• 대한기계학회논문집
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• 제18권3호
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• pp.573-583
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• 1994

In this study, the shock characteristics for high velocity impact phenomena during the initial shock state by the long rod penetrator are calculated. From these results we re-analyze the one-dimensional hydrodynamic penetration theory by introducing the effective area ratio calculated from the mushroomed strain which is dependent on impact velocity. Calculated penetration depth and mushroomed strain show good agreement with high velocity impact experimental data. In addition we visualize the shock wave propagation in a transparent acryle block.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1589-1597
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• 1997

The high-velocity impact forging process with eccentric loading condition is analyzed using the explicit time integration finite element method. In order to consider the strain hardening, strain rate hardening and thermal softening effects, which are frequently observed in high-velocity deformation phenomena, the Johnson-Cook constitutive model is applied to model the workpiece. It is assumed that the material response of the dies is elastic in the study. As a result of the eccentric loading simulation, it is found that the increase of the eccentric ratio and the allowable tilting angle cause the decrease of the maximum forging load and the blow efficiency, and it is also found that the forging load and the blow efficiency generated in the high-velocity impact forging process with three-dimensional geometry can be obtained efficiently.

• Steel and Composite Structures
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• 제22권4호
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• pp.777-796
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• 2016

In this paper, the behavior of woven E-glass fabric composite laminate was experimentally investigated under quasi-static indentation and high velocity impact by flat-ended, hemispherical, conical (cone angle of $37^{\circ}$ and $90^{\circ}$) and ogival (CRH of 1.5 and 2.5) cylindrical perforators. Moreover, the results are compared in order to explore the possibility of extending quasi-static indentation test results to high velocity impact test results in different characteristics such as perforation mechanisms, performance of perforators, energy absorption, friction force, etc. The effects of perforator nose shape, nose length and nose-shank connection shapes were investigated. The results showed that the quasi-static indentation test has a great ability to predict the high velocity impact behavior of the composite laminates especially in several characteristics such as perforation mechanisms, perforator performance. In both experiments, the highest performance occurs for 2.5 CRH projectile and the lowest is related to blunt projectiles. The results show that sharp perforators indicate lower values of dynamic enhancement factor and the flat-ended perforator represents the maximum dynamic enhancement factor among other perforators. Moreover, damage propagation far more occurred in high velocity impact tests then quasi-static tests. The highest damage area is mostly observed in ballistic limit of each projectile which projectile deviation strongly increases this area.

• Composites Research
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• 제24권6호
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• pp.49-55
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• 2011

복합재는 금속보다 높은 비강성과 비강도를 갖는 장점 때문에 군용기와 민항기의 주요 구조물로 사용이 증대되고 있다. 하지만 복합재의 기계적인 특성은 충격에 의해 심각하게 저하된다. 특히, 우박, 고속 택싱에 의한 파편과의 고속 충격은 작은 질량임에도 불구하고 구조물과 서브시스템에 심각한 손상을 줄 수 있다. 그러나 한 가지 센서 또는 기존의 기법을 사용하여 복합재의 손상을 탐지하기는 쉽지 않다. 본 논문에서는 복합적층판의 고속충격에 의한 손상 개시와 전파를 모니터링하기 위해 PVDF 센서와 AE 센서를 사용하였다. 센서 신호를 분석하기 위해 웨이블릿 변환을 사용하였다. 충격에너지가 증가할수록 고주파 신호가 증가하였고 PVDF 센서와 AE 센서 신호에서 유사한 경향을 알 수 있었다. 결과적으로 복합적층판의 고속충격손상을 감지하고 특성화하는 다양한 센싱 기법을 제시하였다.

• Structural Engineering and Mechanics
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• 제40권5호
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• pp.595-616
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• 2011

Impact experiments have been carried out on concrete slabs. The first group was traditionally manufactured, densely reinforced concrete targets, and the next were ordinary Portland and calcium aluminate cement based HPSFRC (High performance steel fiber reinforced concrete) and SIFCON (Slurry infiltrated concrete) targets. All specimens were hit by anti-armor tungsten projectiles at a muzzle velocity of over 4 Mach causing destructive perforation. In Part I of this article, production and experimental procedures are described. The first group of specimens were ordinary CEM I 42.5 R cement based targets including only dense reinforcement. In the second and third groups, specimens were produced using CEM I 42.5 R cement and Calcium Aluminate Cement (CAC40) with ordinary reinforcement and steel fibers 2 percent in volume. In the fourth group, SIFCON specimens including 12 percent of steel fibers without reinforcement were tested. A high-speed camera was used to capture impact and residual velocities of the projectile. Sample tests were performed to obtain mechanical properties of the materials. In the companion Part II of this study, numerical investigations and simulations performed will be presented. Few studies exist that examine high-velocity impact effects on CAC40 based HPSFRC targets, so this investigation gives an insight for comparison of their behavior with Portland cement based and SIFCON specimens.

• 대한기계학회논문집A
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• 제40권10호
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• pp.857-864
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• 2016

항공산업의 발달로 하늘에는 많은 비행기, UAV, 드론이 비행하고 있다. 비행기와 UAV는 빠른 속도로 비행하며 드론의 프로펠러는 빠른 속도로 회전하고 있다. 이렇게 빠른 속도의 비행체간의 충돌은 비행기 운항과 승객의 안전성을 위협하고, 지상에 있는 인명과 재산에 피해를 줄 수 있다. 비행체의 운항속도는 음속(340m/s) 내외이며, 프로펠러의 회전 속도는 그 보다 작은 속도 영역이다. 현재까지의 충돌 실험은 공기의 힘을 이용한 방식으로 충돌 속도를 얻었고, 공기 팽창에 따른 넓은 공간을 필요로 한다. 하지만 전자기력 발사장치는 그보다 작은 공간에서 충분한 속도를 얻을 수 있다.(~500m/s) 본 논문에서는 전자기력 발사장치의 설계와 이에 따른 제작에 관한 방법을 제시하고자 한다.

• Structural Engineering and Mechanics
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• 제63권2호
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• pp.207-215
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• 2017

The paper presents the studies carried out on low velocity impact of Ultra high performance concrete (UHPC) panels of size $350{\times}350{\times}10mm^3$ and $350{\times}350{\times}15mm^3$. The panels are cast with 2 and 2.5% micro steel fibre and compared with UHPC without fiber. The panels are subjected to low velocity impact, by a drop-weight hemispherical impactor, at three different energy levels of 10, 15 and 20 J. The impact force obtained from the experiments are compared with numerically obtained results using finite element method, theoretically by energy balance approach and empirically by nonlinear multi-genetic programming. The predictions by these models are found to be in good coherence with the experimental results.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.865-868
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• 2002

This study investigated the shape deformation of ball projectile(5.56mn) under the low energy impact by the use of the drop weight impact tester. ball projectile(5.56mm) consisted of the copper face with a lead core. The impact conditions were changed with the variations of the mass and the drop height of the impact tup. Shape deformation of ball projectile(5.56mm) after low velocity impact was measured using a video microscope and CCD camera. The test result showed that impact energy by changing of drop height of the impact tup affected shape deformation of ball projectile(5.56mm). So, it is important to study the relativity between shape deformation of ball projectile(5.56mm) and ballistic protection of plate(such as hybrid composite laminates) under the high velocity impact.

• Steel and Composite Structures
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• 제49권3호
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• pp.281-291
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• 2023

Due to the fact that the nonlinear low-velocity impact response of graphene platelets reinforced metal foams (GPLRMF) doubly curved shells have not been investigated in the existing works, this paper aims to solve this issue. Using Reddy's high-order shear deformation theory (HSDT), the nonlinear governing equations of GPLRMF doubly curved shells are obtained by Euler-Lagrange method, discretized by Galerkin principle, and solved by the fourth-order Runge-Kutta method to obtain the impact force and central deflection. The nonlinear Hertz contact law is applied to determine the contact force. Finally, the impacts of graphene platelets (GPLs) distribution pattern, porosity distribution form, porosity coefficient, damping coefficient, impact parameters (radius and initial velocity), GPLs weight fraction, pre-stressing force and different shell types on the low-velocity impact curves are analyzed. It can be found that, among the four shell structures, the impact resistance of spherical shell is the best, while that of cylindrical shell is the worst.

• 대한기계학회논문집
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• 제18권3호
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• pp.600-611
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• 1994

The purpose of this research is to propose a model for the prediction of residual strength. For this purpose, two-paremeter model based on Caprino's is developed and formulated by the ratio of indentation due to impact and normalized residual strength. The damage zone is considered only as an indentation. Impact tests are carried out on laminated composites by steel balls. Test material is carbon/epoxy laminate. The specimens are composed of $[{\pm}45^{\circ}/0^{\circ}/90^{\circ}]_2$ and $[\pm}45^{\circ}]_4$ stacking sequence and have $0.75^T{\times}0.26^W{\times}100^L(mm) dimension. A proposed model shows a good correlation with the experimental results And failure mechanism due to high impact velocity is discussed on CFRP laminates to examine the initiation and development of damage by fractography and ultrasonic image ststem. The effect of the unidirectional ply position on the residual strength is considered here.