Papers by Author: Gang Chen

Abstract: Basing on that skutterudites-based thermoelectric module may be applied to the vehicle exhaust power generation system, a multi-field of thermal mechanical-electrical coupled model was established and investigated by finite-element method. The thermal stresses, open circuit voltage, output power and conversion efficiency of thermoelectric module (TEM) are calculated and obtained. The service environment is simulated with the hot side temperature data obtained by experimental measurements. An independent tank is adopted on the cold side, to develop a temperature difference for electric producing, and then achieve the thermoelectric conversion. By analyzing the working properties of TEM, the mechanical properties and thermoelectric characteristics are also discussed, which provides guidance for TEM practical application.

Abstract: The current research explores the effect of alternating magnetic field on corrosion rate and products compositions of 45 steel, by use of electrochemical test, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The calculated inhibition efficiency of the alternating magnetic field based on electrochemical corrosion rate is up to 16.66%. Electrochemical corrosion morphology and surface products were also discussed. The surface of specimen is uniform and compact in magnetized sea water relation to that in 3.5% NaCl solution and sea water. The corrosion products of 45 steel in sea water are FeCl2•4H2O, Fe(OH)3 and FeOOH. However, the corrosion products of 45 steel in magnetized sea water are FeOOH, Fe3O4 and FeCl3•6H2O chiefly.

Abstract: A significant challenge in encapsulation process of solar cell module is to reduce breakage rates. In encapsulation and service process of the solar cell module, since the mismatch of heat expansion coefficients of various materials, and temperature difference of material interface in service of module, the residual stresses is caused in each material layer of solar cell module. Analytical model was established to analyze the distribution of temperature and residual stress in encapsulation and service process of the solar cell module. The validity of the analytical model is verified by comparing with finite element method (FEM) results. The residual stresses are obtained during encapsulation of solar cell module, and the thermal stress is reverse in encapsulation and service process of the solar cell module. The effect of thermal stress on structure strength of solar cell module is discussed in detail.

Abstract: The small punch creep (SP-C) test technique is a new method which is applied to evaluate the high temperature creep properties of materials by using miniature specimen. In the present paper, the Finite Element Method (FEM) is employed to simulate the SP-C test in order to investigate the effects of test parameters on testing results of the SP-C test. In this attempt, we perform systematic numerical simulations of SP-C tests by changing friction coefficient, specimen thickness, the diameter of punch ball and the inner diameter of lower die, and discuss the effects of the variation of test parameters on test results in detail. The resulting regression equations for assessing the effects of testing parameters on test results are obtained. It is found that the test results are influenced significantly by the specimen thickness, the diameter of punch ball and the inner diameter of lower die. However, the effects of friction coefficient on the results of the SP-C test can be neglected.

Abstract: Creep behavior of SUS304 stainless steel is studied by small punch creep (SP-C) test. Series of SP-C testing for SUS304 stainless steel are carried out at 600°C. The time dependence of the central deflection is obtained by the SP-C testing at different load level and the creep deflection curves are quantitatively similar to those observed in conventional uniaxial creep testing. In this paper, an analytic approach based on Chakrebarty’s membrane-stretch model is used to interpret the SP-C test method. The relationship between specimen central deflection and equivalent strain is deduced, and the relationship between load and equivalent stress are established. The creep stress exponent of SUS304 stainless steel is determined by the theory formula and the data obtained in the SP-C testing. Comparison of the creep stress exponent of the Norton equations in SP-C testing and conventional creep testing is performed. The results show that the creep stress exponent is well consistent with conventional experimental results.

Abstract: The Small Punch Creep Tests (SP-C tests) are simulated by a Finite Element Method (FEM). The objective of the present study is to establish a foundation for the SP-C test method by investigating the deformation and stress state of the SP-C test specimen. The emphasis is placed on the dependence relation of the creep strain and the stress on the measurable quantities, such as applied loads and the central deflections. Simulation works are conducted for two different materials, one is the tungsten-alloyed 9% Cr ferritic steel and the other is 12Cr1MoV steel. The numerical results for the central deflection versus time curves are quantitatively similar to the experimental results obtained on tungsten-alloyed 9% Cr ferritic steels. From the numerical results, the relationship between the central deflection and the equivalent creep strain is approximately independent of load, temperature, and material properties. The magnitude of the equivalent stress in the central region of the SP-C specimen shows no significant change with respect to time at the secondary creep stage, an approximate equation is proposed for the assessment of the equivalent stress in the SP-C specimen. As a farther result, the high temperature creep properties of the 12Cr1MoV steel and tungsten-alloyed 9% Cr ferritic steel are appraised by numerical simulation. The results are in good agreement with the results from the standard test method. The results indicate that the small punch test technique is an effective method for the evaluation of the high-temperature creep properties of materials.

Abstract: The present paper investigates the creep phenomenon of the functionally graded materials under high temperature environment by the computational micromechanical method (CMM). Based on the real microstructure of the functionally graded interlayer with different component volume fractions, the emulation experiment is implemented for the creep test numerically and the creep parameters are obtained. A further series of simulation works are carried out to investigate the creep phenomenon of FGM interlayers in more detail. Numerical results show that the creep phenomenon is obvious not only for the metal-rich interlayers but also for the ceramic-rich interlayers. The creep property of ceramic/metal interlayer depends on the material’s properties of the ceramic obviously. It is remarkable that the creep strain rate of the ceramic/metal interlayer is larger than the corresponding one of pure metal under the same load when the modulus of the ceramic component is lower than the one of the metal component.

Abstract: The numerical simulation for the Small Punch creep (SP-C) tests is conducted using a Finite Element method. The objective of the present study is to obtain the deformation states of the SP-C specimen and to estimate the feasibility of SP-C test method for high-temperature creep properties. The emphasis is put on the relationship between the equivalent creep strain and the central deflection of the SP-C specimen. The time history of central deflection and equivalent creep strain is obtained by finite element method and the effects of the load, temperature and material properties on the relationship of central deflection and equivalent creep strain are discussed. From the numerical results, the relationship between the central deflection and the equivalent creep strain is approximately independent of load, temperature, and material properties. As a farther result, the high temperature creep properties of the 12Cr1MoV steel are appraised by numerical simulation. The results are in good agreement with the results from the standard test method. The results indicate that the small punch test technique is an effective method for the evaluation of the high-temperature creep properties of materials.

Abstract: This paper studies the optimization problem of composition distribution of functionally graded material (FGM) coating subjected to steady heat flux loading. The investigation object of the paper is an infinite plate substrate with FGM coating in the surface. The materials are heated at the ceramic surface (upside) with a steady high-intensity heat flux input, and cooled at the metal surface (underside) with flowing liquid nitrogen. The thermal stress distribution and the temperature distribution are obtained by formulation. For optimization, the design variables are the thickness of each interlayer and the volume fraction distribution of the coating. The objective function is the danger coefficient and the restricted condition is the total thickness of FGM plate and heat insulation coefficient. In the paper, three different optimization schemes are considered and compared. The µGA and related parameters are discussed in detail. Optimizing the thermal stress distribution and minimizing the danger coefficient are carried out by µGA. The optimization results of composition distribution are gained, and the results show the optimum composition distribution can distinctly reduce the danger coefficient.