• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.138-144
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• 1999

Longitudinal wave and shear wave velocity changes of PMMA Polymer meterial under the the unidirection load were measured. The Third-order elastic modulus and acousto-elastic modulus of PMMA are obtained. The theoretical and experemental values of the velocity change of each wave by stress are compared each other and the validity of theoretical expression is examinated.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.336-342
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• 2006

Uniaxial stress in ail axisymmetric body is the simplest example of ultrasonic stress measurement. However, the birefringence theory cannot be applied for axisymmetric solids because the axisymmetric stress field in the body does not make shy velocity difference in SH waves propagating in the axisymmetric direction. Conventional ultrasonic technique using the time-of-flight method also needs ultrasonic lengths of the unstressed and stressed body, which is very impractical. In this paper, the birefringence effect in axisymmetric solids under uniaxial stress is formulated to evaluate the axial stress inside the solid without measuring tile ultrasonic length. Theoretical derivation for the birefringence characteristics in the axisymmetric solids is made using the longitudinal and shear waves instead of two horizontally polarized shear waves. Tension test is conducted for carbon-steel specimen to measure the birefringence coefficient and investigate the validity of the theory. It is observed from experimental results that the velocity difference in two differently polarized acoustic waves is proportional to the uniaxial stress in the axisymmetric solid with a good agreement with the theoretical value.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.1048-1052
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• 1996

함정용 주기관은 내충격 및 고체음 저감을 위하여 이중탄성지지시스템으로 설치되고 있다. 이중탄성지 지에 의한 방법은 기뢰(mines)의 비접촉 수중폭발 공격으로부터 충격손상을 방지하며, 또한 수중으로 고체음이 전파되어 피탐되는 가능성을 저감하는데 그 목적이 있다.(중략)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1116-1119
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• 2002

최근의 국제화 추세에 따라 국내의 산업규격을 국제규격인 ISO와 부합시키는 방향으로 나아가고 있다. 공동주택의 바닥충격음 문제가 사회적인 관심이 되면서 탄성재료(완충재)를 이용한 뜬 바닥 구조가 많이 사용되고 있다. 탄성재료의 동탄성계수와 바닥충격음의 경량충격음과는 밀접한 관계가 있다.(중략)

• Journal of the Korean Society for Precision Engineering
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• v.14 no.10
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• pp.119-126
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• 1997

The relationship between the applied stresses and the change of elastic wave velocity has been established based on the acoustoelasticity theory. The non-uniform stress field in a loaded specimen has been evaluated from the surface acoustic wave velocity measured by the line-focus acoustic microscopy with the acoustoelastic constants obtained form a calibration test. The evaluated stresses are in good agreement with the results calculated by finite element method.

• The Journal of the Acoustical Society of Korea
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• v.32 no.4
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• pp.301-307
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• 2013

SONAR detection performance is one of the key survivability factors in underwater weapon systems. In order to catch the acoustic ability of SONAR, multilayer SONAR structures are analyzed using the elastic theory. The applied results for the simple models are compared with those from commercial program, ANSYS, and the reliable results are obtained. The analysis of sound pressure level (SPL) and echo reduction (ER) by the thickness change of multilayer SONAR structures are performed using the verified elastic theory. As the thickness of anechoic layer is increased, SPL is distributed evenly and ER is increased slightly with the frequency. In decoupling layers and steel layers, SPL are hardly changed and ER is slightly decreased with the thickness increase of those layers. SPL and ER are not affected by the thickness change of the carbon reinforced plastic (CRP) layer. Therefore, to improve the acoustic ability of multilayer SONAR structures, the thickness increase of the anechoic layer and minimization of the decoupling layer, steel layer and CRP layer are desirable.

• Elastomers and Composites
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• v.35 no.2
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• pp.138-148
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• 2000

In order to investigate the possibility of EPDM micro cellular pad (MCP) as an impact sound insulation product, we studied static/dynamic properties and vibration transfer characteristics of EPDM MCP depending on shape, thickness, degrees of foaming by using material test system (MTS) and lab scale mock-up test apparatus. Static/dynamic rigidity is increased when shape is simple. thickness and degrees of foaming low. We could see that dynamic stiffness is proportional to the transmissibility of EPDM MCP. When dynamic stiffness is increased, characteristic peak at transmissibility curve moves high frequency range or snows increase of maximum value of transmissibility. For lab scale mock-up test and finite element method, EPDM MCP shows low vibration velocity and superior mode shape to just concrete plus slab structure. We could confirm that possibility of EPDM MCP as a impact sound insulation product is high.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.207-210
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• 2000

실내음장을 정밀하게 모사하기 위하여 음의 파동성을 고려한 탄성판의 음향특성을 평가하지 않으면 안된다. 따라서, 본 논문에서는 Baffle에 지지된 탄성판의 음향특성을 정량적으로 나타낼 수 있는 근사적인 평가 값에 대하여 고찰하고, 또한 탄성판의 음향특성의 하나인 방사 어드미턴스에 대하여 이에 대한 음향학적 특성에 대하여 평가한다

• Journal of dental hygiene science
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• v.6 no.4
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• pp.231-235
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• 2006

This study evaluated the properties of polyvinylsiloxane impression materials: Strain-in-compression, Elastic recovery, Consistency, and Wettability. Four polyvinylsiloxane impression materials(Examixfine, GC, Japan; Aquasilultra, Dentsply, USA; Extrude, Kerr, USA; Perfect-F, Handae, Korea) were used in this study. The measured data were analyzed with SPSSWIN 12.0 program. The results were as follows : 1. The strain-in-compression values showed that Extrude had the lowest value, 4.86% and Examixfine had the highest value, 6.78%. Significant difference between Examixfine and Perfect-F was not found but the other groups had significant differences(p = 0.000). 2. In the elastic recovery test, Extrude had the highest, 99.83% and Perfect-F had the lowest, 96.54%. There is no significant difference between Examixfine and Aquasilultra. The other impression material groups showed significant differences(p = 0.000). 3. The measurement of consistency results that the diameter of Examixfine was the largest, 45.12mm and one of Perfect-F was the smallest, 40.28 mm. No differences were shown between Examixfine and Aquasilultra and between Extrude and Perfect-F(p = 0.001). 4. Aquasilultra had a better hydrophilicity($47.85^{\circ}$) than other materials. Perfect-F had a larger contact angle($94.89^{\circ}$) and was hydrophobic. There were significant differences between groups(p = 0.000). 5. As for correlation among the test types, contact angle correlated with strain-in-compression, elstic recovery and consistency. The strain-in-compression had correlation to contact angle and elastic recovery. The elastic recovery correlated with contact angle and strain-in-compression. And the consistency had correlation to contact angle.

• The Journal of Engineering Geology
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• v.16 no.3 s.49
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• pp.235-244
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• 2006

Granite cores were sampled within Korea Atomic Energy Research Institute and cyclic loadings up to 1550 cycles were applied. Microcrack development in samples due to cyclic loading was estimated using Acoustic Emission(AE) method. AE showed two different types depending on numbers of cycle. Type 1 appeared at low cycles and had low energy and diverse frequencies, while type 2 appeared at high cycles and had high energy and uniform frequency. AE property of type 1 indicates voids and pre-existing microcracks in samples may close or propagate up to certain length. Microcracks may be sheared or closed during loading and are recovered from shear or opened during unloading when AE of type 2 were measured. P wave velocities and Felicity ratios were measured at 50, 150, 350, 750, 1550 cycles. P wave velocities were almost the same regardless of number of cycles applied. However, Felicity ratios were much lower than 0.9, indicating that microcracks were developed within samples. This result indicates that Felicity ratio is a better tool than P wave velocity to estimate the damage of rock.