• 터널과지하공간
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• 제21권2호
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• pp.109-116
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• 2011

본 연구에서는 스플릿 홉킨슨 압력봉 실험장비를 적용한 압열인장 실험을 수행하여, 암석의 동적인장강도 및 변형률 속도를 평가하였다. 시료가 파괴되기 전에 시료 내 동적 응력평형상태를 확보하기 위하여 펄스쉐이핑 기법으로 입사파의 증가시간을 제어하였다. 압열인장 실험시료는 Inada 화강암, Kimachi 사암, Tage응회암을 정밀하게 가공하여 제작되었다. 결과로서, Inada 화강암의 동적인장강도는 정적인장강도의 11.9배 이였으며, Kimachi 사암과 Tage 응회암은 각각 8.5배, 9.2배로 평가되었다. 고속카메라를 이용하여 시료 내 축 하중 방향으로 발생하는 인장균열의 발생양상을 관찰하였다.

• Geomechanics and Engineering
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• 제12권1호
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• pp.1-8
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• 2017

An experimental technique for determining the spalling strength of rock-like materials under a high strain rate is developed. It is observed that the spalling strength of a specimen can be determined by only knowing the wavelength, loading peak value and length of the first spallation of an incident wave under a specific loading waveform. Using this method in combination with a split-Hopkinson pressure bar (SHPB) and other experimental devices, the spalling strength of granite specimens under a high strain rate is tested. Comparisons with other experimental results show that the new measuring method can accurately calculate the dynamic tensile strength of rock materials under a high strain rate.

• 대한기계학회논문집A
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• 제32권9호
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• pp.740-753
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• 2008

The conventional Split Hopkinson Pressure Bar (C-SHPB) technique with aluminum pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials such as hot temperature degraded POM (Poly Oxy Methylene) and PP (Poly Propylene) to obtain more distinguishable experimental signals is used to obtain a dynamic behavior of material deformation under a high strain rate loading condition. An experimental modification with Pulse shaper is introduced to reduce the nonequilibrium on the dynamic material response during a short test period to increase the rise time of the incident pulse for two polymeric materials. For the dynamic stress strain curve obtained from SHPB experiment under high strain rate, the Johnson-Cook model is applied as a constitutive equation, and we verify the applicability of this constitutive equation to the probabilistic reliability estimation method. The methodology to estimate the reliability using the probabilistic method such as the FORM and the SORM has been proposed, after compose the limit state function using Johnson-Cook model. It is found that the failure probability estimated by using the SORM is more reliable than those of the FORM, and the failure probability increases with the increase of applied stress. Moreover, it is noted that the parameters of Johnson-Cook model such as A and n, and applied stress affect the failure probability more than the other random variables according to the sensitivity analysis.

• 대한기계학회논문집A
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• 제37권7호
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• pp.891-897
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• 2013

본 논문에서는, 고 변형률 속도에서의 알루미늄 합금의 압축 변형거동을 홉킨슨 압력봉 시험, SHPB 방법을 통해 연구하였다. 이와 함께 음향방출기법이 사용되었고, 웨이브 가이드선을 통해 시편에 연결된 AE 센서를 이용하여 충격 변형시 검출되는 AE 신호를 실시간으로 검출하였다. 검출된 AE 신호를 통해 진폭, 에너지 및 최대 주파수 특성을 분석하였다. 또한 손상 기구에 따른 음향방출신호의 특성을 분석하기 위하여 시험 수행 후 충돌 시험편 표면과 측면을 관찰하였다. 변형률이 높아질수록 AE 진폭과 AE 누적에너지는 증가하였고, AE 최대 주파수는 감소하였다. 각 신호의 특성은 재료의 손상 기구와 밀접한 관련이 있는 것으로 확인되었다.

• Design & Manufacturing
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• 제2권2호
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• pp.1-5
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• 2008

Mechanical properties of the materials used for mold and industrial machinery under high strain rate loading conditions such as high impact loading are required to provide appropriate safety assessment to varying dynamically loaded mechanical structures. The Split Hopkinson Pressure Bar(SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, the dynamic deformation behavior of a brass under high strain rate compressive loading conditions has been determined using the SHPB technique.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1398-1401
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• 2003

Recently, The PolyPropylene(PP) Foam used as Bumper and Helmet is well known as a protective material for products. In this paper, the effect of the density of PP foams on the absorption of the impact energy is implemented. The result of the experiment has revealed that the effect of the high-density PP foams is remarkably increased compared with that of the low-density PP foams. And it also shows that the absorption of the impact energy of PP foams are greatly influenced by the density in impact velocity(220cm/s). These results are expected to be utilized for the technique of manufacturing a optimum impact structure.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1705-1708
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• 2003

The purpose of this study is to investigate the manufacturing technique on the U type Draw-Bending of inner grooved tube. This bending process make the U shape tube by Hair Pin Bending machine. The U type tube requires the quality of product that satisfy sufficient conditions for a heat exchanger. The mandrel components act the important roles that prevent wrinkles and keep the shape of cross section of bended tube at bending process. We performed the FEM simulation using LS-DYNA software and the bending test of inner groove tube and then, compared bending simulation with bending test results about mandrel ball diameter, mandrel position and optimal clearance between mandrel and tube.

• 한국기계가공학회지
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• 제17권4호
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• pp.64-69
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• 2018

This paper investigates the compressive deformation behavior of direct metal tooling (DMT), processing titanium alloy (Ti-6Al-4V) parts under high strain loading conditions. Split Hopkinson Pressure Bar (SHPB) experiments were performed to determine the flow stress and the coefficients of the Johnson-Cook model. This model is described as a function of strain, strain rate, and temperature. SHPB experiments were performed to characterize the deformation behavior of specimens made with 3D printers, using Ti-6Al-4V material under high temperature and dynamic loading.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2009년도 학술대회 초록집
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• pp.198-202
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• 2009

스플릿 홉킨슨 압력 봉(SHPB)실험은 암석 및 콘크리트와 같은 취성재료의 동적 물성과 변형특성을 파악하고 압축 응력-변형율 데이터를 획득하기 위하여 사용된다. SHPB 실험법은 원리상 대상시료가 파괴이전에 동적응력평형 상태와 일정 변형율 속도 조건하여 놓여져 있어야 한다. 이러한 조건을 만족시키기 위하여 충격봉과 입사봉의 충격에 의하여 발생되는 충격 입사파형을 제어할 필요가 있다. 최근에는 원형 디스크를 충격봉과 입사봉 사이에 두어 입사 충격파형을 제어하는 펄스쉐이핑 기법이 적용되고 있다. 본 연구에서는 입사 충격파형을 정밀하게 제어할 목적으로 다양한 형태와 크기의 금속디스크를 대상으로 SHPB 실험을 수행하여 동적 변형 특성을 파악하였다. 펄스쉐이퍼의 두께와 직경이 작아짐에 따라 응력값과 파장은 증가하였다.

• Computers and Concrete
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• 제21권2호
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• pp.209-217
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• 2018

The dynamic compressive behavior of concrete after freezing and thawing tests are investigated by using the split Hopkinson pressure bar (SHPB) technique. The stress-strain curves of concrete under dynamic loading are measured and analyzed. The setting numbers of freeze-thaw cycles are 0, 25, 50, and 75 cycles. Test results show that the dynamic strength decreases and peak strain increases with the increasing of freeze-thaw cycles. Based on the Weibull distribution model, statistical damage constitutive model for dynamic stress-strain response of concrete after freeze-thaw cycles was proposed. At last, the fragmentation test of concrete subjected to dynamic loading and freeze-thaw cycles is carried out using sieving statistics. The distributions of the fragment sizes are analyzed based on fractal theory. The fractal dimensions of concrete increase with the increasing of both freeze-thaw cycle and strain rate. The relations among the fractal dimension, strain rates and freeze-thawing cycles are developed.