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The relationship between the propagation directions of ultrasonic wave and the direction of the principal axis of anisotropy in uni-directional CFRP with straight fiber is well known. However, the behavior of ultrasonic wave in CFRP with curved fibers is not clarified in details. In this paper, numerical analyses using the finite difference method were conducted to visualize the behavior of ultrasonic waves in CFRP with concentrically curved fibers. Numerical simulation results showed the energy of quasi-longitudinal ultrasonic wave curved along the fiber direction. In order to confirm the analytical result, CFRP specimen with curved fibers were prepared by utilizing 3D-printer and the behavior of ultrasonic propagation was observed by using Laser ultrasonic system. The observed results confirmed the analytical results that the ultrasonic wave curved along carbon fibers.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2020-09-09, 資料番号: PA2120053000

We present three-scale modeling of multilayered structures consisting of heterogeneous layers. The presented laminated model is not based on the so-called lamination theory or assumption related to the theories. The framework is based on the multiscale seamless-domain method and homogenization theory. First, we conduct homogenization analysis of the heterogeneous laminate and regard it as being composed of the homogenized anisotropic layers (i.e., the microscopic analysis). Second, we analyze the laminate using the multiscale seamless-domain method (i.e., the mesoscopic and macroscopic analyses). We present numerical examples of heat conduction and elastic deformation for fiber-reinforced composite laminates. In all examples, the proposed multilayered models represented by a small number of points provided solutions as accurate as those of ordinary finite-element models having many nodes.

This study investigated the similarity law of ultrasonic propagation in CFRP with concentrically curved fibers. The similarity law was formulated by introducing a new dimensionless number D. Additionally, the similarity law for a two-dimensionally propagating bulk wave was mathematically proven using the governing equation. A numerical simulation was conducted to visually demonstrate how this similarity law is held in CFRP with concentrically curved fibers. The simulation results revealed that the wavefronts of waves generated at different points had geometrically similar shapes when the D values for each wavefront were identical. The experimental visualization of ultrasonic propagation through a CFRP plate with concentrically curved fibers was also conducted, and the results revealed that the similarity law held in actual CFRP material specimens.

Carbon fibre reinforced polymer (CFRP) composites structures are widely used in aeroplane structures. When a lightning strike affects fasteners or leak electric current of the lightning strike arrives at fasteners, the fasteners play serve as conducting electrodes for the CFRP plate. This current might cause complicated damage in the CFRP plate. The authors have developed self-sensing TDR to detect damage. Self-sensing TDR is used in this study to monitor lightning strike damage around a CFRP plate fastener hole. The lightning strike electric current is applied directly to a fastener. Thereafter, self-sensing TDR is applied. The lightning strike damage is investigated using cross-sectional inspection to clarify the mechanisms of the monitoring using TDR. Results show that the method can detect a 30 kA strike. Peeling of the GFRP insulator causes a characteristic impedance change, which in turn causes signal reflection of the transmission line.

A non-destructive inspection method of carbon fibre reinforced polymer (CFRP) is self-sensing technology that uses carbon fibres as sensors. The technology applies electric current to composites and measures the electrical resistance change to detect damage. Although the technique detects damage precisely, it requires many electrodes on the CFRP surface. Time-domain reflectometry (TDR) has previously been proposed to detect damage over a wide area with a small number of electrodes and applied to detect fibre breakage in unidirectional CFRP ply specimens. In the present paper, experiments are conducted for a cross-ply CFRP laminate subjected to impact damage. Three impact loads are applied and the damage is inspected employing self-sensing TDR and a micro-strip line. Results show that the self-sensing TDR can be applied to laminated CFRP structures that have several fibre directions and when damage such as a delamination crack extends under or close to the micro-strip line.