• 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.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제28회 춘계학술대회논문집
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• pp.75-78
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• 2007

본 연구에서는 터보 팬 엔진 나셀 복합재 구조의 충격 손상에 관한 연구를 수행하였다. 연구 결과의 신뢰성 검증을 위해 선행 연구된 결과와 비교 분석하였다. 샌드위치 구조의 형상은 카본/에폭시 면재와 폼 코어로 형성되어있다. 샌드위치 패널의 유한 요소 해석 결과 해석 결과의 타당성을 확인하였다. 초기 손상이 발생하는 속도가 평가되었고 예측된 속도에서 충격 해석이 수행되었다. 충격 해석 결과 예측된 충격 손상에서 손상이 발생하는 것으로 확인되었다.

• Steel and Composite Structures
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• 제17권4호
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• pp.387-403
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• 2014

This paper presents a high accuracy Finite Element approach for delamination modelling in laminated composite structures. This approach uses multi-layered shell element and cohesive zone modelling to handle the mechanical properties and damages characteristics of a laminated composite plate under low velocity impact. Both intralaminar and interlaminar failure modes, which are usually observed in laminated composite materials under impact loading, were addressed. The detail of modelling, energy absorption mechanisms, and comparison of simulation results with experimental test data were discussed in detail. The presented approach was applied for various models and simulation time was found remarkably inexpensive. In addition, the results were found to be in good agreement with the corresponding results of experimental data. Considering simulation time and results accuracy, this approach addresses an efficient technique for delamination modelling, and it could be followed by other researchers for damage analysis of laminated composite material structures subjected to dynamic impact loading.

• Advanced Composite Materials
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• 제16권1호
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• pp.45-61
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• 2007

This paper describes a damage accumulation mechanism in cross-ply CFRP laminates $[0_2/90_2]_{2S}$ subjected to out-of-plane loading. Drop-weight impact and static indentation tests were carried out, and induced damage was observed by ultrasonic C-scan and an optical microscope. Both tests gave essentially the same results for damage modes, sizes, and load-deformation history. First, a crack occurred in the bottom $0^{\circ}$ layer accompanying some delamination along the crack caused by bending stress. Then, transverse cracks occurred in the middle $90^{\circ}$ layer with decreasing contact force between the specimen and the indenter. Measured local strains near the impact point showed that the stress state changed from a bending dominant state to an in-plane tensile dominant state. A cohesive interface element was used to simulate the propagation of multiple delaminations and transverse cracks under static indentation. Two types of analytical models are considered, one with multiple delaminations and the other with both multiple delaminations and transverse cracks. The damage obtained for the model with only multiple delaminations was quite different from that obtained from the experiment. However, the results obtained from the model with both delaminations and transverse cracks well explain the characteristics of the damage obtained in the experiment. The existence of the transverse cracks is essential to form the characteristic impact damage.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
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• pp.129-134
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• 2003

The importance of understanding the response of structural composites to impact and CAI cannot be overstated to develop analytical models for impact damage and CAI strength predictions. This paper presents experimental findings observed from quasi-static lateral load tests, low velocity impact tests, CAI strength and open hole compressive strength tests using 3mm thick composite plates ($[45/-45/0/90]_{3s}$ - IM7/8552). The conclusion is drawn that damage areas for both quasi-static lateral load and impact tests are similar and the curves of several drop weight impacts with varying energy levels (between 5.4 J and 18.7 J) fallow the static curve well. In addition, at a given energy the peak force is in good agreement between the static and impact cases. From the CAI strength and open hole compressive strength tests, it is identified that the failure behaviour of the specimens was very similar to that observed in laminated plates with open holes under compression loading. The residual strengths are in good agreement with the measured open hole compressive strengths, considering the impact damage site as an equivalent hole. The experimental findings suggest that simple analytical models for the prediction of impact damage area and CAI strength can be developed on the basis of the failure mechanism observed from the experimental tests.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.244-249
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• 2011

The potential hazards resulting from a low-velocity impact (bird-strike, tool drop, runway debris, etc.) on aircraft structures, such as engine nacelle or a leading edges, has been a long-term concern to the aircraft industry. Certification authorities require that exposed aircraft components must be tested to prove their capability to withstand low-velocity impact without suffering critical damage. In most of the past research studies unloaded specimens have been used for impact tests, however, in reality it is much more likely that a composite structure is exposed to a certain stress state when it is being impacted, which can have a significant effect on the impact performance. And the radiated impact sound induced by impact is analyzed for the damage detection evaluation. In this study, an investigation was undertaken to evaluate the effect in-plane loading on the impact force and sound of composite laminates numerically.

• 대한기계학회논문집
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• 제19권4호
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• pp.1033-1040
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• 1995

To simulate strength reliability and durability of ceramic parts under gas turbine application environments, particle impact damage behaviors in silicon carbide oxidized at 1673 K and 1523 K for 200 hours in atmosphere were investigated. The long-term oxidation produced a slight increase in the static fracture strength. Particle impact caused a spalling of oxide layer. The patterns of spalling and damage induced were dependent upon the property and impact velocity of the particle. Especially, the difference in spalling behaviors induced could be explained by introducing the formation mechanism of lateral crack and elastic-plastic deformation behavior at impact sit. At the low impact velocity regions, the oxidized SiC showed a little increase in the residual strength due to the cushion effect of oxide layer, as compared with the as-received SiC without oxide layer.

• Steel and Composite Structures
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• 제3권4호
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• pp.289-306
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• 2003

A series of tests was conducted to study the behaviour of steel-composite sandwich beams under low velocity hard impact. Damage characteristic and performance of sandwich beams with different spacing of shear connector were evaluated under impact loading. Thin steel plates were used as top and bottom skins of the sandwich beams and plain concrete was used as the core material. Shear connectors were provided by welding of angle sections on steel plates. The sandwich beams were impacted at their midpoint by a hemi-spherical nose shaped projectile dropped from various heights. Strains on steel plates were measured to study the effects of impact velocity or impact momentum on the performance of sandwich beams. Spacing of shear connectors is found to have significant effects on the impact response of the beams.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.2661-2665
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• 2011

In order to evaluate the structural integrity of a GFRP composite bogie frame due to flying railway ballast, the low velocity impact test and compressive test after impact was conducted for glass fiber/epoxy 4-harness satin woven laminate composites applied to skin part of a bogie frame. The impact test was performed using a instrumented impact testing system with energy levels of 5J, 10J and 20J and the designed impactor based on typical railway ballast shapes such as sphere, cube and cone to simulate the ballasted track environments. The compressive strength was tested to according to ASTM D7137 to evaluate the degradation of mechanical property of impact damaged laminate composites. The results showed that the damage area and the degradation of compressive strength after impact for laminate composites was increased with increase in impact energy for all ballast shapes and was particularly most influenced by cone ballast shape.

• 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.