Papers by Keyword: Thermal Stress Analysis

Abstract: This paper presents a summary of a live demonstration for a numerical simulation of laser welding process using Ansys Workbench platform. The main steps of this simulation are: creating the geometric model, mesh generation, defining contacts, applying initial conditions and boundary conditions, defining thermal loads, general setting and solving the transient thermal analysis and finally the coupling of this analysis with a structural one to predict stresses due to the thermal field generated by the thermal analysis. After solving, the results are visualized and interpreted.

Abstract: Fly-ash concrete used in massive concrete structure has superior advantages to reduce hydration heat. On the other hand, the fly-ash concrete has negative property of low strength development at early age because pozzolanic reaction of fly-ash activates at mature age, such as after 28 days. To investigate these characteristics of fly-ash used in concrete, the present study discusses thermal cracking possibility of fly-ash concrete by using FE analysis software. The present study employs prediction formulae proposed by Zhang and Japanese design code in the simulations. The objects in this study are normal strength concrete mixed of fly-ash up to 50% of replacement ratio to cement. The comparative investigations show that temperature effect is more significant than strength development at early age. Based on the analytical study, high volume fly-ash concretes of 30-50% of the replacement ratio can be concluded as effective and useful materials to reduce the cracking possibility in massive concrete structures. Keywords-Fly-ash concrete; Early Age, Prediction Formulae for Strength; Thermal Stress Analysis

Abstract: The comprehensive application and potential danger of high temperature autoclave was discussed. The influence of thermal stress of autoclave in the reaction process of prepare biodiesel was studied. Utilizing simulation software, visualization of the structure and security was finished and thermal stress mould of ANSYS was employed to analyze the thermal stress distribution and deformation of autoclave. After the 3D (3 dimension) autoclave body model was created by AutoCAD, ANSYS Multiphysics was used to simulate the change of thermal stress of autoclave. Taking direct method for example, the whole simulation process was introduced. Validating by some equipment necessarily, the results of analysis are credible.

Abstract: Fatigue damage caused by alternating operational stresses in terms of temperature or pressure change is the one of important damage mechanisms in the nuclear power plants (NPPs). Although components important to safety were designed to withstand the fatigue damage, cumulative usage factor (CUF) at some locations can exceed the design limit beyond the design life. So, it is important to monitor the fatigue damage of major components during the long term operation. To evaluate fatigue damage, the Green’s function approach has been generally used. In this approach, thermal stresses can be directly calculated from the convolution integration on the coolant temperature history and Green’s function. And, Green’s function is defined as a stress variation at the arbitrary point when the coolant temperature is increased as a unit step. However, this approach cannot be applied to the fatigue analysis using temperature-dependent material properties because it is assumed that the system is linear. In this paper, the modified Green’s function approach considering temperature-dependent material properties is proposed by using neural network. To verify the modified Green’s function method, thermal stresses by the proposed method are compared with those by finite element analysis (FEA) at the transition wall of reactor pressure vessel and the analysis results between two methods are well agreed. Finally, it is anticipated that more precise fatigue evaluation is performed by using the proposed method.

Abstract: Several cracks were found on some actual floating roofs of a crude oil tank in the oil refinery located in southern Japan. We assumed that one of reasons would be due to thermal stress caused by temperature changes during the day. In order to consider whether the thermal stress could the cause damages on the floating roof, strain and temperature were measured on the actual floating roof by using optical fiber gauges. Furthermore, thermal stress analysis was carried out as effective analysis.

Abstract: As is known that the vacuum circuit breaker contact materials of breaking capacity and welding performance are affected by the mechanical properties and fracture characteristics of contact material, but they haven't been paid attention now. The mechanical failure for circuit breaker contact wear is studied and the process characteristics are described for contact opening and closing. When the thermal stress analysis for the moving contact is finished, the displacement and stress cloud map can be gotten by the thermal deformation of moving contact. When the crash analysis for the static and moving contact is finished, the deformation of contact can be gotten. In this analysis, a reference will be provided for the same type of circuit breaker contacts designed in the future and some relevant measures can be taken to prolong the mechanical life of breakers.

Abstract: The ethylene cracking furnace tube is one of the most important components of an ethylene cracking furnace. Carburization of furnace tube is one of the most important causes which lead the tube to fail. In this paper, the model that describes diffusion of carbon and the precipitation of carbides was established based on Fick’ law and equilibrium constant method. The finite difference method was adopted to simulate the distribution of carbon concentration. By applying the model, the distribution of carbon concentration along thickness in HP-Nb tubes was predicted for the different service times. According to the temperature distribution of furnace tube, obtained by the analysis of heat transfer, the thermal stresses of the furnace tube with various carburization extents were analyzed by using the finite element code ABAQUS for the actual heating process of an ethylene cracking furnace. The analysis results show that the maximum circumferential thermal stress exists near the inner wall of the carburized tube, which usually causes cracking of the carburized tube along the longitudinal direction.

Abstract: The temperature and strain distributions of the mockup composed of Cu-alloy with distinct structural material (SS316L and China Low Activation martensitic steel (CLAM)) were calculated and analyzed, based on a high heat flux (HHF) test recently reported with heat flux of 3.2MW/m². The calculated temperature and strain results in the first wall (FW), in which SS316L is as the structural material, showed good agreement with HHF test. By substituting CLAM steel for SS316L the contrast analysis indicates that the thermo-mechanical property for CLAM steel is better than that of SS316 at the same condition. Furthermore, the temperature and strain distributions of the FW were calculated under the condition of normal ITER operation: the surface heat flux is about 0.5MW/m² and volumetric heating due to neutron radiation is on the order of 15~20 MW/m².

Abstract: The thermal stress and thermal fatigue life for three different microgyroscope chip models were investigated in this paper. The deformation and stress distribution in chip, at interface between microgyroscope and chip, and in the spring of microgyroscope were obtained for three different microgyroscope chip models by the finite element method. The results show that for the simplified model, no obvious differences from linear or nonlinear analyses are obtained and the fatigue life of microgyroscope chip can be predicted with the properly simplified model. Also, the model having the same process in fabricating microgyroscope and carrier has better reliability. This paper provides an effective method for the reliability analysis of microgyroscope chip.

Abstract: This paper describes a theoretical and experimental analysis on full-filed stress distribution from thermoelastic measurements and its application to determination of stress concentration. The sum of the principle stress can be measured by Thermal Stress Analysis (TSA). Lock-in Thermography is very effective tool to measure the structure stress distribution by its high thermal resolving. In this study, the thermoelastic effect theory is described and the relationship between the temperature and the applied stress is developed in an elastic material. Experiments were carried out with 2A12 aluminium alloys plate and ones with hole structure under cyclic load. The thermoelastic effect coefficient is obtained for 2A12 aluminium alloys materials, and the effect law is analyzed that the stress value measured was affected by load frequencies. The optional load frequency is obtained, and that is, the load frequency is selected greater than 3.5Hz for 2Al12 materilas, and it was found that the structure stress can be evaluated with good accuracies by the lock in thermography. The experiment was carried out for aircraft components stress distribution measurement and structure stress analysis. The experimental results show the stress concentration position is easy found from stress distribution by lock-in thermography.