• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.10a
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• pp.55-61
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• 2000

Tungsten heavy metal is characterized bi a high density and novel combination of strength and ductility. Among them, 90W-7Ni-3Fe is used for applications, where the high specific weight of the material plays an important role. They are used as counterweights, rotating inertia members, as well as for defense purposes(kinetic energy penetrators, etc.). Because of these applications, it is essential to detemine the dynamic characteristics of tungsten alloy. In this paper, Explicit FEM(finite element method) is employed to investigate the dynamic characteristics of tungsten heavy metal under base of stress wave propagation theory for SHPB, and the model of specimen is divided into two parts to understand the phenomenon that stress wave penetrates through each tungsten base and matrix. This simulation results were compared to experimental one and through this program the dynamic stress-strain curve of tungsten heavy metal can be obtained using quasi static stress-strain curve of pure tungsten and matrix.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.4
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• pp.43-49
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• 2003

This research work has been carried out for finding J-integral in mode II of CFRP(carbon fiber reinforced plastics) laminate plates based on the classical bar theory in dynamic conditions with consideration of the effect of inertia forces, eventually to lead to finding the dynamic inter-layer fracture toughness. Dynamic inter-layer fracture toughness was found by a self-made ENF(End Notched Flexure) experimental apparatus using Split Hopkinson's Bar(SHPB), and also observed the variation of the fracture toughness haying different resin contents and fiber arrangements of CFRP specimen([$0_3^{\circ}/90_3^{\circ}/0_6^{\circ}/90_3^{\circ}/0_3^{\circ}$], [$0_{20}^{\circ}$], [$0_5^{\circ}/90_{10}^{\circ}/0_5^{\circ}$]). As an experimental result, in either cases of quasi-static or dynamic load condition, the critical load and the inter-layer fracture toughness increased sharply depending on the increase of resin contents. Therefore, it could, be concluded that the effect by resin contents is the major factor determining the inter-layer fracture toughness in the CFRP laminate plates.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.8 s.173
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• pp.92-99
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• 2005

Tungsten heavy metal is characterized by a high density and novel combination of strength and ductility. Among them, 90W-7Ni-3Fe is used for applications, where the high specific weight of the material plays an important role. They are used as counterweights, rotating inertia members, as well as fur defense purposes(kinetic energy Penetrators, etc.). Because of these applications, it is essential to detemine the dynamic characteristics of tungsten alloy. In this paper, Explicit FEM(finite element method) is employed to investigate the dynamic characteristics of tungsten heavy metal under base of stress wave propagation theory for SHPB, and the model of specimen is divided into two parts to understand the phenomenon that stress wave penetrates through each tungsten base and matrix. This simulation results were compared to experimental one and through this program, the dynamic stress-strain curve of tungsten heavy metal can be obtained using quasi static stress-strain curve of pure tungsten and matrix.

• Computers and Concrete
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• v.21 no.4
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• pp.399-406
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• 2018

The present study focuses on the performance of basalt fiber reinforced concrete (BFRC) lining in tunnel situated in sandstone rock when subjected to internal blast loading. The blast analysis of the lined tunnel is carried out using the three-dimensional (3-D) nonlinear finite element (FE) method. The stress-strain response of the sandstone rock is simulated using a crushable plasticity model which can simulate the brittle behavior of rock and that of BFRC lining is analyzed using a damaged plasticity model for concrete capturing damage response. The strain rate dependent material properties of BFRC are collected from the literature and that of rock are taken from the authors' previous work using split Hopkinson pressure bar (SHPB). The constitutive model performance is validated through the FE simulation of SHPB test and the comparison of simulation results with the experimental data. Further, blast loading in the tunnel is simulated for 10 kg and 50 kg Trinitrotoluene (TNT) charge weights using the equivalent pressure-time curves obtained through hydrocode simulations. The analysis results are studied for the stress and displacement response of rock and tunnel lining. Blast performance of BFRC lining is compared with that of plain concrete (PC) and steel fiber reinforced concrete (SFRC) lining materials. It is observed that the BFRC lining exhibits almost 65% lesser displacement as compared to PC and 30% lesser displacement as compared to SFRC tunnel linings.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.237-240
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• 2004

High strain-rate deformation behavior of NiAl/Ni micro-laminated composites was characterized by split hopkins on pressure bar(SHPB). When the strain rate increased, the compressive stress of micro-laminated composites were increased a little. When the intermetallic volume fraction increased, the compressive stress of micro-laminated composites increased linearly irrespective of strain rate. Absorbed energy during the quasi-static and SHPB tests was calculated from the integrated area of stress-strain curve. Absorbed energy of micro-laminated composites deviated from the linearity in terms of the intermetallic volume fraction but merged to the value of intermetallic as the strain rate increased. This was due to high tendency of intermetallic layer for the localization of shear deformation at high strain rate. Microstructure showing adibatic shear band(ASB) confirmed that the shear strain calculated from the misalignment angle of each layer increased and ASB width decreased when the intermetallic volume fraction. Simulation test impacted by tungsten heavy alloy cylinder resulted that the absorbed energies multiplied by damaged volume of micro-laminated composites were decreased as the intermetallic volume fraction increased. Fracture mode were changed from delamination to single fracture when the intermetallic volume fraction and this results were good matched with previous results[l] obtained from the fracture tests.

• Structural Engineering and Mechanics
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• v.55 no.4
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• pp.857-869
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• 2015

The aluminum 7075-T6 is known as an alloy widely used in aircraft structural applications, which does not exhibit strain rate sensitivity during dynamic compressive tests. Despite mechanical importance of the material, there is not enough attention to determine appropriate sample dimensions such as a sample diameter relative to the device bar diameter and sample length to diameter (L/D) ratio for dynamic tests and how these two parameters can change mechanical behaviors of the sample under dynamic loading condition. In this study, various samples which have different diameters of 31.8, 25.4, 15.9, and 9.5 mm and sample L/D ratios of 2.0, 1.5, 1.0, 0.5, and 0.25 were tested using Split Hopkinson Pressure Bar (SHPB), as this testing device is proper to characterize mechanical behaviors of solid materials at high strain rates. The mechanical behavior of this alloy was examined under ${\sim}200-5,500s^{-1}$ dynamic strain rate. Aluminum samples of 2.0, 1.5 and 1.0 of L/D ratios were well fitted into the stress-strain curve, Madison and Green's diagram, regardless of the sample diameters. Also, the 0.5 and 0.25 L/D ratio samples having the diameter of 31.8 and 25.4 mm followed the stress-strain curve. As results, larger samples (31.8 and 25.4 mm) in diameters followed the stress-strain curve regardless of the L/D ratios, whereas the 0.5 and 0.25 L/D ratios of small diameter sample (15.9 and 9.5 mm) did not follow the stress-strain diagram but significantly deviate from the diagram. Our results indicate that the L/D ratio is important determinant in stress-strain responses under the SHPB test when the sample diameter is small relative to the test bar diameter (31.8 mm), but when sample diameter is close to the bar diameter, L/D ratio does not significantly affect the stress-strain responses. This suggests that the areal mismatch (non-contact area of the testing bar) between the sample and the bar can misrepresent mechanical behaviors of the aluminum 7075-T6 at the dynamic loading condition.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.2
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• pp.206-216
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• 2017

This paper studies on the dynamic properties of Ti-6Al-4V alloy. After forming the four different micro structures(equiaxed, lamellar, and 2 bimodals) through heat treatments, static and dynamic properties of each structure were investigated quantitatively. Dynamic behaviors of the alloy are observed by the compressive split Hopkinson pressure bar(SHPB) tests. In additon, parameters of Johnson-Cook equation were determined from the SHPB test results. In order to verify the suitability of the parameters, high velocity impact tests were performed and the results were compared with the numerical analysis results. Although the flow stress and the fracture strain of the bimodal structures were higher than those of the equiaxed structure at the static tests, the superior dynamic properties were observed at the equiaxed structure due to the effects of higher maximum flow stress and fracture strain. From the numerical analysis, J-C parameters which are determined on this study describe well the dynamic behavior of Ti-6Al-4V alloy. Experimental and analysis results are consistent with ${\pm}5%$ of an average error.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.148-151
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• 2003

The purpose of this study is to investigate the manufacturing technique on the U type Draw-Bending of inner groove tube. 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.

• Geomechanics and Engineering
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• v.12 no.1
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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.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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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.