• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.119-122
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• 2003

This report describes the procedure of detailed design and structural test for the composite flexure which is a part of the hingeless hub system. First, stacking sequence design for composite flexure was done, and structural analysis by using NASTRAN was made to verify structural stability and safety. Using FPS installed at KIMM, composite flexure was laid up and cured using a autoclave. Before rotor ground test, the basic structural tests such as a bench test, tensile strength test and shear strength test, for flexure, were accomplished. Through replacing existing metal hub part with new fabricated composite flexure, improvement of aeroelastic stability and weight reduction were achieved. This result will be applied to composite rotor system design fur helicopter.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.173-176
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• 2002

This paper describes the design procedure of composite parts for hingeless hub system of helicopter. These composite parts are composed of flexure and sleeve. The design of this composite flexure is an important technique in hingeless hub system since the rotor system stability and dynamic characteristics depends on this flexure characteristics. The objective of this research is to replace the existing metal hub parts with composite to improve the performance and stability. First, the coupon test of candidate composite material for hub parts was conducted. The hub parts was designed based on test results and the manufacturing possibility by using Fiber Placement System(FPS) was checked. Also the dynamic analysis and stress analysis of composite hub parts was conducted. Through this research, we will find out the possibility of replacing existing metal hub parts with composite.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.127-134
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• 2001

In this paper flexure-compression characteristics of concrete filled glass fiber reinforced composite pile was studied. Confinement model of composite pile was derived from experimental data. Also numerical method to find P-M diagram of composite pile was developed. The flexure-compression test results were compared with analytical P-M diagram and it is demonstrated that they agree well each other. Utilizing these results, pilot composite pile was designed and fabricated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.98-105
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• 2005

This paper presents the result of the aeroelastic stability test of the small-scaled hingeless hub system with composite paddle blades in hover and forward flight conditions. Excitation tests of hingeless hub system installed in GSRTS(General Small-scale Rotor Test System) at KARI(Korea Aerospace Research Institute) were carried out to get lead-lag damping ratio of blades with flexures as hub flexure. MBA(Moving Block Analysis) technique was used for the estimation of lead-lag damping ratio. First, blades with metal flexures, then with composite flexures of the same dynamic properties of rotor system as metal one were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Composite flexures were found to have better damping characteristics over metal ones in the non-rotating vibration test, and it was confirmed that the use of composite flexures would give observable improvement in aeroelastic stability compared to metal ones in all test conditions.

• Journal of Mechanical Science and Technology
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• v.16 no.4
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• pp.512-521
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• 2002

The flap-lag-torsion coupled aeroelastic behavior of a hingeless rotor blade with composite flexures in hovering flight has been investigated by using the finite element method. The quasisteady strip theory with dynamic inflow effects is used to obtain the aerodynamic loads acting on the blade. The governing differential equations of motion undergoing moderately large displacements and rotations are derived using the Hamilton's principle. The flexures used in the present model are composed of two composite plates which are rigidly attached together. The lead-lag flexure is located inboard of the flap flexure. A mixed warping model that combines the St. Versant torsion and the Vlasov torsion is developed to describe the twist behavior of the composite flexure. Numerical simulations are carried out to correlate the present results with experimental test data and also to identify the effects of structural couplings of the composite flexures on the aeroelastic stability of the blade. The prediction results agree well with other experimental data. The effects of elastic couplings such as pitch-flap, pitch-lag, and flap-lag couplings on the stability behavior of the composite blades are also investigated.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.33-44
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• 2003

This paper describes the design and analysis technology of composite flexure and composite paddle-type blade which are all key technologies on hingeless rotor system. Through replacing the existing metal or engineering plastic flexure part with composite part, Several required structural analysis were accomplished, which are static analysis by using NASTRAN and dynamic analysis by using FLIGHTLAB. The dynamic characteristics of composite hingeless hub attached with paddle-type blade was also investigated. Further more, small-scaled paddle-type blade was designed using froude scaled properties of existing full size blade. Through this design procedure of composite paddle-type blade, the structural design method was achieved. These results will be applied to accomplishing current project named as "the development of next-generation helicopter rotor system."

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.21-24
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• 2001

Due to many advantage of advanced composite materials, researches on the composite marine pile is initiated. In this paper, structural characteristics of concrete filled glass fiber reinforced plastic (GFRP) composite pile model are studied. Through 4-point flexural test with various level of axial force, the performance of composite pile model was analyzed. Also numerical method to find P-M interaction diagram of composite pile was developed. It is showed that result of numerical method agrees well with experimental results, thus it is anticipated that numerical procedure can be utilized for design purpose.

• International Journal of Concrete Structures and Materials
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• v.10 no.sup3
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• pp.109-121
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• 2016

Recently, as the use of high-performance materials and complex composite methods has increased, the need for advanced design specifications for steel-concrete composite structures has grown. In this study, various design provisions for ultimate flexural strengths of composite beams were reviewed. Design provisions reviewed included the load and resistance factor design method of AISC 360-10 and the partial factor methods of KSSC-KCI, Eurocode 4 and JSCE 2009. The design moment strengths of composite beams were calculated according to each design specification and the variation of the calculated strengths with design variables was investigated. Furthermore, the relationships between the deformation capacity and resistance factor for flexure were examined quantitatively. Results showed that the design strength and resistance factor for flexure of composite beams were substantially affected by the design formats and variables.

• Steel and Composite Structures
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• v.39 no.4
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• pp.383-399
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• 2021

In the study, three 1:3-scale unequal span steel-concrete composite substructures with top-seat angle and double web angle connection were designed and identified as specimens GTSDWA-0.6, GTSDWA-1.0, and GTSDWA-1.4. Pseudo-static tests and refined numerical model analysis were conducted to examine the anti-progressive collapse performance of a semi-rigid steel-concrete composite substructure. The results indicated that the failure modes of the three specimens revealed that the fracture occurred in the root of the long leg of the top/seat angle in tension at the connection. With increases in the span ratio of the left and right composite beams, the bearing capacities of the composite substructures decreased, and the corresponding displacement increased. With respect to GTSDWA-0.6 and GTSDWA-1.4, the resistance due to the short composite beam corresponded to 62% and 60%, respectively, and the total resistance provided by the short composite beam exceeded that of the long composite beam. With respect to GTSDWA-1.0, the resistance due to the left and right composite beams was similar. All three specimens underwent the flexure mechanism and flexure-axial mixed mechanism stages. They resisted the external load mainly via the flexure mechanism. Moreover, the addition of stiffeners on both sides of the top and seat angles is advantageous in terms of improving the collapse resistance and ductility of unequal span composite substructures.

• Journal of Biomedical Engineering Research
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• v.17 no.3
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• pp.327-336
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• 1996

This study was performed to investigate the effec% of immersion in water and thermal cycling on the mechanical peoperties of light cured restorative composite resins. Five commerically available light-cured composite resins(Photo Clearfil A : CA, Lite-Fil A . LF, Clearril Photo Posterior CP, Prisms AP.H.. PA, 2100 : ZH) were unto The specimens of 12 m in diameter and 0.7 m in thickness were made, and an immersion in $37^{\circ}C$ water for 7 days and a thermal cycling of 1000 cycles at 15 second dwell time each in $5^{\circ}C$ and $55^{\circ}C$ baths were performed. Biaxial flexure test was conducted using the ball-on-three-ball method at the crosshead speed of 0.5mm/min. In order to investigate the deterioration of composite resins during the thermal cycling test, Weibull analysis for the biaxial flexure strengths was done. Fracture surfaces and the surfaces before and after the thermal cycling test were examined by SEM. The highest Weibull modulus value of 10.09 after thermal cycling tests which means the lowest strength variation, was observed in the CP group, and the lowest value of 4.47 was obsered in the LF Group. Biaxial flexure strengths and Knoop hardness numbers significantly decreased due to the thermal cycling ($\textit{p}$< 0.01), however, they recovered when specimens were drie4 The highest biaxial flexure strength of 125.65MPa was observed in the ZH group after the thermal cycling test, and the lowest value of 64.86MPa was observed in the CA group. Biaxial flexure strengths of ZH and CP groups were higher than those of PA, CF, and CA groups after thermal cycling test($\textit{p}$< 0.05). Knoop hardness numbers of CP group after the thermal cycling test was the highest(95.47 $\pm$ 7.35kg/$mm^2$) among the samples, while that of CA group was the lowest(30.73 $\pm$ 2.58kg/$mm^2$). Knoop hardness numbers showed the significant differences between the CP group and others after the thermal cycling test(($\textit{p}$< 0.05). Fracture surfaces showed that the composite resin failure developed along the matrix resin and the filler/resin interface region, and the cracks propagated in the conical shape from the maximum tensile stress zone.