• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.92-99
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• 2006

Design capability for high safety vehicle with light weight is crucial to enhancing competitive power in vehicle market. The structural foam can contribute to restraining section distortion in body members undergoing bending collapse at vehicle crash. In this study, first, the validation of analysis model including structural foam model for simulating fracture behavior was discussed, and the bending collapse characteristics of five representative section types were analyzed and compared. Next, with changing the laminate foam shape, load carrying capability and absorbed energy were observed. The results suggests a design strategy of body members filled with laminate foam, leading to effectively elevating bending collapse characteristics with weight increase in the minimum.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.331-338
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• 2023

Modern bulletproof armor must be light and have excellent penetration resistance to ensure the mobility and safety of soldiers and military vehicles. The ballistic performance of heterogeneous structures of laminated flat plates as bulletproof armor depends on the arrangement of constituent materials for the same weight. In this study, we analyze bulletproof performance according to the stacking sequence of laminated bulletproof armor composed of Kevlar, ultra-high molecular weight polyethylene, and ethylene-vinyl-acetate foam. A ballistic analysis was performed by colliding a 7.62 × 51 mm NATO cartridge's M80 bullet at a speed of 856 m/s with six lamination arrangements with constituent materials thicknesses of 5 mm and 6.5 mm. To evaluate the bulletproof performance, the residual speed and residual energy of the projectile that penetrated the heterogeneous laminated flat plates were measured. Simulation results confirmed that the laminated structure with a stacking sequence of Kevlar, ultra-high molecular weight polyethylene, and ethylene-vinyl-acetate foam had the best bulletproof performance for the same weight.

• Journal of the Korean Society of Safety
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• v.33 no.2
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• pp.8-13
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• 2018

The light weight composite materials have been replacing in high performance structures. The object of this study is to examine the effects of the initial crack location about a delamination in a PVC foam cored sandwich composite that is used for the strength improvement of structures. The initial crack location and fiber laminates thickness were changed with several types. The MMB specimen was used for evaluating the fracture toughness and crack behaviors. The material used in the experiment is a commercial twill carbon prepreg in CFRP material and Airex in PVC foam core. Sandwich laminate composites are composed by PVC foam core layer between CFRP face sheets. The face sheets were fabricated as 2 types of 5 and 8 plies. The initial cracks were located in a PVC form core and the interface of upper CFRP sheet. From the results, the crack initiation was affected with the location of the initial crack inserted in the PVC foam core. Among them, the initial crack at 1/3 of the upper part of the PVC foam core was the most rapid progression. And the critical energy release rate was $0.40kJ/m^2$, which is the lowest value when the initial crack was inserted into the interface between a PVC foam core and CFRP laminated with 5 plies. Meanwhile, the highest value of $1.27kJ/m^2$ was obtained when the initial crack was located at the center line in case of the 8 plies.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.13 no.3
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• pp.97-109
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• 2005

A canard type aircraft, which has good wing stall and stall/spin-proof characteristics, is under development. The aircraft prototype has full-depth core sandwich type wing and fixed landing gear, and has been built for test flights. Newly developing aircraft will be equipped with retractable landing gear and conventional foam core sandwich laminate structures and multi-rib wings. In this study, we present the structural test procedure and result for aircraft Firefly.

• Composites Research
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• v.12 no.6
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• pp.74-82
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• 1999

The static and fatigue characteristics of polyurethane foam cored sandwich structures are investigated. Three types of the specimens with the glass fabric faces and the polyurethane foam core are used; non-stitched. stitched, and stiffened sandwich specimen. Especially additional structural reinforcements with the twisted polyester and glass fiber for thickness direction are made to stitched sandwich structure panel to minimize the delamination of structure which is stitched the upper and lower faces through the core and the resin is impregnated Into stitched fiber with the characteristics of low viscosity of resin at resin flow temperature and cured together with during the curing process. Bending strength of stitched specimen which is 50 mm $50{\times}50{\;}mm$ pitched is improved by 50 % as com-pared with non-stitched specimen and stiffened specimen is improved 10 times more than non-stitched structure. After fatigue testing of $10^6$cycles by 20% of ultimate load under monotonic load, the bending fatigue strength of non-stitched specimen is decreased by 27% of monotonic bending strength, 39% for stitched structure and 20% for stiffened specimen. To verify the aging effect of polyurethane form core, Ultrasonic C-scanning equipment is used to detect the damage of skin laminate alone after fatigue test. From results of UT C-scan images, there is no defect that can be damaged occurred during fatigue test. It is concluded that the decrease of bending strength for foam cored sandwich specimen is caused by the decrease of stiffness due to the aging of polyurethane foam core during fatigue cycles.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.3
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• pp.29-37
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• 2000

Because the previous design procedure for the composite wind turbine blade structure using trial and error method takes long time, a improved design procedure by using the program based on classical laminate theory was proposed to reduce the inefficient element. According to the improved design procedure, limitation of strains, stresses and displacements specified by international standard specification IEC1400-1 for the composite wind turbine blade were applied to sizing the structural configuration by using the rule of mixture and the principal stress design technique with a simplified turbine blade. Structural safety for strength and buckling stability was confirmed by the developed analysis program based on the laminate theory to minimize the design procedure. After modifying the preliminary design result with additional structural components such as skin, foam sandwich and mounting joints, stresses, strains, displacements, natural frequency, buckling load and fatigue life were analyzed by the finite element method. Finally these results were confirmed by comparing with IEC1400-1 specification.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.692-697
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• 2005

A canard type aircraft, which has good wing stall and stall/spin proof characteristics, is being developed. The previous first and second prototypes, having full depth core sandwich type wing and fixed landing gear, was built for test flights. Newly developing Firefly will be equipped with retractable landing gear and conventional foam core sandwich laminate for wing and fuselage. For manufacturing, composite material process has been studied including coupon tests. Wet lay-up onto foam core with glass fabric using lay-up mold has been chosen, and composite material parts are cured under room temperature and atmospheric pressure condition. In general, molded parts show so good surface smoothness and standardized quality that are best in mass production. In this study, we present the mold technology and development status for small aircraft firefly.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.2
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• pp.202-208
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• 2003

In this paper, we proposed a microstrip patch array antenna for DBS reception which had high gain and high tilted angle through mutual coupling driver patch to parasitic patch in H-plane edge and broadside direction in different layers. It was designed and fabricated in 16$\times$8 array by using low cost polyester based copper-clad laminate and foam instead of high cost dielectric substrate. It had gain of 22.9 dBi, beamwidth of 4.6$^{\circ}$, and tilted angle from broadside direction of 43.9$^{\circ}$.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.3
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• pp.350-359
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• 2017

This paper presents a new holistic development approach for the carbon continuous-fiber composite frame of an automotive sunroof assembly. The original steel frame has been designed to get higher bending stiffness with its corrugated cross-sectional shape. The new approach uses the prepregs of a fast cure epoxy and PCM manufacturing processing. For higher productivity, the new frames feature a very simple plat cross sectional shape but achieve high bending stiffness through the laminate design. The sandwich structure with a PET foam core was presented. The frames were made of carbon UD laminae covered single carbon fabric on the outer surfaces. The fabrics provide torsional stiffness and also hold the carbon UD fibers floating in the low viscous epoxy resin of prepregs at the curing temperature during processing. The final product yields approximately 18 % savings in weight compared with the original.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.18-21
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• 2004

A GFRP based composite blade was developed for a 750kW wind energy conversion system of type class I. The blade sectional geometry was designed to have a general shell-spar structure. The load cases specified in the IEC61400-1 international specification were considered. For withstanding all relevant extreme loads, the structural analysis for the complete blade was performed using a commercial FEM code. The static load carrying capacity, buckling stability, blade tip deflection and natural frequencies at various rotational speeds were evaluated to satisfy the strength requirements in accordance with the IEC61400-1 and GL Regulations. For designing a lightweight blade, the thickness and the lay-up pattern of the skin-foam sandwich structures were optimized iteratively using the DOT program T-bolts were used for joining the blade root and the hub, which were modeled using a 3D FE volume model. In order to confirm the safety of the root connection, the static stresses of the thick root laminate and the steel. bolts were predicted by taking account of the bolt pretension and the root bending moments. The calculated stresses were compared with the material strengths.