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.
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Periodicity behavior was observed after droplet collision in viscous solutions with controlled glycerol concentrations onto a PDMS surface. No periodic movement was observed in the droplets at glycerol concentrations of 50% or more. In contrast, the vertical diameter of the droplets increased and decreased periodically at glycerol solution concentrations of 40% or less. Moreover, there was little change in the periodicity of the impacting droplet movement, and the vibration frequency was measured at approximately 80 to 98 Hz in the entire range. The maximum droplet spreading factor after collision decreased significantly with increasing glycerol concentrations of 40% or more (Ohnesorge number 1.4 × 10-2 or more). The results suggest that the effect of viscosity became greater than that of the solution surface tension with increasing glycerol concentrations.
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High-strength steel, which has higher strength than ordinary steel, has emerged as a representative lightweight material because of its superior price competitiveness and easy application of manufacturing processes compared to other lightweight materials such as nonferrous metals and sandwich plates. Thus, the purpose of this study was to reduce the thickness and light weight of parts by applying high strength steel more than 600 MPa to various body parts. TR590 and DP590 high tensile steels were applied to the reinforcement seat belt front top and bottom components respectively. To this end, the impact simulation was performed, and the safety of the parts was investigated through FE-Analysis. Prototype molding evaluation confirmed the possibility of mass production of reinforcement seat belt front upper and lower components, using high tensile steel.
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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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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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.
The additive manufacturing (AM) process is known to have a major influence on environmental impact. To find out AM process with lower environmental impact in the product manufacturing process, this study compares material extrusion (Fused Deposition Modeling, FDM), powder bed fusion (Laser Sintering, LS) and material jetting processes (Poly-Jet, PJ) for 200 NIST test artifacts, using data from the specification and software of three 3D printers (J750, P770 and uPrint SE Plus), the findings from various literature and Ecoinvent of SimaPro 8.4 database. The results showed that the effects of materials on the environment were the severest for LS (20.45 Pts) and the least for FDM (10.38 Pts) although the effects of power consumption on the environment were severest for FDM (126.91 Pts) and least for LS (20.18 Pts). To reduce the emission to environment in PJ and FDM, it is recommended to improve their printing speed and reduce power consumptions of waterjet and auxiliary equipment for support removal.
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The design of subminiaturized natural fragment warhead is based on the analysis of its effectiveness against target personnel. Toward this end, the personnel incapacitation probability suggested by Sperrazza and Kokinakis was used. The effectiveness of various natural fragment warhead designs was analyzed by altering the fragment mass, velocity, number, and the target distance. A preliminary optimal design value of the natural fragment warhead in a subminiaturized missile was suggested, which was greater than the threshold value of the fragment mass to cope with air resistance. We also determined that the appropriate fragment mass was about 2.1204 × 10-4 kg (3.3 grain) in case of a subminiature warhead. This work facilitates the development of final optimal design stage of the natural fragment warhead in a subminiaturized missile and can also be utilized for the analysis and design of different types of fragment warhead.
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Analysis Method based on Probability Equation and Analysis Method based on Test in order to Estimate the Target Incapacitation Distance of Fragmentation Warhead Joo Hyun Baek, Young Hwan Jo, Byung Uk Lee, Gu Hyun Ryu Journal of the Korean Society for Precision Engineering.2020; 37(10): 751. CrossRef
Determination Method of Main Warhead Detonation Delay Time based on the Analysis about the Protection Capability of Target and the Scattering Behavior of Explosive Reactive Armor Joo Hyun Baek, Se Lin Yu, Geun Jong Jeon, Won Young Lee, Young Hwan Jo, Byung Uk Lee Journal of the Korean Society for Precision Engineering.2019; 36(10): 937. CrossRef
Generally speaking, the high speed forming process is suitable for the precise manufacturing of hard-to-form and high strength materials. This study conducted microscale embossing and punching experiments by establishing a forming system that uses a laser induced acceleration. The changes in the flyer velocity with the laser energy, flyer thickness, and flyer diameter were measured using a high speed camera, and the effects of the noted acceleration characteristics of flyers on processing performance were investigated. It is particularly important that in the case of punching, the advantages of high speed processing, in which the accuracy was improved by increasing the shear zone of the workpiece, were identified. Significantly in the case of embossing, it was observed that the formability improved by increasing the flyer velocity as the flyer diameter decreased. However, in the case when the flyer thickness was decreased, increased energy was consumed in the plastic deformation of the flyer, and the advantages of high speed forming could not be realized. For this reason, further research is needed to take advantage and optimize the forming process using the laser induced acceleration through experiments which are noted as considering the various process variables and materials.
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Performance evaluation of laser shock micro-patterning process on aluminum surface with various process parameters and loading schemes Dae Cheol Choi, Hong Seok Kim Optics and Lasers in Engineering.2020; 124: 105799. CrossRef
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.
Shot peening is widely used to improve the fatigue life and strength of various mechanical parts and an accurate method is important for the prediction of the compressive residual stress caused by this process. A finite element (FE) model with an elliptical multi-shot is suggested for random-angled impacts. Solutions for compressive residual stress using this model and a normal random vertical-impact one with a spherical multi-shot are obtained and compared. The elliptical multi-shot experimental solution is closer to an X-ray diffraction (XRD) than the spherical one. The FE model’s peening coverage also almost reaches the experimental one. The effectiveness of the model based on an elliptical shot ball is confirmed by these results and it can be used instead of previous FE models to evaluate the compressive residual stress produced on the surface of metal by shot peening in various industries.
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