• International Journal of Aeronautical and Space Sciences
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• v.14 no.2
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• pp.140-145
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• 2013

The development of high performance fabrics have advanced body armor technology and improved ballistic performance while maintaining flexibility. Utilization of the shear thickening phenomenon exhibited by Shear Thickening Fluids (STF) has allowed further enhancement without hindering flexibility of the fabric through a process of impregnation. The effect of STF impregnation on the ballistic performance of fabrics has been studied for impact velocities below 700 m/s. Studies of STF-impregnated fabrics for high velocity impacts, which would provide a transition to significantly higher velocity ranges, are lacking. This study aims to investigate the effect of STF impregnation on the high velocity impact characteristics of Kevlar fabric by effectively dispersing silica nanoparticles in a suspension, impregnating Kevlar fabrics, and performing high velocity impact experiments with projectile velocities in the range of 1 km/s to compare the post impact characteristics between neat Kevlar and impregnated Kevlar fabrics. 100 nm diameter silica nanoparticles were dispersed using a homogenizer and sonicator in a solution of polyethylene glycol (PEG) and diluted with methanol for effective impregnation to Kevlar fabric, and the methanol was evaporated in a heat oven. High velocity impact of STF-impregnated Kevlar fabric revealed differences in the post impact rear formation compared to neat Kevlar.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.1
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• pp.53-60
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• 2018

For test on flooring board laminated with PVC decoration materials in order to replace the current surface materials such as HPL in decoration wood-based flooring board. the Results of comparison and analysis are as follows: For thermal conductivity, flooring board decorated with PVC did not show huge differences when temperature was rising and lowering compared to the flooring materials laminated with the existing HPL surface materials. It seems the most meaningful results for using it as indoor flooring materials. That is, in Korea where there is the culture focusing on ondol heating, use amount of heat energy and efficiency of flooring materials are very important and sensitive issues, involving immediately with household economy of final consumers, and it might be a criteria to judge basic performances required as flooring materials. As a result of the analysis on mandatory durability test items such as abrasion resistance, absorption width expansion rate, impact resistance, surface hardness, and impact absorption for flooring materials, compared to flooring board laminated with general HPL surface decoration materials, decoration wood-based flooring board laminated with PVC surface decoration materials which is higher abrasion resistance with smaller transformation and has better durability and impact absorption of the surface, is available for actual application as indoor flooring board, and for replacing surface decoration materials impregnated with heat-hardened resion such as HPL.

• Journal of the Korean Institute of Gas
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• v.12 no.4
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• pp.41-45
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• 2008

This paper presents the numerical study on the strength safety and displacement behaviors of a helmet, which is to protect impact forces and to absorb the impact energy. Four different helmet models including a bead frame and a corrugation damper have been analyzed for the stress and the displacement characteristics by using the finite element method. The computed FEM results show that the bead frame on the summit area of the helmet is very useful to increase the strength safety of the helmet, and the corrugation damper on the lower part of the helmet may increase the energy absorption capacity. Thus, this paper recommends the bead frame and the corrugation damper as new design elements of the helmets.

• Structural Engineering and Mechanics
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• v.82 no.1
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• pp.81-92
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• 2022

Ultra-high performance fiber reinforced concrete (UHPFRC) is a composite building material with high ductility, fatigue resistance, fracture toughness, durability, and energy absorption capacity. The aim of this study is to develop a nonlinear finite element model that can simulate the response of the UHPFRC beam exposed to impact loads. A nonlinear finite element model was developed in ABAQUS to simulate the real response of UHPFRC beams. The numerical results showed that the model was highly successful to capture the experimental results of selected beams from the literature. A parametric study was carried out to investigate the effects of reinforcement ratio and impact velocity on the response of the UHPFRC beam in terms of midpoint displacement, impact load value, and residual load-carrying capacity. In the parametric study, the nonlinear analysis was performed in two steps for 12 different finite element models. In the first step, dynamic analysis was performed to monitor the response of the UHPFRC beam under impact loads. In the second step, static analysis was conducted to determine the residual load-carrying capacity of the beams. The parametric study has shown that the reinforcement ratio and the impact velocity affect maximum and residual displacement value substantially.

• Computers and Concrete
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• v.24 no.3
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• pp.193-206
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• 2019

Although concrete is the most widely used construction material, its deficiency in shrinkage and low tensile resistance is undeniable. However, the aforementioned defects can be partially modified by addition of fibers. On the other hand, possibility of adding waste materials in concrete has provided a new ground for use of recycled concrete aggregates in the construction industry. In this study, a constant combination of recyclable coarse and fine concrete aggregates was used to replace the corresponding aggregates at 50% substitution percentage. Moreover, in order to investigate the effects of fibers on mechanical and durability properties of recycled aggregate concrete, the amounts of 0.5%, 1%, and 1.5% steel fibers (ST) and 0.05%, 0.1% and 0.15% polypropylene (PP) fibers by volumes were used individually and in hybrid forms. Compressive strength, tensile strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption, toughness, elastic modulus and shrinkage of samples were investigated. The results of mechanical properties showed that PP fibers reduced the compressive strength while positive impact of steel fibers was evident both in single and hybrid forms. Tensile and flexural strength of samples were improved and the energy absorption of samples containing fibers increased substantially before and after crack presence. Growth in toughness especially in hybrid fiber-reinforced specimens retarded the propagation of cracks. Modulus of elasticity was decreased by the addition of PP fibers while the contrary trend was observed with the addition of steel fibers. PP fibers decreased the ultrasonic pulse velocity slightly and had undesirable effect on water absorption. However, steel fiber caused negligible decline in UPV and a small impact on water absorption. Steel fibers reduce the drying shrinkage by up to 35% when was applied solely. Using fibers also resulted in increasing the ductility of samples in failure. In addition, mechanical properties changes were also evaluated by statistical analysis of MATLAB software and smoothing spline interpolation on compressive, flexural, and indirect tensile strength. Using shell interpolation, the optimization process in areas without laboratory results led to determining optimal theoretical points in a two-parameter system including steel fibers and polypropylene.

• Composites Research
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• v.37 no.1
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• pp.46-52
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• 2024

The development of transportation methods has improved human transportation convenience and made it possible to expand the travel radius of people with disabilities who have difficulty moving. However, in the case of WAV (wheelchair Accessible Vehicle), the safety that may occur in a vehicle accident is still lower than that of regular passenger seats. In particular, in the case of a rear-end collision that may occur in a defenseless situation, it can cause fatal neck injuries to disabled passengers. Therefore, a more detailed design plan must be reflected in the headrest to be applied to WAV. In this study, a multi-cell headrest was proposed to implement local compression characteristic distribution of the headrest during rear-end collision of WAV. Afterwards, a correlation analysis was performed between the passenger's NIC (Neck Injury Criterion) and impact energy absorption using the data set construction through analysis and the clustering results using k-means clustering. As a result of clustering, it was confirmed that data clusters with similar characteristics were formed, and a correlation analysis between NIC and impact energy absorption through the characteristics of each cluster was performed. As a result of the analysis, it was confirmed that the softer the cell compression characteristics in Mid3 and Mid6, the more impact energy absorption increases, and the harder the cell compression characteristics in Front2, Mid3, and Mid6, the more effective it is in reducing NIC.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.3
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• pp.461-470
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• 2002

The present paper investigates the effect of hot isostatic pressing (HIPing) on mechanical properties, e.g., tensile strength, ductility and impact absorption energy of sand and die casted aluminum alloys. After HIPing at various temperatures and pressure conditions, uniaxial tensile test and Izod impact test of the samples were carried out. The experimental results showed improvements in uniaxial tensile strength, elongation and Izod impact toughness of sand casted aluminum alloy, while deterioration of a tensile strength fur die casted aluminum alloy. The effect of HIPing for microstructure of the cast aluminum alloy was also investigated.

• Journal of the Korean Society of Safety
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• v.17 no.3
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• pp.7-12
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• 2002

The object of this paper is to investigate collapse characteristics of CF/Epoxy(Carbon Fiber/Epoxy resin) composite tubes on the change of interlaminar number and fiber orientation angle of outer and to evaluate reappearance of collapse characteristics on the change of tension strength of fibers under static and impact axial compression loads. When a CF/Epoxy composite tube is mushed, static/impact energy is consumed by friction between the loading plate and the splayed fiends of the tube, by fracture of the fibers, matrix and their interface. In general, CF/Epoxy tube with 6 interlaminar number(C-type) absorbed more energy than other tubes(A, B, D-types). The maximum collapse load seemed to increase as the interlaminar number of such tubes increases. The collapse mode depended upon orientation angle of outer of CF/Epoxy tubes and loading status(static/impact). Typical collapse modes of CF/Epoxy tubes are wedge collapse mode, splaying collapse mode and fragmentation collapse mode. The wedge collapse mode was shorn in case of CF/Epoxy tubes with 0$^{\circ}$ orientation angle of outer under static and impact loadings. The splaying collapse mode was shown in only case of CF/Epoxy tubes with 90$^{\circ}$ orientation angie or outer under static loadings, however in impact tests those were collapsed in fragmentation mode. So that CF/Epoxy tube with 6 interlaminar number and 90$^{\circ}$ outer orientation angle presented to the optimal collapse characteristics.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.3
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• pp.34-39
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• 2008

In this study, CFRP(Carbon Fiber Reinforced Plastics) that has high specific strength and elastic modulus and low thermal strain was used as a material for the lightweight structural member. CFRP is a fiber material as anisotropic material. The anisotropic material is characterized by the change of its mechanical properties according to stacking orientation angle. CFRP orientation angle was oriented in [A/B]s in order to examine the effect of CFRP orientation angle on the characteristics of energy absorption. CFRP is very weak to the impact from the outside. So, when impact is applied to CFRP, its strength is rapidly lowered. The hybrid material was manufactured by combining CFRP to aluminum which is lightweight and widely used for structural members of the automobile. The hybrid member was shaped as a side member that could support the automobile engine and mount and absorb a large amount of impact energy at the front-end in case of automobile collision. The bending test device was manufactured in accordance with ASTM standard, and mounted to UTM for bending test. For comparing bending characteristics of the hybrid member with those of Aluminum and CFRP member, tests were performed for aluminum, CFRP and hybrid member, respectively.

• Journal of the Korean Society for Railway
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• v.3 no.1
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• pp.27-33
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• 2000

In this paper, numerically evaluated is the crashworthiness of the new design of the standard Korea Electric Multiple Unit Train(K-EMU)[developed by the Korea Railway Research Institute]. The 4-car consist of K-EMU is analyzed under collision conditions such as normal coupling, heavy shunting, light collision and heavy collision to collide against another stationary one at 5 kph, 10 kph, 25 kph and 32 kph, respectively. Energy absorbing capacity of its draftgear commercially available in the market and to be equipped in K-EMU is evaluated under each collision condition. Analytical results show that draftgear only is not enough to provide necessary energy absorbing capacity. It is therefore concluded that additional energy absorbers like mechanical fuses should be adopted to improve the crashworthiness of K-EMU.