Laminated carbon fiber reinforced polymer (CFRP) composites have been used in many aircraft components. Because it is quite difficult to detect delamination cracking visually, many cracking monitoring methods have been proposed. One of these methods is the self-sensing method, where electrical resistance change is used to detect the damage to the laminated CFRP. For a thick CFRP plate, however, a delamination crack is usually accompanied by a dent. The dent causes a decrease in the electrical resistance of the CFRP plate. Although dent monitoring using this decrease in electrical resistance has been proposed, it is also important to clarify the mechanism of the decrease in electrical resistance. In this study, therefore, experimental investigations were undertaken to understand the mechanism of the decrease in electrical resistance induced by the dent. An elastic-plastic finite element analysis was also performed to confirm the material deformation under the dent. We found that a decrease in the fiber spacing in the thickness direction caused by plastic deformation causes contact between the fibers, and this causes the decrease in the electric resistance in the thickness direction.

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Laminated CFRP structures are applied to many aerospace structures. Although CFRP laminates have high specific strength and specific stiffness, an impact load easily creates damage such as delamination cracking, matrix cracking, and fiber breakage. Damage to laminated CFRP is usually difficult to detect by visual inspection. As a result, damage monitoring systems are required for large laminated CFRP structures. Many researchers have already proposed self-sensing monitoring systems which measure electrical resistance changes in the laminated CFRP. This method, however, requires a lot of electrodes. In the present study, a new time domain reflectometry (TDR) method using an electrical pulse signal and reinforcement carbon fiber sensors is adopted as a monitoring method. The method is applied to a 2-m long CFRP strip plate specimen to detect an ideal damage mechanical notch using a reflected pulse signal. In addition, the effect of the orthotropic conductance of the CFRP plate is experimentally investigated using multiple electrodes, and is shown to be negligible.

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This study is an analytical investigation of time domain reflectometry (TDR) for carbon fiber reinforced polymer (CFRP) composites using numerical simulation software. This process is called self-sensing TDR because the carbon fibers themselves are used as the sensors. A previous study conducted experimental investigations of this process using parallel aluminum plates. This study uses finite difference time domain analysis for simulations of a transmission line structure for the self-sensing TDR. Details of the effects of the orthotropic electric conductance are investigated analytically. The simulation results show that the electromagnetic waves propagate rapidly in the transverse direction and that the effects of the orthotropic conductance seem to be negligible. An additional simulation using a pair of square CFRP plates reveals that the electromagnetic wave is affected by the orthotropic conductance. The effect is nevertheless very small when compared with the actual ratio of the electric conductance between the fiber direction and the transverse direction.

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In the present paper, we derive a solution for two circular elastic inclusions that are perfectly bonded to an elastic medium (matrix) of infinite extent under in-plane deformation. These two inclusions have different radii, central points, and elasticities. The matrix is subjected to arbitrary loading by, for example, uniform stresses, as well as to a concentrated force at an arbitrary point. In this paper, we present a solution under uniform stresses at infinity as an example. The solution is obtained through iterations of the Mö bius transformation as a series with an explicit general term involving the complex potential of the corresponding homogeneous problem. This procedure is referred to as heterogenization. Using these solutions, several numerical examples are presented graphically.

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