• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1335-1343
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• 2012

In this study, the lightweight modular design of hybrid railway carbody structures made of sandwich composites and aluminum extrusions was investigated by using topology and size optimization techniques. The topology optimum design was used to select the best material for parts of the carbody structure at the initial design stage, and then, the size optimum design was used to find the optimal design parameters of hybrid carbody structures using first-order and sub-problem methods. Through the topology optimization analysis, it was found that aluminum extrusions were suitable for primary members such as the underframe and lower side panel module to improve the stiffness and manufacturability of the carbody structures, and sandwich composites were appropriate for secondary members such as the roof and middle side panel module to minimize its weight. Furthermore, the results obtained by size optimization analysis showed that the weight of hybrid carbody structures composed of aluminum extrusions and sandwich composites could be reduced by a maximum of approximately 17.7% in comparison with carbody structures made of only sandwich composites.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2328-2335
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• 2002

A hybrid composite material has many potential usage due to the high specific strength and the resistance to fatigue, when compared to other composite materials such as fiber reinforced plastic(FRP) and metal matrix composite(MMC). However, the fracture mechanism of hybrid composite material is extremely complicated because of the bonding structure of metals and FRP. In this study, Al 7075 sheets and carbon epoxy preprags were used to fabricate the hybrid composite. Recently, nondestructive technique has been used to evaluate the fracture mechanism of these composite materials. AE technique was used to clarify the microscopic damage behavior and failure mechanism of A17075/CFRP hybrid composite. It was found that AE paralneters such as AE event, energy and amplitude were effective to evaluate the failure process of Al 7075/CFRP composite. In addition, the relationship between the AE signal and the characteristics of fracture surface using optical microscope was discussed.

• Composites Research
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• v.26 no.2
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• pp.85-90
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• 2013

This paper presents the fabrication and 3-point flexion testing of carbon fiber reinforced polymer (CFRP) composite face/aluminum honeycomb core sandwich panels. Specimen sandwich panels were fabricated with three honeycomb types (3.18 mm, 4.76 mm, and 6.35 mm cell size) and three panel radii (flat, r = 1.6 m, r = 1.3 m). The curved sandwiches were fabricated normally with the core in the W-direction. The tensile mechanical properties of the CFRP $2{\times}2$ twill fabric face laminate were evaluated (modulus, strength, Poisson's ratio). The measured values are comparable to other CFRP fabric laminates. The flat sandwich 3-point flexion test core shear strength results were 11-30% lower than the manufacturer published data; the test set-up used may be the cause. With a limited sample size, the 1.3 meter panel curvature appeared to cause a 0.8-3.8% reduction in ultimate core shear strength compared to a flat panel.

• 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.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.120-125
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• 2000

A heddle frame is the major part of a loom that produces woven cloth by insertion of weft yarns between warp yams. Warp yarns are manipulated by many heddles fixed in a heddle frame. Recently, the up and down speed of heddle frames has been increased much for the increase of productivity, which induces higher inertial stresses and vibrations in the heddle frame. The heddle frame has the rectangular cross-section. For the design of box type beams of rectangular cross-section, extensional stiffness EA, flexural stiffness El, and torsional stiffness GJ as well as the vibration characteristics are important and should be simultaneously considered. Tn this paper, the vibration characteristics of the composite and the composite sandwich beams for high-speed heddle frame were tested by impulse frequency response.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.234-237
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• 2001

In this study, efforts were made to understand the propagation of electromagnetic wave through the foam core sandwich structure by the analytical model. Foam core sandwich structure is composed of glass/epoxy composite skins and foam core. Transmittance and reflectance of the arbitrary linearly polarized incident TEM waves through the unidirectional composites, foam and foam core sandwich structures were determined as functions of thickness, fiber orientation of composites, incident angle and polarization angle by the analytical model. From the results of the analysis, the general tendency of transmittance and reflectance of electromagnetic wave through composites, foam and foam core sandwich structures was obtained.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.65-68
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• 2004

A new multifunctional sandwich composite was investigated in this paper. The honeycomb core of this composite was filled with viscoelastic material in order to obtain an improved impact performance. The fillings in the honeycomb cells was hoped to provide the act of energy dissipation in this combined material system. Low-velocity drop-weight test was set up to the specimens with various stacked carbon/epoxy laminate facesheets, $[0/90]_{4s},\;[0/45/-45/90]_{2s}$. Load and energy history were checked and compared for the both groups of specimens, with and without rubber fillings. Further, the damaged faces were inspected visually by ultrasonic C-scan.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.290-293
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• 2004

In this paper a new sandwich composite is developed by injection silicone rubber into the honeycomb core. This composite material is designed to have a improved damping performance. For verification damping tests were conducted to the specimens with different stacked USNl25 carbon/epoxy prepreg laminate facesheets, $[0/90]_{4s},\;[0/45-45/90]_{2s},\;[45/-45]_{4s}$. Frequency response, displacement response and damping ratio were checked and compared for the both groups of specimens, with and without rubber fillings. The experimental results provided a good agreement with our original material design concept.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.29-33
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• 2000

The purpose of this paper is to determine the effect of the autoclave inner pressure rate, heat-up rate, tool round angle, Thickness of core, height of joggle on defects, and to minimize the defects of aircraft sandwich structure reinforced with honeycomb core occurred in autoclave processing. The results showed that the geometry of aircraft sandwich structure and tool such as tool round angle, Thickness of core, height of joggle, and the autoclave cure conditions such as inner pressure rate, heat up rate strongly affected the core movement, core wrinkle, bridge phenomenon of prepreg and depression of core that occurred in autoclave processing.

• Composites Research
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• v.13 no.2
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• pp.81-90
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• 2000

For automotive applications, a sandwich sheet which was made of a 5182 aluminum alloy (AA5182) sheet and a polypropylene (PP) sheet, AA5182/PP/AA5182, has been developed. In order to evaluate its formability, the forming limit diagrams (FLD) of the 5182 aluminum alloy sheet with 0.2mm thickness and the sandwich sheet with 1.2mm thickness have been obtained based on the modified Marciniak-Kuczynski (M-K) theory. To account for the anisotropy of the sheet, Hill's 1948 yield function has been applied. The FLD of the sandwich sheet was predicted to be better than that of the AA5182 sheet, which was well confirmed by experiments.