• Composites Research
• /
• v.23 no.5
• /
• pp.15-21
• /
• 2010

In this study, repair and maintenance schemes of the damaged composite structure was investigated, and a repair process of the carbon/epoxy laminate composite structure was investigated numerically and experimentally. The composite laminates were damaged by drop weight type impact test machine. The damaged composite structure was repaired using external patch repair method after removing damaged area. The compressive strength test and analysis results after repairing the impact damaged specimens were compared with the compressive strength test and analysis results of undamaged specimens and impact damaged specimens. Finally, the strength recovery capability by repairing were investigated.

• Composites Research
• /
• v.25 no.4
• /
• pp.105-109
• /
• 2012

Recently, development of a small aircraft has been carried out for the BASA(Bilateral Aviation Safety Agreement) program in Korea. This aircraft adopted all composite structures for environmental friendly by low fuel consumption due to its lightness behavior. However the composite structure has disadvantage which is very weak against impact damages. Therefore, damage allowable design of aircraft structure must be performed considering compressive fracture strength. This point is very important for certification of composite structure aircraft. In this paper, it is performed the research on damage tolerance of thick laminate adopting aircraft structure. The damage tolerance of three different types of thick laminates such as no damage, open hole and impact damage is evaluated under compression loading.

• Composites Research
• /
• v.27 no.2
• /
• pp.77-81
• /
• 2014

In this study, it was performed damage assessment and repair of small scale aircraft adopted on composite. This aircraft adopted the sandwich structure to skin of wing. This study aims to investigate the residual strength of sandwich composites with nomex honeycomb core and carbon fiber face sheets after the open hole damage by the experimental investigation. The 4-point bending tests were used to find the bending strength, and the open hole was applied to introduce the simulated damage on the specimen. The bending strength test results after open hole were compared with the results of no damaged specimen test. In addition, The damaged composite structure was repaired using external patch repair method after removing damaged area. After that, this study presents comparison results of the experimental investigation between the damaged and the repaired specimen. It was found that the bending strength of repaired specimen was recovered up to 95% of undamaged specimen.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2004.05a
• /
• pp.96-96
• /
• 2004

고성능 섬유강화 복합재는 비강성과 비강도가 높고 내부식성과 피로특성이 우수하지만 외부에서 가해지는 하중에 의해 수지, 강화섬유와 수지와의 경계면, 적층 경계면 등에 육안으로 식별하기 어려운 손상이 유발될 가능성이 있으며 이로 인해 구조재로서의 역할을 하지 못하는 경우가 발생한다. 최근에는 외부하중으로 인해 복합재 구조재에 손상이 발생한 경우 자가치료제가 저장된 마이크로캡슐을 이용하여 손상을 보수하려는 시도가 행해지고 있다.(중략)

• Composites Research
• /
• v.26 no.2
• /
• pp.79-84
• /
• 2013

The prediction and analysis procedure of fatigue damage crack growth life for a stiffener bonded composite laminate panel including center hole and edge notch damage, was studied. It was performed on the basis of fatigue damage growth test results on a laminated skin panel specimens and the analysis results of stress intensity factor for the stiffener bonded composite panel. According to the comparison between experimental test and prediction results of fatigue damage growth life, it was concluded that the residual strength and damage tolerance assessment can be carried out along to the edge notch crack growth.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.9
• /
• pp.862-868
• /
• 2010

Development of a small scale aircraft has been carried out for the BASA(Bilateral Aviation Safety Agreement) program in Korea. This aircraft adopted all the composite structures for environmental friendly by low fuel consumption due to its lightness behavior. However the composite structure has s disadvantage which is very weak against impact due to foreign object damages. Therefore the aim of this study is focusing on the damage evaluation and repair techniques of the aircraft composite structure. The damages of composite laminates including the carbon/epoxy UD laminate and the carbon/epoxy fabric face sheets-honeycomb core sandwich laminate were simulated by a drop weight type impact test equipment and the damaged specimen were repaired using the external patch repair method after removing damaged area. The compressive strength test and analysis results after repairing the impact damaged specimens were compared with the compressive strength test and analysis results of undamaged specimens and impact damaged specimens. Finally, the strength recovery capability by repairing were investigated.

• Composites Research
• /
• v.18 no.6
• /
• pp.26-33
• /
• 2005

The mechanical properties of composite materials may severely degrade in the presence of damage. Especially, the high-velocity impact such as bird strike, a hailstorm, and a small piece of tire or stone during high taxing, can cause considerable damage to the structures and sub-system in spite of a very small mass. However, it is not easy to detect the damage in composite plates using a single technique or any conventional methods. In this paper, the PVDF(polyvinylidene fluoride) film sensors were used for monitoring high-velocity impact damage initiation and propagation in composite laminates. The WT(wavelet transform) and STFT(short time Fourier transform) are used to decompose the sensor signals. A ultrasonic C-scan and a digital microscope are also used to examine the extent of the damage in each case. This research shows how various sensing techniques, PVDF sensor in particular, can be used to characterize high-velocity impact damage in advanced composite.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.46 no.6
• /
• pp.471-478
• /
• 2018

Static tests of the composite wing structure were performed to verify damage tolerance design. Both 5 cases of DLLT and 3 cases of DULT were completed to meet requirements for static strength. After inducing BVID and open hole damages on the critical areas of the composite wing based on associated regulations, the DULT and fracture test were performed. In major wing parts, the measured strains and displacements agreed well with those of structural analysis. The initial structural fracture occurred at the area having minimum margin of safety as expected by analysis. As a result, it was confirmed that results from analytic model and strength evaluation were similar to behaviors of the composite wing structure.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.49 no.1
• /
• pp.13-20
• /
• 2021

In this paper, a new algorithm is proposed to estimate the damage size by combining the reflected area with the reflected position and extracting contours in proportion to the maximum value of pixels from the visible image. The cumulative summation feature vector algorithm is used to obtain the area of the reflected signal. To get the position of the reflected signal, the signal correlation algorithm is used to decompose the reflected signal from the damage. The proposed algorithm is tested and validated for composite panels. Repetitive experiments are performed and it is confirm that the proposed algorithm is reproducible. Further, it is verified that the damage size can be estimated appropriately by the proposed algorithm.

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