• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.310-315
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• 2003

This paper described that rotating test and fatigue test of a small-scale hingeless hub system with composite rectangular blades. Generally Rotating stability and fatigue test technique is one of Key-technology on test and evaluation for helicopter rotor system Rotating test of hingeless rotor system was achieved by means of rotor vibration characteristic and aeroelastic stability test GSRTS, equipped with hydraulic actuator and 6-component rotating balance was used to test hingeless rotor system especially for an observation of blade motion including flawing, lagging and feathering. Rotating test was done in hover and forward flight condition. Small-scaled blade fatigue test condition was determined by blade load analysis with the reference table of composite materials(S-N curve). Fatigue test bench was developed for the estimation of blade fatigue life, and tested its characteristic.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.22-26
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• 2002

The goal of this study is to replace the current forward 2-piece propeller shaft of 8 ton large truck made of steel with 1-piece composite propeller shaft. A low cost Glass/Epoxy composite propeller shafts were successfully developed, which satisfy requirements such as the capacity of static torque transfer, fatigue strength and bending natural frequency. Devising secure joining method of a composite tube and metal yoke was the most critical issue in successful development of a high torque composite propeller shaft. In this study, joining method using thermal interference fit was adopted for composite to metal joint. Optimum conditions of heating temperature and interference level of thermal interference fit were determined from thermal stress analysis using 3D finite element method. Static torsion test, fatigue test, RPM and balance test were performed to verify the design.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.57-60
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• 2003

This Paper contains the development procedure of Mach small-scaled composite rotor blade for helicopter articulated rotor system. This mach small-scaled composite blade design is conducted by using CORDAS program developed by KARI. The Dynamic analysis for an articulated rotor system with this blade is conducted by using FLIGHTLAB which is commercial software for helicopter analysis. Also the optimizing procedure of iterative design was described. The designed composite blades were manufactured after establishing the effective curing method. For small-scaled rotor test, strain gauges were embedded in composite blade spar to obtain bending & torsion strain value. To verify sectional properties of a blade, the bench test is accomplished. After comparing a designed data and tested data, Dynamic Calculation was repeated using tested data. Through this research, experiences of mach small-scaled composite blade development were accumulated and will be applied to the related research field.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.97-103
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• 2008

Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.7-11
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• 2011

A velocity-compounded(VC) turbine for the 75ton turbopump was developed as an improved performance backup for the single-rotor baseline turbine. Curvic coupling was adopted for the power transmission between the rotors and shaft. High temperature torsion test and spin test was performed for the curvic coupling design validation. Aerodynamic performance test revealed that VC turbine can generate 20.5% higher specific power than the baseline turbine.

• Progress in Superconductivity and Cryogenics
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• v.20 no.4
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• pp.31-35
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• 2018

When REBCO coated conductors (CCs) are applied to superconducting devices such as coils and magnets, they are subjected to deformation in various modes such as compression/tension bending, uniaxial/transverse tension and torsion. Despite outstanding performances by REBCO CC tapes, their electromechanical properties have been evaluated primarily under uniaxial tension, therefore data about the critical current ($I_c$) response in the compressive strain region are lacking. In this study, the characteristic responses of $I_c$ in REBCO CC tapes under bending strains in the range from tensile to compressive were evaluated. The springboard bending beam was used, wherein the CC tape sample was soldered onto the surface of the springboard. A Goldacker-type bending test rig, which lacks a support holding the sample during testing, was used as a comparator. Degradation in $I_c$ behaviors, including strain sensitivity, in differently processed REBCO CC tapes were examined based on the test rig used.

• Journal of the Korea Concrete Institute
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• v.20 no.4
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• pp.503-511
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• 2008

This paper presents the results of an analytical and experimental study on the performance of reinforced concrete beams subjected to pure torsion. The main parameters of the experimental tests were amount of torsional reinforcement and the ratio of the transverse torsional reinforcement to the longitudinal torsional reinforcement. The test results indicated that the maximum amount of torsional reinforcement required in ACI 318-05 code underestimated almost twice as much as the observed maximum amount of torsional reinforcement. Comparisons between the tested and calculated torsional behaviors of the 102 beams showed that the torsional failure modes of ACI 318-05 code disagreed with the observed failure modes. In addition, the torsion provisions in ACI 318-05 code overestimate the torsional strength of the RC beams in which relatively large amount of torsional reinforcement were reinforced, while underestimate for the beams with small amount of torsional reinforcement. This discrepancy between the theoretical ultimate torsional strength as given by the ACI 318-05 code and the experimental one can be due to neglecting the tension stiffening effect and the contribution of the torsional strength by concrete.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.221-228
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• 2003

The stress corrosion index of Kumamoto andesite are evaluated by two types of testing method. One is the uniaxial compression test under various water vapor pressures, and the other is the double torsion (DT) test under a constant water vapor pressure. For the uniaxial compression tests, the uniaxial compressive strength increases linearly with decreasing water vapor pressure on the double logarithmic coordinates. As the results, the stress corrosion index obtained is estimated 44. On the other hand, in the DT test, the relaxation (RLX) test and the constant displacement rate (CDR) test were conducted. For the CDR test, as the displacement rate of loading point increases, the crack velocity increases. However, the fracture toughness is constant regardless of the change in displacement rate and the average fracture toughness is evaluated $2.07MN/m^{3/2}$. For the RLX test, the crack velocity-stress intensity factor curves are smooth and linear. The stress corrosion index estimated from the curves is 37. Comparing stress corrosion indexes in the uniaxial compression test and the DT test, there is no significant difference in these values, and they are considered to be in coincident each other regardless of testing methods. Therefore, it is concluded that stress corrosion is one of material constants of rock.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.1039-1044
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• 2015

During the development of vehicles, durability tests are time consuming and costly. Recently, automobile companies have attempted to develop their own durability evaluation procedures by modifying and complementing . In this paper, we propose an integrated computer-aided engineering (CAE) method to evaluate the durability of a torsion beam axle (TBA). We compare this method with the standardized durability evaluation method used by an actual automobile company in order to determine the feasibility of this method. We compare the results with the test result data to enable us to estimate the reliability of the analysis results. In this study, we analyze the processes and results of the quasi-static fatigue analysis, and found improved methods and problems. Furthermore, we perform a thorough test using the requirements of the actual company. Based on the results, the structural analysis process in the quasi-static fatigue analysis method was superseded by the multi-body dynamics analysis process. Generally, this method is referred to as the resonance-fatigue analysis method.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.5
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• pp.127-133
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• 2005

Rotary swaging is one of the incremental forming process which is a chipless process using the reduction of cross-sections of bars, tubes and wires. The TDS(Tube Drive Shaft) of monobloc used in automotive has been developed by the rotary swaging process. The mechanical characteristics of swaged parts such as the hardness, thickness and roughness are also estimated to conduct experimental analyses of rotary swaging process with the materials of 34Mn5 Furthermore the change in the vibration mode of TDS due to design parameters, which are the tube length, diameter and thickness, has been investigated and analysed. The weight of the TDS product is smaller by about $12.8\%$ than that of SDS with the same performance. It could be evidently found that the TDS is designed to be much lighter than SDS (Solid Drive Shaft). This advantage might give some possibility to improve the NVH (Noise-Vibration-Harshness) characteristics. A maximum torque and a total number of torsional repetitions for the TDS is checked and measured to know the torsional intensity and fatigue strength through the static torsion test and torsional durability test, respectively. A total number of the torsional repetitions up to the fracture for the TDS is greater than 250,000 times.