• Proceedings of the Korean Reliability Society Conference
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• 2006.05a
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• pp.158-164
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• 2006

The creep behavior of newly developed composite geogrids which consists of PET yarns sheathed in PP were evaluated using SIM. For the SIM procedure, three test parameters, the applied loads, temperature steps and number of ribs were investigated, The study confirmed that temperature steps of 10 and 14$^{\circ}C$ up to 80$^{\circ}C$ are applicable for composite geogrids due to the different transition temperatures between two materials. At applied loads of 40 and 50%, only primary creep state was measured, while secondary creep state appeared at the applied loads of 60%, The lifetimes of composite geogrids were estimated at each of loading level using statistical reliability analysis technique. The results show that the lifetimes longer than 100 years can be predicted within 16 hours. Therefore, SIM is very effective and economical accelerated creep test methods, especially for lifetime prediction. This gives guidelines for users to select the appropriate factor of safety against creep considering the field condition within shorter test times.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.229-240
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• 2002

This paper is an experimental and numerical work of Investigating the bearing capacity of shallow foundation of rubble mound under eccentric loads. Parametric centrifuge model tests at the 50g level environments with the model footings in the form of strip footing were performed by changing the loading location of model footing, relative density and materials for ground foundation. For the model ground, crushed rock sampled from a rocky mountain was prepared with a grain size distribution of having an identical coefficient of uniformity to the field condition. Model ground was also prepared with relative densities of 50 % and 80 %. For loading condition, model tests with and without eccentric load were carned out to investigate the effect of eccentric loads and a numerical analysis with the commertially available software of FLAC was performed. For numerical estimation with FLAC, the hyperbolic model of a nonlinear elastic constitutive relationship was used to simulate the stress-stram constitutive relationship of model ground and a series of triaxial compression test were carried out to find the parameters for this model Test results were analyzed and compared with Meyerhof method (1963), effective area method based on the limit equilibrium method, and a numerical analysis with FLAC.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.3
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• pp.118-126
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• 2002

TiCN thin films were deposited on tool steels at $510^{\circ}C$ by PECVD from a $TiCl_4+N_2+CH_4+H_2+Ar$ gaseous mixture. The microstructures and preferred orientation were investigated. The micro-scratch tests were performed using a system equipped with an acoustic emission sensor. Critical loads were determined to evaluate the adhesion of TiCN to substrate. The influences of the microstructures of substrates, double layered coatings, and coatings after nitriding(duplex coating) were investigated. The experimental results showed that the microstructures of substrates and double layered coating did not affect the critical loads considerably. By the duplex coating, critical loads were not always increased. In some cases, duplex coatings decreased critical loads significantly despite of absence of black layer. In this study, we tried to relate the results of scratch test to the residual stress analysis. Nitriding before the coating reduces the tensile residual stress in the film, which gives rise to low critical load in scratch test.

• Journal of the Korean Society for Railway
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• v.19 no.6
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• pp.777-784
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• 2016

In this study, regulation of the performance test load of a vibration-proof fastening system used in urban railways was established through evaluation of the loads that it bears in the field. In order to investigate the range of the dynamic stiffness of the vibration-proof fastening system, dynamic stiffness tests were carried out for three types of vibration-proof fastening system that can be domestically supplied. Train and track interaction analyses in the frequency domain were carried out to evaluate the dynamic wheel loads. The track irregularity, which is a very important input factor in train and track interaction analysis, was considered as a PSD (Power Spectral Density) function, which was derived based on the measured data. The loads on the vibration-proof rail fastening system were evaluated considering various operating conditions in the urban railway. Regulation of the performance test load of the vibration-proof rail fastening system was established based on the evaluated loads.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.5
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• pp.552-558
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• 2016

A control rod drive mechanism(CRDM) is a reactor regulating system, which inserts, withdraws or maintains a control rod within a reactor core to control the reactivity of the core. The CRDM for Jordan Research and Training Reactor with 5MW power has been designed and fabricated based on the HANARO’s experience through KAERI and DAEWOO consortium. This paper describes the seismic test results to demonstrate the operability, the drop performance and the structural integrity of CRDM during or after seismic excitations. The seismic tests are carried out under 5 OBE and 1 SSE loads at three Test Rigs simulating the reactor structure and the pool top. From the tests, the CRDM is smoothly driven without a malfunction of stepping motor under OBE load. The pure drop time under OBE and SSE loads is measured as 1.169s and 1.855s to meet the design requirement. Also, it is found that the CRDM maintains the structural integrity without a change of the function and natural frequency before and after seismic loads.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.12
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• pp.104-110
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• 2019

A nanosatellite designed by the Korea Microgravity Science Laboratory (KMSL) is currently under development. The KMSL nanosatellite is designed to perform two different scientific missions in space. To successfully complete missions, a variety of tests must be conducted to verify the performance of the designed satellite before launch. As part of the qualification test campaign, the KMSL nanosatellite underwent high level vibrational tests (to comply with Falcon 9 qualification level) to demonstrate the integrity of the system. The purpose of this study is to demonstrate that the primary structure and all electronic and mechanical components can withstand the vibrations and the loads experienced during the launch period. To this end, the KMSL nanosatellite was exposed to static and dynamic loads and various types of vibrations that are inevitably produced during the space vehicle launch period. The vibration test results clearly demonstrated that all avionics and mechanical components can withstand the vibrations and the loads applied to the KMSL nanosatellite's body through a Pico-satellite Orbital Deployer (POD).

• Wind and Structures
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• v.23 no.5
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• pp.385-403
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• 2016

The across-wind dynamic loads on L-shaped tall buildings with various geometric dimensions were investigated through a series of wind tunnel testing. The lift coefficients, power spectral densities and vertical correlation coefficients of the across-wind loads were analyzed and discussed in details. Taking the side ratio and terrain category as key variables, empirical formulas for estimating the across-wind dynamic loads on L-shaped tall buildings were proposed on the basis of the wind tunnel testing results. Comparisons between the predictions by the empirical formulas and the wind tunnel test results were made to verify the accuracy and applicability of the proposed formulas. Moreover, a simplified procedure to evaluate the across-wind dynamic loads on L-shaped tall buildings was derived from the proposed formulas. This study aims to provide a simple and reliable way for the estimation of across-wind dynamic loads on L-shaped tall buildings.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.853-856
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• 2002

Rocket propulsion systems generate very high-level noise (acoustic loads), which is due to supersonic jet emitted by rocket engine. In practice, the sound power level of rocket propulsion systems is over 180 dB. This high level noise excites rocket structures and payloads, so that it causes the structural failure and electronic malfunction of payloads. Prediction method of acoustic loads of rocket enables us to determine the safety of payloads. A popular prediction method is based on NASA SP-8072. This method was used to predict the acoustic loads of KSR-III rocket. Measurement of acoustic loads by KSR-III propulsion system was performed in the stage qualification test. The predicted results were compared with the measured ones.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1252-1257
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• 2003

This paper present a procedure of meter-out flow control method for dump valve in full-scale airframe test. Emergency stop, which results in dump state, can be happened during full-scale airframe test by several causes. Because servo valve can't control hydraulics actuator in the dump state, pressure in cylinder chamber may rise abruptly and overload can be acted to the test article. In this paper, the procedure and technology of orifice setting are investigated to protect the test article from unexpected loads by dump. The test results show that the presented methods decrease peak loads and improve unloading characteristics of hydraulic actuators in the dump state.

• Journal of Aerospace System Engineering
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• v.15 no.4
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• pp.40-46
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• 2021

At launch, satellites are exposed to various types of structural loads, such as quasi-static loads, sinusoidal vibrations, acoustic/random vibrations, and shocks. The launch environment test is aimed at verifying the structural stability of the test object against the launch environment. Various types of launch environments are simulated by simple vibration, acoustic, and shock tests considering possible test conditions in ground. However, the difference between the launch environment and the test environment is one of the causes of excessive testing. To prevent overtesting, a notching technique that adjusts the frequency range and the input load considering the design load is applied. For notching, specific procedures are established considering the satellite development concept, selected launch vehicle, higher system requirements, and test target level. In this study, the notching method, established procedure, and development of a notching toolkit for efficient testing are described.