Key Engineering Materials Vols. 345-346

Abstract: In this paper, an adaptive strategy based on a B-spline wavelet Galerkin method is discussed. The authors have developed the wavelet Galerkin Method which utilizes quadratic and cubic B-spline scaling function/wavelet as its basis functions. The developed B-spline Galerkin Method has been proven to be very accurate in the analyses of elastostatics. Then the authors added a capability to adaptively adjust the special resolution of the basis functions by adding the wavelet basis functions where the resolution needs to be enhanced.

Abstract: The finite element alternating method (FEAM) was extended to obtain fracture mechanics parameters and elasto-plastic stress fields for 3-D inner cracks. For solving a problem of a 3-D finite body with cracks, the FEAM alternates independently the finite element method (FEM) solution for the uncracked body and the solution for the crack in an infinite body. As the required solution for a crack in an infinite body, the symmetric Galerkin boundary element method formulated by Li and Mear was used. For elasto-plastic numerical analysis, the initial stress method proposed by Zienkiewicz and co-workers and the iteration procedure proposed by Nikishkov and Atluri were used after modification. The extended FEAM was examined through comparing with the results of commercial FEM program for several example 3-D crack problems.

Abstract: In serrated chips of difficult-to-machining materials such as medium carbon steel and titanium alloy during metal cutting process at high strain rates, the fine grain structure of the narrow shear bands which results from thermal softening due to severe deformation have been observed. However, the theories which have been developed to analyze continuous chip formation and most FEM analyses based on the conventional models such as Johnson-Cook and Zerilli-Armstrong flow stress model fail to explain the adiabatic shear band formation and the serrated chip formation. This paper discusses the characteristic of the new flow stress model in the previous investigation [1,2] and FEM simulation results to predict the serrated chip formation results are shown.

Abstract: This study focused on observing the melting phenomena and investigated a principle factor of enhanced heat transfer in phase change material when the ultrasonic vibrations were applied during the melting process. For visualization, particle image velocimetry and thermal-vision camera for observing the flow phenomenon was used. Also, experiments were performed to obtain the experimental results such as melting time and temperature distribution. Besides, structural vibration simulator which is applying a coupled finite element-boundary element method (Coupled FE-BEM) was used for calculation of acoustic pressure occurred by ultrasonic vibrations in liquid region. The results of experimental and numerical observations show that acoustic streaming induced by ultrasonic vibrations is one of the prime effects acoustically enhanced phase change heat transfer and help to accelerate the melting of phase change material. Also, the application technique of visualization and computational simulation introduced in this study is very useful and important to analyze the mechanical behavior of material in a fast fluid dynamic or acoustic field.

Abstract: In the present study, aluminum alloy casting mold which consist of eight pieces is introduced as a new technique of tire manufacturing. For the numerical analysis, finite element method (FEM) was used to investigate the thermal strain of casting mold using aluminum alloy during the cooling process. In the concrete, the temperature distributions on the inside of each casting mold, the displacement and stress occurred by temperature variations are investigated to predict the accurate measurement variations of casting mold during the cooling process. In the end, numerical simulation results such as temperature distributions, displacement and stress are presented to help to make the effective and the best mold products. Moreover, the introduced technique of numerical simulation applying a FEM is very useful and important things in the mechanical behavior of materials, especially needs the accuracy improvement such as aluminum alloy casting mold products.

Abstract: The combat car used the heavy duty diesel engine must have a large output for maintaining excellent mobility. The compacted graphite iron (CGI) is a material currently under study for the heavy duty diesel engine demanded for high torque, durability, stiffness, fatigue. In this study, three dimensional finite element model of a heavy-duty diesel engine was developed to conduct the stress analysis by using property of CGI. The use of CGI property on the FE model was expected to result in improved distribution of distortions and stresses. The loading conditions of engine are assembly load and operational gas load.

Abstract: The optimization of gate valve was performed using Kriging based approximation model. The DACE modeling, known as the one of Kriging interpolation, is introduced to obtain the surrogate approximation model of the function. In addition, we describe the definition, the prediction function and the algorithm of Kriging method and examine the accuracy of Kriging by using validation method.

Abstract: DOE (design of experiments) was applied to the design of a knuckle as a part of a suspension system. Specifically, knuckle made of aluminum alloy was optimized considering the strength. On the other hand, design variables were set as shape variables. During structural optimization using DOE, an orthogonal array strategy was developed to determine the optimum design. The relevant discrete variables were treated as levels. Since the conventional orthogonal array did not consider the constraint, however, the characteristic function was defined to include the effect of constraint feasibility. The general DOE was expanded to include problems with constraints related to the new characteristic function.

Abstract: Although steel-concrete interface has significant influence on bonding strength and shear strength, the composite structure with the consideration of the interface fracture has been rarely conducted. In this study, sensitivity analyses are performed to find out steel-concrete interface characteristics by using interface finite elements, defined as elastic-plastic behavior. In order to verify computational accuracy, the analyzed interface properties are compared with experimental results. Generally, interface in steel-concrete composite structure plays a critical role of controlling bonding strength as well as transferring loads between steel and concrete. The composite interface should be avoided to reach to an interface fracture condition; otherwise composite structure may deviate from intended behavior even under low stress state. It is then led to catastrophic fracture or collapse of the structure. This study shows that interface properties of steel-concrete can be analyzed by using the interface element, and the results provide more reliable prediction for the steel-concrete composite behavior.

Abstract: Mechanism of transformation plasticity (TP) is discussed from continuum mechanics viewpoint, and derivation of TP law from the unified thermo-mechanical and transformation plasticity constitutive equation. Result of identified TP coefficient for a chromium steel (JIS SCr420) by use of multi-functional testing machine is introduced as one of the material data together with other data to the simulation of a quenching process by use of newly developed code COSMAP. The simulated distribution of temperature, phases and stress/distortion are compared with the experimentally measured values to verify the accuracy.