• 대한기계학회논문집A
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• 제20권6호
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• pp.1903-1912
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• 1996

A quantitative study of impact damage of a soda-lime glass was carried out. An initiation and a propagation of cracks by the impact of two inds of steel ball was investigated. The fron, side and rear view of cracks were observed by a stereo-microscope. And the lowering of the benidng strength due to the impact of steel balls was examined through the 4-point bending test. A transparent glass is very helpful to understand and analyze the impact damage behavior of another brittle matereial. A deagdram about crack patterns according to the threshold impact velocity was sketched. A ring crack and a cone crack were formed at the low impact velocity. And as the impact velocity was higher, initial lateral crack was generated on the slanting surface of cone crack, and radial cracks were generated from the outermost ring crack. When the impact velocity of steel balls exceed a critical velocity, the contact site of specimens were crushed. According to the propagation of a cone crack, a rapid strength degradation occurred. In the specimen having crushed region, a bending strength was converged to a constant value instead of strength degradation.

• 한국정밀공학회지
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• 제27권2호
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• pp.94-101
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• 2010

Composite materials have a higher specific strength and modulus than traditional metallic materials. Additionally, these materials offer new design flexibilities, corrosion and wear resistance, low thermal conductivity and increased fatigue life. These, however, are susceptible to impact damage due to their lack of through-thickness reinforcement and it causes large drops in the load-carrying capacity of a structure. Therefore, the impact damage behavior and subsequently load-carrying capacity of impacted composite materials deserve careful investigation. In this study, the residual strength and impact characteristics of plain-woven CFRP composites with impact damage are investigated under axial tensile test. Impact test was performed using drop weight impact tester. And residual strength behavior by impact was evaluated using the caprino model. Also we evaluated behavior of residual strength by change of mass and size of impactor. Examined change of residual strength by impact energy change through this research and consider impactor diameter in caprino model.

• Steel and Composite Structures
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• 제19권2호
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• pp.417-439
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• 2015

Many methods are developed for strengthening of reinforced concrete structural members against the effects of shear. One of the commonly used methods in recent years is turned out to be bonding of fiber reinforced polymers (FRP). Impact loading is one of the important external effects on the reinforced concrete structural members during service period among the others. The determination of magnitude, the excitation time, deformations and stress due to impact loadings are complicated and rarely known. In recent year impact behavior of reinforced concrete members have been researched with experimental studies by using drop-weight method and numerical simulations are done by using finite element method. However the studies on the strengthening of structural members against impact loading are very seldom in the literature. For this reason, in this study impact behavior of shear deficient reinforced concrete beams that are strengthened with carbon fiber reinforced polymers (CFRP) strips are investigated experimentally. Compressive strength of concrete, CFRP strips spacing and impact velocities are taken as the variables in this experimental study. The acceleration due to impact loading is measured from the specimens, while velocities and displacements are calculated from these measured accelerations. RC beams are modeled with ANSYS software. Experimental result and simulations result are compared. Experimental result showed that impact behaviors of shear deficient RC beams are positively affected from the strengthening with CFRP strip. The decrease in the spacing of CFRP strips reduced the acceleration, velocity and displacement values measured from the test specimens.

• Structural Engineering and Mechanics
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• 제85권6호
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• pp.755-764
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• 2023

The article examines the impact response of the sandwich beam furnished by a novel bilayer core as inspired by the woodpecker's head architecture under different repeatedly exerted low-velocity impact loadings by employing the finite element package, ABAQUS. The sandwich beam forms four essential parts comprising bottom and top carbon fiber reinforced polymer laminates encasing bilayer core made of laterally arched solid hot melt adhesive material and aluminum honeycomb. Impact loadings are implemented repeatedly with a steel hemisphere impactor for various impact energies, 7.28 J, 9.74 J, and 12.63 J. Essentially, the commonly concentrated stresses at the impact region are regulated away by the arched core in all considered cases thus reducing the threat of failure. The sandwich beam can resist up to 5 continual impacts at 7.28 J and 9.74 J but only up to 3 times repeated loads at 12.63 J before visible failure is noticed. In the examination of several key impact performance indicators under numerous loading cases, the proposed beam demonstrates favorably up to 1.3-11.2 higher impact resistance efficacies compared to existing designs, therefore displaying an improvement in repeated impact resistance of the new design.

• 한국정밀공학회지
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• 제25권8호
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• pp.80-87
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• 2008

This paper investigated into the impact characteristics of the stainless sheet with thickness of 0.7 mm on the stretching boundary condition through three-dimensional finite element analysis. High speed tensile tests were carried out to obtain strain-stress relationships with the effects of the strain rate. The FE analysis was performed by the ABAQUS explicit code. In order to improve an accuracy of the FE analysis, the hyper-elastic model and the damping factor were introduced. Through the comparison of the results of the FE analyses and those of the impact tests, a proper FE model was obtained. The results of the FE analyses showed that the absorption rate of energy maintains almost 82.5-83.5% irrespective of the impact energy level and the diameter of the impact head. From the results of FE analyses, variations of stress, strain, dissipation energy, strain energy density, and local deformation characteristics in the stainless sheet during the collision and the rebound of the impact head were quantitatively examined. In addition, it was shown that the fracture of the specimen occurs when the plastic strain is 0.42 and the maximum value of the plastic dissipation energy of the specimen is nearly 1.83 J.

• 한국산학기술학회논문지
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• 제11권8호
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• pp.2741-2749
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• 2010

본 논문은 필라멘트 와인딩 공법으로 제조된 복합재 압력용기의 충격손상 및 이에 대한 표면 보호재료의 영향을 평가한 것이다. 낙하식 충격시험기를 이용하여 기본 패널과 보호재료(고무, kevlar/epoxy 및 glass/epoxy)가 표면에 접착되어 있는 보호 패널에 대한 저속 충격시험을 실시하였다. 복합재 압력용기의 손상 저항성에 대한 표면 보호재료의 영향을 정량화하기 위하여 충격손상 파라미터를 도입하였다. 복합재 압력용기의 손상 저항성은 충격압자의 형상과 관계없이 표면 보호재료의 영향을 크게 받았으며 이러한 표면 보호재료중 glass/epoxy가 가장 큰 보호효과를 나타내었다.

• Composites Research
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• 제28권2호
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• pp.58-64
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• 2015

본 논문에서는 샌드위치 복합재 패널로 제작되는 사용후 핵연료 수송용기 충격완충체의 유효등가 유한 요소모델을 제시하는데 목적을 둔다. 샌드위치 복합재 패널은 금속재 면재와 각각 우레탄 폼, 발사목 그리고 레드우드 심재로 구성되었다. 충격완충체의 유효등가 유한요소 모델은 샌드위치 복합재 패널의 저속충격 시험과 해석결과와의 비교를 통해 제시되었으며, LS-DYNA 3D를 사용한 동적 외연 유한요소해석에 의해 수행되었다. 시험과 해석 결과, 충격완충체 샌드위치 패널의 유한요소 모델은 적층쉘 요소의 면재와 솔리드요소의 심재를 사용한 기존의 혼합모델링 기법에 비해 면재와 심재 모두 솔리드 요소를 적용하는 방법이 더 정확한 결과를 나타냄을 확인하였다. 이때 발사목과 레드우드 심재는 요소제거 기능을 갖는 솔리드 요소로 모델링 되는 것이 추천되어진다.

• 대한금속재료학회지
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• 제47권3호
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• pp.155-168
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• 2009

In this study, microstructural investigation was conducted on the separation phenomenon occurring during Charpy impact tests of API X80 linepipe steels. Particular emphasis was placed on the role of microstructural phases present in the API X80 steels such as acicular ferrite, bainite, and hard secondary phases. Detailed microstructural analysis of fractured impact specimens showed that highly elongated bainite worked as prior initiation sites for separations, and that the number and length of separations increased with increasing volume fraction of bainite. In the steels having high work hardenability, tearing-shaped separations were found because the hammer-impacted region was seriously hardened during the impact test, which led to the reduction in the impact toughness. As the test temperature decreased, the tendency of separations increased, but separations were not observed when the cleavage fracture prevailed at very low temperatures. Thus, the minimization of the formation of bainite and secondary phases in the steels would be beneficial for preventing or minimizing separations because separations deteriorated low-temperature impact toughness.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.64-66
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• 2005

In order to evaluate impact characteristics for the laminates with or without delaminations, carbon fiber/epoxy laminated composite were fabricated. After trying several ways to develop delaminations within the laminates, an insertion of teflon-tape was found to be most effective. The locations for delamination was determined after several trial-and-error experiments. The low impact energy did not produce measurable difference for composites with or without delamination, which indicated the presence of impact energy threshold. The impact chacteristics for composites with the delamination were found to be different from those for composites with other type of defect including fiber failures.

• International Journal of Safety
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• 제1권1호
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• pp.7-12
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• 2002

This paper demonstrates the impact stresses and wave propagation characteristics of glass/epoxy laminates subjected to the low-velocity impact by a steel ball theoretically and experimentally. A plate finite element model in conjunction with experimental contact laws is used for the theoretical investigation. The specimens for statical indentation and impact test are composed of $[0/45/0/-45/0]_28 and [90/45/90/-45/90]_28$ stacking sequences and have clamped-simply supported boundary conditions. Finally, these two results are compared and then the impulsive stress and wave propagation characteristics of this laminated composite are studied.