• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.02a
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• pp.464-470
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• 2002

본 연구에서는 초음파를 사과의 비파괴 품질판정에 이용하기 위한 기초 연구로서 사과 표면에 입사, 반사되는 초음파 신호를 계측 및 분석하기 위한 시스템을 구축하고 저장기간에 따른 사과의 초음파 특성을 계측하였으며, 그 결론은 다음과 같다. 1. 구성된 비 접촉식 초음파 장치를 이용하여 전압-시간 그래프에서 전압의 진폭(PTP)값을 구하였고 신호처리용 프로그램을 이용하여 획득한 신호를 주파수 영역에서 분석하여 피크주파수, 영역별 에너지 밀도함수 등을 구하였다. 2. 사과의 초음파 특성을 분석한 결과 사과의 저장기간은 초음파 응답신호의 진폭(PTP) 및 제 3영역 에너지 스펙트럼 밀도함수와 높은 상관성이 있는 것으로 나타났다. 3. 초음파를 농산물의 비파괴 품질판정에 적용시 문제가 되고 지는 센서와 시료와의 접촉응력에 의한 응답신호의 변형에 의한 문제를 해결하고자 비 접촉식 센서를 사용하였으며, 실제 농산물에 적용이 가능한 것으로 판단되었다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.252-252
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• 2004

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.240-244
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• 2017

Experimental verification in the rig test stage for component development is a vital link between the aeromechanical design and structural integrity validation process. Based on this premise, Non-Intrusive Stress Measuring System was adopted on the axial compressor test rig to measure the static and dynamic tip deflection of all blades by using tip-timing sensors. Through analyzing vibration characteristics, we evaluated the vibratory stresses seen on the blades fatigue critical location; detected synchronous resonances which are the source of High Cycle Fatigue (HCF) in blades; presented non-synchronous vibration response by aerodynamic excitation and individual blade mis-tuning patterns.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.47-54
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• 2006

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomena are negligible. However, the terms of effective stresses are divided into the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by ${\alpha}$ parameters and ${\beta}$ exponents that are experimentally determined. The ${\beta}$ exponents are controlled by contact effects of particulate materials (sizes, shapes, and structures of particles) and the ${\alpha}$ parameters are changed by contact behaviors among particles, material properties of particles, and type of packing (i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies by using bender elements. Results show the shear wave velocity depends on the stress-induced anisotropy for round particles. Furthermore, the shear wave velocity is dependent on particle alignment under the constant evvective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully estimated and used for the design and construction of geotechnical structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.2
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• pp.101-111
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• 1994

Electronic speckle pattern interferometry(ESPI) using a CW laser, a video system and an image processor were applied to the in-plane displacement measurements. Unlike traditional strain gauges or Moire method, ESPI method requires no special surface preparation or attachments and it can be measured in-plane displacement without any contact and real time. In this experiment, specimen was loaded in paralled with a loa cell. The specimen was plance to which strain gauges was attached. The study provides an example of how ESPI have been used to measure displacement and strain distribution in this specimen. The results measured by ESPI were compared with the data which were measured by strain gauge method in tensile testing.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.145-152
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• 2010

This study evaluated the fatigue degradation in a SUS316L specimen using the nonlinear ultrasonic method. The nonlinearity of the ultrasonic wave was estimated by a relative nonlinear parameter defined as the ratio of the amplitudes for the fundamental wave to the second harmonic wave. In the experiment, a measurement system with contact transducers was constructed; reliable measurements were assured by keeping measurement conditions consistent and reducing extra harmonics generated in the measurement system. Two types of SUS316L specimen were used in experiments; a rotating bar fatigue specimen and a tensile fatigue specimen. The fatigue condition used was high cycle fatigue. The former specimen had a cylindrical shape and was used to observe the change in the nonlinear parameter after fatigue accumulation in a specimen. The latter was a plate-shaped specimen and was used to confirm the change in the nonlinear parameter at the position where the fatigue stress was concentrated. The measured nonlinear parameter showed a strong correlation to the damage level in both fatigue tests.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.94-100
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• 2002

This paper is concerned with the development, and performance test of LIPCA (Lightweight Piezo-composite Curved Actuator) that is lighter than other conventional piezo-composite type actuators. LIPCA is composed of top fiber composite layers with a high modulus and low CTE (Coefficient of Thermal Expansion), a middle PZT cermaic wafer, and base layers with a high modulus and high CTE. The performance of each actuator was evaluated using an actuator test system consisting of an actuator supporting jig, a high voltage actuating power supplier, and a non-contact laser measuring system. The simply supported condition actuator was excited by the power supplier with 1.0Hz cycle and up to $100\sim400V_{pp}$. The displacement at the center point of actuator was measured with non-contact laser displacement measuring system, It has been shown that the LIPCA-C2 can 34% decrease in mass and 13% increase in displacement compared to THUNDER.