• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.383-388
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• 2001

Effects of particle property variation of cone crack shape according to impact velocity in silicon carbide materials were investigated. The damage induced by spherical impact having different material and size was different according to materials. The size of ring cracks induced on the surface of specimen increased with increase of impact velocity within elastic contact conditions. The impact of steel particle produced larger ring cracks than that of SiC particle. In case of high impact velocity, the impact of SiC particle produced radial cracks by the elastic-plastic deformation at impact regions. Also percussion cone was formed from the back surface of specimen when particle size become large and its impact velocity exceeded a critical value. Increasing impact velocity, zenithal angle of cone cracks in SiC material was linearly decreasing not effect of impact particle size. An empirical equation, $\theta=\theta_{st}-\upsilon_p(180-\theta_{st})(\rho_p/\rho_s)^{1/2}/415$, was obtained from the test data as a function of quasi-static zenithal angle of cone crack($\theta_{st}$), the density of impact particle(${\rho}_p$) and specimen(${\rho}_s$). Applying this equation to the another materials, the variation of zenithal angle of cone crack could be predicted from the particle impact velocity.

• 한국운동역학회지
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• 제21권4호
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• pp.411-420
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• 2011

The purpose of this investigation was to determine whether correlations exist between balance and impact velocity, angular position, and maximum velocity of a club during drive swing. Twelve skilled golfers were recruited in this study. They were asked to perform ten swing trials and two trials were selected for analysis. Balance parameters were calculated via the force platform while kinematic variables were determined by using the Qualisys system. The results of the present study demonstrated that the average of COP velocity was faster in the medio-lateral direction rather than the anterio-posterior direction. Also, left foot's COP velocity and free torque were greater than the right foot's before impact. The range of the right foot's COP in the anterio-posterior direction before impact were correlated with the club velocity and angular position at impact. There was a negative correlation between the left foot's COP velocity before the impact and the velocity at impact. Additionally, the range and RMS of the left foot's free torque affected on the club angular position at impact and the maximum velocity at release, respectively. Finally, a negative correlation existed between the range of the right foot's free torque after the impact and club's maximum velocity at release.

• Journal of Korean Neurosurgical Society
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• 제38권1호
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• pp.41-46
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• 2005

Objective : A study of the histopathologic and neurobehavioral correlates of cortical impact injury produced by increasing impact velocity using the controlled cortical impact[CCI] injury model is studied. Methods : Twenty-four Sprague-Dawley rats [$200{\sim}250g$] were given CCI injury using a pneumatically driven piston. Effect of impact velocity on a 3mm deformation was assessed at 2.5m/sec [n=6], 3.0m/sec [n=6], 3.5m/sec [n=6], and no injury [n=6]. After postoperative 24hours the rats were evaluated using several neurobehavioral tests including the rotarod test, beam-balance performance, and postural reflex test. Contusion volume and histopathologic findings were evaluated for each of the impact velocities. Results : On the rota rod test, all the injured rats exhibited a significant difference compared to the sham-operated rats and increased velocity correlated with increased deficit [p<0.001]. Contusion volume increased with increasing impact velocity. For the 2.5, 3.0, and 3.5m/sec groups, injured volumes were $18.8{\pm}2.3mm^3$, $26.8{\pm}3.1mm^3$, and $32.5{\pm}3.5mm^3$, respectively. In addition, neuronal loss in the hippocampal sub-region increased with increasing impact velocity. In the TUNEL staining, all the injured groups exhibited definitely positive cells at pericontusional area. However, there were no significant differences in the number of positive cells among the injured groups. Conclusion : Cortical impact velocity is a critical parameter in producing cortical contusion. Severity of cortical injury is proportional to increasing impact velocity of cortical injury.

• 대한기계학회논문집A
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• 제26권2호
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• pp.380-386
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• 2002

Damage behaviors induced in silicon carbide by an impact of particle having different material and size were investigated. Especially, the influence of the impact velocity of particle on the cone crack shape developed was mainly discussed. The damage induced by spherical impact was different depending on the material and size of particles. Ring cracks on the surface of specimen were multiplied by increasing the impact velocity of particle. The steel particle impact produced larger ring cracks than that of SiC particle. In the case of high velocity impact of SiC particle, radial cracks were produced due to the inelastic deformation at the impact site. In the case of the larger particle impact, the damage morphology developed was similar to the case of smaller particle one, but a percussion cone was farmed from the back surface of specimen when the impact velocity exceeded a critical value. The zenithal angle of cone cracks developed into SiC material decreased monotonically with increasing of the particle impact velocity. The size and material of particle influenced more or less on the extent of cone crack shape. An empirical equation, $\theta$= $\theta$$\sub$st/, v$\sub$p/(90-$\theta$$\sub$st/)/500 R$\^$0.3/($\rho$$_1$/$\rho$$_2$)$\^$$\frac{1}{2}$/, was obtained as a function of impact velocity of the particle, based on the quasi-static zenithal angle of cone crack. It is expected that the empirical equation will be helpful to the computational simulation of residual strength in ceramic components damaged by the particle impact.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.284-288
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• 2003

This study was investigated the nondestructive characteristics of the damage caused by low-velocity impact on symmetric cross-ply laminates. These laminates were $[0^{\circ}/90^{\circ}]{_{16s,}}\;{_{24s,}}\;{_{32s,}}\;{_{48s}}$, that is, the thickness was 2, 3, 4 and 6 mm. The impact machine, model 8250 Dynatup Instron, was used a drop-weight type with gravity. The impact velocities used in experiment were 0.75, 0.90, 1.05, 1.20 and 1.35 m/sec. The load and deformation were increased as impact velocity increase. Even if the load increased with laminates thickness in same impact velocity, the deformation decreased. The extensional velocity was a quick as laminate thickness increase in same impact velocity and as impact velocity increase in same laminate thickness. In ultrasonic scans, damaged area was represented an dimmed zone. This is due to the fact that the wave, after having been partially reflected by the defects, has not enough energy to tough the oposite side or to come back from it. The damaged laminate areas were different according to the laminate thickness and the impact velocity. The extensional velocities became lower in if direction and higher in $0^{\circ}$ direction when the size of the defects increases. But, it was difficult to draw any conclusion for the extensional velocities in $45^{\circ}$ direction.

• 한국해양공학회지
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• 제19권1호
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• pp.39-43
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• 2005

The study investigated the nondestructive characteristics of damage, caused by law-velocity impact, on symmetric cross-ply laminates, composed of [0o/90o]16s, 24s, 32s, 48s. The thickness of the laminates was 2, 3, 4 and 6 mm, respectively. The impact machine used, Model 8250 Dynatup Instron, was a drop-weight type that employed gravity. The impact velocities used in this experiment were 0.75, 0.90, 1.05, 1.20 and 1.35 m/sec, respectively. Both the load and the deformation increased when the impact velocity was increased. Further, when the load increased with the laminate thickness in the same impact velocity, the deformation still decreased. The extensional velocity was quick, as the laminate thickness increased in the same impact velocity and the impact velocity increased in the same laminate thickness. In the ultrasonic scans, the damaged area represented a dimmed zone. This is due to the fact that the wave, after the partial reflection by the deflects, does not have enough energy to touch the opposite side or to come back from it. The damaged laminate areas differed, according to the laminate thickness and the impact velocity. The extensional velocities are lower in the 0o direction and higher in the 90o direction, when the size of the defect increases. However, it was difficult to draw any conclusion for the extensional velocities in the 45o direction.

• 한국항공우주학회지
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• 제50권7호
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• pp.465-470
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• 2022

본 논문은 알루미늄 6061의 고속 충격 해석과 고속 충격 시험 결과를 비교 검증하여 금속 재료의 고속 충격에 의한 거동 특성을 연구하였다. 고속 충격 해석을 위해 만능재료시험기를 이용한 준정적 시험과 Hopkinson bar를 이용한 동적 시험을 통해 Huh-Kang 모델과 Johnson-Cook 파손 모델의 계수를 구했다. LS-DYNA 프로그램 해석을 이용하여 관통 속도와 형상을 결과로 예측했고 고속 충격 시험기를 이용한 시험 결과와 비교하였다. 이를 바탕으로 항공기 가스터빈 엔진 블레이드 컨테인먼트 평가 연구에 적용하고자 한다.

• International Journal of Aeronautical and Space Sciences
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• 제14권2호
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• pp.140-145
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• 2013

The development of high performance fabrics have advanced body armor technology and improved ballistic performance while maintaining flexibility. Utilization of the shear thickening phenomenon exhibited by Shear Thickening Fluids (STF) has allowed further enhancement without hindering flexibility of the fabric through a process of impregnation. The effect of STF impregnation on the ballistic performance of fabrics has been studied for impact velocities below 700 m/s. Studies of STF-impregnated fabrics for high velocity impacts, which would provide a transition to significantly higher velocity ranges, are lacking. This study aims to investigate the effect of STF impregnation on the high velocity impact characteristics of Kevlar fabric by effectively dispersing silica nanoparticles in a suspension, impregnating Kevlar fabrics, and performing high velocity impact experiments with projectile velocities in the range of 1 km/s to compare the post impact characteristics between neat Kevlar and impregnated Kevlar fabrics. 100 nm diameter silica nanoparticles were dispersed using a homogenizer and sonicator in a solution of polyethylene glycol (PEG) and diluted with methanol for effective impregnation to Kevlar fabric, and the methanol was evaporated in a heat oven. High velocity impact of STF-impregnated Kevlar fabric revealed differences in the post impact rear formation compared to neat Kevlar.

• 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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.228-233
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• 2001

It is well known that composite laminates are easily damaged by low velocity impact. The damage of composite laminates subjected to impact loading are occurred matrix cracking, delamination, and fiber breakage. The damage of matrix cracking and delamination are reduced suddenly the compressive strength after impact. This study is to evaluate impact characteristics and the relationship between impact force and inside damage of composite laminates by low velocity impact loading. UT C-scan is used to determine impact damage areas by impact loading.