• Explosives and Blasting
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• v.35 no.2
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• pp.9-17
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• 2017

The Wheatstone bridge is an important electrical circuit that is widely used to measure extremely small resistance changes in strain gages. The strain gages are attached to the structure or specimen whose deformation is to be detected. The Wheatstone bridge finds one of its major applications in the areas of static and dynamic strength tests for various engineering materials. In the split Hopkinson pressure bar (SHPB) system, for example, the bridge circuit is required to measure the dynamic strains of the incident and transmitted bars along which the stress wave propagates. In this article, the principles of the Wheatstone bridge circuit are in detail explained for easy reference during laboratory experiments associated with rock dynamics. Especially, the circuit arrangements of the quater, half, and full bridges are presented with their basic uses.

• Explosives and Blasting
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• v.38 no.3
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• pp.30-43
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• 2020

Rock dynamics is a relatively new discipline to study the mechanical behaviors of rock materials (or rock masses) under dynamic loading conditions. Many rock mechanics and rock engineering issues are concerned with the dynamic phenomena such as mining development, civil engineering, earthquake, military science, and various disasters. The significance of rock dynamic researches has been increased in these days. This paper introduces conventional experimental techniques for rock dynamic experimental methods and the particular characteristics of rock dynamic behaviors with several remarkable recent studies.

• Tunnel and Underground Space
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• v.18 no.6
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• pp.457-464
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• 2008

Dynamic fracture mechanism of rock is important to improve rapid excavation method and develop precise damage assesment of rock mass in the vicinity of an excavation. In order to investigate dynamic fracture characteristics and dynamic damage mechanism of brittle materials, this study employed pulse shape-controlled Split Hopkinson Pressure Bar (SHPB) system. The P- and S-wave velocities of the tested samples were measured before and after tests to examine damage of the samples. The decay ratios of the Ultrasonic wave velocities increased with impart velocities and the samples which have lower strength showed higher permanent strain significantly.

• Tunnel and Underground Space
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• v.22 no.5
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• pp.339-345
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• 2012

Information on the deformation behavior and fracture strength of rocks subjected to dynamic loadings is important to stability analyses of underground openings underground vibration due to rock blasts, earthquakes and rock bursts. In this study, Split Hopkinson Pressure Bar (SHPB) system was applied to estimate dynamic compressive and tensile fracture strengths of limestone and also examine deformation behavior of limestones under dynamic loadings. A micro-focus X-ray CT scanner was used to observe non-destructively inside the impacted limestone specimens. From the dynamic tests, it was revealed that the limestone have over 140MPa dynamic compressive strength and the strain-rate dependency of the strength. Dynamic Brazilian tensile strength of the limestone exceeds 21MPa and shows over 3 times static Brazilian tensile strength.

• Tunnel and Underground Space
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• v.19 no.6
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• pp.545-557
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• 2009

In order to investigate dynamic damage mechanism of brittle materials, Split Hopkinson Pressure Bar (SHPB) have been adapted to apply different impact levels to rocks in South Korea. High resolution X-ray Computed Tomography (CT) was used to estimate the damage in tested rock samples nondestructively. The cracks which are parallel to the loading axis are visible on the contact surface with the incident bar under lower level of impact. The surface cracks disappeared with increment of impact level due to confined effect between the incident bar and sample, while axial splitting are happened near the outer surface.

• Explosives and Blasting
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• v.38 no.1
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• pp.23-29
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• 2020

The measurement technique with dynamic shock sensor was widely used in academic experiment for blasting and impact. However, most of dynamic sensors are expensive so that it needs to be protected by external housing structures or damping devices. In this study, the calibration method for dynamic shock sensor under the distortion by external structures. Hopkinson pressure bar system was adopted to measure the input acceleration to the sensor, and it was compared to the acceleration measured by accelerometer with customized damping device. Consequently, it is conclued that this method can be useful to calibrate the dynamic shock sensor under the linear distortion.