• Advances in concrete construction
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• v.16 no.2
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• pp.119-126
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• 2023

Steel fiber reinforced self-compacting concrete (SFRSCC) has good workability such as high flowability and good cohesiveness. The workability, compressive strength, splitting tensile strength, and anti-penetration characteristics of three kinds of SFRSCC were investigated in this paper. The fraction of steel fibers of the SFRSCC is 0.5%, 1.5% and 2.0% respectively. The results of the static tests show that the splitting tensile strength increases with the increase of fraction of steel fibers, while the compressive strength of 1.5% SFRSCC is lowest. It is demonstrated that the anti-penetration ability of 1.5% SFRSCC subjected to a velocity projectile (200-500 m/s) is better than 0.5% and 2.0% SFRSCC according to the experimental results. Considering the steel fiber effects, the existing formula is revised to predict penetration depth, and it is revealed that the revised predicted depth of penetration is in good agreement with the experimental results. The conclusion of this paper is helpful to the experimental investigations and engineering application.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.3
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• pp.576-585
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• 2002

A three-dimensional Lagrangian explicit time-integration finite element code for analyzing the dynamic impact phenomena was developed. It uses four node tetrahedral elements. In order to consider the effects of strain rate hardening, strain hardening and thermal softening, which are frequently observed in high-velocity deformation phenomena, Johnson-Cook model is used as constitutive model. For more accurate and robust contact force computation, the defense node contact algorithm was adopted and implemented. In order to evaluate the performance of the newly developed three-dimensional hydrocode NET3D, numerical simulations of the oblique impact of mild steel plate by mild steel sphere were carried out. Ballistic limit about various oblique angle between 0 degree and 80 degree was estimated through a series of simulations with different initial velocities of sphere. Element eroding by equivalent plastic strain was applied to mild steel spheres and targets. Ballistic limits and fracture characteristics obtained from simulation were compared with experimental results conducted by Finnegan et al. From numerical studies, the following conclusions were reached. (1) Simulations could successfully reproduce the key features observed in experiment such as tensile failure termed "disking"at normal impacts and outwards bending of partially formed plus segments termed "hinge-mode"at oblique impacts. (2) Simulation results fur 60 degrees oblique impact at 0.70 km/s and 0.91 km/s were compared with experimental results and Eulerian hydrocode CTH simulation results. The Lagrangian code NET3D is superior to Eulerian code CTH in the computational accuracy. Agreement with the experimentally obtained final deformed cross-sections of the projectile is excellent. (3) Agreement with the experimental ballistic limit data, particularly at the high-obliquity impacts, is reasonably good. (4) The simulation result is not very sensitive to eroding condition but slightly influenced by friction coefficient.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.3
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• pp.147-154
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• 2014

In the context of an increasing need for safety in concrete structures under blast and impact loading condition, the behavior of concrete under high strain rate condition has been an important issue. Since concrete subjected to impact loading associated with high strain rate shows quite different material behavior from that in the static state, several material models are proposed and used to describe the high strain rate behavior under blast and impact loading. In the process of modelling high strain rate conditions with these material models, mesh dependency in the used finite element(FE) is the key problem because simulation results under high strain-rate condition are quite sensitive to applied FE mesh size. This paper introduces an criterion which can minimize the mesh-dependency of simulation results on the basis of the fracture energy concept, and HJC(Holmquist Johnson Cook) model is examined to trace sensitivity to the used FE mesh size. To coincide with the purpose of the perforation simulation with a concrete plate under a projectile(bullet), the residual velocities of projectile after perforation are compared. The analytical results show that the variation of residual velocity with the used FE mesh size is quite reduced and accuracy of simulation results are improved by applying a unique failure strain value determined according to the proposed criterion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1125-1131
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• 2014

This work presents a vulnerability assessment procedure for a complex structure using vibration characteristics. The structural behavior of a three-dimensional framed structure subjected to impact forces was predicted using the spectral element method. The Timoshenko beam function was applied to simulate the impact wave propagations induced by a high-velocity projectile at relatively high frequencies. The interactions at the joints were analyzed for both flexural and longitudinal wave propagations. Simulations of the impact energy transfer through the entire structure were performed using the transient displacement and acceleration responses obtained from the frequency analysis. The kill probabilities of the crucial components for an operating system were calculated as a function of the predicted acceleration amplitudes according to the acceptable vibration levels. Following the proposed vulnerability assessment procedure, the vulnerable positions of a three-dimensional combat vehicle with high possibilities of damage generation of components by impact loading were identified from the estimated vibration responses.

• Structural Engineering and Mechanics
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• v.42 no.6
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• pp.831-847
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• 2012

Impact from water-borne debris during tsunami and flood events pose a potential threat to structures. Debris impact forces specified by current codes and standards are based on rigid body dynamics, leading to forces that are dependent on total debris mass. However, shipping containers and other debris are unlikely to be rigid compared to the walls, columns and other structures that they impact. The application of a simple one-dimensional model to obtain impact force magnitude and duration, based on acoustic wave propagation in a flexible projectile, is explored. The focus herein is on in-air impact. Based on small-scale experiments, the applicability of the model to predict actual impact forces is investigated. The tests show that the force and duration are reasonably well represented by the simple model, but they also show how actual impact differs from the ideal model. A more detailed three-dimensional finite element model is also developed to understand more clearly the physical phenomena involved in the experimental tests. The tests and the FE results reveal important characteristics of actual impact, knowledge of which can be used to guide larger scale experiments and detailed modeling. The one-dimensional model is extended to consider water-driven debris as well. When fluid is used to propel the 1-D model, an estimate of the 'added mass' effect is possible. In this extended model the debris impact force depends on the wave propagation in the two media, and the conditions under which the fluid increases the impact force are discussed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.9
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• pp.774-781
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• 2018

In this investigation, a gas gun is proposed driven by carbon dioxide gas and installed on a quadcopter-type small unmanned drone for the purpose of cattle vaccination, and we developed a launcher and its connection unit. The system consists of a commercial drone, a gas gun, a solenoid valve, and the remote communication controller, etc. The velocity of launched projectile is measured, and the full system is finally validated through ground test and flight examination loaded for the real aircraft. The feasibility is checked if this technology is applicable to various disease abatement and hazard mitigation in the fields of agriculture and fire-fighting with the present research and development.

• Journal of the Korea Institute of Building Construction
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• v.23 no.6
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• pp.715-726
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• 2023

This study suggested that protective panels should be installed as sacrificial members as a safety design method for structures with potential explosions such as hydrogen charging stations to minimize direct damage to the structure and have resilience. To this end, the focus of the experiment is on quantitatively evaluating the impact of the structure when the protection panel is installed closely or spaced apart from the structure in a high-speed collision situation of the projectile. The experimental design used steel plates instead of concrete structural members mainly used in the past for excellent reproducibility, and the impact of structural members was compared and analyzed through deformation differences on the back of the steel plate. In addition, the impact of changes in the physical properties of the elastic body used as a separation material for the protective member and the difference in shock wave transmission time according to the protective member and the elastic body on the structural member was investigated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.953-960
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• 2013

This study aimed to investigate the penetration characteristics of a segmented penetrator with normal and inclined angles. The length to diameter ratio (L/D) of the segmented penetrator was varied as 1.0, 0.5, and 0.25. Moreover, impact velocities of 1.5, 2.0, and 2.5 km/s and inclination angles of $15^{\circ}$, $30^{\circ}$, and $45^{\circ}$ were successively applied. The AUTODYN-3D code was used to simulate the penetration performance of the segmented penetrator. The results show that the penetration performance of the segmented penetrator with steel plates was obviously higher than that of the corresponding continuous penetrator with steel plates. The outstanding penetration performance of the segmented penetrator can be observed when the impact velocity was 2.0 km/s and L/D = 1. In this case, the penetration performance of the segmented penetrator was 7% higher than that of the corresponding continuous penetrator. This trend was attributable to the interaction between the reactive plate and the projectile. The extent of the interaction relies on the relative velocities of the plate and projectiles, inclination angle, and number of segmented penetrators. It was proven that the penetration performance of the segmented penetrator can be improved by increasing the impact velocity, number of segmented penetrators between segments, and penetrator length.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.6
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• pp.761-768
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• 2013

New warheads are designed and developed to be highly lethal when used as part of ballistic missile payloads. There are many trades associated with the design of a central warhead core, mainly dealing with the projectiles or penetrators. Obviously, a payload-type configuration is very susceptible to kills from one projectile because of the high impacts required for bomblet or submunition payloads. Based on these requirements, the optimum kill vehicle configuration will have the smallest mass and relative velocity that will kill all the submunitions. The designs of the penetrator shape and size are directly related to the space and weight of the warhead. The shape, size, L/D, penetrator material, and manner in which they are inserted inside the surrounding explosive segments are critical in achieving successful penetrator design. The AUTODYN-3D code was used to study the effect of penetrator penetration. The objective of numerical analysis was to determine the penetration characteristics of the penetrator produced by hypervelocity impacts under different initial conditions such as initial velocity, shape, and L/D of the penetrator.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.1
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• pp.100-108
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• 2015

The purpose of this study is to evaluate the effect of improvement on the impact resistance and strength properties of cement composites by surface modification of aramid fiber. For aramid fiber reinforced cement composites, therefore, dispersion capability and the bonding efficiency between the fibers and the cement composite material need to be improved. It is possible by modifying surface properties to hydrophobic, it is considered that oiling agent ratio of 1.2 % and improvement of performance is in need to be investigated. In this study, short aramid fibers were mixed by different fiber length and oiling agent ratio. And improvement of strength properties and impact resistance performance of hybrid cement composites were evaluated under the influence of steel fiber. As a result, strength properties of aramid fiber reinforced cement composites are different by mixing ratio of fiber, oiling agent ratio and length of fiber. In case of cement composites which have same volume fraction and fiber length, tensile strength and flexural strength were improved with increase of the emulsions throughput of the fiber surface. The results of evaluation on the static strength properties had effects on impact resistance performance by high-velocity impact. And it was observed that the scabbing of rear was suppressed with increase of the oiling agent ratio.