shock resistance.
TL;DR: In this article, the role of thermal strain ageing, subgrain formation, dislocation density, high temperature void formation and grain boundary segregations has been studied and the number of cycles needed for the formation of microcracks has been established.