Effect Of Thermal Shock Research Articles

Thermal damage of tungsten-armored plasma-facing components under high heat flux loads

Fusion energy is expected as a promising candidate for alternative next generation energy. For fusion reactor, the plasma facing components (PFCs) are the most critical components to achieve this goal. PFCs will suffer severe thermal shock due to repective cyclic high heat flux (HHF) loads. This paper investigates the effects of thermal shock and damage behavior of tungsten armored PFCs under steady, transient and combined thermal loads. The distribution of stress field is analyzed, and crack initiation is predicted using the extended finite element method (XFEM). The unique features of thermal-mechanical behavior of tungsten armored PFCs under simulated service condition are discussed. The dominant factor of the cracking of the tungsten armor is the brittleness of tungsten below ductile-to-brittle transition temperature (DBTT). Under the steady loads, the cracking position is apt to near the interface of tungsten armor and the interlayer, and the threshold of cracking is between 14 MW/m2 and 16 MW/m2. With 6 MW/m2 steady loads, applying 1 ms duration of transient load, the cracking threshold is between 0.2 GW/m2 to 0.4 GW/m2. The depth of cracking increases from 100 um to 500 um with the transient load increasing from 0.4 GW/m2 to 1.0 GW/m2. Researches are useful for the design and structural optimization of tungsten-armored PFCs, and the long-term stable operation of further reactor.

Effects of osmotic and thermal shock on the invasive aquatic mudsnail Potamopyrgus antipodarum: mortality and physiology under stressful conditions

Invasive freshwater species, such as the exotic mollusc Potamopyrgus antipodarum (New Zealand mudsnail), can frequently survive under harsh conditions, including brackish and hypoxic environments. We experimentally assessed the effects of osmotic (0, 10, 20, 25 and 30 psu) and thermal (20 °C) shock on mortality, activity and physiology of P. antipodarum collected at Capitol Lake, Olympia, Washington, USA, during winter and spring seasons when environmental temperature was 5 and 10 °C respectively. We measured standard metabolic rate and enzymatic activities (malate dehydrogenase, lactate dehydrogenase, alanopine dehydrogenase) in snails after a 10-day acclimation period at high salinity. Significantly higher mortalities were observed at higher salinities; the strongest effects occurred on snails collected at the end of winter, and exposed to 30 psu and 20 °C (100% mortality in 3 days). When snails were collected during the spring, 100% mortality was observed after 40 days at 30 psu and 20 °C. Standard metabolic rates were significantly lower when snails were exposed to salinities of 25 and 30 psu, even after 10 days of acclimation. Enzymatic activities showed small but significant declines after 10 days at 30 psu reflecting the declines observed in overall metabolism. The physiological tolerances to temperature and salinity displayed by this population of P. antipodarum make its eradication from Capital Lake difficult to achieve.

Effect of thermal shock on the strength and fracture behavior of pre-flawed granite specimens under uniaxial compression

An understanding of high temperature effect on the strength and fracture behavior of rock is a key concern in underground engineering. To study the strength evolution and cracking process of thermally-damaged rock, granite specimens containing pre-existing flaws were heated to different high temperatures and subjected to uniaxial compression. In this study, the pre-heated granite specimens were cooled to room temperature slowly in oven or rapidly in water. The mechanical test showed that the peak strength and elastic modulus of granite decreased slightly below 300 °C and then decreased significantly with the temperature. During the loading, a photographic, acoustic emission (AE) monitoring and a digital image correlation method were used to capture the crack evolution, AE and strain field of granite specimens. The experimental results demonstrated that strain concentration bands were first emanated from the tips of pre-existing flaws and developed with continuous increase of external stress, followed by the propagation and coalescence of macro crack. An optical microstructure observation test was carried out to explore the mechanisms of high temperature and cooling rate in altering mechanical properties of granite. At last, the influence of pre-existing flaw on the mechanical behavior of granite was illustrated by numerical simulation. The experimental and numerical results are expected to enhance the understanding of fracture mechanism of rock with respect to high temperature treatment and provide guidance in the analysis and design of deep underground engineering application.

Microstructural evolution and cyclic oxidation of Pt-Al-YSZ coating under thermal shock

In this research, the effect of thermal shock has been investigated on the microstructure and cyclic oxidation of Pt-Al-7%YSZ coating applied on Rene-80 superalloy. The microstructural evaluation and phase identification were performed by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). The thermal shock test consisted of repeated cycles of rapid cooling between 900 °C and 400 °C. Prior to the thermal shock test, the specimen coated by Pt-electroplating, high-activity low-temperature (HALT) aluminizing and the thermal spray of YSZ ceramic layer. From surface towards the substrate; the coating consisted of 5 layers including: 7% YSZ, PtAl2 + β-(Ni,Pt)Al, β-(Ni,Pt)Al with fine precipitates rich in α-(Cr) and α-(W), precipitate-free β-NiAl, and inter-diffusion zone next to the specimen surface. After the thermal shock test, spallation and delamination have been observed in the YSZ layer. The Pt-Al layer was found in upper and lower parts of the coating with different Pt concentration. Also, the chemical composition of the Pt-Al layer demonstrated the removal of PtAl2 particles and β transformation to both γ and γ′ phases. Degradation of Pt-Al layer occurred by ratcheting the thermally grown oxide (TGO), rumpling, and cavitation. Comparison of weight changes showed that the thermal shock resistance is improved by Pt-Al-7% YSZ coating.

Effects of osmotic and thermal shock on the invasive aquatic mudsnail Potamopyrgus antipodarum: mortality and physiology under stressful conditions

Effects of osmotic and thermal shock on the invasive aquatic mudsnail Potamopyrgus antipodarum: mortality and physiology under stressful conditions

Numerical simulations of water spray on flame deflector during the four-engine rocket launching

This paper aims to study on the cooling effect with two types of water spray nozzle on the flame deflector during the four-engine launch vehicle take-off. To accurately simulate the two-phase flow of the rocket gas with multispecies and the water spray, the three-dimensional compressible Navier-Stokes equations, discrete ordinates methods and realizable k-Ɛ turbulence model are used to establish the rocket supersonic plumes impact model. The Eulerian dispersed phase (EDP) model was used to simulate the water spray into the exhaust gas. The accuracy and effectiveness of the gas-liquid flow model are verified by a good agreement between simulation results and experimental data. On this basis, a series of numerical simulation studies under different water injection position are performed. The results show that the high temperature regions, along the axis of engines on the deflector plate, have no significant temperature decreasing effect by water spray from the nozzles mounted on the apex of the deflector, and the high temperature converts a large quantity of water into vapor near the plume boundary, which would decrease the flow conductivity. With the cooling spray nozzle fixed directly to the deflector plate, the temperature decrease effect is obvious and the effect of thermal shock on deflector plate induced by exhaust plume is reduced, so that it can prevent the flame deflector from thermal ablation. The study results provide indepth information and engineering guidance for designing the water spray systems and increasing the safety of the launch process.

Fracture behavior of magnesia refractory materials under combined cyclic thermal shock and mechanical loading conditions

AbstractTo investigate the effect of cyclic thermal shock and mechanical loading on the fracture behavior of magnesia refractories showing different brittleness, the as‐received and cyclic thermally shocked specimens are subjected to monotonic and cyclic wedge splitting test. The whole duration of test is monitored by digital image correlation and acoustic emission. Both thermal and mechanical fatigue resistance increase with the reduction of brittleness. Repetitive thermal shock results in pronounced reduction of strength. However, the specific fracture energy and nonlinearity increase after exposure to thermal shock due to the expanded micro‐crack network inducing the development of a significant fracture process zone. Periodic loading mainly leads to the decrease of strain bearing capacity, as the fatigue loads favor the extension of crack tip instead of fracture process zone expansion. The combined application of periodic thermal shock and mechanical loads gives a new insight into the progressive damage behavior of refractory under critical conditions.

Numerical modelling of heat shock‐assisted rock fracture

SummaryThis paper presents a numerical investigation on the effects of thermal shock as a pretreatment of rock prior to comminution. More specifically, the effect of heat shock‐induced cracks on the uniaxial compressive strength of rock is numerically studied. The chosen constitutive model of rock employs a (strong) embedded discontinuity finite element formulation to describe cracks. The thermomechanical problem that governs the heat shock pretreatment of rocks is considered as an uncoupled problem because of a highly dominating role of the external heat influx. Two solution methods of the global problem are presented: an explicit‐explicit dynamic scheme and an implicit‐implicit quasi‐static scheme. The model performance is tested in simulations on heterogeneous numerical rock samples subjected first to a heat shock pretreatment and then to a mechanical compression test. According to the results, the compressive strength of intact granite rock having the axial splitting failure mode can be substantially reduced by heat shock pretreatment.

Influence of thermal shock on the mitigation of calcium sulfate crystallization fouling under subcooled flow boiling condition

Fouling is a common and high cost problem in various heat transfer equipment. Different on-line and off-line solutions were recommended for fouling mitigation in the recent years. Thermal shock technique which is performed by sudden decrease or increase in heated surface temperature is known as one of the on-line ways to mitigate fouling. In this research, several experiments performed in order to investigate the effects of thermal shock on the fouling mitigation in a vertical upward annulus under subcooled flow boiling conditions for calcium sulfate (CaSO4) aqueous solution. The experiments conducted at different levels of operating conditions such as fluid bulk temperatures (55–75 °C), volume flow rates (2.5–5.5 l/min), heat fluxes (8–95 kW/m2), and calcium sulfate aqueous solution concentrations (1.75–2.2 g/l). The results revealed that at higher fouling resistance approximately above 0.1 m2 K/kW, thermal shock could successfully disintegrate and deteriorate the fouling layer, and return the heat transfer surface to its initial condition.

THE PECULIARITIES OF THERMO-INDUCED KINETICS IN THICK FILMS OF SPINEL-TYPE CERAMICS

Introduction. Today the problem of stabilization of exploitation parameters of functional elements of electron tech-nique become very actually. In this reason in modern radio-electronic equipment the functional elements based on thick films technology with high structure compactness and enough stability to environmental influences are widely used. Purpose. The aim of this work is establishment kinetics of thermoinduced degradation in thick films of spinel-type ceramics based on mixed transition-metal oxymanganites. Methods. The degradation tests were carried out in the long-term isothermal exposure of samples (356 hours) at the 170C in the heat camera HPS 222. Electrical resistances of ceramics samples were measured using digital multime-ter В7-27А/1. The measurements of nominal resistance R were carried out at 25C after certain hours of corresponding stages of thermoexposure during 64, 104, 144, 198, 251, 304 and 356 hours. The relative resistance drift ΔR/R0 (R0 – initial resistance, ΔR – change of electrical resistance caused by degradation test) was used as controlled parameter. The control of temperature was carried out by thermometer ТО-ЦО24. With a purpose of adequate mathematical description of the observed degradation kinetics, the numerical values of different fitting parameters in corresponding relaxation functions were calculated in such a way to minimize the mean-square deviation err of the experimentally measured points from the chosen relaxation function. Results. As a result of experimental study of thermoexposure the effect of thermal shock at the 170оC was re-vealed in Cu0,8Ni0,1Co0,2Mn1,9O4 and Cu0,1Ni0,8Co0,2Mn1,9O4 and sample, while in Co-enriched samples the effect of smooth decrease of electrical resistance was observed.Conclusion. The kinetics of thermodegradation of electrical resistance at 170оC in Cu0,1Ni0,8Co0,2Mn1,9O4 and Cu0,8Ni0,1Co0,2Mn1,9O4 samples were caused by homogeneity structure of sample, while in the Co-enriched compo-sition – contribution of thermoinduced diffusive processes of contacts materials as well as burning of organic binding.

Biochemical and haematological responses to thermal stress in Labeo rohita (Hamilton, 1822) fingerlings

An experiment was conducted to understand the effect of thermal shock on stress and recovery in Labeo rohita (Hamilton, 1822) fingerlings. L. rohita fingerlings were exposed to a temperature of 380C for 2 h and permitted to recuperate afterwards for 48 h. Primary and secondary stress parameters were analysed after 2, 4, 8, 12, 24 and 48 h of recovery. The activity of glucose-6-phosphate dehydrogenase and acetylcholine esterase reduced significantly (p<0.05). Erythrocytes, haemoglobin, respiratory burst activity and lysozyme levels increased significantly (p<0.05) by 7.31, 23.91, 109.09 and 70.13% after thermal shock, whereas leucocytes, serum protein, albumin and globulin showed a reverse trend. During recovery, biochemical parameters normalised in 48 h. However, immunological variables such as serum total protein, albumin and globulin, and histopathological changes in gill and kidney tissues did not return to normal condition.

Effects of thermal shock due to rapid cooling on the mechanical properties of sandstone

Underground engineering can lead to high-temperature disasters in which the rocks surrounding underground structures are heated because of the presence of a high-temperature source. The surrounding rock will experience rapid cooling with the subsequent disaster relief efforts. Thus, it is important to elucidate the effects of rapid thermal cooling (RTC) on the physical and mechanical properties of rocks for real-world engineering applications. In this study, the effects of RTC treatments on the physical and mechanical properties of sandstone were examined at temperatures ranging from 100 to 800 °C through uniaxial compression tests, wave velocity tests, acoustic emission tests, and scanning electron microscopy. The results show that the decrement ratios for both the P-wave velocity and the density of sandstone increased with increases in temperature, and the decrement ratio for the density lagged behind that of the P-wave velocity. The uniaxial compressive strength and elastic modulus values for the sandstone samples varied similarly with increases in temperature following RTC treatments. The variations were divided into three stages: a stable stage, a slow falling stage, and a quick falling stage. Moreover, under uniaxial compressions, no changes in the ductility of the sandstone samples were observed following the RTC treatments, and the specimens were brittle in nature during the postpeak stage.

Combined effect of laser thermal shock and helium ion irradiation on W-Y2O3 composites

Tungsten can be the preferred plasma-facing material for nuclear fusion reaction. In this work, W-Y2O3 composite powder was successfully fabricated through the wet chemical method, and bulk materials were obtained by rolling and high temperature annealing. W-2 vol% Y2O3 was exposed to 80 eV helium ion irradiation with a flux of 1.5 × 1022 ions/(m2·s) at 1503–1553 K to assess its thermal shock resistance and helium ion irradiation damage behavior. The thermal shock behaviors of samples were studied under a laser beam. The energy densities of the laser thermal shock were 0.32, 0.48, and 0.64 GW/m2. W-Y2O3 was compared with commercial pure tungsten. The hardness of pure tungsten and W-Y2O3 before and after helium irradiation was measured by using a micro-hardness tester. The surface micrograph after helium ion irradiation and thermal shock was observed through scanning electron microscopy. Results show that W-Y2O3 composite materials have better resistance to laser thermal shock than pure tungsten.

Mode I and Mode II Granite Fractures after Distinct Thermal Shock Treatments

AbstractIn this study, the effect of thermal shock (TS) on the mechanical properties of granite is investigated. Two schemes are performed to provide different cooling rates for the TS processes. D...

Effects of thermal shock on the microstructures, mechanical and thermophysical properties of SiCnws-C/C composites

In order to understand the effects of thermal shock cycles between 1100 °C and room temperature on SiC nanowires reinforced carbon/carbon (SiCnws-C/C) composites, their microstructure, internal friction behavior, coefficient of thermal expansion (CTE), flexural strength and fracture morphology before and after different thermal shock cycles were studied. The results show that the fiber/matrix (F/M) interface debonding and matrix cracks are the main reasons for the increase of porosity. The SiCnws-C/C composites has the largest internal friction in the whole testing frequency after 10 thermal cycles. The CTE of the composites first decreases and then increases to some extent with the increase of the thermal cycles. The flexural strength of SiCnws-C/C composites increases by 23% after 10 thermal cycles, and then reduces to 92% of the original strength after 20 thermal cycles. The increase of flexural strength and internal friction after 10 thermal cycles is associated with the appropriate F/M interface weakening and the increased d002 values, which also results in the decrease of CTE. Compared to C/C composites, the better thermal shock resistance of SiCnws-C/C composites is attributed to the nanoscale strengthening mechanism brought by SiC nanowires, including their pull-out and bridging.

Combined effect of thermal shock and hot corrosion on the failure of yttria stabilized zirconia thermal barrier coatings

The thermal barrier coatings (TBCs) of 8wt.% yttria stabilized zirconia (8YSZ) on a GH2132 alloy were deposited by air plasma spraying. The combined effect of thermal shock and hot corrosion on the failure of TBCs was highlighted investigated. The results showed that the combined effect of hot corrosion and thermal shock was prone to induce the failure of TBCs. The main failure of TBCs under the combined effect was in the form of penetrating crack to the bondcoat/substrate interface and oxidation at the penetrating crack front.

Damage Analysis of High-Temperature Rocks Subjected to LN2 Thermal Shock

Liquid nitrogen (LN2) fracturing is a technology that can dramatically enhance the stimulation performances of high-temperature reservoirs, such as hot dry rock geothermal and deep/ultra-deep hydrocarbon reservoirs. The aim of the present study was to investigate the damage characteristics of high-temperature rocks subjected to LN2 thermal shock, which is a critical concern in the engineering application of LN2 fracturing. In our work, the rocks (granite, shale and sandstone) were slowly heated to different temperatures (25 °C, 150 °C and 260 °C) and maintained at the target temperatures for 10 h, followed by LN2 quenching. After thermal treatments, we tested the physical and mechanical properties of the rocks to evaluate their damages. Additionally, sensitivities of the three rocks to thermal shock were also compared and analyzed. According to our experiments, LN2 thermal shock can enhance the permeability of the rocks and deteriorate their mechanical properties significantly. Increasing rock temperature helps strengthen the effect of LN2 thermal shock, leading to more severe damage. Inter-granular cracking is the primary contribution to the rock damage in the LN2 cooling process. Compared with granite and shale, sandstone is less sensitive to LN2 thermal shock. The lower sensitivity of sandstone to thermal shock is mainly attributed to its larger pore spaces and weaker heterogeneity of mineral thermal expansion. The present paper can provide some guidance for the engineering application of LN2 fracturing technology.

Synthesis and thermal shock evaluation of porous SiC ceramic foams for solar thermal applications

AbstractReticulated porous ceramics with structural features spanning across multiple length scales are emerging as the primary media in a variety of demanding mass and heat transfer applications, most notably solar‐assisted synthetic fuel processing. In this study, we focus on engineering of the open pore silicon carbide (SiC)‐based foams in such catalytic applications. We evaluate the mechanical integrity and thermal stability of these porous structures. X‐ray tomography analyses of the 3D structures reveal the presence of dual pore size distribution different by up to an order of magnitude in length scale. We further study the effect of thermal shock—induced via water quenching—on the SiC structures and we conclude that the mechanical properties of the ceramic foams are significantly reduced after thermal stress. Comparison of SEM micrographs—before and after thermal shock—reveals that needle‐like features appear inside the foam matrix. These elongated defects may be responsible for structural and mechanical weakening.

The coupling effects of laser thermal shock and surface nitridation on mechanical properties of Zr-based metallic glass

Laser processing is a versatile tool for applications in the field of metallic glasses (MGs). Previous studies reported that surface nitridation, i.e. the formation of ZrN phase, occurred when laser irradiation of Zr-based MG was performed in nitrogen gas. Additionally, it was reported that laser thermal shock usually softened the irradiated surface. Therefore, the coupling effects of laser thermal shock and surface nitridation on mechanical characteristics of Zr-based MG should be further clarified. For this purpose, in this study, laser irradiation of Zr-based MG was conducted under various experimental conditions, followed by evaluating the surface characteristics by X-ray diffraction (XRD), nanoindentation, and energy-dispersive X-ray (EDX) spectroscopy. Experimental results indicated that the nanoindentation hardness, serrated flow, and surface shear bands were significantly affected by laser irradiation in nitrogen gas. Both surface softening and hardening were observed which depended on the experimental conditions. A competition mechanism between laser thermal shock and the introduction of ZrN phase was employed to rationalize these results. Furthermore, the affecting layer of ZrN phase along the depth direction was measured by EDX. The obtained results suggest a new method to introduce secondary phase into Zr-based MG surface and further to tune the mechanical characteristics of MGs.

Evaluation of post-thermal shock effects in Carrara marble and Santa Caterina di Pittinuri limestone

This article describes the effect of thermal shock on the petrographic and petrophysical properties of two Italian carbonate building stones: Carrara marble from the Apuan Alps in Tuscany and ‘Santa Caterina di Pittinuri’ limestone, from Sardinia.The samples were exposed to two thermal cycles to study surface and inner stone decay. The changes induced by thermal shock were assessed in terms of microstructural alterations measured with ultrasonic pulse velocity, Hg intrusion porosimetry, polarised light and fluorescent optical microscopy and micro-computed tomography. Variations in surface microhardness were also measured. The marble developed a dense network of pseudo-parallel intercrystalline, intracrystalline and transcrystalline microcracks, whereas the limestone underwent no significant microcracking. Those findings attested to lower resistance to thermal shock in marble calcite crystals than in limestone sparite cement and micrite. Thermal shock, an accelerated weathering technique, simulates possible stone exposure to high temperatures over long periods of time. Here the method was used to evaluate and compare microcrack distribution and orientation in the two heritage stones studied.