• Geomechanics and Engineering
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• 제17권3호
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• pp.261-270
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• 2019

Because the estimation of the tensile strength is very important in any geotechnical project, many attempts have been made to determine. But the immediate determination of the tensile strength is usually difficult owing to well-shaped specimens, time-consuming, expensive and sometimes unreliable. In this study, engineering properties of several ultramafic rock samples were measured to assess the correlations between the Brazilian Tensile Strength (BTS) and degree of serpentinization, physical, dynamic and mechanical characteristics. For this purpose, a comprehensive laboratory testing program was conducted after collecting thirty-two peridotite and fifty-one serpentinite rock samples, taken from central Greece, in accordance with ASTM and ISRM standards. In addition, a representative number of them were subjected to petrographic studies and the obtained results were statistically described and analysed. Simple and multiple regression analyses were used to investigate the relationships between the Brazilian Tensile Strength and the other measured properties. Thus, empirical equations were developed and they showed that all of the properties are well correlated with Brazilian Tensile Strength. The curves with the $45^{\circ}$ line (y = x) were extracted for evaluating the validity degree of concluded empirical equations which approved approximately close relationships between Brazilian Tensile Strength and the measured properties.

• 터널과지하공간
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• 제22권5호
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• pp.339-345
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• 2012

동적하중 하에서 암석의 변형거동 및 파괴강도는 발파, 지진 또는 암반돌출의 지진동에 의한 지하구조물의 안정해석에 중요하다. 본 연구에서는 스플릿 홉킨슨 압력봉(SHPB) 충격실험시스템을 석회암시료의 일축압축시험과 압열인장시험에 적용하여 고변형률과 동적강도 평가를 수행하였다. 충격봉의 발사속도를 제어하여 파괴강도 이하 동적응력 상태에서의 석회암시료의 동적응력-변형거동을 분석하였다. 시료 내 파괴여부 및 파괴양상을 파악하기 위하여 Micro-focus X-ray 단층촬영을 수행하였다. 동적 압축강도 실험결과, 석회암시료의 동적압축강도는 변형율속도 의존성을 보였으며, 동적 압축파괴강도는 140 MPa 이상으로 평가되었다. 동적 압열 인장 실험결과, 석회암시료의 동적 압열인장강도는 21 MPa 이상으로 정적 압열인장강도보다 3배 이상 높은 것으로 평가되었다.

• Geomechanics and Engineering
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• 제23권5호
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• pp.467-480
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• 2020

The failure behavior and tensile strength of sandstone materials under different strain rates are greatly different, especially under static loads and impact loads. In order to clearly investigate the failure mechanism of sandstone materials under static and impact loads, a series of Brazilian disc samples were used by employing green sandstone, red sandstone and black sandstone to carry out static and impact loading splitting tensile tests, and the failure properties subjected to two different loading conditions were analyzed and discussed. Subsequently, the failure behavior of sandstone materials also were simulated by finite element code. The good agreement between simulation results and experimental results can obtain the following significantly conclusions: (1) The relationship of the tensile strength among sandstone materials is that green sandstone < red sandstone < black sandstone, and the variation of the tensile sensitivity of sandstone materials is that green sandstone > red sandstone > black sandstone; (2) The mainly cause for the difference of dynamic tensile strength of sandstone materials is that the strength of crystal particles in sandstone material, and the tensile strength of sandstone is proportional to the fractal dimension; (3) The dynamic failure behavior of sandstone is greatly different from that of static failure behavior, and the dynamic tensile failure rate in dynamic failure behavior is about 54.92%.

• 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.

• Structural Engineering and Mechanics
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• 제86권5호
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• pp.607-619
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• 2023

This study, it was tried to evaluate the asphalt behavior under tensile loading conditions through indirect Brazilian and direct tensile tests, experimentally and numerically. This paper is important from two points of view. The first one, a new test method was developed for the determination of the direct tensile strength of asphalt and its difference was obtained from the indirect test method. The second one, the effects of particle size and loading rate have been cleared on the tensile fracture mechanism. The experimental direct tensile strength of the asphalt specimens was measured in the laboratory using the compression-to-tensile load converting (CTLC) device. Some special types of asphalt specimens were prepared in the form of slabs with a central hole. The CTLC device is then equipped with this specimen and placed in the universal testing machine. Then, the direct tensile strength of asphalt specimens with different sizes of ingredients can be measured at different loading rates in the laboratory. The particle flow code (PFC) was used to numerically simulate the direct tensile strength test of asphalt samples. This numerical modeling technique is based on the versatile discrete element method (DEM). Three different particle diameters were chosen and were tested under three different loading rates. The results show that when the loading rate was 0.016 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis till coalescence to the model boundary. When the loading rate was 0.032 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis. The branching occurs in these cracks. This shows that the crack propagation is under quasi-static conditions. When the loading rate was 0.064 mm/sec, mixed tensile and shear cracks were initiated below the loading walls and branching occurred in these cracks. This shows that the crack propagation is under dynamic conditions. The loading rate increases and the tensile strength increases. Because all defects mobilized under a low loading rate and this led to decreasing the tensile strength. The experimental results for the direct tensile strengths of asphalt specimens of different ingredients were in good accordance with their corresponding results approximated by DEM software.

• 화약ㆍ발파
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• 제39권1호
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• pp.10-21
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• 2021

암석이나 콘크리트와 같은 취성재료는 재료에 동하중이 가해질 때에는 큰 변형률속도 의존성을 보인다. 이는 취성재료의 역학적 성질이 하중속도에 따라 크게 변화할 수 있음을 의미한다. 이런 성질 때문에 취성재료의 변형률속도 의존성은 발파공학이나 암석동역학 문제를 풀 때 반드시 고려해야 할 중요한 사항들 중의 하나이다. 하지만 불행하게도 국내의 경우, 암석이나 여타의 취성재료들의 동적물성을 특성화하는 연구들은 아직 미진한 상태에 있다. 본 연구에서는 거창 화강암과 고강도 콘크리트 시편의 동적특성을 파악하기 위해 홉킨슨 압력봉을 이용하여 동적 인장시험을 실시하였다. 시험방법으로는 ISRM이 제안한 동적 압열시험과 박리시험을 채택하였다. 일반적으로, 고변형률속도 하에서는 후자의 방법이 더 우수한 것으로 알려져 있다. 이들 두 종류의 시험을 실시한 결과, 시편들의 동적 인장강도가 거의 비슷하게 나타났다. 하지만 저자들은 애초에 시험방법에 따라 측정강도가 상이할 것으로 예상했었다. 따라서 서로 다른 방법을 적용했음에도 측정 강도가 비슷하게 나타난 것은 오히려 시험과정에서 어떤 오류가 개입된 것으로도 볼 수 있으므로 후속연구를 통해 이 부분에 대해 상세조사를 수행할 예정이다.