Magnitude Of Thermal Stresses Research Articles

Quantifying the potential of evidence-based planting-pattern for reducing the outdoor thermal stress from a bio-meteorological perspective in tropical conditions of Indian cities.

The impact of declined natural greenery and increased built surfaces exacerbates heat stress in urban areas causing limited usage of outdoor spaces. Greenery strategies such as trees are capable of mitigating outdoor thermal stress gain because of their phytological properties. While urban greenery guidelines have suggested the ad-hoc procedure of tree planting-schemes based on aesthetic-value, soil-water preservation etc., understanding of their morphological character help in regulating extreme thermal condition. Hence, this study aims to investigate the most efficient planting pattern based on canopies densities and trees clusters for reducing the outdoor thermal stress from bio-meteorological perspective.It initiates with the measurement of the site's morphological and meteorological attributes in existing commercial market of Bhopal City which has a humid sub-tropical climate (Aw, Koppen climate categorization). Furthermore, it leads to the development of 4-different iterated clusters incorporating moderate to high-density canopies and their overlaps pattern to estimate reduction potential in outdoors using field surveys and validated simulation model. The reduction potential in terms of magnitude and duration of thermal stress is quantified across 3-thermal variables i.e., air temperature, mean radiant temperature and universal thermal climate index. Results indicate highly-dense canopies are more effective in reducing greater magnitude of thermal stress along longer duration. Also overlapped planting pattern within the same canopy density does not make significant difference in stress reduction as compared to the changing the densities. This study will help planners and landscape architects to adopt evidence-based planting-pattern strategies for improving outdoor microclimate.

ВЛИЯНИЕ ТЕРМОДИНАМИЧЕСКИХ ПАРАМЕТРОВ ПЛАЗМЕННОЙ СТРУИ НА АДГЕЗИОННУЮ ПРОЧНОСТЬ ГАЗОТЕРМИЧЕСКИХ ПОКРЫТИЙ

Gas-thermal spraying of metals and alloys makes it possible to obtain coatings with high performance properties on the surfaces of parts. These coating methods can be effectively used in the restoration of worn-out parts of machines and equipment of various types, which, in the face of large-scale sanctions, is one of the most important tasks of technological independence of Russian industries. (Research purpose) The research purpose is searching for the regularities of the influence of the main thermodynamic parameters of the plasma jet on the adhesive strength of the formed coatings. (Materials and methods) The deposition of refractory metals and alloys on a graphite substrate was carried out using the UPU-3 plasma installation. The temperature and velocity of the particles during plasma spraying of the wire were determined according to the generally accepted method. The average mass temperature of the particles in the considered section of the plasma jet was estimated by the increment of the enthalpy of the particles of the deposited metal. When calculating the heating temperature of the particles of the sprayed powder material, it was assumed that the temperature field of the gas stream beyond the nozzle section is determined by the thermophysical properties of plasma-forming gases and the conditions of heat exchange of the jet with the environment. The adhesive strength of the coatings was measured by the shear method. To estimate the values of residual stresses, temperature fields in the deposited layer and substrate were studied. (Results and discussion) The existing theoretical ideas about the physical processes in the formation of gas-thermal coatings were analyzed. The main thermophysical characteristics of the plasma jet affecting the sputtering of various powder and wire materials were considered. The factors ensuring the maximum adhesion strength of gas-thermal coatings to the surface of the composite material were determined. (Conclusions) It has been proved that the temperature of the particles of the sprayed material determines the adhesion strength of the coatings. The magnitude of thermal stresses occurring in coatings depends on the ratio of the thermophysical constants of the coating material and the substrate. To obtain coatings with maximum adhesive strength during high-temperature spraying of the material, it is necessary to additionally take into account the conditions determined by the forces of mechanical engagement of deforming particles.

Calculation and properties of thermal stress of monolayer film and solution of thermal stress of multilayer infrared antireflection coating by finite element analysis

The deposition of infrared antireflection coatings on silicon lenses is a widely practiced technique that has been extensively investigated by researchers over an extended period. Thermal stress is essential to the adhesion between the film and the substrate. To measure the magnitude of thermal stresses, we use the mechanical analysis method to convert thermal stresses into shearing and peeling stresses. Expressions for these two stresses are then derived. Then, we analyzed the effect of the monolayer film's properties on the silicon substrate's stress. The results indicate that peeling stress is the main factor affecting the adhesion between the film and the substrate, and various approaches can be employed to successfully mitigate the peeling stress exerted on the substrate. The influence of the multilayer film's structure on the peeling stress experienced by the silicon substrate was investigated through the utilization of finite element analysis. In this study, three distinct infrared antireflection coatings were deposited on silicon substrates individually. Subsequently, these coated substrates underwent rigorous environmental testing. The findings from this testing confirmed the accuracy of the stress analysis results obtained by finite element analysis for the multilayer film. Our research has resulted in solutions for determining the magnitude of shearing and peeling stress. We have employed finite element analysis to identify a suitable structure for an antireflection coating that exhibits minimal peeling stress. This advancement has the potential to improve the effectiveness of design processes and the adaptability of infrared antireflection coatings in various environmental conditions.

Thermal and structural performance of additively manufactured ceramic porous media burners

This study examines the effect of porosity, topology and material composition on the performance of additively manufactured ceramic porous media burners. Thermal-structural simulations of triply periodic minimal surfaces (TPMS) were performed to investigate thermal-stress magnitude and distribution. Alumina and mullite TPMS structures were 3D-printed and tested in a methane-air combustion experiment, where the mullite structures showed superior durability compared to alumina. X-ray imaging revealed notable correlation between predicted high tensile stress regions and experimental crack formation. At equivalent porosity and cell size, TPMS structures with higher specific surface area and tortuosity were found to have lower thermal strain and propensity for structural failure. Structures with these features, namely diamond and I-WP, demonstrated favorable thermal and structural behavior under identical thermal conditions. These findings can guide the design and manufacturing of high-temperature applications with embedded porous structures, such as heat exchangers, catalytic converters, and thermal management systems.

Numerical simulation and optimization of In-Vessel primary heat exchangers of NHR200-II

NHR200-II is a multipurpose small integral pressurized water reactor. The primary heat exchangers of NHR200-II are in-vessel single-phase heat exchangers. The primary heat exchangers adopted a tube-in-tube bundle design to improve compactness; however, a significant weakness of the tube-in-tube bundle is the nonuniform thermal expansion between the inner and outer tubes owing to the inhomogeneous tube-temperature distribution. To minimize the thermal stress, the inner and outer tube diameters were optimized using numerical simulations. The nonuniform mass flow rates and temperature fields in each channel and tube were calculated using the optimal tube sizes, and the axially averaged temperatures of the inner and outer tubes were also calculated. The present prediction of nonuniform temperature fields can be used as the input to estimate the magnitude of thermal stress in the assessment of the structural integrity of the primary heat exchangers of NHR200-II.

Decompression and Fracturing Caused by Magmatically Induced Thermal Stresses

AbstractStudies of host rock deformation around magmatic intrusions usually focus on the development of stresses directly related to the intrusion process. This is done either by considering an inflating region that represents the intruding body, or by considering multiphase deformation. Thermal processes, especially volume changes caused by thermal expansion are typically ignored. We show that thermal stresses around upper crustal magma bodies are likely to be significant and sufficient to create an extensive fracture network around the magma body by brittle yielding. At the same time, cooling induces decompression within the intrusion, which can promote the appearance of a volatile phase. Volatile phases and the development of a fracture network around the inclusion may thus be the processes that control magmatic‐hydrothermal alteration around intrusions. This suggests that thermal stresses likely play an important role in the development of magmatic systems. To quantify the magnitude of thermal stresses around cooling intrusions, we present a fully compressible 2D visco‐elasto‐plastic thermo‐mechanical numerical model. We utilize a finite difference staggered grid discretization and a graphics processing unit based pseudo‐transient solver. First, we present purely thermo‐elastic solutions, then we include the effects of viscous relaxation and plastic yielding. The dominant deformation mechanism in our models is determined in a self‐consistent manner, by taking into account stress, pressure, and temperature conditions. Using experimentally determined flow laws, the resulting thermal stresses can be comparable to or even exceed the confining pressure. This suggests that thermal stresses alone could result in the development of a fracture network around magmatic bodies.

Thermal fatigue and cracking behaviors of asphalt mixtures under different temperature variations

Thermal cracking is one of the most annoying distresses in asphalt pavements. The cracking of asphalt pavements caused by extremely low temperature and the damage of thermal fatigue caused by repeated temperature variations are particularly pronounced. The service condition of asphalt pavements has been affected significantly. Laboratory experiments with cyclic loads simulating the actions caused by repeated temperature variations on pavements have been conducted in many previous studies to investigate the thermal fatigue characteristics of asphalt mixtures. In those studies, an equivalent cyclic mechanical stress that can be applied by an actuator was mostly used to replace the cyclic thermal stress induced by a temperature variation. It could simplify the experimental process but could not consider the performances of asphalt mixtures varying as a function of temperature. In the present study, the thermal fatigue properties and cracking behaviors of asphalt mixtures were comprehensively investigated through a modified thermal stress restrained specimen test (TSRST) and the numerical analysis. Various temperature ranges (-20 to −10 °C, −10 to 0 °C), cyclic cooling rates (10 °C/h, 20 °C/h), low-temperature performance cooling rates (10 °C/h, 8 °C/h, 6 °C/h, 4 °C/h, 2 °C/h) and pre-crack dimensions were considered for the study to address the influences of those parameters on the analysis results. Based on the testing and simulation results, it was found that the effects of thermal fatigue on asphalt mixtures under different temperature variations and cooling rates were quantified, and the damage characteristics of the asphalt mixtures were also explored. The results showed that under the low-temperature performance state, the thermal stress of asphalt mixtures increases with a uniform cooling rate and it could be obtained that the faster the cooling rate, the larger the thermal stress generated. In the cyclic thermal stress test, due to the viscoelastic properties of asphalt mixtures, the thermal stress showed significant stress relaxation phenomena under the temperature variations. The magnitude of thermal stress decreased gradually within each cycle. It demonstrates that under the same temperature variation, the thermal stress decreases continuously with the increasing thermal cycles. Through the numerical simulation, it was clear that under different temperature ranges and cooling rates, the magnitude of thermal stress increased with the temperature range decreased, whereas the magnitude of thermal stress increased with an acceleration of the cooling rate. The lower temperature range induced a larger stress intensity factor (KI), which implies a faster cracking evolution. Analyzing the effects of different pre-crack dimensions on the number of temperature cycles, the height of pre-crack showed significant effects on the number of temperature cycles than width.

Influence of heat-protective coatings on the temperature state of tractor diesel pistons

BACKGROUND: The paper presents the results of thermometry of pistons with the TsNIDI type combustion chamber (CC) of the D-240 and the D-245 tractor diesel engines. Various constructive and technological measures aimed at increasing the thermal resistance of pistons are considered.
 AIMS: To evaluate the effect of heat-protective coatings on the temperature state of pistons with the TsNIDI type combustion chamber.
 METHODS: Motor bench tests of the D-240 and the D-245 diesel engines, equipped with pistons with heat-protective coatings (HPC) on the bottom, were carried out. In the process of research, the influence of the HPC on the thermal state of the pistons as well as on the power and economic indicators of these diesel engines was studied.
 RESULTS: It is established that hard anodizing leads to a slight decrease in temperatures and their differences at characteristic points of the piston in stationary and non-stationary diesel operation modes. It is noted that the slow rise in temperature at the bottom of the piston is caused by a decrease in the amount of heat supplied to it due to the low thermal conductivity of the oxide layer. It is shown that the PN85Yu15 gas-plasma coating leads to a significant decrease in temperatures and their differences along the piston bottom. It is determined that this coating helps to reduce the specific effective fuel consumption due to the reduction of the ignition delay period in the combustion process. It is noted that a slower growth rate of temperatures and their differences, especially in the zone of the edge of the CC, should reduce the magnitude of thermal stresses, and therefore increase the thermal resistance of the experimental pistons.
 CONCLUSIONS: It is revealed that the most effective way to reduce the heat stress of the piston is the application of heat-protective coatings on its bottom. The influence of the abovementioned coatings on the nature of the temperature distribution and their differences in the piston head is investigated.

EXPERIMENTAL AND NUMERICAL ANALYSIS FOR THERMAL PROBLEM OF FRICTIONAL BRAKE SYSTEM

The present work aims to validate the experimental results of a new test rig built from scratch to evaluate the thermal behavior of the brake system with the numerical results of the transient thermal problem. The work was divided into two parts; in the first part, a three-dimensional finite-element solution of the transient thermal problem using a new developed 3D model of the brake system for the selected vehicle is SAIPA 131, while in the second part, the experimental test rig was built to achieve the necessary tests to find the temperature distribution during the braking process of the brake system. We obtained high agreement between the results of the new test rig with the numerical results based on the developed model of the brake system. It was found in some cases the local zones with extreme heat generated in contacting surfaces due to the non-uniformity of the contact pressure during the braking process, where this phenomenon can be led to an increase in the magnitudes of thermal stresses. It was found that the most significant factor on the level of generated temperatures (heat generation) is the initial vehicle's velocity. Furthermore, it was found that the maximum difference between the experimental and numerical results was not exceeding 6%.

Experimental and Numerical Analysis for Thermal Problem of Frictional Brake System

The purpose of the present work is to evaluate the validate the experimental results of new test rig that built from scratch to evaluate the thermal behavior of the brake system with the numerical results of the transient thermal problem. The present work consists of two parts; in the first part, the finite element solution using 3D model of brake system for selected vehicle is SAIPA 131, for transient thermal problem, where a new finite element model has been developed using COMSOL 5.5 software. While in the second part, the experimental test rig was built to achieve the necessary tests to find the temperature distribution during the braking process. It was obtained high agreements between the new test rig with numerical results based on the developed model of the brake system. It was appeared in some cases local zones with extreme heat generated in contacting surfaces due to the non-uniformity of the contact pressure during the braking process, where this can be led to increase the magnitude of thermal stresses. Build a calibrate a new test rig of the brake system to evaluate the thermal behaviour and performance of the brake system. Also, it was validated the experimental results with the numerical results of the transient thermal problem and it was obtained an acceptable agreement (difference between them is not exceeding 6 %). Also, it was developed a new finite element model of the brake system to find the solution of the transient thermal problem.

Impact assessment of the IGR graphite block uneven impregnation with uranium on thermal strength properties

The paper presents the results of a numerical interdisciplinary analysis of the fuel element of a heat capacity type research pulsed reactor (IGR). The fuel element of the IGR reactor is a graphite block impregnated with a solution of uranyl dinitrate. During the operation of the reactor, graphite blocks can be heated to high temperatures in a short period of time, which, together with the uneven impregnation of the block with uranium, which is due to the technological process of its manufacture, leads to the appearance of internal structural stresses. The purpose of this work is to make numerical estimation of the magnitude of thermal stresses arising in a graphite block. To carry out such an assessment, two computational models of a graphite block were built. One model is designed to perform neutron-physical calculations using a verified model of the IGR reactor core and the MCNP code, the other is designed to perform thermal strength analysis in the ANSYS software package. Thermal strength analysis includes two stages of calculations – thermal and structural (strength). Both models developed in the way to have the most similar topology, since this directly affects the correct distribution of the energy release over the volume of the block when transferring the results of the neutron-physical calculation to the thermal model. The operation of a graphite block as part of the reactor core was simulated during a start-up lasting 4 s at a stationary power of 2 GW, followed by cooling down for 5 s. Numerical values and distribution diagrams of temperature and stresses arising in the volume of the block are obtained. The results of the analysis confirm the effect of the uneven impregnation of the graphite block of the IGR reactor with a solution of uranyl dinitrate on its thermal strength characteristics.

Finite element simulation of thermal stress in RF magnetron sputtered SiC coating as tritium penetration barrier

The magnitude of thermal stress in the tritium penetration barrier coating is crucial during RF (radio frequency) magnetron sputtering preparation. The thermal stress would cause the delamination or crack on the coating, which seriously affects the structural stability of the coating. In this work, a finite element model represented the SiC tritium penetration barrier coating system was established. The relevant parameters which affected the magnitude of thermal stress of the system were discussed in detail. The shear and radial stresses in the system were also evaluated in order to identify the locations where the materials were prone to failure. Then, the propagation of multiple surface cracks in the system was investigated. Finally, the thermal stress was optimized by an Al2O3 interlayer. The outcomes indicated that the addition of the Al2O3 interlayer alleviated the stress at the interface and enhanced the mechanical stability and adhesive strength of the coating.

Heat stress and sperm production in the domestic cat

This study aimed to assess 1) the effect of high environmental temperatures on sperm production and 2) the effectiveness of a temperature-humidity index (THI) to predict the degree of thermal stress in a cat model. Semen collection was performed by electroejaculation for 18 mo in 20 tomcats maintained under controlled photoperiod. Still, temperature and humidity were not experimentally manipulated to describe the effect of natural climate conditions on seminal samples. Ejaculates (n = 512) were then grouped according to temperature records of the sampling day and compared by temperature and THI index. Significant lower sperm parameters and increase sperm tail abnormalities were observed during warm environments (temperature and THI). Concentration and total sperm count were the most affected parameters. Environmental temperatures of 28.5 °C with 54% relative humidity (THI = 77.07) and 27.9 °C with 66% humidity (THI = 77.84) were upper thresholds of moderate thermal stress. Moreover, days with relative humidity near 90% led to severe thermal stress with temperatures as low as 26.6 °C (THI = 78.88). The current study demonstrates the detrimental effect of high environmental temperatures on sperm quality in the domestic cat. This effect is observed at lower temperatures when high relative humidity is present. In this sense, the THI was a reliable predictor of the magnitude of thermal stress experienced by cats. Thus, cats from reproductive programs should be maintained under controlled photoperiod cycles with temperatures around 20 °C and humidity around 70% to avoid semen detrimental effects.

Design of thermal and environmental barrier coatings for Nb-based alloys for high-temperature operation

The design of thermal and environmental barrier coatings (T/EBCs) applied to Nb-based alloys for high-temperature operation (>1200 °C) was studied. Different multilayer T/EBCs consisting of rare earth aluminates, silicates, and zirconates (with Y 3 Al 5 O 12 (YAG), Y 2 SiO 5 (YMS), and Gd 2 Zr 2 O 7 (GZO) as exemplars) are proposed. Mechanics models were used to determine the magnitude of thermal stresses developed and the tendency for delamination or penetration cracking. The calculated energy release rates (ERRs) for crack formation show that the T/EBC composed of a porous YAG layer (porosity > 0.15) and a dense YAG + YMS layer is effective in preventing the delamination and can potentially arrest cracks penetrating from the surface before reaching the substrate. Phase equilibria calculations indicate that all combinations are stable to above their expected use temperatures. The greatest likelihood for melting is the scenario where a YAG + YMS solid mixture contains excess SiO 2 due to process variability, but even in this case the melting temperature, 1430 °C, exceeds the corresponding temperature in the prescribed temperature profile. • Multilayer thermal/environmental barrier coatings inhibit crack growth. • Rare earth aluminate and silicate coatings are suitable for Nb-based alloy. • Phase mixtures have better properties but lower melting temperatures. • Columnar porosity in coating reduces energy release rate for crack formation.

Caster roll failure prevention – Prognosis & diagnosis through monitoring system of machine cooling water circuit

Rourkela Steel Plant has two slab casters having soft water circuit for machine cooling. Each caster segments comprises of solid forged steel rolls with water-cooling hole in guide roll. Failure of these rolls due to thermal fatigue restricts the efficiency of continuous casting operation. The main reason for roll breakage due to thermal fatigue is the reduced volume of water through the internal cooling hole and allowing rolls operating temperature to increase. The magnitude of thermal stress is influenced by the external and internal roll cooling efficiency since it controls the magnitude of ΔT. Impairment of internal cooling efficiency can lead to development of fire cracks of the bore surface and finally leading to roll failure. To prevent the caster roll failure due to thermal fatigue as a sequel to impairment of internal water cooling efficiency, the need was to install a system for real time measurement of water flow, pressure and temperature of inlet and outlet water through these segments. A system for real-time measurement of these parameters was installed in the caster segment of Steel Melting Shop- Rourkela Steel Plant for prognosis and diagnosis of the impairment of the internal cooling water circuit. Through the various dashboards, it was possible to monitoring the inlet – outlet water flow rate, pressure difference and differential temperature. Diagnosis of the causes of the rise in differential temperature was made possible through the water flow rate and pressure indications in the dash board. Through the monitoring system for machine cooling water circuit it was possible to reduce the caster roll failure due to thermal fatigue through proper diagnosis and prognosis. The monitoring systems for machine cooling water circuit has been effectively used for preventing the failure of caster rolls due to reduced thermal stresses and improve the machine availability.

The importance of 1.5°C warming for the Great Barrier Reef.

Tropical coral reefs are among the most sensitive ecosystems to climate change and will benefit from the more ambitious aims of the United Nations Framework Convention on Climate Change's Paris Agreement, which proposed to limit global warming to 1.5° rather than 2°C above pre-industrial levels.Only in the latest Intergovernmental Panel on Climate Change focussed assessment, the Coupled Model Intercomparison Project phase 6 (CMIP6), have climate models been used to investigate the 1.5° warming scenario directly. Here, we combine the most recent model updates from CMIP6 with a semi-dynamic downscaling to evaluate the difference between the 1.5 and 2°C global warming targets on coral thermal stress metrics for the Great Barrier Reef (GBR). By ~2080, severe bleaching events are expected to occur annually under intensifying emissions (shared socioeconomic pathway SSP5-8.5). Adherence to 2° warming (SSP1-2.6) halves this frequency but the main benefit of confining warming to 1.5° (SSP1-1.9) is that bleaching events are reduced further to 3 events per decade. Attaining low emissions of 1.5° is also paramount to prevent the mean magnitude of thermal stress from stabilizing close to a critical thermal threshold (8 Degree Heating Weeks). Thermal stress under the more pessimistic pathways SSP3-7.0 and SSP5-8.5 is three to fourfold higher than the present day, with grave implications for future reef ecosystem health. As global warming continues, our projections also indicate more regional warming in the central and southern GBR than the far north and northern GBR.

Correlation between intermediary metabolism, Hsp gene expression, and oxidative stress-related proteins in long-term thermal-stressed Mytilus galloprovincialis.

Long-term exposure of Mytilus galloprovincialis to temperatures beyond 26°C triggers mussel mortality. The present study aimed to integratively illustrate the correlation between intermediary metabolism, hsp gene expression, and oxidative stress-related proteins in long-term thermally stressed Mytilus galloprovincialis and whether they are affected by thermal stress magnitude and duration. We accordingly evaluated the gene expression profiles, in the posterior adductor muscle (PAM) and the mantle, concerning heat shock protein 70 and 90 (hsp70 and hsp90), and the antioxidant defense indicators Mn-SOD, Cu/Zn-SOD, catalase, glutathione S-transferase, and the metallothioneins mt-10 and mt-20. Moreover, we determined antioxidant enzyme activities, oxidative stress through lipid peroxidation, and activities of intermediary metabolism enzymes. The pattern of changes in relative mRNA expression levels indicate that mussels are able to sense thermal stress even when exposed to 22°C and before mussel mortality is initiated. Data indicate a close correlation between the magnitude and duration of thermal stress with lipid peroxidation levels and changes in the activity of antioxidant enzymes and the enzymes of intermediary metabolism. The gene expression and increase in the activities of antioxidant enzymes support a scenario, according to which exposure to 24°C might trigger reactive oxygen species (ROS) production, which is closely correlated with anaerobic metabolism under hypometabolic conditions. Increase and maintenance of oxidative stress in conjunction with energy balance disturbance seem to trigger mussel mortality after long-term exposure at temperatures beyond 26°C. Eventually, in the context of preparation for oxidative stress, certain hypotheses and models are suggested, integrating the several steps of cellular stress response.

Effect of wiper on thermal stresses during direct chill casting of magnesium alloy

Understanding the thermomechanical behaviour of an alloy during the Direct Chill (DC) casting process is essential to alleviate the defects in the casting. In this work, conventional direct chill casting process is numerically modelled for evaluating the thermal stress profiles in the casting of AZ31 magnesium alloy. A cooling strategy is used where a wiper is positioned below the mold to reduce the cooling intensity and magnitude of thermal stresses. In this work, the effect of the wiper on the reduction of thermal stress is analysed in detail during the DC casting of AZ31 magnesium alloy. A 2-D computational domain growing along with the casting speed is used to replicate the DC casting process. The temperature and stress profiles are calculated by sequentially solving the energy and momentum balance using the Finite Element Method. The effect of a cooling strategy, on the variation of radial, axial and circumferential stresses is analysed. It is observed that there is a decrease in the circumferential and radial stresses developed in the billet below the mold. Implementation of wiper resulted in higher temperature billet surface which led to reduction of the stresses both in the circumferential and radial direction.

Research on thermal shock resistance of porous refractory material by strain-life fatigue approach

The study aims to investigate the effects of pore structure on the thermal shock resistance of porous refractory materials. Porous material is constituted by a solid frame and the pores filling with air. A direct thermo-mechanical coupling simulation and strain-life approach were employed to predict the number of thermal shock cycles of the materials; thus, influences of the porosity and distribution of pores on the thermal shock resistance were studied. The specimen was subjected to a mechanism of thermal shock damage in which alternating thermal stress under cyclic ‘hot’ and ‘cold’ shock. The simulation results show that the magnitude of thermal stress is large during the thermal shock process. And the residual thermal stresses generate at the solid/air interface since stress gradients occur inside the bulk. Furthermore, higher or lower porosity had no positive effect on the thermal shock resistance of the porous material; the highest thermal shock resistance was attained at a porosity of 20%. The uniform distribution of pores is favorable to improve the thermal shock resistance of materials of high porosity. The validation test results show that the number of thermal shock cycles of the two samples in the experiments were closer to the situations of chaotic pore distributions in the simulations.

Macro-micro mechanical properties of building sandstone under different thermal damage conditions and thermal stability evaluation using acoustic emission technology

Changes in the internal structure and mechanical stability of building sandstone under fire and high-temperature have been the focus of many studies. We aimed to study the macro and micro mechanical properties of building sandstone under different thermal damage conditions and evaluate its thermal stability. Consequently, in this work, changes in mechanical properties of sandstone are evaluated after subjecting the material to heat treatment at different temperatures. Besides, the causes of mechanical deterioration of sandstone after high-temperature treatment are analyzed and the damage evolution of sandstone is characterized by acoustic emission (AE) technology. Following the high-temperature treatment, the macro and micro properties of building sandstone show an obvious change, and the wave velocity decreases as a cubic polynomial. The peak stress of sandstone under load decreases gradually after the action of temperature, and the impact of temperature change on the internal composition of sandstone, especially the decrease of SiO2 content and the increase of porosity, is mainly responsible for mechanical degradation. The AE characteristics of sandstone under unconstrained heating, uniaxial loading at room temperature, and heating loading conditions were tested. The accumulative ring ratio of AE increased linearly with the increase of temperature or deformation, and the correlation coefficient was higher. The correlation coefficient under temperature and loading was more than 0.94. The magnitude of thermal stress in sandstone during the heating process was analyzed theoretically, and static damage factor and dynamic damage factor were calculated quantitatively with wave velocity and AE as characteristic parameters. A compound damage factor is proposed, that is, composite damage includes both thermal damage and loading damage. Our results are of great significance to the stability evaluation of building sandstone subjected to fire and high temperatures.