Electrical Resistance Change Method Research Articles

電気容量変化の交流周波数依存を用いたＣＦＲＰの成形モニタリング

Authors have developed an electric resistance change method for monitoring delaminations of CFRP laminates. The method employs reinforcement fibers as sensors, and the electrodes are co-cured. In the present study, the cocured electrodes are adopted as sensors for monitoring of degree of cure. The present study proposes a new method for monitoring of the degree of cure without embedding or attaching sensors on the basis of the electrical capacitance change. Applying alternating current during curing process between the electrodes provides dielectric properties of CFRP composites. As same as the conventional dielectric sensors for cure monitoring, the degree of cure of composites is monitored by means of measuring the dielectric constant of the composites here. The dielectric constant of the epoxy resin changes as the change of the frequency of the applied alternating current. Using the dependency of the applied alternating current of the dielectric constants, the degree of cure is directly measured without curve fitting and without cumbersome measurements with DSC. The proposed method is applied to a single ply CFRP and a multi-ply CFRP laminate here. As a result, the method shows excellent estimations of the degree of cure without additional sensors.

1318 フィラメントワインディング構造への電気抵抗変化法の適用

1318 フィラメントワインディング構造への電気抵抗変化法の適用

Delamination monitoring of graphite/epoxy laminated composite plate of electric resistance change method

The present paper employs the electric resistance change method for monitoring of location and size of a delamination crack of graphite/epoxy composite laminates. The method is applied to a plate-type specimen with an embedded delamination of cross-ply and quasi-isotropic laminates. Ten electrodes made from copper foil are mounted on the specimen top surfaces. An embedded delamination crack is created by a static indentation test, and the electric resistance changes are measured using a conventional strain gage amplifier. Response surfaces are adopted as a tool for solving inverse problems to estimate location and size of delamination crack from the measured electric resistance changes of all segments between electrodes. As a result, the present method successfully provides estimations of location and size of the embedded delamination for graphite/epoxy laminated composites.

Measurement of orthotropic electric conductance of CFRP laminates and analysis of the effect on delamination monitoring with an electric resistance change method

Since delaminations of composite laminates are usually invisible or difficult to detect by visual inspections, delamination causes low reliability for primary structures. Automatic systems for delamination identifications in-service are desired in order to improve this low reliability. The present study employs an electric resistance change method for detection of delaminations. Since the method adopts reinforcement carbon fibre itself as sensors for delamination detections, this method does not cause reduction of static strength or fatigue strength; also, this method is applicable to existing structures. In the present study, a relationship between fibre volume fraction and orthotropic electric conductivities is confirmed by experimentation and the effect of measured orthotropic electric conductance on delamination monitoring is discussed analytically with FEM analyses. Two types of cross-ply laminates are prepared for delamination monitoring analyses: [0/90]s and [90/0]s. Electric resistance changes due to delamination creation are discussed for both specimen types with results of electric current density diagrams. As a result, it can be concluded that the fibre volume fraction has a large effect on electric conductance of the transverse and thickness directions, and electric conductance of the thickness direction has significant effects on delamination detection with the electric resistance change method.

Delamination identification of cross-ply graphite/epoxy composite beams using electric resistance change method

Detection of delaminations is a difficult task for visual inspections. Difficulty of detection underlines the importance of development of smart structures for monitoring delaminations of graphite/epoxy laminated composites. This study employs an electric resistance change method for identification of delamination location and size; applicability of the method is investigated experimentally using beam-type specimens fabricated from cross-ply laminates. On the specimen surface, multiple electrodes are mounted by co-curing copper foil to measure electric resistance changes. Interlamina shear tests are conducted to create a practical delamination crack in a beam-type specimen. Five beam specimen types were made and tested. A large number of tests were conducted to obtain a data set for solving inverse problems to estimate delamination location and size from measured electric resistance changes. Response surfaces are employed for a solver of inverse problems instead of well-known artificial neural networks. As a result, the method successfully identifies delamination location and size for these beam type specimens. To obtain practically efficient estimation performance, at least five electrodes are indispensable for these beam type specimens.

114 Bearing Failure Detection of Bolted Composite Joints Using Electric Resistance Change Method

114 Bearing Failure Detection of Bolted Composite Joints Using Electric Resistance Change Method

435 電気抵抗変化法を用いた CFRP 知的はく離検出の同定精度向上

435 電気抵抗変化法を用いた CFRP 知的はく離検出の同定精度向上

電気抵抗変化による擬似等方ＣＦＲＰ積層平板埋没はく離の検出知的構造

In the present study, an electric resistance change method is employed for the identifications of location and size of the embedded delaminations of quasi-isotropic laminates. Indentation tests are conducted to create embedded delamination cracks in the quasi-isotropic laminate of CFRP. Two lines and five columns of electrodes are mounted on the plate surface for measurements of electric resistance changes due to delamination creations. Response surface methodologies are applied to obtain the relation between the delaminations and measured electric resistance changes. As a result, the method can successfully estimate the location and size of embedded delaminations of quasiisotropic laminates, and the effect of the stacking sequence for identification is clarified.

複合材料 ＣＦＲＰ平板の埋没はく離同定への電気抵抗変化法の適用

In the present study, an electric resistance change method is adopted for the identifications of location and size of the embedded delaminations. Indentation tests are conducted to create embedded delamination cracks in CFRP plates. Two lines and eight columns of electrodes are mounted on the plate surface for measurements of electric resistance changes due to delamination creations. Response surface methodologies are applied to obtain the relation between the delaminations and measured electric resistance changes. The effect of temperature change is experimentally measured using the plate specimen. As a result, the method can successfully estimate the location and size of embedded delaminations, and the effect of the temperature change is neglectable by using compensation for temperature change.

電気抵抗変化を用いたＣＦＲＰ層間はく離検出の診断手法の検討 応答曲面とニューラルネットワークの比較

The present study employs an electric resistance change method for identifications of delamination cracks. For the method, diagnostic tools for the inverse problems to identify the delamination crack location and size from the electric resistance changes are discussed. FEM analyses are conducted to obtain electric resistance changes due to delamination crack creations with fiveelectrode type specimens. By comparisons of the estimations with the Artificial Neural Networks (ANNs) and with the response surfaces (RS), a better diagnostic tool is discussed in detail. As a result, because of overlearning of neural network, the presumed error of new data with ANNs is large, and the RS using quadratic polynomials is a better tool than ANNs for identifications of delamination crack location and size using electric resistance change.

Effects of Stacking Sequence and Number of Electrodes on Detection of Delamination of CFRP Using Electric Resistance Change.

In the present study, an electric resistance change method is adopted for the identifications of delamination crack location and size of CFRP laminates, and possibility of identification of delamination cracks is experimentally investigated by using cross-ply laminates. 3-point-bending tests to create delamination cracks are conducted using CFRP composite specimens with multiple electrodes, and electric resistance changes due to the delamination are measured. Response surfaces to estimate delamination location and size from electric resistance changes are constructed. In this method, stacking sequence and number of electrodes largely affect reliability of identification of the delamination location and size. In order to estimate these effects, a large number of experiments are conducted by using five kinds of specimens that have different stacking sequences and number of electrodes. As a result, the electric resistance change method can be useful for structures monitoring of laminate of various stacking sequences, and five electrodes are needed for high reliability.

121 電気抵抗変化を用いた損傷同定逆問題への応答曲面法の適用(ニューラルネットワークとの比較)

The present study employs and electric resistance change method for identifications of delamination cracks. For the method, appropriate number of electrodes to identify delaminations is investigated, and the diagnostic tool for the inverse problems to identify the delamination crack location and size from the electric resistance changes is discussed. FEM analyses are conducted to obtain electric resistance changes due to delamination crack creations with three-electrode, four-electrode and five-electrode type specimens. Using the artificial neural networks (ANNs), the required number of electrodes for identifications of delamination cracks location and size from the electric resistance changes is investigated. By comparisons of the estimations with the ANNs and with the response surfaces (RS), a better diagnostic tool is discussed in detail. As a result, the five-electrode type specimen is shown to be better for the identifications, and the RS using quadratic polynomials is a better tool than ANNs for identifications of delamination crack location and size using electric resistance change.

Smart Structure for Delamination Detection of CFRP Using Response Surface of Electric Resistance Change of Multiple Electrodes.

Compression strength and stiffness of laminated CFRP structural components are severely degraded by delaminations. The delaminations are unfortunately invisible or difficult to inspect by naked eyes. This brings significance of development of smart structures for detection of delaminations of CFRP. In the present study, an electric resistance change method is adapted for identifications of delamination crack position and size of CFRP laminates, and possibility of identification of delamination cracks is experimentally investigated by using cross ply laminates. 3-point-bending test are conducted using specimens with multiple electrodes to generate delamination cracks. Firstly, response surface to predict electric resistance change are constructed from measured electric resistance change. Secondary, design of experiments are conducted for inverse problem to predict delamination crack position and size from electric potential changes. Finally, response surface to predict delamination crack position and size are constructed. Using the response surface method with design of experiments, delamination crack position and size are predicted within practical precision without consideration of fracture mechanism.

Dependence of electromigration rate on applied electric potential

Copper films, current stressed under in-situ, ultra-high vacuum (UHV), clean surface conditions, have an activation energy for electromigration that lies in the range of values obtained for surface diffusion. Recent field ion microscope studies of {001} fcc metal surfaces showed that an electric field applied to the surface can influence the rate of surface diffusion. In the present work, positive and negative potentials were applied to copper stripes undergoing electromigration damage under UHV, clean surface conditions. Activation energies were measured as a function of applied potential using an electrical resistance change method. The results show a strong dependence of the activation energy for electromigration on the sign and magnitude of the applied potentials. Positive potentials raise the activation energy while negative potentials lower it. These results are in agreement with what one would expect from field ion microscopy electric field effect experiments. They may also have practical implications in possibly controlling the rate of electromigration damage in passivated metal interconnects used in microelectronics where the damage mechanisms may involve volume, grain boundary, interfacial and surface diffusion processes.

Electromigration in vacuum evaporated Cu films

Copper is a potential substitute for Al in integrated circuit metallizations because of its lower electrical resistivity and its greater resistance to electromigration damage. Changes in the properties of Al and Cu films when they undergo electromigration stressing are compared. Measurements, carried out in vacuum, were made of the electrical resistance, times to failure, and activation energies. Scanning electron microscopy was used to characterize topographic changes. It is shown that a careful electrical resistance change method for measuring activation energies for electromigration damage is more reproducible than the time-to-failure method. Cu also shows less films thinning prior to failure than Al. For the same fractional change in electrical resistance, the hillocks on Cu are more crystallographic and the voids are larger and more numerous than in Al.