Inertial navigation technology originally designed for precise guidance of missiles is widely used in weapon systems. Guided missiles have become supersonic and high maneuverability with advancement of science and technology. Antivibration performance against high vibration and shock energy is accordingly required. Sensors of an Inertial Navigation System (INS) have a high sensitivity. Conversion coefficients for acceleration values and bias errors in signals must be minimized. A vibration isolator is generally applied to protect INS by attenuating the vibration and shock energy transmitted from dynamic disturbances. The stiffness and damping are changed using highly damped materials such as elastomers that must be protected from disturbances. A vibration isolator is widely used in various fields. However, it is important to understand characteristics of a vibration isolator composed of elastomer because it has nonlinearities such as hyperelasticity and viscoelastic as well as damping characteristics. In this study, a COTS vibration isolator suitable for INS was selected through theoretical approach. Response characteristics of the system in a vibration and shock environment were analyzed through FEM analysis and vibration and shock test. In addition, through repeated excitation test, reproducibility and structural stability were confirmed when the vibration isolator was installed in the system.

With the advancement of microstructure manufacturing technology, an array of functional surfaces based on micro/nano structures have been developed. Recently, there has been active research in the development of functional surfaces using composite materials that combine the properties of two different materials. One notable area of research is the creation of functional surfaces that utilize magnetic force to actuate microstructures. Typically, these surfaces are produced using a composite material that blends a flexible, easily deformable material with iron particles that respond to magnetic force. However, the inclusion of iron particles in the flexible material can increase its Young’s modulus, making it more challenging to effectively actuate the microstructures. To address this issue, our paper presents a fabrication method that allows for the effective actuation of microstructures by removing the residual layer of the composite material. This method enables the arrangement of iron particles at the end of the microstructure, maximizing the bending of the microstructure when magnetic force is applied. Furthermore, we conducted experiments to actuate microstructures with varying ratios of iron particles, confirming the effectiveness of this fabrication method.

The Technical Specification for Interoperability (TSI) legally mandates the prediction and verification process of the Reliability, Availability, Maintainability and Safety (RAMS) in signaling and communication systems. Recently, domestic regulations, including the Railroad Safety Act, have been strengthened in order to better meet the requirements for participating in international projects. To comply with these regulatory requirements, manufacturers and development organizations must prepare verification data pertaining to the reliability and safety of railway components and related systems. This paper aims to analyze the requirements of Failure Mode, Effects and Criticality Analysis (FMECA) through international laws and standards, and subsequently propose a compliant FMECA system for the domestic railway industry. The proposed FMECA system is then compared with the analysis results of actual failure data to determine its suitability for establishing a Reliability, Availability, Maintainability (RAM) verification standard for railway products in relation to conformity assessment.

Hybrid mobile robot is the system that will practically combine legged walking and skated driving in the same system. Therefore, this robot has own problems of inverse kinematics that are not considered in typical walking robots. In this paper, I fully categorized the inverse kinematics problems for hybrid mobile robot with general motion by walking and driving on an inclined plane, including switching end-effectors between foots and blades. I also solved the inverse kinematics for each case of problems. I here actively adopted the coordinate transformation derived from the inclined plane to cope with the random motion of foots and blades on the plane. I then presented several examples of the inverse kinematics problems with specific situations, and verified the validity of the analysis method from the results.

In general, rotor inertia has an inversely proportional relationship with proportional gain and bandwidth in a turret speed control system of machine tools; thus, this system has a disadvantage, such as weak disturbance caused by a decrease in the damping ratio and an increase in bandwidth due to low rotor inertia. This paper proposes a damping compensator that is resistance to disturbances in order to improve the above problems. The proposed damping compensator reduces the residual vibration induced in the transient state by using a digital high-pass filter. The experimental results showed that the overshoot was reduced by about 5.5% in the speed response and by about 20% in the torque response in the no-load condition. Under the load condition of 4.8 N.m, the torque response showed that the undershoot was reduced by about 26%.

Energy devices in modern society require high efficiency, carbon neutrality, and the capability of distributed power generation. A fuel cell is an energy conversion device, that satisfies all of these requirements. However, most fuel cells use hydrogen as a fuel, and more than half of hydrogen is currently produced through hydrocarbon reforming, resulting in significant energy loss. Additionally, the storage and supply of hydrogen require costly systems, and a large amount of energy is consumed during compression or liquidation processes. This paper develops a solid oxide fuel cell, that uses hydrocarbon directly as fuel to resolve this problem. A small amount of Ru is mixed with the Ni-based electrode, for the effective internal reforming of hydrocarbons. For rapid deposition of YSZ electrolytes, we developed a reactive sputtering process, using a DC power source. The developed thin-film solid oxide fuel cell, showed a performance of 76 mW/cm² at 500℃ using methane as fuel.

Interest in the use of thin film of Ruthenium-Samaria doped ceria cermet (Ru-SDC) as anode in solid oxide fuel cells is increasing due to its high oxygen storage capacity and high chemical and thermal stability. To have enough structural integrity between sputtered Ru-SDC films and underlying substrates, good adhesion property is required. In this work, scratch resistance and failure mode for Ru-SDC films with various SDC composition were investigated using a scratch test method employing linearly increasing load from 1 to 50 N using a 200 μm radius Rockwell C indenter. Scratched surfaces were examined with a field emission scanning electron microscope. Chemical compositions in scratch tracks were analyzed by energy dispersive X-Ray spectroscopy. Critical loads for films with different SDC ratios were assessed and associated failure modes were identified. The highest scratch resistance among tested film compositions was the one that contained 50% of SDC. Failure modes of tested films regardless of the ratio of SDC were identified to be the initiation of tensile cracks with rapid increase of friction coefficient followed by chipping, and eventually the generation of a severe crack network.

Recently, instrument stages using flexure guide mechanisms and piezo actuators have been widely used for an ultra-precision positioning system in various industries. Research into ultra-precision position control aiming at nanoscale position errors during stage driving is being actively conducted, as well as various studies on the motion profile adjusting the reference input. In this study, we suggested a motion profile with snap and feedforward for use with a high speed nano scanning system, as compared and analyzed with the position tracking error through feedback control, and also compared to the related feed with the forward control noted as minimized at the position error to 14.19 nm. As a result, a tracking error when applying the fourth profile with snaps to the piezoelectric stage, is obtained with an error reduction effect of about 15%, as compared to when the second profile is applied.

Sound waves propagate in a manner in which energy is transmitted by adjacent molecules in the medium. These adjacent molecules exhibit inherent sound wave characteristics, such as height and wavelength, depending on the sound frequency. The Helmholtz resonator, one of the well-known acoustic elements, comprises a neck and a cavity, and features a resonance at a specific frequency related to structural dimensions. The acoustic characteristics of the Helmholtz resonator can be explained by a lumped spring-mass system in mechanical engineering; the resonant frequency can be calculated with the same analysis. The Helmholtz resonator is widely used as an acoustic filter as it can re-radiate sound waves with the opposite phase and significantly attenuate the original sound wave in the resonance frequency range. In this study, we fabricated a Helmholtz resonator-inspired film-type acoustic absorber (FAA), comprising a microscale resonator array made with polydimethylsiloxane (PDMS). Through acoustic attenuation experiments, the FAA revealed that the novel attenuation values reached up to 36.3 dB mm-1. Additionally, a continuous fabrication of the FAA was achieved via a custom-built roll-type equipment.

Majority of deformation and ruptures as a result of severe deformation of mechanical structures are due to the existence of cracks or cracks generated through specific situations. These cracks causes stress concentration and eventually ruptures under lower load conditions than they are designed to withstand. In this study, simulation tensile analysis was done by designing compact tension specimen models with the number of holes that existed inside and the materials of the test specimens by focusing on the effects of the cracks. The study results from all the analysis (deformations, equivalent stress and strain energy) confirmed that the specimen models having two holes had better strength characteristics than those with only one hole. Additionally, the durability and strength characteristics of specific mechanical structures against the load improved through appropriate arrangement of holes thereby reducing stress generation. As such the results of this study could be utilized as the basic data for future researches on composite materials and sandwich type homogenous materials. Furthermore, the study results can assist in designing more durable products.

This study focuses on these issues and includes the static fracture experiments with two forms of specimens; aluminum foam DCB and TDCB bonded with the type of mode III, a simulation static analysis to verify this experiment, and analysis of fracture behavior of adhesive interface of structures attached with aluminum foam by shape and thickness. The thickness of DCB and TDCB specimens designed in this study are set as variable t, and each thickness is t = 35 mm, 45 mm, 55 mm. According to forced displacements, the maximum reaction forces of DCB specimens due to thickness were approximately 0.35 kN, 0.45 kN, 0.54 kN, and the maximum reaction force of TDCB were approximately 0.4 kN, 0.52 kN, and 0.63 kN respectively. We expect the data according to variables to be easily investigated without a separate testing process, and effective analysis of the mechanical characteristics of aluminum foam DCB and TDCB.

Heat treated die steels are durable and resistant to abrasion. However, machining them is not very efficient. To improve the machinability using the end-milling process for high hardness die steels, we proposed an end-mill shape through analysis of the cutting force and simulation. In this study, we determined the important factors affecting the cutting force among several elements of end-mill shape using the customized cutting simulator and the design of experiments (DOE) technique. After the selecting the effective factors based on the simulation and DOE results, various end-mills were fabricated by adjusting the parameters. In the experiment, the cutting force between 1 pass and 40 pass were measured and the average value compared with each end-mill shape. Edge radius, radial relief angle and axial relief angle were selected as a key parameters and optimized by measuring the cutting force through repeated and well controlled experiments. In conclusion, the effective factors were confirmed and we could now determine the optimum shape of end-mill to minimize the cutting force for high hardness die steels.

The demand for inspection of high-speed systems for machined Carbon Fiber Reinforced Plastics parts for automobileindustry and aviation industry is constantly rising. One of the factors that degrade the performance of an inspection system is micro-vibration from the ground or structure where is placed. Various isolation systems that suppress the vibration have been studied classified as either passive or active system. The passive system is composed of a spring and a damper while the active system suppresses the vibration through an electronic control system using sensors and actuators. In this study, a voice coil motor (force constant 55N/A) acting as the actuator is optimally designed using permeance method and sequential quadratic programming algorithm to suppress the vibration and reaction force by a specimen moving stage. The two optimized voice coil motors are attached to a pneumatic mount that has an advantage in design based on the force and size constraints required by the user for an active vibration isolator with velocity sensors (GS-11d). The active vibration isolation system with the four active vibration isolators -23 dB and -20 dB at resonance frequencies in horizontal and vertical transmissibility performs better than a passive vibration isolation system.

Thin film solid oxide fuel cells (TF-SOFCs) are considered to be a promising next generation energy conversion device. TFSOFCs have many advantages such as rapid turn-on and off, fuel flexibility, material flexibility, high power density and availability of compact system. Electrodes and electrolytes of TF-SOFCs are fabricated by thin film processes. In order to fabricate high performance TF-SOFCs, proper thin film processes have to be used due to the unique requirements of each part of the TF-SOFCs. This paper reviews the thin film deposition process for fabrication of TF-SOFCs and the advantages and disadvantages of physical and chemical vapor deposition processes. In addition, materials prepared through thin film processes and the performance results of TF-SOFCs are reviewed.