Maximum Thermal Strain Research Articles

Experimental analysis of glass failure criteria under different thermal conditions

The initiation of the first crack mainly determines the criteria for glass failure. However, the extended consequences of cracking, with the formation of multiple cracks merging, result in fallout conditions under varying thermal loads that become more critical. Point-supported glass arrangements are globally used in high-rise and energy-efficient buildings for architectural ingenuity aimed at a low budget. However, the formation of cracks due to thermal load resulting in glass breakage could infuriate the overall fire dynamics of the enclosed area. Therefore, experimental study and prediction of glass failure become very crucial. The present experimental study focuses on finding the most critical parameter that may quantify the cause of glass failure and further breakage in fallout conditions under varying thermal loads. 45 experiments were carried out on float glass of 300 × 300 mm2 with 4 mm, 6 mm, 8 mm, 10 mm, and 12 mm with continuous fuel supply arrangements. Critical parameters analysed were the time of crack initiation, glass temperature at the time of cracking, maximum temperature difference at glass failure, and thermal strain caused by the temperature difference on the glass surface. The range of minimum and maximum temperature difference recorded on the glass surface for the present study was between 30–35°C and 55–60°C at the breakage time for all the experiments. The Maximum temperature difference measured was 56.99°C on the 12 mm glass surface, and the corresponding maximum thermal strain found was 482 × 10−6 mm/mm. The maximum heat release rate was found to be approximately 200 kW. Maximum heat flux was found in the range of 10.33 kW/m2 to 21.14 kW/m2. A correlation was also developed using the least square method for all the thicknesses, which is well correlated with the glass thickness per unit length.

Coupled Thermo-Structural analysis of absorber tube for direct steam generation in parabolic trough solar collector

The absorber tube is a key component of a parabolic trough solar collector, and the bending of the absorber has an important role in receiver failures. The detailed survey of existing commercial solar power plants reveals that 55 % of failures happened due to the rupture of glass envelope and 29 % due to the loss in annulus vacuum. In this study, coupled thermal–hydraulic and structural stability analyses have been performed to understand the thermo-structural performance of absorber tubes under realistic operating conditions of direct steam generation processes. The fluid flow and heat transfer equations have been solved using the FVM scheme, and structural equations have been solved using the FEM scheme. The impacts of absorber material selection have been studied using steel absorbers and copper-steel bimetallic absorbers. The study has been performed for operating pressure of 60 bar and 100 bar, mass flow rates of 0.4 kg/s and 0.6 kg/s, and DNI of 750 W/m2. The temperature gradient, deflection, strain, and stress in the absorber wall have been analyzed. It has been observed that the temperature gradient in the absorber could be reduced by 51 % and deflection by 40 % using a copper-steel bimetallic absorber instead of the steel absorber. The maximum thermal strain observed under the subjected boundary condition in the steel absorber is 6.27 mm/m, and in the bimetallic absorber is 6.06 mm/m. Further, the maximum equivalent stress of 31.1 MPa in the steel absorber and 39.8 MPa in the bimetallic absorber has been observed. The present work is useful for understanding the absorber's thermo-structural functionality in the preheating, evaporation, and superheating stages of direct steam generation in solar collectors.

Performance studies of novel all-glass heat pipe evacuated collector tube integrating numerical simulation and experiment method

Metal heat pipe evacuated collector tube (ECT) suffer from cracks in the joint between the glass outer layer and the metal heat pipe due to the large difference in thermal expansion coefficients of glass and metal, resulting in non-industrialization. In this paper, the metal heat pipe is replaced with a glass heat pipe to form an all-glass heat pipe ECT to address the air-tight sealing problem, and a reflective film was added to the lower part of the outer tube to improve energy. According to these results, the thermal stress of 0.279 MPa is well below the bearing range of 40–120 MPa, and the maximum thermal strain of 0.175 mm/mm is also far less than the affordable value of 120 mm/mm, inducting the all-glass structure fully copes with the transient local heating changes. The optical efficiency is increased by 0.17 % by the addition of the reflective film, and yielding an energy output of 87 W and a maximum volume fraction of 4.8 % for liquid–water in the quasi-thermal equilibrium state. At the same time, the evaporation operating speed of the vapor can be increased by improving the solar radiation flux density and reducing thermal losses, and optimizing the multi-level and cross-scale vapor vortices can also improve the convective heat transfer rate, so they are future directions for development. However, there are the limitations of decreasing the thermal conductivity and increases the resistance due to the heat pipe conversion from metal to glass.

Flexural performance of weld-strengthened steel beam-square column joints subjected to axial column loading

This study proposes a novel strengthened joint with external rib plates for the H-shaped-beam square-column (HBSC) steel frame. The thermal effect of welding under load on the flexural performance of this joint was examined experimentally, numerically, and theoretically, both during and after the welding process. The following significant findings have been reported. The rib plates do not convey the axial pressure when welded to the column wall; consequently, the maximum thermal strain occurs on the column wall below the weld seams, reducing the column's stiffness and negatively contributing to the joint's flexural resistance. While the rib plates transmit force when they are welded to the angle steel, at this time, the rib plates experience the most significant thermal strain. The thermal effects of welding have been evaluated using a finite element model (FEM). Considering thermal effects, the FEM suggests a reduction factor of 0.90 for the load-bearing capacity. The yield strength of the strengthened joint is roughly double that of the unstrengthened joint, indicating that the reinforcement is effective. The initial stress ratio of the column must be kept below 0.7 to limit the rate at which the yield strength of the strengthened joint decreases as the compressive load increases. The stress distribution ratio between the vertical rib and the column wall has been determined using a simplified mechanical model. Based on the yield line principle, a formula for calculating the yield capacity of the strengthened joint has been derived.

Printability and microstructure of directed energy deposited SS316l-IN718 multi-material: numerical modeling and experimental analysis

In the present paper, the interrelated aspects of additive manufacturing-microstructure-property in directed energy deposition of SS316L-IN718 multi-material were studied through numerical modeling and experimental evaluation. The printability concept and solidification principles were used for this purpose. The printability analysis showed that the SS316L section is more susceptible to composition change and lack of fusion, respectively due to the high equilibrium vapor pressure of manganese and the more efficient heat loss in the initial layers. However, the IN718 section is more prone to distortion due to the formation of a larger melt pool, with a maximum thermal strain of 3.95 × 10−3 in the last layer. As the process continues, due to heat accumulation and extension of the melt pool, the cooling rate decreases and the undercooling level increases, which respectively result in coarser microstructure and more instability of solidification front in the build direction, as also observed in the experimental results. The difference is that the dendritic microstructure of the IN718 section, due to the eutectic reaction L → γ + Laves, is formed on a smaller scale compared to the cellular microstructure of the SS316L section. Also, the decrease in cooling rate caused the secondary phase fraction in each section (delta ferrite in SS316L and Laves in IN718) to increase almost linearly. However, the hardness calculation and measurement showed similarly, even though with the transition from SS316L to IN718 the hardness is significantly increased due to higher yield strength of the matrix and the presence of Laves intermetallic phase (~ 260 HV0.3), the hardness in each section decreases slightly due to the coarsening of the microstructure from the initial layer to the final.

Reacting flow coupling with thermal impacts in a single solid oxide fuel cell

Thermal impacts are the major concern for the designs of electrolyte of Solid Oxide fuel cells (SOFCs) due to the high temperature operating conditions. In this study, the coupling dynamics of electrochemical reacting flows with heat transfer and generations of thermal strains and stresses (thermal impact) of solid electrolyte and porous electrodes are investigated in a single SOFC by numerical simulations. Modeling results from a test case show that the coupling is necessary as the electrochemical and thermal properties of the cell strongly depends on temperature, meanwhile, the thermal strains and stresses on temperature gradients. The differences in current density and thermal strain gradients predicted by coupling and decoupling simulations are as larger as 20% because of the strong dependents of ionic conductivity of the electrolyte material on temperature, the maximum thermal strain, thermal stresses, and temperature are all about 5%. It is identified that the high operation voltage benefits to the thermal strain, which decreases 20% when the cell operating from 0.5 V–0.7 V.

Parabolic trough receiver with corrugated tube for improving heat transfer and thermal deformation characteristics

A symmetric outward convex corrugated tube design is introduced for parabolic trough receivers with the aim of increasing their heat transfer performance and reliability. An optical–thermal–structural sequential coupled method was developed to analyze the heat transfer performance and thermal deformation of the glass cover and metal tube of the parabolic trough receiver. The developed coupled method has been validated with experimental results conducted in the DISS test facility in Spain. The numerical results indicated that the introduction of a symmetric outward convex corrugated tube design for the metal tube of the parabolic trough receiver can effectively enhance the heat transfer performance and decrease the thermal strain. The effective heat transfer coefficient can be increased up to 8.4% and the maximum thermal strain of metal tube can be decreased up to 13.1% when symmetric outward convex corrugated tube is used at Re=81728, p/D=4.3. In addition, regression correlations are put forward in order to find an effective heat transfer coefficient and effective Nusselt number for the fluid flow in the parabolic trough receiver.

Estimating quench residual stresses in cylindrical steels bars: Excluding the effects of phase transformation

Uncoupled thermo-mechanical finite element analyses, using ABAQUS, are conducted to determine residual stresses created by quenching of 316 stainless steel and AISI 1020 low-carbon steel cylindrical bars. It is found that the magnitude of the residual stresses can be determined from an estimate of the thermal strain difference created in the bars during quenching. It is shown that the strain difference is a function of the Biot and Fourier numbers and the initial and final quench temperatures. The results of the analyses are used to create a diagram with non-dimensional axes with residual stress as a function of maximum thermal strain. The residual stresses are normalised with respect to the room temperature yield strength and the thermal strain normalised with respect to the room temperature yield strain. It is proposed that quench residual stresses can be estimated using this diagram irrespective of the quench conditions and bar diameter for steels. This is provided if there is no phase transformation during quenching. It is shown that if the normalised thermal strain is greater than about 3.6, the surface residual hoop and axial stresses are equal to the compressive room temperature yield strength, while the interior tensile stresses linearly increase (approximately) with thermal strain.

Finite Element Analysis of the Piston Thermal Load in a Diesel Engine

Three-dimensional modeling and finite element analysis on the diesel engine piston is carried out in the paper. The distribution of temperature, stress and strain within piston at the rated conditions of the engine are obtained from the simulation. The calculated temperature is consistent with the results of the piston surface temperature which is obtained by hardness plug method, thus confirming the model's validity. The calculated maximum temperature is 374 °C and the minimum temperature is 144 °C. The maximum stress is 118MPa located between the piston skirt above the pin hole and the third ring groove. The maximum thermal strain appears at the piston top with the value of 6.29×10-3. Finally, the temperature simulation of the piston adopted oil-splashing cooling is implemented. It is proved that thermal load can be further reduced through cooling measure.

Strain Analysis for Quality Factor oft he Layered Mg0.93Ca0.07TiO3-(Ca0.3Li0.14Sm0.42)TiO3Ceramics at Microwave Frequencies

Microwave dielectric properties of the layered and functionally graded materials (FGMs) of 0.93 Ca 0.07 TiO₃ (MCT) and ( 0.3 Li 0.14 Sm 0.42 )TiO₃ (CLST) were investigated as a function of the volume ratio of two components. Dielectric constant was decreased with an increase of the volume ratio of MCT which had a lower dielectric constant thant CLST. For the layered FGMs specimens, the difference of thermal expansion coefficients between two components induced thermal strain to dielectric layers, which was confirmed by the plot of Δk (X-ray diffraction peak width) versus k (scattering vector) using the double-peak Lorentzian function, f(x). Quality factor of the specimens was affected by the thermal strain of dielectric layer, especially MCT layer. For the specimen with the volume ratio of MCT/CLST = 2, the qulaity factor of the specimen showed a minimum value due to the maximum thermal strain fo MCT layer.

Interfacial thermal stress analysis of an elliptic inclusion with a compliant interphase layer in plane elasticity

Stresses induced by thermal mismatch are known to be a major cause of failure in a wide variety of composite materials and devices ranging from metal–ceramic composites to passivated interconnect lines in integrated circuits. One of the most effective procedures used to reduce these thermal stresses is the addition of a compliant intermediate or interphase layer between the different material components. This paper is concerned with the interfacial thermal stress analysis of an elliptic inclusion embedded within an infinite matrix with uniform change in temperature. A compliant interphase layer is assumed to occupy the region between the inclusion and the matrix. This interphase layer is modeled as a spring layer with vanishing thickness (henceforth referred to as the interface between the inclusion and the matrix). Its behavior is based on the assumption that tractions are continuous but displacements are discontinuous across the interface. Complex variable techniques are used to obtain infinite series representations of the thermal stresses which, when evaluated numerically, demonstrate how the peak interfacial thermal stresses vary with the aspect ratio of the inclusion and the parameter h describing the interface. In addition, and perhaps most significantly, for different aspect ratios of the elliptic inclusion, we identify a specific value (h∗) of the interface parameter h which corresponds to the maximum peak thermal stress along the inclusion–matrix interface. Similarly, for different aspect ratios, we identify a specific value of h (also referred to as h∗ in the paper) which corresponds to the peak maximum thermal strain energy density along the interface (J. Appl. Mech. 57 (1990) 956–963). In each case, we plot the relationship between the new parameter h∗ and the aspect ratio of the ellipse. This gives significant and valuable information regarding the failure of the interface using two established failure criteria.

A study on the thermal behavior in microaccelerometer manufacturing processes

Single crystal silicon (SCS) is used in a variety of microsensor applications in which stresses and other mechanical effects may dominate device performance. One of major problems associated with the manufacturing processes of the microaccelerometer based on the tunneling current concept is temperature gradient and thermal stressess. This paper deals with finite element analyses of residual stresses causing popping up, which are induced in micromachining processes of a microaccelerometer. The authors model temperature-dependent mechanical properties during focused ion beam (FIB) cutting and Pt deposition processes. The maximum thermal strain of 0.0012 occurred at the readout gap of the microaccelerometer during the Pt deposition process. The stress produced during the heating process of FIB cut was also found to be about 33–36 MPa and cooling process the maximum equivalent stress of about 34MPa still at the right corner of readout gap. The calculated maximum displacement occurred at the readout gap was 0.14 μm. This is still smaller than the popping up of about 2 μm observed in the experiment. The reason for this popping up phenomenon in munufacturing processes of microaccelerometer may be the bending of the whole wafer or it may come from the way the underetch occurs. Different SOI material and a new geometry of the accelerometer are under investigation. We want to seek after the real cause of this pop up phenomenon and diminish this by changing munufacturing processes of microaccelerometer.

ＬＣＴコイル国内実験の機械的結果

Domestic test of the Japanese LCT coil was carried out in Japan Atomic Energy Research Institute (JAERI). Mechanical characteristics of the test coil were measured during the cool-down, warm-up and charge-up test by strain gauges and displacement gauges attached directly to the test coil.During the cool-down test, the maximum temperature difference in the test coil was controlled within 96K in order to avoid excessive thermal strain. Maximum thermal strain in conductor and helium vessel in the circumferential direction was 170ppm, and-950ppm in cool-down test.The test coil was able to charge up to the rated current in very stable, and run-away of strain was not observed both in conductor and in helium vessel. The test results obtained in rated current operation were compared with the calculation. Some differences in the distribution of conductor strain were found by the comparison, and several technical subjects both in measurement and in calculation became clear.As the result of the domestic test, mechanical data base for large coil design was accumulated.

Optimal Schedules for Rapid Starting and Loading of Steam Turbines

Starting and loading rates of a steam turbine are limited by thermal fatigue resulting from nonuniform heating of parts. The paper presents the derivation of a method for calculating steam valve opening transients leading to the shortest time for starting and/or loading. The steam schedules are subjected to constraints relating to the measure of damage--the maximum thermal strain in the shell and in the rotor of the turbine. A numerical example is given for illustration of the method. Formulas are derived for calculating control transients when the desired strain transients in the rotor and the shell are given.