• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.198-202
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• 2009

Split Hopkinson pressure bar(SHPB) is used to obtain compressive stress-strain data and deformation characteristics of brittle materials such as rock and concrete. SHPB demands both dynamic stress equilibrium condition and nearly constant strain rate before the failure of the specimen. Pulse shape technique, which places a thin metal disk between launched impact bar and incident bar, should be adopted to satisfy both conditions. In this study, metallic disks with various shapes were used to control the incident impact wave. The results show that the peak value of stress and the length of waves increased with decreasing thickness and diameter of the pulse shaper. In order to investigate shape and strain rate-dependency of the pulse shapers, dynamic compressive stress-strain curves were obtained and analyzed.

• Explosives and Blasting
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• v.35 no.3
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• pp.15-20
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• 2017

In order to obtain the dynamic response behavior of the rock subjected to blasting loading, a shock-proof high sensitivity impact sensor which can measure high frequency dynamic force and strain events should be adopted. Because the impact sensors which uses quartz and piezoelectric element are costly, generally the strain measurement-based impact (SMI) sensors are applied to high speed loading devices. In this study, dynamic Brazilian tension tests of granitic rocks was conducted using the Nonex Rock Cracker (NRC) reaction driven-high speed loading device which adopts SMI sensors. The dynamic response of the granite specimens were monitored and the intermediate strain rate dependency of Brazilian tensile strengths was discussed.

• The Korean Journal of Rheology
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• v.10 no.3
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• pp.173-183
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• 1998

본 연구에서는 Advanced Rheometric Expansion System(ARES)를 사용하여 대진폭 진동 전단 변형하에서 발생하는 폴리이소부틸렌(PIB) 농후 용액의 비선형 점탄성 거동을 저 장탄성율과 동적점도의 변형량 의존성 및 응력파형의 fast Fourier transform(FFT) 해석을 통해 고찰하였다. 스트레인 진촉을 단계적으로 증가시키면서 측정한 동적 점탄성으로 부터 저장탄성율 및 동적점도의 선형응답한계를 결정하고 이들에 미치는 각주파수의 영향을 조사 하였다. 그리고 응력파형의 Fourier 전개로부터 유도되는 비선형 점탄성함수를 사용하여 비 선형 거동을 설명하였다. 끝으로 비선형 점탄성 거동의 정도를 나타내는 비선형 거동 지수 를 정의하고 이들에 미치는 각주파수의 영향에 대해 검토하였다. 이상의 연구를 통해 얻어 진 결과를 요약하면 다음과 같다.(1) 선형 응답한계는 고분자 용액의 특성시간의 역수보다 높은 각주파수 범위에서는 일정한 값을 유지하지만 특성시간의 역수보다 낮은 각주파수 영 역에서는 각주파수가 감소할수록 증가한다. (2)선형응답한계 이상의 대변형하에서는 3차비선 형 점탄성 함수 이상의 고차항의 영향이 크게 작용하며 이로인해 비선형 거동이 발생된다. (3) 스트레인 진폭을 단계적으로 증가시키면서 측정한 저장탄성율 및 동적점도의 변형량 의 존성은 응력파형의 Fourier transform으로부터 유도된 1차 비선형 점탄성 함수의 변형량 의 존성을 나타낸다 (4) 저장탄성율 및 동적점도의 변형량 의존성으로부터 유도된 비선형 거동 지수는 탄성적 서질과 점성적 성질에 대한 비선형 특성을 평가하기 위한 유요한 방법으로 인정된다. (5) 비선형 점탄성 거동의 정도를 나탄는 비선형 거동지수는 특정한 각주파수에서 최대치를 가지며 또한 탄성적 거동이 점성적 거동에 비해 더욱 큰 각주파수 의존성을 나타낸다.

• Tunnel and Underground Space
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• v.18 no.3
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• pp.214-218
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• 2008

Dynamic fracturing of anisotropic granite was investigated by SHPB (Split Hopkinson Pressure Bar). Energy absorption during the test and maximum stress were increased as strain rate increased. Maximum stresses in every direction were dependent on the strain rate but not so sensitive to anisotropy. Elastic wave velocity was decreased as strain rate increased and dependent on strain rate in every direction. Especially, elastic wave velocity decreased more rapidly in a strong rock.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.573-579
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• 2016

Studies on the deformation behavior of materials subjected to impact loads have been carried out in various fields of engineering and industry. The deformation and fracture of members for these machines/structures are known to correspond to the intermediate strain-rate region. Therefore, for the structural design, it is necessary to consider the dynamic deformation behavior in these intermediate strain-rate ranges. However, there have been few reports with useful data about the deformation and fracture behavior at intermediate strain-rate ranges. Because the intermediate strain-rate region is located between quasi-static and high strain-rate regions, it is difficult to obtain the intermediate strain-rate using conventional reasonable test equipment. To solve this problem, in this study, the measurement reliability of the constructed drop-bar impact tensile test apparatus was established and the dynamic behavior at the intermediate strain-rate range of carbon steels was evaluated by utilizing the apparatus.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.78-89
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• 1993

A new theory based on the modified momentum and energy conservation has been proposed in order to overcome the drawbacks included in previous theories which are used for the determination of dynamic yield stresses and the investigation of dynamic behavior of metals. Then the improvements suggested by the new theory have been manifested through the analysis of the error included in the measurement of deformed length and through the comparison between the new theory, existing theories, and experimental results performed by previous workers. Meanwhile rod impact test has been performed which uses a compressed- air system for the acceleration of flat-ended cylindrical free-cutting brass rods. From the geomtrical measurements of deformed length, the dynamic yield stress of free-cutting brass has determined.

• Magazine of the Korea Concrete Institute
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• v.2 no.2
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• pp.73-80
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• 1990

The current analytical techniques for R/C elements under severe dynamic repeated loads, like earth¬quake or impact, have two major problems; one is that the effects of strain rate are not considered and the other one is the current analytical model was developed based on flexural behavior only. This study develops computer software that can idealize the flexural and shear behavior of R/C elements using several parameters and also can consider the effects of strain rate. The analytical results using the developed technique were compared with serveral experimental results and they were generally satisfied.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.1
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• pp.85-92
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• 2015

This article presents the dynamic instability response of sigmoid functionally graded material plates on elastic foundation using the higher-order shear deformation theory. The higher-order shear deformation theory has ability to capture the quadratic variation of shear strain and consequently shear stress through the plate thickness. The governing equations are then written in the form of Mathieu-Hill equations and then Bolotin's method is employed to determine the instability regions. The boundaries of the instability regions are represented in the dynamic load and excitation frequency plane. The results of dynamic instability analysis of sigmoid functionally graded material plate are presented using the Navier's procedure to illustrate the effect of elastic foundation parameter on dynamic response. The relations between Winkler and Pasternak elastic foundation parameter are discussed by numerical results. Also, the effects of static load factor, power-law index and side-to-thickness ratio on dynamic instability analysis are investigated and discussed. In order to validate the present solutions, the reference solutions are used and discussed. The theoretical development as well as numerical solutions presented herein should serve as reference for the dynamic instability study of S-FGM plates.

• Composites Research
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• v.31 no.5
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• pp.221-226
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• 2018

The Split Hopkinson Pressure Bar(SHPB) has been the most widely used apparatus to characterize dynamic mechanical behavior of materials at high strain rates between $100s^{-1}$ and $10,000s^{-1}$. The SHPB test is based on the wave propagation theory which was developed to give the stress, strain and strain rate in the specimen using the strains measured in the incident and transmission bars. In this study, the SHPB was directly designed and fabricated for the dynamic mechanical properties of fiber reinforced plastic (FRP) composites. In addition, this apparatus was verified for the validity by comparing the strain data obtained through the high speed camera and Digital Image Correlation(DIC) during the high strain rate compression test of the self-reinforced polypropylene composite (SRPP) specimen.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.47-47
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• 2004

충격하중을 받는 재료의 거동에 관한 연구는 공학의 넓은 분야에 깊은 관계를 가지고 있다. 특히 동적하중을 받는 경계조건 하에서 사용되는 구조물을 정밀하게 설계 제작하는 필요성이 고조됨에 따라 여러 재료들의 고변형률 속도로 변형될 경우에 대한 역학적인 성질이 중요한 과제로 떠오르고 있다. 구조물의 건전성과 신뢰성을 향상시키기 위해서는 구조물이 실제적으로 받는 여러 조건의 하중하에서의 실험적으로 정밀하게 획득된 정확하고, 완벽한 재료 물성치가 필요하다. (중략)