Failure mechanism for metal cylinder under explosive loading

This paper presents the numerical study of dynamic fracture for metal cylinder under internal explosive loading. Also, the effects of fracture models and groove designs on fracture behavior are investigated. For the dynamic hardening behavior, the Lim-Huh model including the thermal softening effect is adopted [1, 2]. Also, the Lou-Huh fracture model considering the strain rate dependency is used for fracture prediction [3]. The tensile fracture occurs first at the outer surface, and the shear fracture is observed near the inner surface. In addition, finite element analyses are performed to study the effect of various groove designs on dynamic fracture; single U-groove and V-groove at the outer surface. The tensile and shear fracture lines are predicted near the groove tip and inner surface, respectively. It is concluded that the stress triaxiality parameter is one of the critical factors in the dynamic fracture prediction of the metal cylinder.

     

Investigation of open-type 1 kW-scale thermochemical heat storage system with zeolite 13X for power-to-heat applications

This study investigated thermochemical heat storage with zeolite 13X to provide an insight into the design and operation of a heat storage system for power-to-heat (P2H) applications. The heat storage system consists of a storage chamber with 21.2 liters of its capacity stacked by zeolite 13X. Experiments were conducted based on the variation of operating parameters, such as charging temperature, absolute humidity, and flow rate. The results show that the amount of available heat linearly increases with charging temperature; that is, its value at 220 °C is twice that at 100 °C. The maximum energy storage density is calculated as 0.56 GJ/m³. The average heat power varies in the range of 0.4–0.7 kW depending on the amount of supplied water. In addition, a linear correlation between the reacted water and discharged heat is provided. It was confirmed that the thermal storage efficiency was 60–70 %.

     

Acoustic radiation from modal vibration of automotive brake drum

The vibro-acoustic characteristics of an automotive brake drum is studied by applying a hybrid approach, which combines a numerical vibration analysis with an analytical acoustic solution. Specifically, structural vibration of a drum is investigated with the numerical finite element analysis, and vibratory displacements of the outer surface of the drum is approximated by simple mathematical expressions. Then, radiation of sound from the drum vibration is calculated using well-known theoretical solutions based on the simplified modal displacements. Finally, the calculation results are compared with those obtained by full numerical analyses. The results show that the numerical-analytical hybrid method allows relatively accurate calculation of vibro-acoustic properties of a brake drum under realistic boundary conditions.     

Characterization of magnetic materials using a scanning microwave microprobe

We investigated the electromagnetic properties of metals of iron, nickel, cobalt, aluminum, gold, copper, silver, and permalloy thin films on SiO(2) substrates using a near-field microwave microprobe. The electromagnetic properties of metal sheets were estimated by measuring the microwave reflection coefficient S(11) and compared with the theoretical values. We observed the hysteresis behavior of permalloy thin films on SiO(2) substrates using a near-field scanning microwave microprobes (NSMM) system. Experimental results are in good agreement with the theoretical model of transmission theory. In order to better characterize the electromagnetic properties of metals and magnetic metals instead of the usual method, we take advantage of the noncontact microprobing evaluation capabilities using a near-field microwave.     

Effect of interlayer on structure and performance of anode-supported SOFC single cells

To lower the operating temperatures in solid oxide fuel cell (SOFC) operations, anode-supported SOFC single cells with a single dip-coated interlayer were fabricated and the effect of the interlayer on the electrolyte structure and the electrical performance was investigated. For the preparation of SOFC single cells, yttria-stabilized zirconia (YSZ) electrolyte, NiO-YSZ anode, and 50% YSZ-50% strontium-doped lanthanum manganite (LSM) cathode were used. In order to characterize the cells, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were utilized and the gas (air) permeability measurements were conducted for gas tightness estimation. When the interlayer was inserted onto NiO-YSZ anode, the surface roughness of anode was diminished by about 40% and dense crack-free electrolytes were obtained. The electrical performance was enhanced remarkably and the maximum power density was 0.57W/cm(2) at 800 degrees C and 0.44W/cm(2) at 700 degrees C. On the other hand, the effect of interlayer on the gas tightness was negligible. The characterization study revealed that the enhancement in the electrical performance was mainly attributed to the increase of ion transmission area of anode/electrolyte interface and the increase of ionic conductivity of dense crack-free electrolyte layer.     

Numerical study on characteristics of turbulent two-phase gas-particle flow using multi-fluid model

The purpose of this research is to study numerically the turbulent gas-particle two-phase flow characteristics using the Eulerian-Eulerian method. A computer code is developed for the numerical study by using the k-ɛ-k _p two-phase turbulent model. The developed code is applied for particle-laden flows in which the particle volume fraction is between 10⁻⁵ and 10⁻² for the Stokes numbers smaller than unity. The gas and particle velocities and the particle volume fraction obtained by using this code are in good agreement with those obtained by a commercial code for the gas-particle jet flows within a rectangular enclosure. The gas-particle jet injected into a vertical rectangular 3D enclosure is numerically modeled to study the effect of the Stokes number, the particle volume fraction and the particle Reynolds numbers. The numerical results show that the Stokes number and the particle volume fraction are important parameters in turbulent gas-particle flows. A small Stokes number (St ≤ 0.07) implies that the particles are nearly at the velocity equilibrium with the gas phase, while a large Stokes number (St ≥ 0.07) implies that the slip velocity between the gas and particle phase increases and the particle velocity is less affected by the gas phase. A large particle volume fraction (α _p ≥ 0.0001) implies that the effect of the particles on the gas phase momentum increases, while a small particle volume fraction (α _p ≤ 0.0001) implies that the particles would have no or small effect on the gas flow field. For fixed Stokes number and particle volume fraction, an increase of the particle Reynolds number results in a decrease of the slip velocity between the gas and particle velocities.     

Stress analysis of two-dimensional cellular materials with thick cell struts

Finite element analyses (FEA) were performed to thoroughly validate the collapse criteria of cellular materials presented in our previous companion paper. The maximum stress (von-Mises stress) on the cell strut surface and the plastic collapse stress were computed for two-dimensional (2D) cellular materials with thick cell struts. The results from the FEA were compared with those from theoretical criteria of authors. The FEA results were in good agreement with the theoretical results. The results indicate that when bending moment, axial and shear forces are considered, the maximum stress on the strut surface gives significantly different values in the tensile and compressive parts of the cell wall as well as in the two loading directions. Therefore, for the initial yielding of ductile cellular materials and the fracture of brittle cellular materials, in which the maximum stress on the strut surface is evaluated, it is necessary to consider not only the bending moment but also axial and shear forces. In addition, this study shows that for regular cellular materials with the identical strut geometry for all struts, the initial yielding and the plastic collapse under a biaxial state of stress occur not only in the inclined cell struts but also in the vertical struts. These FEA results support the theoretical conclusion of our previous companion paper that the anisotropic 2D cellular material has a truncated yield surface not only on the compressive quadrant but also on the tensile quadrant.     

Fatigue life analysis of wheels on guideway vehicle using multibody dynamics

A guideway vehicle is used in automobile, semiconductor and LCD manufacturing industries to transport products efficiently. Since the operating speed of the guideway vehicle should be increased for maximum productivity, the weight of the vehicle has to be reduced, and this weight reduction may cause a failure of a part in the system. Therefore, the estimation of the fatigue life of the parts becomes an important problem. In this study, the fatigue life of the wheels in the guideway vehicle is estimated using an S-N curve. To obtain the fatigue life of a part, the S-N curve, the dynamic stress time history applied to the part, and the material property of the part are required. The S-N curve of the driving wheel is obtained from the fatigue experiment on wheels. To obtain the material properties of the driving wheel, which is composed of aluminum with urethane coating, the result of a compression hardware test and static analysis of the wheel’s FE model are used. The dynamic stress time history influencing the driving wheel can be obtained from linear superposition of the dynamic load time history and the static stress. The dynamic load time history is estimated by multibody dynamic analysis, and the static stress is obtained by finite element analysis.     

Research on characteristics and effects of combustion performance by amplified ignition energy in CVCC system

Journal of Mechanical Science and Technology - This study was conducted to analyze the flame characteristics, which is generated through the combustion process according to air/propane mixture...     

Design optimization of extruded preform for hydroforming processes based on ideal forming design theory

The conventional practice to predict preform shapes in hydroformimg processes based on finite-element analysis and/or experiment is an iterative procedure and requires many trials. In this paper, a computationally efficient direct design method, which effectively improves the design procedure, was introduced. The direct design method based on ideal forming theory, which was successfully applied for the design of flat blanks for stamping processes, was extended for the design of non-flat preform for tube hydroforming processes. A preform optimization methodology for non-flat blank solutions was proposed based on the penalty constraint method for the cross-sectional shape and length of a tube. The hybrid membrane/shell method was employed to capture thickness effect while maintaining membrane formulation in the ideal forming theory. Several classes of examples were analyzed to verify the current formulation.