• Composites Research
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• 제25권5호
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• pp.147-153
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• 2012

본 논문에서는 복합재 적층판의 고속충격 관통에너지를 예측하는 방법 중 하나인 정적압입 관통 실험을 수행하였다. 정적압입 관통 에너지를 정확히 분석하기 위해서 세 가지 방법을 이용하였다. 첫 번째로 AE 센서 신호 변화를 이용해서 압입 관통 지점을 판단하고 관통 에너지를 구하는 방법, 두 번째는 관통된 시편에 다시 관통실험을 수행하여 두 에너지 차를 이용해서 구하는 방법, 세 번째는 재수행한 관통실험의 하중-변위 그래프에서 최대하중지점을 압입 관통 지점으로 판단하고 에너지를 구하는 방법이다. 위 방법들에 의한 관통에너지 예측 결과를 제시하였고 고속충격 실험 결과와 비교하여 타당성을 검증하였다.

• Structural Engineering and Mechanics
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• 제43권2호
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• pp.199-209
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• 2012

Two carbon fiber composite laminates, $[0/90]_{2S}$ and $[0/+45/90/-45]_S$, were considered in this work to find out the perforation threshold energy to complete the perforation process and the corresponding maximum contact force. Explicit finite element commercial software, LS-DYNA, was used to predict these values. According to the simulation results, these two types of composite laminates were tested by using a vertical drop-weight testing machine. After testing, the damage condition of these specimens were observed and compared with the results from finite element analysis. The testing results indicate that the perforation threshold energy is 6 Joules for $[0/90]_{2S}$ and 7 Joules for $[0/+45/90/-45]_S$, which is in good agreement with the simulation results. Also, the maximum contact force at the case of perforation threshold energy is the lowest as compared to the maximum contact forces occurring at the impact energy that is larger or less than the perforation threshold energy.

• Composites Research
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• 제26권1호
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• pp.21-28
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• 2013

본 논문에서는 유효 면적의 제한이 있는 복합재 적층판의 탄도한계속도를 예측하였다. 탄도한계속도를 예측하기 위해 정적압입 관통실험과 고속충격 실험 그리고 준실험식을 이용하였다. 정적압입 관통실험을 통해 하중-변위 데이터를 취득하고 이를 이용해서 관통에너지를 측정하였다. 고속충격 실험을 통해 실제 관통 속도 및 관통 에너지를 측정하였다. 정적압입 관통실험과 고속충격 실험을 통해 구한 에너지를 이용해 준실험식을 만들고, 준실험식과 고속충돌 실험결과와 비교해 보았다. 위 방법을 이용해 탄도한계속도를 예측하였고 정적압입 관통 실험과 준실험식에 의한 탄도한계속도 예측의 타당성을 확인하였다.

• 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.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2004년도 춘계학술대회 논문집
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• pp.95-99
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• 2004

본 연구에서는 충돌문제에 있어서 비교적 높은 활용도를 지니고 있는 범용 유한요소해석코드 LS-DYNA3D를 사용해 판부재에 충돌체가 충돌하는 경우, 내충돌성을 평가하였다. 속도가 41.56m／s-118.9m／s로 비교적 고속인 충돌문제부터 속도가 544.05m／s-800m／s인 초고속 충돌문제까지 시리즈 해석을 하였다. 이를 통해 판부재에 다양한 속도의 충돌체가 충돌하는 경우에 있어 피충돌체의 관통 유무를 평가할 수 있는 경험식을 구하고자 한다.

• Composites Research
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• 제26권3호
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• pp.175-181
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• 2013

고속충격을 받는 복합재 적층판의 충격거동 특성 중에서 관통 후 잔류속도, 시편에 의한 충격흡수에너지 그리고 충격손상영역에 대한 평가와 예측이 중요하다. 본 논문에서는 고속충격을 받는 Carbon/Epoxy 복합재 적층판의 잔류속도와 흡수에너지를 준실험적 방법을 통하여 예측할 수 있는 방법을 제안하였다. 고속충격에 의한 시편의 흡수에너지를 정적에너지와 동적에너지로 구분하였으며 정적에너지는 보강섬유의 파손과 정적 탄성에너지와 관련 있는 준정적압입실험을 통한 관통에너지를 사용하였다. 동적에너지는 고속충격 시 시편 일부의 움직임과 관련한 운동에너지에 대하여 몇 가지 모델을 제안하여 비교하였다. 공압을 이용한 고속충격실험을 수행하고 예측 값과 비교 분석하였다. 시편의 손상영역은 C-scan을 통하여 측정하였다. 관통한계속도보다 큰 초기 속도인 경우, 정적에너지인 관통에너지 뿐 만 아니라 시편의 동적 에너지가 시편 전체 흡수에너지에 크게 기여함을 알 수 있었다.

• Earthquakes and Structures
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• 제20권4호
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• pp.377-388
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• 2021

Thin perforated Steel Plate Shear Walls (SPSWs) are among the most common types of seismic energy dissipation systems to protect the main boundary components of SPSWs from fatal fractures in the high-risk zones. In this paper, the cyclic behavior of the different circular hole patterns under cyclic loading is reported. Based on the experimental results, it can be concluded that a change in the perforation pattern of the circular holes leads to a change in the locations of the fracture tendency over the web plate, especially at the plate-frame interactions. Accordingly, the cyclic responses of the tested specimens were simulated by finite element method using the ABAQUS package. Likewise, perforated shear panels with a new perforation pattern obtained by implementing Topology Optimization (TO) were proposed. It was found that the ultimate shear strength of the specimen with the proposed TO perforation pattern was higher than that of the other specimens. In addition, theoretical equations using the Plate-Frame Interaction (PFI) method were used to predict the shear strength and initial stiffness of the considered specimens. The theoretical results showed that the proposed reduced coefficients relationships cannot accurately predict the shear strength and initial stiffness of the considered perforated shear panels. Therefore, the reduced coefficients should be adopted in the theoretical equations based on the obtained experimental and numerical results. Finally, with the results of this study, the shear strength and initial stiffness of these types of perforated shear panels can be predicted by PFI method.

• 한국자동차공학회논문집
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• 제3권5호
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• pp.38-46
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• 1995

In this paper, an experimental study on the effects of the impact damage and the perforation characteristic of CFRP laminates with different fiber stacking orientation and ply number was done through an observation of interrelations between the impact energy vs. transmitted energy and the impact energy vs. absorbed energy per unit volume. The velocities of the ball before or after impact are measured by the high-speed camera. And when CFRP laminates are subjected to tranverse impact by a steel ball(${\phi}10$), the delamination shapes generated by impact damage are observed by using SAM (Scanning acoustic Microscope).

• Steel and Composite Structures
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• 제36권2호
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• pp.143-161
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• 2020

In nanosized structures as the surface area to the bulk volume ratio increases the classical continuum mechanics approaches fails to investigate the mechanical behavior of such structures. In perforated nanobeam structures, more decrease in the bulk volume is obtained due to perforation process thus nonclassical continuum approaches should be employed for reliable investigation of the mechanical behavior these structures. This article introduces an analytical methodology to investigate the size dependent, surface energy, and perforation impacts on the nonclassical bending behavior of regularly squared cutout nanobeam structures for the first time. To do this, geometrical model for both bulk and surface characteristics is developed for regularly squared perforated nanobeams. Based on the proposed geometrical model, the nonclassical Gurtin-Murdoch surface elasticity model is adopted and modified to incorporate the surface energy effects in perforated nanobeams. To investigate the effect of shear deformation associated with cutout process, both Euler-Bernoulli and Timoshenko beams theories are developed. Mathematical model for perforated nanobeam structure including surface energy effects are derived in comprehensive procedure and nonclassical boundary conditions are presented. Closed forms for the nonclassical bending and rotational displacements are derived for both theories considering all classical and nonclassical kinematics and kinetics boundary conditions. Additionally, both uniformly distributed and concentrated loads are considered. The developed methodology is verified and compared with the available results and an excellent agreement is noticed. Both classical and nonclassical bending profiles for both thin and thick perforated nanobeams are investigated. Numerical results are obtained to illustrate effects of beam filling ratio, the number of hole rows through the cross section, surface material characteristics, beam slenderness ratio as well as the boundary and loading conditions on the non-classical bending behavior of perforated nanobeams in the presence of surface effects. It is found that, the surface residual stress has more significant effect on the bending deflection compared with the corresponding effect of the surface elasticity, Es. The obtained results are supportive for the design, analysis and manufacturing of perforated nanobeams.

• Structural Engineering and Mechanics
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• 제77권3호
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• pp.329-342
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• 2021

In this paper, the effect of different steel bar configurations on the quasi-static punching and impact response of concrete slabs was studied. A total of forty RC square slab specimens were cast in two groups of concrete strengths of 40 and 63 MPa. In each group of twenty specimens, ten specimens were reinforced at the back face (singly reinforced), and the remaining specimens were reinforced on both faces of the slab (doubly reinforced). Two rebar spacing of 25 and 100 mm, with constant reinforcement ratio and effective depth, were used in both singly and doubly reinforced slab specimens. The specimens were tested against the normal impact of cylindrical projectiles of hemispherical nose shape. Slabs were also quasi-statically tested in punching using the same projectile, which was employed for the impact testing. The experimental response illustrates that 25 mm spaced rebars are effective in (i) decreasing the local damage and overall penetration depth, (ii) increasing the absorption of impact energy, and (iii) enhancing the ballistic limit of RC slabs. The ballistic limit was predicted using the quasi-static punching test results of slab specimens showing a strong correlation between the dynamic perforation energy and the energy required for quasi-static perforation of slabs.