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

• Composites Research
• /
• v.34 no.6
• /
• pp.357-372
• /
• 2021

The energy harvesting device is known to be promising as an alternative to solve the resource shortage caused by the depletion of petroleum resources. In order to overcome the limitations (environmental pollution and low mechanical properties) of piezoelectric elements capable of converting mechanical motion into electrical energy, many studies have been conducted on a polymer matrix-based composite piezoelectric energy harvesting device. In this paper, the output performance and related applications of the reported piezoelectric composites are reviewed based on the applied materials and processes. As for the piezoelectric fillers, zinc oxide, which is advantageous in terms of eco-friendliness, biocompatibility, and flexibility, as well as ceramic fillers based on lead zirconate titanate and barium titanate, were reviewed. The polymer matrix was classified into piezoelectric polymers composed of polyvinylidene fluoride and copolymers, and flexible polymers based on epoxy and polydimethylsiloxane, to discuss piezoelectric synergy of composite materials and improvement of piezoelectric output by high external force application, respectively. In addition, the effect of improving the conductivity or the mechanical properties of composite material by the application of a metal or carbon-based secondary filler on the output performance of the piezoelectric harvesting device was explained in terms of the structure of the composite material. Composite material-based piezoelectric harvesting devices, which can be applied to small electronic devices, smart sensors, and medicine with improved performance, can provide potential insights as a power source for wireless electronic devices expected to be encountered in future daily life.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.5
• /
• pp.497-502
• /
• 2015

In this paper, a stress function-based approach was proposed to analyze the reduction of free-edge peeling stress in smart composite laminates using piezoelectric actuator under bending load. Electro-mechanically coupled governing equation was obtained by complimentary virtual work principle. The stress state was solved by the generalized eigenvalue procedure. The free-edge peeling stress of smart composite laminates was reduced by the piezoelectric actuation. The reduction rate of peeling stress in cross-ply composite laminate is larger than that in angle ply composite laminate.

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

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.05a
• /
• pp.207-210
• /
• 2002

This paper is concerned with the experiments on the active vibration control of a plate with piezoceramic sensors and actuators. The natural frequencies of the composite plate featured by a piezo-film sensor and piezo-ceramic actuator are calculated by using the modal analysis method. Modal coordinates are introduced to obtain the state equations of the structural system. Six natural frequencies were considered in the modelling, because robust control theory which has inherent robustness to structured uncertainty is adopted to suppress the transients vibrations of a glass fiber reinforced(GFR) composite beam. A robust controller satisfying the nominal performance and robust performance is designed using robust theory based on the structured singular value. Simulations were carried out with the designed controller and effectiveness of the robust control strategy was verified by results.

• 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.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2011.04a
• /
• pp.311-314
• /
• 2011

최근 콘크리트 구조물의 안전성강화를 위해 탄소섬유 강화 플라스틱(CFRP) 보강 공법이 널리 사용되고 있지만 잘 알려진 바와 같이 CFRP 보강재와 콘크리트 표면사이의 부착면 탈락은 보강재 자체의 손상보다 발생할 확률이 높고 이러한 부착면 탈락은 보강의 효과를 무의미하게 만들기 때문에 구조물 전체의 파괴로 직결될 수 있다. 이에 본 연구에서는 CFRP 부착면 탈락손상을 실시간으로 검색하기 위해 압전센서를 사용하는 구조물 건전성 평가 기술을 적용하였다. 이의 검증을 위해 CFRP로 보강된 콘크리트 보를 제작하였고 3단계로 증가하는 부착면 탈락 손상을 발생시켰다. 손상 증가 단계마다 CFRP 표면에 배열된 압전센서로부터 임피던스와 유도초음파 신호를 계측하였고 손상에 따른 신호변화를 정량화하기 위해 손상지수인 RMSD를 계산하였다. 더 구체적인 부착면 탈락 손상위치 탐색을 위해서 두 가지 계측 기법으로부터 구해진 RMSD 값를 중첩시키는 Superposed RMSD 가 제안되었다. 구해진 Superposed RMSD 값을 사용하여 커브 피팅이 수행되었고 도출된 커브의 최고값에 해당하는 위치값을 찾아 실제 손상위치와 비교함으로써 제안된 기법의 가능성을 검증해 보았다.

• Composites Research
• /
• v.12 no.2
• /
• pp.1-9
• /
• 1999

The piezoelectric material connected to external electric networks possesses frequency dependent stiffness and loss factor which are also affected by the shunting circuit. The external electric networks are generally specialized for two shunting circuits: one is the case of a resistor alone and the other is the combination of a resistor and an inductor. For resistive shunting, the material properties exhibit frequency dependency similar to viscoelastic materials, but are much stiffer and more independent of temperature. Shunting with a resistor and inductor introduces an electrical resonance, which can change the characteristics of structural resonance optimally in a manner analogous to a PMD (proof mass damper). Passive damping enhancement of composite beam using piezoelectric material connected to external electrical networks is achieved and presented in this paper.

• Electronics and Telecommunications Trends
• /
• v.27 no.1
• /
• pp.1-18
• /
• 2012

미래 사회는 나노기술(NT)을 바탕으로 IT-ET-BT 기술이 융합된 유비쿼터스 사회로 진화하고 있으며, 미래 산업 사회로의 전환을 위해서는 성능개선이 아닌 성능한계 돌파의 패러다임 전환이 가능한 임계성능의 나노 소재/신소자의 개발이 절실히 요구되고 있다. 또한 차세대 단말기는 휴대성의 편리함, 융복합화/다기능화, 인간 친화형이 요구되고, flexible/stretchable/bendable한 형태로 발전하고 있는 상황이다. 나노 피에조트로닉스(nanopiezotronics) 기술은 역학적 에너지를 전기적 에너지로 변환하는 나노 발전 소자(nanogenerator)의 원리를 기반으로 하며 나노선, 나노벨트와 같은 1차원적 나노구조 소재의 압전성과 반전도성이 결합된 특성을 이용한 신기능의 미래 IT 융합 나노 전자/에너지 소자를 구현하는 기술로서 미래 유망 기술로 부각되고 있다. 현재 기술 수준은 압전 전계 효과 트랜지스터, 압전-다이오드, 압전 센서, 압전 나노 발전 소자 등과 같은 prototype 소자를 제작하는 수준에 머무르고 있으나 향후 초고감도 압전 센서, 자가발전 MEMS/NEMS 및 나노 시스템, 스마트 웨어러블 시스템, 건강 모니터링 시스템, 인체 삽입형 소자, portable 및 투명 유연 전자소자 등의 다양한 미래 융합 나노 소자 및 시스템에 광범위한 활용이 가능하며, 향후 신기능의 소자/부품/시스템 창출을 위한 기술로 자리매김할 것으로 전망된다. 본고에서는 압전 나노선, 나노튜브, 나노섬유 등의 1차원적 나노구조체 기반의 nanopiezotronics 기술과 최근의 연구결과들을 소개한다.

• Composites Research
• /
• v.29 no.6
• /
• pp.379-387
• /
• 2016

Structural model of laminated composite plate based on the first order shear deformation theory and subjected to a combination of piezoelectric, electromagnetic and thermal fields is established. Coupled equations of motion are derived via Hamilton's principle on the basis of electromagnetic and piezoelectric equations which are involved in constitutive equations. Proportional control and velocity feedback control logics are applied via boundary control moments and forces. Variations of dynamic chasracteristics of composite plate with collocated piezoelectric sensor and actuators, electromagnetic field and temperature gradient are investigated and it reveals that dynamic characteristics of structure can be effectively controlled by utilizing the piezoelectric effect and ply angles of fiber reinforced composites.