• Composites Research
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• v.29 no.2
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• pp.73-78
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• 2016

In this paper, The concept of a wheel with carbon fiber composite is to replace the conventional material used for a wheel hub, such as plastic, with a disk-type hub made of carbon fabric and epoxy resin. The impact load from the ground under real conditions was considered; a low-velocity impact test was conducted to evaluate the impact performance of the carbon wheel and compare it with that of a conventional plastic wheel. This study applied a 70 J impact load as a test condition. The impact energy was controlled in the test by adjustment of height and weight of impactor. The use of a carbon disk wheel hub was confirmed to reduce weight and generate an excellent repulsive force at low energy under conditions similar to real driving conditions. The results showed that the maximum load increased proportionally depending on the impact load, but the growth of the maximum load was reduced at a 20 J impact load and tended to decrease at a 45 J impact load. The carbon wheel showed excellent properties ; the level of rebounding was 35.3% and 19.1% of the total impact energy at impact loads of 5 J and 10 J, respectively. On the other hand, the carbon disk wheel rebounded less than 5% of the total energy due to crack generation of the thin carbon hub for impact loads of more than 20 J.

• Composites Research
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• v.20 no.4
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• pp.42-50
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• 2007

This paper describes the results of experiments and numerical simulation studies on the low-velocity impact damage of two different sandwich composite panels for application to bodyshell and floor structure of the BIMODAL tram vehicle. Square test samples of 100mm sides were subjected to low-velocity impact loading using an instrumented testing machine at four impact energy levels. Part of this work presented is focused on the finite element analysis of low-velocity impact response onto a sandwich composite panels. It is based on the application of explicit finite element (FE) analysis codes LS-DYNA 3D to study the impact response of sandwich structures under low-velocity impact conditions. Material testing was conducted to determine the input parameters for the metallic and composite material model, and the effective equivalent damage model for the orthotropic honeycomb materials. Numerical and experimental results showed a good agreement for damage area and the depth of indentation of sandwich composite panels created by the impact loading.

• Composites Research
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• v.16 no.4
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• pp.66-73
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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 3 mm 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) follow the static curve well. In addition, at a given energy the peak force is in good agreement between the static and impact cases. It is identified that the failure behaviour of the specimens from the CAI strength tests was very similar to that observed in laminated plates with open holes under compression loading. The residual strengths art: in good agreement with the measured open hole compressive strengths. considering the impact damage site area, 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.439-442
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• 2009

In this study, the residual strength of CFRP filament winding pressure vessel after low velocity impact was evaluated quantitatively. After impact test, the pressure vessel was sectioned to produce 25 mm-wide ring specimen and the bursting pressure of this specimen was measured. A finite element model was also fabricated to investigate the deformation and stress distribution characteristics of the impacted CFRP vessel. The degradation of the residual strength along with the increase of impact energy was successfully measured and reviewed.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.183-192
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• 2011

The demand for weight saving and high performance of aircraft require the more uses of composite materials. However the complicate behaviors and various failure characteristics restrict usage of composite materials. Low-velocity impact damage is a major concern in the design of structures made of composite materials, because impact damage is hidden and cannot be detected by visual inspection. Especially, the reduction on compressive strength after impact is influenced by the ply delaminations introduced as damage by impact event. In this research, the numerical analysis was performed to investigate impact damage and compressive strength after impact. It was found that impact force history and compressive strength after impact calculated by the numerical analysis were compared and shown a good agreement with experimental results.

• Composites Research
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• v.20 no.5
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• pp.1-6
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• 2007

This study was performed to make a comparison on low-velocity impact behavior between graphite/epoxy composite laminate and steel plate. In order to validate the proposed scheme fur the impact behavior of the plate, the Karas's impact model was used. The impact models for this comparative study are the graphite/epoxy composite plate having $[0/90/45/-45/-45/45/90/0]_{8S}$ laminate sequence and the steel plate with a steel ball impactor. The low-velocity impact behaviors for two types of plates were comparatively investigated and performed by considering different impactor velocities and weights respectively. In this investigation, it was found that the composite laminate has impact energy absorption effect due to more flexible behavior than the steel plate, and also it has better characteristics on impact damage and weight.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.2
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• pp.51-56
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• 2003

The piezoelectric thin film(PVDF: polyvinylidene fluoride) sensors having good dynamic sensing charachteristics can be used to monitor low vwlocit impact on composite structures. The impact response function for composite sandwich beam was derved. The impact tests at low energy without inducing damage were performed on the instrumented drop weight impact tester. The measured signals of PVDF sensors attached on the surface of the beam agreed well with the simulated signals. And the inverse technique was applied to reconstruct the impact forces from the PVDF sensor signals. Most of reconstructed impact forces showed good agreement with the measured forces. The comparison results showed that the piezoelectric thin film sensor can be used to monitor the low velocity impact on composite sandwich structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.9-10
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• 2010

In this study, the static and low velocity impact tests for two-way concrete specimens strengthening with the CFRP sheets were carried out. The specimens that had a dimension of $50{\times}350{\times}350mm$ with 40 MPa plain concrete and steel fiber reinforced concrete which had same mixture to plain concrete and 0.75% steel fibers were fabricated. The specimens reinforced with the CFRP or steel fibers showed mixed failure modes, splitting and punching, also splitting cracks and fragments were much reduced than plain concrete specimens'. Two-way concrete members reinforced with the CFRP and steel fiber simultaneously dissipated 6.8 times larger energy than not-retrofitted members' under the low-velocity impact loading.

• Composites Research
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• v.13 no.1
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• pp.40-49
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• 2000

The objective of this research is to develop the impact monitoring techniques providing impact identification and damage diagnostics of smart composite laminates susceptible to impacts. This can be implemented simultaneously by using the acoustic waves by the impact loads and the acoustic emission waves from damage. In the previous research, we have discussed the impact location detection process in which impact generated acoustic waves are detected by PZT using the improved neural network paradigm. This paper describes the implementation of time-frequency analysis such as the Short-Time Fourier Transform (STFT) and the Wavelet Transform (WT) on the determination of the occurrence and the estimation of damage.

• Composites Research
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• v.15 no.5
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• pp.7-13
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• 2002

The piezoelectric thin film sensor has good characteristics to observe the impact responses of composite structures. The capabilities for monitoring impact behavior of Gr/Ep laminates subjected to damage-induced impact using the PVDF(polyvinylidene fluoride) film sensor were examined. For a series of low-velocity impact tests from low energy to damage-induced energy, simulated sensor signals were compared with measured signals and the PVDF film sensor. Local impact damages(matrix cracking and delamination) were found at three impact tests, but the measured signals agreed well with the simulated sensor signals based on the linear relationship between the impact forces and the PVDF film sensor signals. And the inverse technique was applied to reconstruct the impact forces using the PVDF film sensor signals. Most of reconstructed impact forces had good agreement with the measured forces. The comparison results showed that the local damage due. to low-velocity impact didn't disturb the global impact responses of composite laminates and the reconstruction of impact forces from PVDF sensor signals wasn't affected by the local damage.