Delamination Monitoring Research Articles

403 電気抵抗変化によるCFRP厚板の層間はく離モニタリングに及ぼす残留応力の影響(GS5(1) 実験,計測,モニタリング)

403 電気抵抗変化によるCFRP厚板の層間はく離モニタリングに及ぼす残留応力の影響(GS5(1) 実験,計測,モニタリング)

Smart Cure Monitoring Method of Carbon/Epoxy Laminates Using Electric Capacitance Change with Applied Alternating Current Frequency

Authors have developed an electric resistance change method for delamination monitoring of carbon/epoxy composite laminates. The method employs reinforcement fibers as sensors; electrodes are co-cured. Co-cured electrodes for delamination monitoring are adopted in the present study as sensors for monitoring the degree of cure. This study proposes a new method using electrical capacitance change for monitoring the degree of cure without using additional sensors. Applying alternating current between electrodes during the cure process provides dielectric properties of carbon/epoxy composites. As with the conventional cure monitoring method using extra dielectric sensors, the degree of cure of composites is monitored by measuring the dielectric constant of composites. The dielectric constant of epoxy resin changes concomitant with change of frequency of applied alternating current (AC). Using dependency of the applied AC frequency of the dielectric constant, the degree of cure is measured directly. The proposed method is applied to single and multi-ply carbon/epoxy composite laminates. The method demonstrates excellent estimations of the degree of cure without additional sensors.

Nonlinear analysis and damage monitoring of a one-sided patch repair with delamination

A simple analytical model using beam theory is developed to study a one-sided patch structure with delamination, considering the effect of large deflection and thermal stress. The method is based on the concept of equivalent delamination, which is analytically defined and employed to describe delay in load transfer between patch and parent plate with eccentrically aligned neutral axes. The analytical model has closed form solutions and good agreement with nonlinear finite element analysis (FEA) as well as experimental results is shown. The relation between the delamination propagation and the strains at monitoring locations is derived and feasibility of delamination monitoring based on surface strains is analytically demonstrated.

Delamination monitoring of laminated composites subjected to low-velocity impact using small-diameter FBG sensors

Abstract Small-diameter fiber Bragg grating (FBG) sensors were applied for the monitoring of delamination induced by low-velocity impact. The FBG sensors were embedded into carbon fiber reinforced plastic (CFRP) laminates [04/904/04]. Using a drop-weight impact tester, an impact loading was applied to the laminates at four impact energy levels. After the impact tests, the internal damages including delaminations were observed by ultrasonic C-scan, and the reflection spectra from the embedded FBG sensors were measured. The form of the spectrum changed sensitively depending on the delamination size. Furthermore, the spectra were calculated theoretically for confirmation of the measured spectra. Since the change in the measured spectrum was consistent with that in the calculated spectrum, the relationship between the delamination size and the form of the spectrum could be clarified. From the results, the present method using small-diameter FBG sensors was found to be effective for the monitoring of the delamination.

1702 電位差法によるCFRP積層板はく離モニタリング : 等価導電率による実験回数削減法(J08-1 材料モニタリング,損傷検知・抑制,J08 知的材料・構造システム)

1702 電位差法によるCFRP積層板はく離モニタリング : 等価導電率による実験回数削減法(J08-1 材料モニタリング,損傷検知・抑制,J08 知的材料・構造システム)

受動型電気ポテンシャルCT法による複合材内はく離状欠陥の同定およびモニタリング

受動型電気ポテンシャルCT法による複合材内はく離状欠陥の同定およびモニタリング

電位差法を用いたＣＦＲＰ積層板のはく離モニタリング―規格化電位差法の適用とはく離形状の影響評価―

Monitoring of delamination is indispensable for CFRP structures. In authors' previous studies, the delamination can be monitored with electric resistance change method. This method provided excellent performance of estimations. However, the method requires complicated electric circuits and uses a two-probe method: electrical resistance at electrodes has significant effect. To resolve these problems, an electrical voltage change method is adopted in the present study. Since the electrical voltage change method provides poor performance of estimations in our previous study, the present study employs a standardization method that has shown significant improvement of estimations for the electrical resistance change method. Moreover, the effect of zigzag shape of delaminations caused by the matrix cracking on the performance of estimations is investigated using FEM analyses. As a result, the electrical voltage change method shows good performance of estimations for delaminations located near the edges of the specimen and poor performance near the middle of the specimen. The zigzag shape has large effect on the performance of estimations when the delamination locates near the middle of the specimen. FEM analyses show the small electrical current through the thickness direction near the middle of the specimen causes these effects on the performance of estimations.

電位差法を用いたＣＦＲＰ積層板のはく離モニタリング―同定誤差原因と２段階はく離同定による改善―

Monitoring of delamination is indispensable for CFRP structures. In authors' previous studies, the delamination can be monitored with the electric resistance change method. This method provided excellent performance of estimations. However, the method requires complicated electric circuits and uses a two-probe method: electric resistance at the electrodes has significant effect. To resolve these problems, an electrical voltage change method is adopted in the present study. Since the electrical voltage change method provides poor performance of estimations in our previous study, the present study employs a standardization method that has shown significant improvement of estimations for the electrical resistance change method. As a result, the electrical voltage change method shows good performance of estimations for delaminations located near the edges of the specimen and poor performance near the middle of the specimen. The zigzag shape has large effect on the performance of estimations for the delamination near the middle of the specimen. In this paper, two-stage delamination monitoring method that is not affected by the shape of delamination is proposed. The validity of this method is verified using the FEM analysis.

電位差法を用いたCFRP積層板のはく離モニタリング(OS1-3 はく離モニタリング,OS1 構造ヘルスモニタリング)

電位差法を用いたCFRP積層板のはく離モニタリング(OS1-3 はく離モニタリング,OS1 構造ヘルスモニタリング)

Experimental Cost Reduction for Delamination Monitoring of CFRP Beam Using Electrical Resistance Change with Neural Networks(International Workshop on Smart Materials and Structural Systems, W03 Jointly organized by Material & Processing Division, Material & Mechanics Division, Dynamics & Control Division and Space Engineering Division.)

Experimental Cost Reduction for Delamination Monitoring of CFRP Beam Using Electrical Resistance Change with Neural Networks(International Workshop on Smart Materials and Structural Systems, W03 Jointly organized by Material & Processing Division, Material & Mechanics Division, Dynamics & Control Division and Space Engineering Division.)

電気抵抗変化法によるCFRP積層板のはく離モニタリングでの電気抵抗減少メカニズム(OS1-3 はく離モニタリング,OS1 構造ヘルスモニタリング)

電気抵抗変化法によるCFRP積層板のはく離モニタリングでの電気抵抗減少メカニズム(OS1-3 はく離モニタリング,OS1 構造ヘルスモニタリング)

Monitoring delamination of laminated CFRP using the electric potential change method: Application of normalization method and the effect of the shape of a delamination crack

Monitoring for delamination is indispensable for carbon fiber reinforced plastic (CFRP) structures. The authors previously reported delamination monitoring using the electric resistance change method; which provides excellent estimations. However, the method requires complicated electric circuits and uses a two-probe method, in which electric resistance change at the electrodes has a significant effect. To overcome these problems, the present study adopted an electric potential change method. Since this method had poor estimation performance in our previous study, here we employed a normalization method that showed significant improvements in the estimations using the electric resistance change method. Moreover, the effect on the estimation performance of delamination with a zigzag shape caused by matrix cracking is investigated using FEM analyses. In the results, the electric potential change method shows good performance of estimations for delaminations located near the edges of the specimen but poor performance near the middle of the specimen. The zigzag shape has a large effect on the performance of the estimations when the delamination crack locates near the middle of the specimen. FEM analysis shows that a small electric current through the thickness direction near the middle of the specimen causes large effects on estimation performance.

Multi-prove electric potential change method for delamination monitoring of graphite/epoxy composite plates using normalized response surfaces

Delamination is a significant defect of laminated composites. The present study employs an electric potential change method in an attempt to identify internal delaminations experimentally. The method adopts reinforcing graphite fibres as sensors. In our previous paper, a two-prove method was adopted for the electric-resistance change measurements because of the simplicity. The two prove method is not appropriate for a precise measurement, and it tends to include a large experimental error in the electric resistance change owing to the electric resistance change at the electrodes. Instead, the present paper employs a multiple-prove method for the measurements. In the present study, high precise measurement system of electric voltage change is developed, and the electric voltage measurement method is adopted for identification of embedded delamination location and size. Measured electric potential data are normalized for creations of response surface to identify the delamination. As a result, the new multi-prove electric potential method is shown to be effective for the identifications of embedded delamination cracks of graphite/epoxy composite laminates.

OS09W0317 Unsupervised damage detection of CFRP structure with statistical diagnostic method

Structural health monitoring is a noticeable technology for advanced composite structures and civil structures. The present paper proposes a new diagnostic tool for the structural health monitoring that employs a statistical diagnosis of self-learning method. Most of the structural health monitoring systems adopt parametric method based on modeling or non-parametric method such as artificial neural networks. The former method requires modeling of each structure and latter method requires data for the training. And these modeling and data for the training demand much cost. The new statistic diagnosis method does not require the complicated modeling and a learning data of damaged structure for the artificial neural networks. The present study deals monitoring of delamination of composite beam using change of strain judged by the statistical tools such as Response Surface and F-Statistics. Response surfaces among the measured strain data of surface of composite beam are produced at intact state and monitoring state, and the difference of the each response surface is statistically tested using F-test. As a result, the new method successfully diagnoses the damage without using modeling and a learning data of damaged structure.

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.

Fiber optic sensors in concrete: the future?

Fiber optic sensing systems have been successfully developed for many engineering applications. The objective of this review paper is to assess the potential of fiber optic sensors for the monitoring of concrete structures. In this paper, some current applications of fiber optic sensors in concrete structures are first reviewed to demonstrate their applicability in conventional monitoring applications. The advantages of optical sensors over electrical gauges and transducers are also discussed. Then, we will focus on two novel fiber optic sensors for the monitoring of cracking and delamination in concrete structures without requiring a priori knowledge of the damage locations. Through these two examples, it is demonstrated that the proper design of optic sensors can provide useful sensing capabilities unprecedented with conventional sensors. With further research focusing on the development of novel sensing concepts and the reduction of sensor cost, the widespread use of optical sensors in concrete structures can become a reality in the future.

115 自己学習型統計的損傷検出法を用いた複合材料梁の層間はく離検出

Structural health monitoring is a noticeable technology for aged civil structures. The present paper proposes a new diagnostic tool for the structural health monitoring that employs a statistical diagnosis of self-learning method. Most of the structural health monitoring systems adopt parametric method based on modeling or non-parametric method such as artificial neural networks. The new statistic diagnosis method does not require the complicated modeling and a large number of data for the training of the artificial neural networks. The present study deals monitoring of delamination of composite beam using change of strain judged by the statistical tools such as Response Surface and F-Statistics. The new method successfully diagnoses the damage without using modeling and a large number of data for training.