Effect of velocity variation on carbon/epoxy composite damage behavior

Baluch, Abrar H,Kim, Chun Gon SAGE Publications 2016 Journal of composite materials Vol.50 No.15

<P>In this paper, the damage mechanism for carbon fiber-reinforced polymers composites was studied from low- to high-velocity impact for different velocity ranges. Initially, the composites were manufactured by using CU125NS prepreg in quasi-isotropic 16 layers pattern [0/+/- 45/90](2s) in autoclave by adopting standard procedures. Specimens were also exposed to the simulated LEO environment and 0.42% total mass loss occurred due to out-gassing. Afterwards, the specimens were impacted with Al2017-T4 spherical projectiles of 5.56mm in diameter, 0.25g in weight for different velocities ranging from 500m/s to 2200m/s. With the impact velocity increase, the energy absorption was found to increase in the composite specimens, while the ratio of energy absorbed to total impact energy remains the same on average. Mainly, the fiber breakage and matrix fracture play a critical role in energy absorption, but delamination contribution also found increasing trend with the increase of impactor velocity. Afterwards, C-SCAN analyses were conducted to investigate the damage patterns, and it was found that the damage area increased with higher velocities. The delamination contribution increased on average by 12.7% for the velocity range of 2200m/s in comparison to that for 502m/s. On the basis of these findings, it was concluded that the contribution of fiber breakage, matrix fracture and delamination towards the damage mechanism of composites is greater for higher velocities.</P>

Behavior of composite structures orientations towards their failure and damage

Baluch, Abrar H,Kim, CG SAGE Publications 2015 Journal of composite materials Vol.49 No.29

<P>In this paper, carbon/epoxy composites were employed as a potential candidate for spacecraft structural shielding along with the new concept of geometric configurations according to the threat severity to maximize the impactor energy absorption to improve performance. Carbon/epoxy composites of quasi-isotropic 16 layers [0/ ± 45/90]<SUB>2s</SUB> were manufactured using an autoclave, and the specimens were exposed to a low Earth orbit environment, which produced an average total mass loss of 0.42%, mainly due to outgassing. Al2017-T4 spherical projectiles with a diameter of 5.56 mm weight of 0.25 g were used as the impactor in the velocity range of 1500 ± 500 m/s. Earlier experimentations showed the superiority of obliquity towards energy absorption for single bumpers. Double bumpers with one 45° obliquity at 100 mm standoff absorbed 14% more specific energy than double bumpers with one at 30°; both of them were found to be superior to normal–normal bumpers by 40% and 30% on average, respectively. By CSCAN, it was also found that oblique impact on the first bumper resulted in less damage on the rear bumper and resulted in the superiority of the proposed geometric configurations, which enabled enhanced protection and designs according to threat severity.</P>

수중 불분리성 그라우트 개발 기술 동향

( Khaqan Baluch ),김정규 ( Jung-gyu Kim ),김종관 ( Jong-gwan Kim ),유지윤 ( Ji-yun Yu ),양형식 ( Hyung-sik Yang ) 대한화약발파공학회 2020 화약발파 Vol.38 No.4

수중 불분리성 그라우트는 수중 현장에 광범위하게 사용된다. 그러나 접합강도, 펌프 능력 및 강도 손실과 같은 주요 문제점이 여전히 존재한다. 본 연구에서는 자기충전, 비파괴 방지 그라우트 연구에 기초하여 이 분야의 현황을 파악하기 위해 수중 시공 및 카르스트 공동 실링에 관한 연구 동향에 대해 검토하였다. 그라우트를 수중에 사용할 경우, 공기 중에서 시공하는 것에 비해 강도와 접합강도가 손실될 것이다. 이를 방지하기 위해 고점도의 그라우트를 통해 카르스트 공동을 실링하고 있지만, 대심도에서는 그라우트의 펌핑 능력에 심각한 문제를 발생시키므로 기존의 수중 불분리성 그라우트와 콘크리트는 대심도 환경에 적합하지 않음을 의미한다. Although anti-washout grouts are used extensively in underwater targets, major constraints continue to be associated with their use. These include poor bonding strength, poor pumpability, and loss of high strength in everyday engineering applications. In this study, based on the literature pertaining to self-compacted, non-dispersive, anti-washout grouts, a review of research trends in anti-washout grouts for underwater construction and sealing of karst cavities was carried out in order to determine the problems faced in this field. Grouts used under water suffer a loss of strength and bonding strength in comparison to grouts cast in air. Researchers are designing high-viscosity grouts to overcome the inrush of water and seal karst cavities; however, in doing so, they have inadvertently caused serious problems pertaining to the pumpability of these grouts and concretes in deep target locations. Thus, the majority of the anti-washout grouts and concretes that have been developed are not applicable to deep target environments, instead being suitable for only near-surface targets.

An Experimental and Numerical Study on the Stemming Effect of a Polymer Gel in Explosive Blasting

Khaqan Baluch,김정규,고영훈,김승준,정승원,양형식,김용기,김종관 대한화약발파공학회 2018 화약발파 Vol.36 No.4

In this study, several concrete-block blast tests and AUTODYN numerical analyses were conducted to analyze the effects of different stemming and coupling materials on explosion results. Air, sand, and polymer gel were used as both the stemming and coupling materials. The stemming and coupling effects of these materials were compared with those of the full-charge condition. Soil-covered or buried concrete blocks were used for field crater tests. It was found from the concrete block tests and numerical analyses that both the crater size and the peak pressure around the blast hole were higher when the polymer gel was used than when the sand and the decoupling condition were used. The numerical analyses revealed the same trend as those of the field tests. Pressure peaks in concrete block models were calculated to be 37, 30, and 16 MPa, respectively, for the cases of the polymer gel, sand, and no stemming and decoupling condition. The pressure peak was 52 MPa in the case of full-charge condition, which was the highest pressure. But the damage area for the case was smaller than that obtained from the use of polymer gel. Full-charge was also used as a reference test.

발파공 내 전색물의 커플링 효과에 대한 AUTODYN 수치해석

( Khaqan Baluch ),고영훈 ( Young Hun Ko ),양형식 ( Hyung-sik Yang ) 대한화약발파공학회 2017 화약발파 Vol.35 No.3

전색물 충전이 발파공에서 주변 암반으로 압력파를 전달하는 데 미치는 영향을 AUTODYN으로 해석하고 비교하였다. 공기, 모래, 물, 10%와 20% 젤라틴의 다섯 전색물을 선정하였다. 수치해석 결과 발파공 주변의 관측점은 전색물에 따라 각각 다른 압력을 보였으며 고압일수록 파쇄도가 높은 것으로 간주하였을 때 20% 젤라틴이 가장 나은 것을 알 수 있었다. 따라서 젤라틴은 충전재로서 모래나 물 이상의 효과를 나타내는 것으로 확인되었다. Coupling effects of the stemming materials for single borehole were studied by AUTODYN analysis and compared to understand the role of different stemming materials on transmitting the pressure from blasthole to the surrounding rocks. Five different material properties, air, sand, water, 10% and 20% gelatin were selected. Authors assumed that high pressure detected in borehole means better fragmentation. Simulations show that these coupling materials lead to different level of pressure in the blasting hole and 20% gelatin turns out to be highest among them. Results show that gelatin can be used as better coupling material than sand or water.

Numerical Study on the Effects of Air Decking in Half Charge Blasting Using AUTODYN

Khaqan Baluch,김정규,김승준,Jin Guochen,정승원,양형식,김남수,김종관 대한화약발파공학회 2018 화약발파 Vol.36 No.4

This numerical study was intended to evaluate the applicability of the half charge blasting to mining and tunnelling. The half charge blasting is a method that two separate rounds are sequentially blasted for the rock burdens in which long blast holes have already been drilled at one operation. The aim of the method is to decrease the construction cost and period in mining and tunnelling projects as well as to increase the blasting efficiency. Several numerical analyses were conducted by using the Euler-Lagrange solver on ANSYS AUTODYN to identify the effects of the suggested method on the blasting results in underground excavations. The overall performance of the suggested method was also compared to an ordinary blasting method. The analysis model was comprised of the Eulerian parts (explosive, air, and stemming materials) and the Lagrangian parts (rock material). As a result, it was found that, owing to the air decks formed in the bottom parts of the long blast holes, the first round of the suggested method presented a higher shock pressure and particle velocities in the vicinity of the blast holes compared to the ordinary blasting method.

Space debris hypervelocity impact on carbon/epoxy spacecraftcomposite structures: Experiments and simulations

A.H.Baluch,Yurim Park,YunHo Kim,C.G.Kim 한국항공우주학회 2013 한국항공우주학회 학술발표회 논문집 Vol.2013 No.4

Hypervelocity impact of space debris is a serious concern for spacecraft shielding system. For this advanced composite materials being utilized in this research for the protection of spacecraft in low Earth orbit region instead of conventional alloys. Afterwards results being validated by using LS-DYNA software. CU125NS prepreg was selected being superior on the basis of previous experimentations, with the stacking sequence of [(0/45/90)₂]s in 16layers. After manufacturing in autoclave, specimens were exposed to LEO environment founding 0.40% total mass loss. Lastly, specimens were being impacted in double configurations by using light gas gun in the velocity range of 1500±500m/s. Postexperimental analysis were done by using C-SCAN and found the main contribution of epoxy and fiber towards energy absorption. In the end, LSDYNA is used with its special SPH module to simulate the hypervelocity impact scenarios and energy absorption patterns and found to be on average 28% deviates from experimental results.

High Velocity Impact Characteristics of Shear Thickening Fluid Impregnated Kevlar Fabric

Park, Yurim,Baluch, Abrar H.,Kim, YunHo,Kim, Chun-Gon The Korean Society for Aeronautical and Space Scie 2013 International Journal of Aeronautical and Space Sc Vol.14 No.2

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.

Personality differences amongst drag racers and archers: implications for sport injury rehabilitation

Rhonda Cohen,Bahman Baluch,Linda J. Duffy 한국운동재활학회 2018 JER Vol.14 No.5

Effects of physical activity on debilitating behaviours in 13- to 20-year-old males with severe autism spectrum disorder

Linda Duffy,Bahman Baluch,Sarah Welland,Evren Raman 한국운동재활학회 2017 JER Vol.13 No.3

The presented study investigated the extent to which engaging in a therapeutic sporting programme in males with severe autism spectrum disorder (ASD) improves the debilitating behaviours commonly associ-ated with ASD. Furthermore, the views of parents of the autistic partici-pants were assessed concerning the effectiveness of the programme. Participants were eight 13- to 20-year-old males born in the United Kingdom from a school and sports college for pupils with severe learn-ing difficulties. The selection was using volunteer sampling from the “Monday Club” initiative, run by Saracens Sports Foundation in part-nership with a local school and specialist sports college. The Gilliam Autism Rating Scale, 3rd edition was administered to identify and mea-sure the severity of ASD behaviours at four time periods namely: at pro-gramme entry as the baseline (Time 1, T1), a second time after 8 weeks (Time 2, T2), a third time after 16 weeks (Time 3, T3), and a fourth time post programme (Time 4, T4). The results showed that for the more se-vere cases of ASD (Autism Index >101) there was no positive change in subscale performance from T1 to T2. For milder cases (Autism Index, 71.100) there were subtle non-significant improvements on the sub-scale scores from T1 to T2. Of the 6 subscales at T2, emotional respons-es, cognitive style, and maladaptive speech approached significance at the P=0.05 level. At T3 and T4, there was also no statistically significant improvement in ASD behaviours compared to the baseline for either condition. Finally parents’ were “very satisfied” with their child’s partici-pation in the physical activity programme.