Thermal Fatigue Analysis Research Articles

Heat transfer and thermo-mechanical analyses of W/CuCrZr monoblock divertor in subcooled flow boiling

It is necessary to take effective cooling methods from the divertor which can sustain one-sided high heat fluxes. In order to ensure the reliability and security of the divertor in fusion reactor, the heat transfer and thermo-mechanical assessment of W/CuCrZr monoblock divertor were conducted. In this paper, the heat transfer enhancements of the subcooled flow boiling in the vertically upward screw tubes, the tubes with twisted tape inserts and the plain tubes were examined by the Fluent software. Then, the thermo-mechanical analyses of the three cooling tubes were performed in this paper. The 3Sm rule, Bree-diagram rule, fatigue, pipe material temperatures and the assessment of critical heat flux (CHF) were compared and analyzed for the three kinds of cooling tubes, which can guide the optimum for the heat transfer and structural analyses of the monoblock divertor. As a result, compared with the screw tube and plain tube, the tube with twisted tape inserts can enhance the heat transfer. Among the three kinds of cooling tubes, secondary stress of tungsten and CuCrZr in the tube with twisted tape inserts were the smallest. Thermal fatigue analyses of the tube with twisted tape inserts were calculated and the tube owned a fatigue life of approximately 0.427 years under the current working conditions.

Life Prediction Method for Thermal Barrier Coating of High-Efficiency Eco-Friendly Combined Cycle Power Plant

Recently, because global warming has become increasingly severe, CO2 emission regulations have become strict. Accordingly, there is an increasing demand for a combined cycle power plant that is eco-friendly and capable of high-efficiency generation using natural gas, which has a relatively low carbon content. In order to improve the efficiency of a combined cycle power plant by increasing the operating temperature, the durability of the hot-section components must be secured. Therefore, thermal barrier coating (TBC) technology has been applied. The TBC is damaged by thermal fatigue during operation. The delamination of the TBC could lead to core component damage. Therefore, studies on the prediction of TBC durability should be conducted before increasing the operating temperature. In particular, because the thermal fatigue life is affected by changes in the TBC structure, there is a demand for a durability evaluation technique that takes this into consideration. In this study, a thermal fatigue analysis was performed that considered the growth of the oxide layer, and a thermal fatigue life prediction equation for the TBC was derived based on the results. The thermal fatigue life was predicted, according to the change in the TBC structure, using the life prediction equation, and it was verified by comparing it with the thermal fatigue test results.

Numerical study on the thermal stratification characteristics of AP1000 pressurizer surge line

The surge line is implemented to connect the pressurizer with reactor cooling system in Pressurized Water Reactor (PWR). The integrity of surge line plays an important role for reactor safe operation. In the literatures, much work has been contributed to the thermal hydraulic characteristics and reliability research on traditional pressurizer surge line. For the advanced Generation-III PWR, the AP1000 adopts a new spiral-shaped pressurizer surge line concept. In this paper, the three-dimensional thermal hydraulic transient characteristics in AP1000 pressurizer surge line are studied and the formation mechanism of surge line thermal stratification phenomenon is investigated. The variation of maximum temperature difference with time in the whole surge line is achieved. Results show that the thermal stratification is becoming weaker along the flow direction and the most dangerous region is the entrance of horizontal position. The thermal stratification affected by the circumference effect is not significant during the surge line thermal fatigue analysis. In addition, through the comparison of temperature distribution in pressurizer surge line between the traditional PWR and AP1000, it can be seen that the AP1000 pressurizer surge line has smaller temperature difference at the corresponding position with shorter period. The new design concept of AP1000 surge line brings a great advantage to reduce the hazard causing by the thermal stratification. This work provides a valuable guideline for the AP1000 pressurizer surge line fatigue assessment.

Evaluation of rigid pavement on apron of terminal 3 Soekarno-Hatta International Airport using finite element method

The development of transportation technology is indicated by the appearance of a new aircraft gear configuration, dual trim. The load repetitions of the movement of aircraft with dual-tridem gears, such as B-777-300ER aircraft with MTOW 28 tons, on Terminal 3 Soekarno-Hatta International Airport (SHIA) apron may cause pavement deformation, resulting in long-term fatigue and structural failures. Therefore, the performance of the existing rigid pavements to hold the loads for the next 20 years should be evaluated. Firstly, the equivalent annual departure and coverage of the aircraft in the airport up to 2037 is calculated. Next, the existing rigid pavement structure of the apron in the airport is modeled using a finite element method to calculate thermal stress and fatigue analysis for either the dowel or the slab. Our study result shows that the coverage value for the next 20 years is 86,534 with the maximum deflection of 0.055 mm and the maximum stress of 0.496834 MPa. The calculated thermal stress is 1.55 MPa, resulting in load repetition for the slab 1,241,484 and an infinite load repetition for the dowel.

Finite element analysis of cross section of TBR tire

With the development of science and technology, finite element analysis technology has gradually become the main means of radial tire analysis. However, most of the theoretical models are mainly analyzed, and there are still some differences between them and the actual tire models. In this article, the constitutive model of Yeoh rubber material is selected for the uniaxial tensile results of various rubber materials used in the tire. The material parameters are determined by the equivalent tensile strain curve of the steel cord. Taking the 12.00R20 tire as an example, with the help of ABAQUS software, a finite element method for the analysis of the tire structure is formed under the working conditions of assembly, punching gas and loading, and the necessary evaluation of the finite element results of the loading condition is also carried out. By analyzing the stress and strain of each part of the tire, the strain ratio can be used as the basis for the further analysis of thermal fatigue, and it also plays a guiding role in improving the design of tire structure.

Numerical study on thermal stress and cold startup induced thermal fatigue of a water/steam cavity receiver in concentrated solar power (CSP) plants

The high temperature receivers in CSP plants should startup frequently, so the thermal stress and the fatigue failure are critical important for its safety and stability. In our present study, a computation model is proposed for a water/steam cavity receiver in CSP plant. The model couples the light propagation, the light-heat conversion, the thermo-elasticity and the thermal fatigue analysis together. Monte Carlo ray tracing method (MCRT), finite volume method (FVM) and boiling heat transfer are coupled to get the thermal boundary of the boiling panel. Finite element method (FEM) is adopted to obtain the temperature and stress–strain distribution of the boiling panel. Elastic stress analysis and equivalent stress fatigue assessment method is used to investigate the fatigue failure of the boiling panel. Two different structures of the boiling panel are researched, following results are obtained: The heat flux on the boiling panel is highly non-uniform and it results in the similar non-uniform distributions of temperature and stress-strain as well as the displacement of the boiling panel. The non-uniform stress-strain leads to the warping of the boiling panel and the largest displacement is in the direction normal to the heat absorbing surface toward the cavity internal, the largest displacement range is 17 cm. Fins of the boiling panel at the elbow region (case-1 in the present study) can lead to hot spots of which the temperature is extremely higher than that of boiling tubes, cutting off the fins at the elbow region (case-2 in the present study) can eliminate the hot spots and has no impact on temperature distribution of the boiling panel’s main part. The temperature difference on the cross section of the boiling tube is very high (about 130 °C while the heat flux is about 350 kW/m2) both in radial and circumferential direction, and this high temperature difference results in the high thermal stress on the boiling panel and the maximum thermal stress occurs at the welding region. The welding quality has a significant impact on the fatigue failure of the boiling panel. For a receiver design life of 20 years, membrane wall with cutting off the fins at the elbow region (case-2 in the present study) is a good design and the welding quality level 3 should be ensured at least and only one cold startup for a day is permitted.

Failure Analysis and Robust Optimization of an Exhaust Manifold Diffuser Plate

Diffuser plates in exhaust system manifolds are designed to provide uniform flow pattern within the manifold for maximum utilization of the catalytic converter substrate during high-temperature applications. In this paper, failure analysis of a diffuser which survived only 20% duration of a manifold crack test and various design optimization studies of the diffuser plate using computer-aided engineering (CAE) analyses are presented. During the manifold crack test, the failure occurred at the inner and outer periphery of the diffuser. Metallurgical failure analysis coupled with CAE thermal fatigue analysis of the component concluded that thermal fatigue was the root cause of the failure. The new recommended robust design showed considerable improvement in the thermal durability of the diffuser plate assembly.

Thermo-structural fatigue analysis of shell and tube type heat exchanger

Increased demand of alternative fuels, need of high pressure and temperature vessels for petroleum refineries, chemical plants gave rise to the development in the pressure vessel technology from last few decades. Many advancements in the field of pressure vessel engineering such as fracture mechanics, fatigue and creep process understanding, new material grades & composite materials, welding techniques such as explosion welding and various finite element analysis techniques like thermal coupled structural, transient thermal, dynamic simulations like response spectrum and nonlinear buckling which accurately assessing the stresses encountered in pressure vessels are developed.This paper describes the means with which one can reasonably accurately ascertain the thermal fatigue analysis of pressure vessel in accordance with design by analysis approach. It highlights the various failure modes, design by analysis approach used for pressure vessel. It allows the engineer to investigate a range of variables within the design process and contributes significantly to the basic requirement of a safe design within an economic framework.

Thermal Fatigue Analysis and Evaluation of Wheel-Rail Contact under Braking Conditions

Recently, reliability design considering the fatigue has been demanded for ensuring the driving safety for the high speed railway. In particular, the railway wheel and rail are subjected not only to mechanical load but also to highthermal load due to frictional heat generated when the railway wheel contacts with the brake shoe during tread braking. As repetitive thermal load accelerates damage to the wheel surface, it leads to shorten the replacement cycle and increase the maintenance cost. Therefore, we expect to achieve the economic efficiency by using the wheel over the life expectancy while maintaining the structural health. Initial braking velocity is one of the main factors affecting the behaviors of contact surface between the wheel and rail. Therefore, it is necessary to evaluate the effect of thermal stress according to it. In this study, through the thermalmechanical analysis considering both mechanical load and thermal load caused frictional heat under braking conditions, thermal stress subjected to the contact surface between the railway wheel and rail was calculated. Based on these results, the thermal fatigue analysis was carried out to evaluate the safety under fatigue and predict the fatigue life.

Thermal mixing of flows in horizontal T-junctions with low branch velocities

High cycle thermal fatigue (HCTF) damage in the vicinity of T-junction piping, where mixing of coolant streams at significant temperature differences occur, is considered to be an important problem in the context of operational safety in nuclear power plants (NPPs). The present study deals with the experimental and numerical investigations of T-junction flow mixing at realistic temperature differences encountered in NPPs. Experiments were carried out at the fluid-structure interaction (FSI) T-junction test facility at the University of Stuttgart. Near-wall thermocouples were used in the mixing zone to record temperature information inside the flow and the structure. A conductivity based wire mesh sensor (WMS) instrumentation designed at the Laboratory of Nuclear Energy Systems at the ETH Zurich for high-pressure high-temperature applications was also used during the measurements to characterize the cross-sectional thermal field in the mixing zone. Aside from experiments, numerical studies were carried out using the large-eddy simulation (LES) turbulence model to gain further insights into the flow mixing behavior and its predictions were validated with measurement data.With a constant mass flow rate ratio (main/branch) of 4:1, thermal mixing tests were carried out at temperature differences (ΔT) between the mixing fluids of 65°C (Case 1) and 143°C (Case 2), respectively. Two distinct flow trends were identified in the mixing region: (i) an unstable stratified flow being subjected to extreme oscillations in case 1 and (ii) a stable stratified flow being subjected to significant buoyancy effects in case 2. Near-wall thermal fluctuations (a factor in thermal fatigue analysis) with highest amplitudes were recorded by the thermocouples located in the vicinity of the stratification layer in both the cases. Frequency analyses of thermal fluctuations using the power spectral density (PSD) method indicates no dominant frequency (spectral peak) in the frequency range identified to be of relevance for HCTF (0.1–10Hz). Instead, the energy of thermal fluctuations were mainly contained in the frequency range of 0.1–2Hz. LES predictions of parameters, viz., mean temperature, thermal fluctuations and its frequency distribution showed good agreement with measurement data.

Thermal fatigue analysis of turbine discs on the base of deformation criterion

The lifetime of turbine discs under complex non-proportional thermo-mechanical cyclic loading is analyzed by means of the direct finite-element simulation of deformation and fracture processes using thermo-elasto-visco-plastic material model and deformation failure criterion. A good agreement is observed in comparison of the obtained number of cycles to macrocrack initiation with experimental results for five turbine discs made from different materials and subjected to various loading conditions.

Conceptual Design Analysis of Tungsten Monoblock Components for KSTAR Divertor

Tungsten (W) monoblock that consists of W according to ITER specifications, oxygen-free high conductive copper (Cu-OFHC), and CuCrZr has been designed in preparation for KSTAR upgrade for steady-state long-pulse operation with 27.5-MW heating power. Finite-element analysis has been performed by ANSYS Workbench. The hydraulic thermomechanical analysis is performed to investigate the optimal design parameters and the expected fatigue lifetime under the operating conditions with 5.4-MW/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{2}$ </tex-math></inline-formula> incident heat flux at the divertor. For a single W monoblock, the optimization gives a W thickness of 5 mm, a side thickness of 2.5 mm, a thickness in the back part of 6 mm, and a Cu-OFHC interlayer thickness of 0.5 mm. For a mock-up consisting of five optimized W monoblocks, the thermal fatigue analysis is performed. As a result, the maximum value of equivalent total strain in the CuCrZr tube is found to be 0.266%, which corresponds to for a fatigue lifetime of 23 000 cycles.

Experimental and numerical analyses on the effect of increasing inflow temperatures on the flow mixing behavior in a T-junction

Thermal degradation of piping induced by high cycle thermal fatigue (HCTF) is of significant importance as operating Nuclear Power Plants (NPP) become older and lifetime extension activities are initiated. In particular, HCTF incidents related to turbulent thermal mixing of fluids in a T-junction piping system are not well understood and could not be adequately monitored using common thermocouple instrumentation. To investigate this phenomenon, an experimental T-junction test facility was commissioned at the University of Stuttgart, known as the Fluid Structure Interaction (FSI) test facility. The paper presents the experimental investigation and the corresponding numerical validation using the large eddy simulation (LES) method to study T-junction flow mixing. Three experimental test cases are investigated with temperature differences (∆T) of 51.5K (Case 1), 76K (Case 2) and 97K (Case 3) between the mixing fluids. A constant mass flow rate ratio (main/branch) of 4:1 is maintained in all the investigated cases. Flow mixing is observed to be incomplete in all the cases, resulting in a thermally stratified flow with an oscillating stratification layer downstream of the T-junction. Mean temperature and root mean square (RMS) temperature fluctuations predicted by LES in the mixing region are found to be in good agreement with measurement data, with the exception of few positions. Amplitudes of temperature fluctuations are observed to be higher near the stratification layer, ranging from 6.3–9.9% of ∆T. Power spectral density (PSD) analyses of temperature fluctuations indicate no dominant frequency (spectral peak) under prevailing flow conditions, an important factor in thermal fatigue analysis, and the energy of these fluctuations are mainly contained in the frequency range of 0.1–2Hz for all the investigated cases. LES is performed using the CFD software ANSYS CFX 14.0.

Limitations of transient power loads on DEMO and analysis of mitigation techniques

The present European standard DEMO divertor target technology is based on a water-cooled tungsten mono-block with a copper alloy heat sink. This paper presents the assessment of the operational space of this technology under static and transient heat loads. A transient thermo-hydraulic analysis was performed using the code RACLETTE, which allowed a broad parametric scan of the target geometry and coolant conditions. The limiting factors considered were the coolant critical heat flux (CHF), and the temperature limits of the materials. The second part of the work is devoted to the study of the plasma strike point sweeping as a mitigation technique for the divertor power exhaust. The RACLETTE code was used to evaluate the impact of a large range of sweeping frequencies and amplitudes. A reduced subset of cases, which complied with the constraints, was benchmarked with a 3D FEM model. A reduction of the heat flux to the coolant, up to a factor ∼4, and lower material temperatures were found for an incident heat flux in the range (15–30)MW/m2. Finally, preliminary assessments were performed on the installed power required for the sweeping, the AC losses in the superconductors and thermal fatigue analysis. No evident show stoppers were found.

Large eddy simulation studies on the influence of turbulent inlet conditions on the flow behavior in a mixing tee

Mixing of coolant streams at significant temperature differences in a mixing tee occurs in the cooling systems (e.g. Residual Heat Removal System) of a nuclear power plant resulting in cyclical thermal fluctuations that may lead to high cycle thermal fatigue (HCTF) in the structure. The present study aims to numerically investigate such a scenario using the large-eddy simulation (LES) method. The LES is based on an experiment conducted at the fluid–structure interaction (FSI) test facility, University of Stuttgart. Hot and cold water streams flow in the main and branch pipes with a temperature difference (ΔT) of 117K. The mass flow rate ratio (main/branch) is 4:1.Two LESs with different inlet conditions are performed to study and compare the effect of each inlet condition on the flow behavior downstream of the mixing tee. They are (i) unperturbed inlet conditions and (ii) inlets with synthetic turbulence. The experimental inflow conditions result in an incompletely mixed thermally stratified flow marked by significant buoyancy effects. Assessment of parameters like mean temperature and velocity predicted by both LESs exhibit very little deviation with each other indicating the insignificant effect of inflow turbulence on the bulk flow. But the inclusion of inflow turbulence is seen to have a non-negligible effect in the assessment of parameters like temperature fluctuations, turbulent kinetic energy and temperature–velocity correlation. The prevailing flow conditions are not seen to induce any dominant frequency of near-wall temperature fluctuations, an important factor in thermal fatigue analysis. Energy content of these fluctuations mainly lies in the frequency range of 0.1–2Hz.

A continuum damage model for creep fracture and fatigue analyses

In this paper a thermodynamically consistent formulation for creep and creep-damage modelling is given. The model is developed for isotropic solids by using proper expressions for the Helmholtz free energy and the complementary form of the dissipation potential, and can be proven to fulfill the dissipation inequality. Also the coupled energy equation is derived. Continuum damage model with scalar damage variable is used to facilitate simulations with tertiary creep phase. The complementary dissipation potential is written in terms of the thermodynamic forces dual to the dissipative variables of creep strain-rate and damage-rate. The model accounts for the multiaxial stress state and the difference in creep rupture time in shear and axial loading as well as in tensile and compressive axial stress. In addition, the model is simple and only four to eight material model parameters are required in addition to the elasticity parameters. A specific version of the proposed model is obtained when constrained to obey the Monkman-Grant relationship between the minimum creep strain-rate and the creep rupture time. The applicability of the Monkman-Grant hypothesis in the model development is discussed. The proposed 3D-model is implemented in the ANSYS finite element software by the USERMAT subroutine. Material parameters have been estimated for the 7CrMoVTiB10-10 steel (T24) for temperatures ranging from 500 to 600 degrees of celcius. Some test cases with cyclic thermal fatigue analysis are presented.

Thermal fatigue analysis model and life prediction of pipe in residual heat removal system

Thermal fatigue analysis model and life prediction of pipe in residual heat removal system

Thermal fatigue crack growth tests and analyses of thick wall cylinder made of Mod.9Cr–1Mo steel

In Japan, the basic designing works for a demonstration plant of Japan Sodium cooled Fast Reactor (JSFR) are now conducted. JSFR is an advanced loop type reactor concept. To enhance the safety and the economic competitiveness, JSFR employs modified 9% chromium–1% molybdenum (Mod.9Cr–1Mo) steel as a material for coolant pipes and components, because the steel has both excellent high temperature strength and thermal properties. The steel has been standardized as a nuclear material in Japan Society of Mechanical Engineers (JSME) code in 2012. In JSFR pipes, demonstration of Leak Before Break (LBB) aspect is strongly expected because the safety assessment may be performed on the premise of leak rate where the LBB aspect is assured. Although the authors have already performed a series of thermal fatigue crack growth tests of austenitic stainless steel cylinders (Wakai et al., 2005), crack growth behavior in the structures made of Mod.9Cr–1Mo steel has not been investigated yet. Especially for the welded joints of Mod.9Cr–1Mo steel, “Type-IV” cracking may occur at heat affected zone (HAZ). Therefore, this study performed a series of thermal fatigue crack growth tests of thick wall cylinders made of Mod.9Cr–1Mo steel including welds, to obtain the crack growth data under cyclic thermal transients. The test results were compared to the analytical results obtained from JAEA's simplified methods (Wakai et al., 2005).

Assessment of microstructural influences on fatigue crack growth by the strip-yield model

The strip-yield model is a common tool to calculate the cyclic crack tip opening displacement and the fatigue crack growth life of structures in case of isothermal fatigue loading. The incorporation of a temperature-dependent yield stress already enables its application in thermal fatigue analyses. A further extension of the strip-yield model is presented here together with simulation results: The rheological Masing model consisting of spring-slider elements connected in parallel is used to describe the material’s stress–strain curve. It results in different yield stresses belonging to the numerous sliding frictional elements. These different yield stresses are randomly arranged along the crack ligament line instead of the usually applied constant yield stress. They depend on temperature as the procedure should still be used at non-isothermal loading. Besides an improved modelling of the mechanical material behavior the consideration of microstructural aspects of fatigue crack growth becomes possible by influencing the values of the yield stresses near the crack initiation site.

Thermal Fatigue Analysis of HSK Shrink Toolholder

The principle which the tool is embedded into the HSK shrink toolholder is expanding with heat and contracting with cold. The thermal cycle that the tool is embedded into or taken out the toolholder is heating toolholder and cooling it quickly. After a few thermal cycles, the HSK shrink toolholder is damaged with the way of thermal fatigue. The analysis of thermal fatigue is transient heat transfer and stress coupling and the temperature distributionstress and strain of every time are gained in thermal cycle. The fatigue of shrink tool holder is strain fatigue by analyzing the stress. The fatigue life is gained with Coffin-Manson formula.