• Composites Research
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• v.15 no.2
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• pp.11-17
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• 2002

The piezoelectric thin film sensor can be used to interpret variations in structural and material properties, e.g. for structural integrity monitoring and assessment. To illustrate one of this potential benefit, PVDF (polyvinylidene fluoride) film sensors are used for monitoring impact damage in Gr/Ep composite panels. Both PVDF film sensors and strain gages are attached to the surface of Gr/Ep specimens. A series of impact tests at various impact energy by changing impact mass the height are performed on the instrumented drop weight impact tester. The sensor responses are carefully examined to predict the onset of impact damage such as indentation, matrix cracking, and delamination, etc. Test results show that the particular waveforms of sensor signals implying the damage initiation and development are detected above the damage initiation impact energy. As expected, the PVDF film sensor is found to be more sensitive to impact damage initiation event than the strain gage.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.237-247
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• 1993

Carbon fiber reinforced plastics(CFRP) have gained increased application in aerospace structures because of their specific strength and stiffness, but are sensitive to impact-induced damage. An experimental investigation was carried out to evaluate the impact resistance of CFRP according to the ply angle. The specimens of angle ply laminate composites were employed with [0.deg. $_{6}$/ .deg.$_{10}$/0.deg.$_{6}$], in which 6 kinds of ply angle such as .deg.=15.deg., 30.deg., 45.deg., 60.deg., 75.deg. and 90.deg. were selected. The impact tests were conducted using the air gun type impact testing machine by steel balls of diameter of 5 mm and 10 mm, and impact-induced damages were evaluated under same impact speed of V=60m/s. The impact damaged zones were observed through a scanning acoustic microscope (SAM). The obtained results were summarized as follows: (1) Delaminations on the interfacial boundaries showed th directional characteristics to the fiber directions. The delamination area on the impact side (interface A) was considerably smaller compared to that of the opposite side (interface B). (2) Cracks corresponding to other delaminations than those mentioned in SAM photographs were also seen on the impact damaged zone. (3) The delamination patterns were affected by the ply-angle, the dimensions of the specimen, and the boundary conditions. (4) The impact damaged zone showed zone showed the delamination on the interfacial boundaries, transverse shear cracks of the surface layer, and bending cracks of the bottom layer.r.r.r.

• Composites Research
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• v.23 no.1
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• pp.8-16
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• 2010

The Fiber/Metal Laminates (FMLs) have been developed as a new composite material for aerospace application to reduce weight and improve damage tolerance. In this study, firstly FMLs were manufactured and the tensile test was performed to investigate the mechanical properties of FMLs. Furthermore, impact behavior of the low velocity on FMLs which consisted of different types of aluminum or fiber/epoxy layers was tested by the drop weight impact tester based on the different impact energy conditions. The load-time and energy-time curves were employed to evaluate the impact performance of different specimens. Moreover, finite element analysis (FEA) was also performed to simulate the tensile test and impact behavior of FMLs under the same conditions with the tests and good agreements have been obtained between the FEA predictions and experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.636-637
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• 2010

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.11
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• pp.1345-1352
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• 2012

This paper aims to evaluate the low-velocity impact responses and mechanical properties of balsa-wood and urethane-foam core materials and their sandwich panels, which are applied as the impact limiter of a nuclear spent fuel shipping cask. For the urethane-foam core, which is isotropic, tensile, compressive, and shear mechanical tests were conducted. For the balsa-wood core, which is orthotropic and shows different material properties in different orthogonal directions, nine mechanical properties were determined. The impact test specimens for the core material and their sandwich panel were subjected to low-velocity impact loads using an instrumented testing machine at impact energy levels of 1, 3, and 5 J. The experimental results showed that both the urethane-foam and the balsa-wood core except in the growth direction (z-direction) had a similar impact response for the energy absorbing capacity, contact force, and indentation. Furthermore, it was found that the urethane-foam core was suitable as an impact limiter material owing to its resistance to fire and low cost, and the balsa-wood core could also be strongly considered as an impact limiter material for a lightweight nuclear spent fuel shipping cask.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.89-92
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• 2002

Traditionally unidirectional laminated composite which are characterized by high specific stiffness and strength were used for structural application. But theses composites are highly susceptible to impact damage because of lower transverse tensile strength. The main failure modes of laminated composite are fiber breakage, matrix cracking and delamination for low velocity impact. The modified failure criterions are implemented to predict these failure modes with finite element analysis. Failure behavior of the woven fabric laminated composite which is used in forehead part of subway to lighten weigh has been studied. The new failure criterions are in good agreement with experimental results and can predict the failure behavior of the woven fabric composite plate subjected to low velocity impact more accurately.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.2
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• pp.102-108
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• 2010

Recently, carbon fiber reinforced plastic(CFRP) composite materials have been widely used in various fields of engineering because of its advanced properties. Also, CFRP composite materials offer new design flexibilities, corrosion and wear resistance, low thermal conductivity and increased fatigue life. However CFRP composite materials 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. By using obtained residual strength and Tan-Cheng failure criterion, residual strength of CFRP laminate with arbitrary fiber angle were evaluated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.1
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• pp.1-9
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• 2010

The purpose of this study is to analyze the bumper mounting structure of passenger vehicles at low speed collision. In order to improve the repairability and damageability of the vehicle, the low speed crash tests of RCAR(Research Council for Automobile Repairs) standard(front & rear 15km/h 40% offset crash test) were carried out for analysis of 3 different types of bumper mounting structures. The results of experiments show that the impact energy absorbing ability of bumper stay with rectangular crash box type vehicle which is inserted into the bumper rail was superior to another two different bumper mounting structures that are applied to many passenger vehicles. In this thesis, well designed bumper mounting structure such as rectangular crash box type can enhance the safety of occupants as well as contribute to reduce repair cost at low collision accident by improving repairability and damageability of vehicle.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.240-244
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• 2005

In this study a simple model is developed that predicts impact damage in a composite laminate using an analytical model. The model uses a non-linear approximation method (Rayleigh-Ritz) and the large deflection plate theory to predict the number of failed plies and damage area in a quasi-isotropic composite circular plate (axisymmetric problem) due to a point impact load at its centre. It is assumed that the deformation due to a static transverse load is similar to that occurred in a low velocity impact. It is found that the model, despite its simplicity, is in good agreement with FEM predictions and experimental data for the deflection of the composite plate and gives a good estimate of the number of failed plies due to fibre breakage. The predicted damage zone could be used with a fracture mechanics model developed by the second investigator and co-workers to calculate the compression after impact strength of such laminates. This approach could save significant running time when compared to FEM solutions.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.110-114
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• 2009

This study is for the evaluation of compressive strength restoration of sandwich composite laminates with adhesively bonded scarf patches. It was used in this study that the sandwich composite laminate with an aluminum honeycomb core and CF1263 woven fabric carbon/epoxy faces was applied to the car body structure for Korean tiling train. In this study, it was damaged by low velocity impact and repaired using scarf repair method. Then, the compressive strength restoration of assessed by compressive after impact (CAI) test. From the test, it could be known that the compressive strength was restored up to 72% by only scarf repair method and 91% applied by an extra ply over the undamaged one.