This study reviewed types and dynamic behavior characteristics of shock-absorbing materials used in spent nuclear fuel transport containers. Among various shock-absorbing materials, wood, honeycomb, and foam materials were the most commonly used. Redwood and balsa wood are sustainable materials with excellent energy absorption properties and natural decomposition, but vulnerable to temperature and humidity. Although honeycomb materials have better mechanical strength than other materials, they only support unidirectional loads. Urethane foam and Fenosol foam materials have lower mechanical strength and lower shock absorption than others, but have higher lightness and fire resistance. They also allow users to control density and produce them. Due to their isotropic characteristics and ease of increasing or decreasing strength by adjusting density, foam materials are better for design and manufacturability than others. Shock-absorbing materials show more complex behavior characteristics than general steel materials. For shock absorption, large deformations are considered up to sections that greatly exceed the elastic region, inevitably increasing the complexity of behavior simulation. During design, to accurately simulate large deformation behavior, it is important to select an appropriate analysis property card and determine major influencing factors. An analysis-based review was additionally conducted for property cards typically applied to foam materials.
The automotive electronic control unit outputs control signals using electrical signals of various input sensors installed in the vehicle to control the state of the engine, automatic transmission, and electric power steering (EPS). These units are installed inside the vehicle or engine room, and the temperature rises and falls by several tens of degrees due to the heat of the engine and the self-heating of the electronic control unit. Therefore, it was exposed to a thermal fatigue environment due to the difference in the coefficient of thermal expansion between the components, which caused frequent component damage. Solder cracks due to thermal fatigue in electronic control units are a key failure mode. However, because of its great heat capacity, the electronic control unit for automobiles took a long time to attain the desired temperature of high or low, and as a result, the 1,000-cycle test for thermal fatigue life verification required 3,167 hours (or 4.4 months). Therefore, in this study, the thermal shock cycle test time for the verification of the thermal fatigue life of electronic control units for automobiles was reduced by dividing it into two types.
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Recently, large-scale accidents caused by minor damage from fatigue failure and impact on structures have been frequently reported. Therefore, a real-time damage monitoring system of structures is considered to be one of the most important technologies to ensure safety in various types of research. The piezoelectric sensor, which has an advantage of converting deformation of a structure into an electrical signal without using an additional power source, has been reported as one of the most suitable methods for real-time monitoring systems. This review aims to describe the structural monitoring system utilizing piezoelectric paint sensors. First, we present the concept of a piezoelectric paint sensor with the advantages of flexibility and piezoelectric performance. Then, factors affecting the performance of the piezoelectric paint sensor are introduced. Finally, an overview of piezoelectric paint sensors for structural monitoring, such as vibration detection and impact monitoring, are provided. The state-of-the-art of the application of the piezoelectric sensor is also introduced, providing feasibility in industrial fields.
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The purpose of this study was to compare ankle joint loads (Linear and Angular Impulses) while descending the stairs and ramp. Ten young male subjects participated in this study. Stairs and ramp of identical slope (30 degrees) were custom-made to include force plates in the middle of pathways. Subjects descended the stairs and ramp at a comfortable speed and posture. The stance period was divided into three phases, weight acceptance (WA), single limb stance, and pre-swing. Three-directional impulses and their sum were derived from the reaction forces and moments at the ankle joint. Differences in impulse sums (Both Linear and Angular) between stairs and ramp were significant only in the early (WA) phase, whereas those of stairs were greater than the ramp. All subjects adopted forefoot strike strategy for the stairs and 80% of the subjects adopted rearfoot strike strategy for the ramp. An increase in the GRF and moment arm of the GRF at the ankle joint in case of forefoot strike may have contributed to the increase in the linear and angular impulse in the early phase of stair descent compared to ramp descent. The results are in agreement with the preference of ramp in the elderly.
In this study, a free-fall drop tester was studied to test the impact reliability of small electronic components. The electronic component was fixed to the drop table and the table was fallen along guide rods. The impact energy was adjusted by the initial drop height, and the impact duration time was adjusted by inserted soft layers under the drop table. Table acceleration was achieved in the form of a half-sine that conforms to international standards. The developed tester was evaluated by a small printed circuit board. It was observed that the developed tester was fully utilized for the impact reliability assessment of electronic components.
The Flywheel Energy Storage System (FESS) stores the electric energy into the rotational kinetic energy of the rotor. The FESS uses housing components so that the rotor spins inside the housing where the vacuum is maintained. Thus, the housing component is exposed to the load due to this pressure difference, and designing the housing that can efficiently support this load is crucial. Meanwhile, in the situation wherein the rotor lifting force is blocked, the rotor drops and damages the system. Thus, it is necessary to equip a structure capable of supporting the corresponding impact of the rotor drop. In this study, the design of the housing components is described by considering the structural robustness of the housing components, under the atmospheric pressure and impact of the rotor drop. For the pressure load, structural analysis was conducted following the different housing lid shapes: concave, convex, and flat. For the impact of the rotor drop, the structural analysis was conducted following the different terminal velocities of the rotating rotor. As a result, the designed housing components comprise a concave housing lid and the safety suspension 1 mm beneath the rotor. Considering the results, it operates stably under the conditions stated above.
Generally, press molds have thermal and mechanical impact wear during usage. To improve the life of the mold, enhancement of mechanical properties such as abrasion resistance and shockproof capability is required. To solve this, we propose the multi-layered cladding process of functional materials with different mixing ratios. AISI-D2 material, known as cold die steel, was used as base material and AISI-M4 and -H13 powders were used for surface cladding on the base metal for high resistance wear and shockproof capability. Four cases of specimens were prepared to compare mechanical properties after tests. Through this study, a specimen multiple cladded with mixing M4 and H13 powders for middle layer and M4 powder only for top layer showed 80% improvement in shockproof capability. We posit that this method based on multi-layer cladding with a combination of functional metal powders increased mold life.
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An airborne black box should preserve the recorded data under the extreme environmental conditions such an aircraft crash. Through the recorded information from the black box, the cause of the aircraft crash can be analyzed. This requires the black box to safely protect its memory board inside from the external forces or heat generated by the aircraft crash. This paper is a case study conducted to develop the black box to satisfy the crash survival requirements of ED-112A, the standard of performance to develop the black box, and optimize its weight and size. Through the sequential design, analysis, and test process, the black box successfully demonstrated the optimized design, analysis and test subjected to crash survival requirements of ED-112A. The prototype of the black box was fabricated and tested for the verification of each analysis within the requirements of ED-112A.
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It was a requirement to use electronic components developed and operated by MANPAD in the military wheel vehicle with greatly improved operational radius and quickness and maneuverability. The objective of this study was to add the structure of the newly developed equipment for future compatibility with each other, and design it according to the requirements of vehicle installation. As the operating environment changes from one type of equipment to another, that is operated by a person, the differences between the environmental specifications and characteristics of the two types of weapons are compared. In addition, dynamic characteristics analysis and testing of equipment units were carried out in order to confirm whether the equipment can be normally operated with the disturbance (vibration / shock) that will be continuously received as the operating environment changes. The physical properties of the PCB components were verified through actual environmental tests after confirming the difference between the values shown between the commercial program and the reference documents.
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Dynamic Characteristic Analysis of an Inertial Navigation System for Guided Weapons Equipped with COTS Vibration Isolator Ho-Ho Lee, Jun-Hyuk Park, Geun-Suk Gil, Jong-Geun Jeon, Ki-Hyuk Kwon, Sang-Chan Moon, Seung-Bok Kwon, Seongho Nam, Chang-Ky Sung Journal of the Korean Society for Precision Engineering.2024; 41(10): 797. CrossRef
Development of Free Fall Drop Tester for Electronic Components In Jun Jung, Jae Young Jang, Dong-Kil Shin Journal of the Korean Society for Precision Engineering.2020; 37(12): 889. CrossRef
The precision-guided projectile is a weapon system for precision attacks, and the cannon-launched projectile is guided by a control device. The electrical actuator system is a subsystem of the control device, and the whole projectile undergoes high axial and lateral impact force for 1 to 10mseconds. In this study, a charpy, and a tensile impact analysis were conducted, using specimens made in the materials of SUS630 and Al7075-T6 to understand fracture mechanics and impact property, such as energy change rate. The impact analysis and gas-gun impact test were conducted, to validate the optimized housing model.
While designing an armored vehicle platform, survivability is the most important capability and so protection design should be performed. In particular, mine protection design should be preferentially considered in a way that can reduce mass casualties. In this study, a simplified model, the main design parameters and their levels were defined, and then mine blast simulations were performed to obtain an effective protection design procedure. Before performing the main simulation, an experiment and simulation for a simple armor plate were performed and compared in order to certify the reliability of the numerical model. Afterwards, simulation cases, which were based on the reasonable numerical model, were defined by the DOE (Design of Experiment). An evaluation of the simulation results was carried out through both the contour and in a statistical manner, via a main effect analysis and ANOVA (Analysis of Variance). Finally, the impact characteristics of a protection parameters under the mine blast were estimated.
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The Study on the Mine Protective Structural Design of Wheeled Armored Vehicle Body Chan Young Park, Kyoung Hoon Lee Journal of the Korean Society for Precision Engineering.2019; 36(3): 255. CrossRef
The development of the lightweight sandwich plate with periodically repeated cores is one of hot issues to reduce the weight of the part. The behavior of the sandwich plate under static and dynamic loads is greatly influenced by the design of the cores. The aim of this paper is to investigate the effects of the corrugated angle on low velocity impact characteristics of the lightweight sandwich plate with corrugated cores. The corrugated core with the fold surface is designed to improve the joining characteristics between cores and skin sheets. The corrugated angle of the corrugated cores ranges from 45o to 90o. Specimens are manufactured from the fused deposition modeling (FDM) process. The characteristics of the fabricated specimen are investigated. Impact experiments are performed using a drop impact tester with a stretching type of fixture and the hemispherical nose of the impact head. From the results of the experiments, the influence of the impact energy and corrugated angle on the failure pattern of the lightweight sandwich plate is examined. The effects of the corrugated angle on critical impact energies for different failure patterns are investigated. Finally, the failure map of the lightweight sandwich plate with corrugated cores is estimated.
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In this study, a numerical analysis on the impact response of HHA (High Hardness Armor Plate) sequences under a 7.62 mm projectile impact was performed to obtain the fundamental design data for a combat-vehicle platform. Recently, the ballistic-protection levels for combat vehicles have increased, and ballistic-protection designs should now be able to deflect multi-hit projectiles. To study the ballistic-impact characteristics, armor-plate sequences of one or two layers with a gap of 0 mm to 2 mm between the front and rear plate were defined under the same weight and thickness. For the certification of the reliability of the numerical model, ballistic tests and an analysis of the single plate under the 7.62 mm projectile impact were performed and analyzed. On the basis of a valid numerical model, a numerical analysis was performed and analyzed. Lastly, it was proved that the performances of the two-layer sequence with the 2 mm gap regarding the impact-response acceleration, deflection efficiency, and penetration depth are the highest.
The goal of this paper is to investigate the effects of out-of-plane deposition angle on product characteristics of a UV photo-curing process. Specimens are manufactured from a commercialized UV photo-curing machine, the NOBEL V1.0. The influence of the out-of-plane deposition angle of the specimen on surface characteristics, including morphology of the sloped surface, pick-to-pick distance of convex region, and roughness of the sloped surface, is examined via the observation of the sloped surface. In addition, the influence of the radius of curvature of the specimen on the surface roughness of the sloped surface is evaluated. The effects of the out-of-plane deposition angle on impact strength of specimens are investigated via Izod impact experiments. Finally, we discuss the influence of the out-of-plane deposition angle on failure characteristics of specimens for impact loads.
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