• Proceedings of the KSME Conference
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• 2005.11a
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• pp.135.1-135.1
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• 2005

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.234-234
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• 2003

• Proceedings of the KSEE Conference
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• 2008.10a
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• pp.61-64
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• 2008

• Structural Engineering and Mechanics
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• v.37 no.1
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• pp.1-15
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• 2011

The response of concrete to transient dynamic loading has received extensive attention for both civil and military applications. Accordingly, thoroughly understanding the response and failure modes of concrete subjected to impact or explosive loading is vital to the protection provided by fortifications. Reactive powder concrete (RPC), as developed by Richard and Cheyrezy (1995) in recent years, is a unique mixture that is cured such that it has an ultra-high compressive strength. In this work, the concrete cylinders with different steel fiber volume fractions were subjected to repeated impact loading by a split Hopkinson Pressure Bar (SHPB) device. Experimental results indicate that the ability of repeated impact resistance of ultra-high-strength concrete was markedly superior to that of other specimens. Additionally, the rate of damage was decelerated and the energy absorption of ultra-high-strength concrete improved as the steel fiber volume fraction increased.

• 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.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.5
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• pp.98-104
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• 2001

A dynamic fracture toughness test method with a chevron notched ceramic specimens is proposed. The notch angles of the chevron specimens were 90, 100$^{\circ}$and 110$^{\circ}$. Finite element analysis(FEA) were done to determine the geometrical properties of chevron-notch specimens according to notch angles. The static fracture toughness of the chevron notched alumina specimen was 3.8MP$\alpha$√m similar to that of the general fracture specimen with a precrack. Dynamic fracture toughness was 4.5 MP$\alpha$√m slightly higher than the static one. These research showed the possibility of the split Hopkinson pressure bar test method using the newly proposed chevron notched specimens to get the dynamic fracture toughness of extremely brittle materials such as ceramics.

• Journal of the Korean Society of Safety
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• v.23 no.6
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• pp.21-27
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• 2008

Polypropylene(PP) foams are widely used as protective materials such as automotive bumper and safety helmet, but whose dynamic behaviour are not well defined. In this paper, the compression tests by Split Hopkinson Pressure Bar were conducted to obtain the stress-strain curve and to investigate the effect of density on the absorption of impact energy in the PP foams. Three kinds of foams were chosen depending upon the density. The result of the experiment has revealed that the stiffness of the low-density PP foam is remarkably increased at high strain rate compared with that of the high-density PP foam. And it is also shown that the absorption of impact energy are greatly influenced by the density of PP foam. These results are expected to be utilized for the development of a protective structure with polymer foams.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.275-278
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it finds use in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. In order to design optimal structural parts made of INCONEL 718, accurate understanding of material's mechanical properties, dynamic behavior and fracture characteristic as a function of strain rates are required. This paper concerned with the dynamic material properties of the INCONEL 718 for the various strain rates. The dynamic response of the INCONEL 718 at intermediate strain rate is obtained from the high speed tensile test machine test and at the high strain rate is from the split Hopkinson pressure bar test. Based on the experimental results, the effects of strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure are evaluated. Experimental results from both quasi-static and high strain rate up to the 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of INCONEL 718.

• Transactions of Materials Processing
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• v.14 no.6 s.78
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• pp.559-564
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• 2005

INCONEL 718, nickel based superalloy, has good formability, high strength, excellent corrosion resistance and mechanical properties at high temperature. Owing to theses attractive properties, it is utilized in applications such as combustion system, turbine engines and nuclear reactors. In such applications, components are typically required to be tolerant of high stress impact loading. This may cause material degradation and lead to catastrophic failure during service operation. Accurate understanding of material's mechanical properties with various strain rates is required in order to guarantee the reliability of structural parts made of INCONEL 718. This paper is concerned with the dynamic material properties of the INCONEL 718 at various strain rates. The dynamic response of the INCONEL 718 at the intermediate strain rate is obtained from the high speed tensile test and at the high strain rate is from the split Hopkinson pressure bar test. The effect of the strain rate on dynamic flow stress, work hardening characteristics, strain rate sensitivity and elongation to the failure is evaluated with the experimental results. Experimental results from both the quasi-static and the high strain rate up to 5000/sec are interpolated in order to construct the Johnson-Cook model as the constitutive relation that should be applied to simulate and design the structural parts made of rNCONEL 718.

• Geomechanics and Engineering
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• v.30 no.5
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• pp.401-411
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• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.