Papers by Keyword: Thermal Stress

Abstract: CMAS attack is known to occur owing to the deposition of volcanic ash onto thermal barrier coating (TBC) surface at a high-temperature environment. The serious problem is TBC spallation resulting from the infiltration of molten volcanic ash into the porous microstructure of TBC. The infiltration induces inner stress and phase transformation, which directly results in those serious problems. In this study, the diffusional equation for expressing the infiltrating process of the molten ash into the porous structure of TBC and the associated constitutive equation considered regarding phase transformation are formulated. The equations are installed into commercial finite element (FE) code (MARC) using the user subroutine. The numerical simulation results are compared with the cross-sectional SEM observation for the volcanic-ash-deposited TBC sample exposed at a high-temperature to confirm verification of the model proposed herein.

Abstract: The paper presents the results of experiments carried out on test samples made from reinforced concrete. Within this experiment, concrete beams with steel reinforcement in the middle were made. The concrete samples were tested by a non-destructive acoustic Impact-echo method before and after high temperature loading (after cooling to room temperature). We focused on the dominant frequencies shift in the frequency spectra obtained by this method. The aim was to assess the ability of aforementioned acoustic method to detect the thermal damage of steel reinforced concrete.

Abstract: Pressurizer surge line is one of the key equipments of nuclear power plants. The thermal stratification due to the intersection of hot and cold fluids inside the pressurizer surge line may affect the safe operation of nuclear power plant. In order to investigate the stress distribution and fatigue characteristics of surge line subjected to long-term thermal stratified loadings, a mechanical model of the surge line was established. And then, according to different temperature distribution assumptions, thermal stress analysis and fatigue assessment were conducted. The results show that the maximum stress appears under the load condition with maximum temperature difference, and finer temperature distribution can obtain more accurate stress and displacement results. The maximum value of fatigue cumulative coefficient appears at the junction of straight pipe and elbow with large temperature difference.

Abstract: In this study, the analysis method for thermomechanical properties of plain-woven composites is developed, and applied to thermoelastoviscoplastic analysis of plain-woven glass fiber-reinforced plastic (GFRP) composites. For this, a time-dependent constitutive equation depending on temperature for matrix materials is incorporated into the micro/meso/macro-scale thermo-elastic homogenization method for plain-woven composites developed by our research group. This method enables us to analyze thermoelastoviscoplastic properties in not only fiber bundles but also fibers and matrix materials in fiber bundles, as well as macroscopic thermal properties. This method is then applied to the thermal expansion analysis of a plain-woven GFRP composite subjected to a macroscopic temperature change from 25°C to 80°C before it is cooled to 25°C. Comparing the analysis results with experimental data, we validate the present method. It is also shown that the present method can evaluate themal residual stress and strain in the composite.

Abstract: In deep water drilling, the existence of boost line makes the wellbore temperature change violently, and the thermal stress caused by it has a great influence on the strength of the riser. The paper considers the variable mass flow caused by the boost line fluid entering the wellbore during deepwater drilling. Based on the principle of conservation of mass and energy, the paper establishes a mathematical model for transient heat transfer in different regions of the wellbore and formation, analyzes the effect of the displacement of boost line on the temperature field of the wellbore, and calculates the transient stress of the casing under thermal effect. The results show that with the increase of cycle time, the temperature of the inner wall of the riser above the critical well depth first decreases and then increases. The thermal stress of the inner wall of the riser first increases and then decreases to zero, and then gradually increases, and the final thermal stress remains unchanged. With the increase of cycle time, the thermal stress of the inner wall of the riser increases with the increase of the circulating temperature of the inner wall of the riser below the critical well depth, and the rate of increase decreases gradually, and the final thermal stress remains unchanged. As the displacement of the riser increases, the circulating temperature of the inner wall of the riser increases, and the thermal stress on the inner wall of the riser increases. The research results can provide reference for the analysis of the factors affecting the riser stress in deep water drilling.

Abstract: Cement-concrete pavement not only has a long service life even at high loads but also has competitive production costs and fewer significant maintenance costs. The concrete road surfaces, thus, are rather economical. In this article, the Vietnamese Standard TCVN 9382 - 2012 was used to determine the heavyweight concrete composition for rural road construction. Assessment of the crack appearance in the concrete block body was made by the temperature field analysis, the thermal stress and cracking index. The conducted studies' result provided with the possibility of obtaining heavyweight concrete from Vietnam local raw materials regarding to the concrete mixture workability of 11-13 cm standard cone, 31-36 MPa compressive strength of heavyweight concrete at the age of 28 - day - normal hardening and 0.30 - 0.42 MPa average water resistance of samples. Using natural pozzolan to replace 20% of mass cement in the concrete mixture leads to a decrease in the concrete strength characteristics at different ages. The concrete compressive strength of composition No2 decreased mostly by 23% at the age of 3 days and least by 14% at the age of 28 days in comparison these values of composition No1. However, all of these concrete compressive strengths at the age 28 days are higher than 30 MPa. Replacing 20% of the mass Portland cement by natural pozzolan in a concrete mix will decrease price for 1 m³ concrete of 219.96 rubles. By applying the computer program MIDAS CIVIL, the maximum temperature in the concrete block center which was determined after 12 hours from the commencement of mixing of raw materials with water, equals to T_max = 34.61 ⁰С. At the same time, the structure temperature difference between the center (node793) and surface (nodes 120 and 898) of the concrete pavement can be neglected because of its insignificance. Besides, the cracking indexes at three hazardous locations of investigated structure are higher than 1, the cement-concrete pavement will be considered as non-appearance of cracks. However, the cracking index at center (node 793) is always less than this on the surface (nodes 120 and 898), equally to higher thermal crack occurrence at center. Therefore, it is necessary to monitor the development and expansion of thermal cracks to ensure the concrete mixture proper care during the hardening process.

Abstract: A thick glass plate was cut by using hot wire. Crack growing was stopped when wire temperature was low. Ligament length decreased with increase in temperature of hot wire and full-cutting was achieved at the temperature of 650°C. The center region in the thickness direction seemed to propagate earlier compared to surfaces regions when the crack propagation was stopped. Finite element thermal stress analysis was carried out. According to distribution of thermal stress inside a glass plate, higher stress was generated in the bottom region at the beginning of the process but occurred in the center region in the later stage as matching with the experimental result.

Abstract: Thermo-structural analysis with advanced composite plates and shells has been performed using Finite element method in order to determine temperature response and associated thermal stress. On solving the Fourier’s heat conduction equation, temperature profile is arrived at, with the assumption of linear/uniform temperature distribution through the thickness. Finite element program is developed for steady-state heat transfer problems using Semiloof shell element. Validation for integrated thermo-structural analysis has been done and compared with the available results from literature. The new results thus obtained are presented in terms of temperature, thermal stress, and displacement. The results obtained will be useful particularly in nuclear reactor vessels and Thermal Protection System (TPS) in aeronautical engineering.

Abstract: This study deals with the effect of high doses of ionizing beta radiation (132, 165 and 198 kGy) on mechanical properties (tensile strength, tensile modulus and elongation) of low and high density polyethylene under thermal loading. The measurement results of this study indicate that with an increasing dose of radiation grows tensile strength and modulus of low and high density polyethylene. For all examined materials were also observed changes in elongation.

Abstract: This paper presents how to derive Airy stress function to obtain the thermal stresses in a tungsten-steel functionally graded solid cylinder with fixed ends in elastic region. Once Airy stress function is derived, the thermal stresses can be found due to the related equations. There is uniform heat generation inside the tungsten-steel functionally graded solid cylinder. Material properties of the functionally graded cylinder (FGC) are assumed to vary radially according to a parabolic form and assumed to be independent of the temperature. These properties are yield strength, modulus of elasticity, coefficient of thermal conduction and coefficient of thermal expansion (CTE). Poisson’s ratio is assumed to be constant as an average value between tungsten’s and steel’s. Airy stress function is derived in terms of these properties to characterize the FGC entirely.