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Carbon fiber reinforced polymers (CFRPs) have high specific strength and many other advantages in mechanical properties compared with conventional metal materials. However, a small out-of-plane impact load can easily cause serious damage in a CFRP laminate because of its laminated structure composed of anisotropic layers. Although ultrasonic inspection is generally performed to detect the damage and estimate its location and size, the method usually requires both long inspection time and a large cost. Thus, a low-cost and in-situ system for monitoring collisions of foreign matters is required to identify the area where the ultrasonic inspection must be conducted. When a foreign matter, which is regarded as a charged body because any object is charged to a greater or lesser extent, approaches and hits grounded electric conductive materials such as a CFRP laminate, an electric current caused by electrostatic induction flows into the ground. We analyzed the electric current and conducted a falling-weight impact test to elucidate the mechanism of generation of the electric current. In addition, we proposed a collision monitoring system which utilizes the characteristic waveform of the electric current and the electrical anisotropy of a CFRP laminate, and conducted a falling-weight impact test to verify the validity of the proposed method. As a result, we succeeded in localizing the collision of the charged body in sufficiently high spatial resolution using the proposed system.

The stress intensity factor can be applied as an evaluation parameter of crack growth under small-scale yielding conditions. Moreover, the stress intensity factor corrected by the plastic zone correction can potentially be used as an evaluation parameter of crack growth for small-scale yielding criteria or beyond these criteria. In the previous study, the plastic zone correction method for that purpose was proposed. The method focuses on the gradient of the stress intensity factor at the crack tip, incorporating the term into the correction formula. To investigate the applicability of the correction experimentally, fatigue crack propagation tests were conducted in this study using three types of specimens with different gradients. The results show that the crack growth rate increased when the gradient was large although the effective stress intensity factor range was the same. This indicates that the gradient of the stress intensity factor at the crack tip affects the stress state in the vicinity of the crack tip and the crack growth rate increases as the gradient increases. When the correction of the stress intensity factor was applied, the crack growth rate could be evaluated independently from the gradient of the stress intensity factor. The correction is applicable around small-scale yielding criteria or beyond these criteria, but is not applicable under sufficiently large-scale yielding conditions.

In recent years, thermoplastic CFRP attracts considerable attention especially in aviation and automobile industries due to weldability of thermoplastic CFRP. Ultrasonic testing (UT) is commonly adopted as a testing method for inspecting weld parts although time cost on UT is thought to be problematic. Since eddy current testing (ET) is used for rapid inspection on electrically conductive materials, this paper presents an eddy current based approach for detecting defects in thermoplastic CFRP welded zones. However, it is difficult for conventional ET to detect delamination which is parallel to eddy current although delamination is one of the common forms of weld defect. To detect delamination in thermoplastic CFRP welded zones, new eddy current based approach which utilizes temperature characteristic of electrical conductivity is proposed. The proposal consists of two steps. Firstly, temperature difference between intact zones and defective zones is caused by heating the one side of the weld part. Secondly, the temperature difference is detected by ET utilizing temperature dependency of electrical conductivity.