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This paper presents an eddy current testing method to detect in-plane fiber waviness in cross-ply carbon fiber reinforced plastic (CFRP) laminates. We propose a method which has high sensitivity to presence of in-plane waviness and can select layers to be inspected. The probe was used to detect artificially induced in-plane waviness in cross-ply CFRP laminates. It was observed that obtained signal has extreme value at the edges and vertex of the waviness, which implies the possibility of precise identification of waviness location. Detectability of subsurface waviness was investigated using 20 layer cross-ply laminate with in-plane waviness at different depths. Experimental results showed that in-plane waviness 18 layers away from the surface could be detected. The minimum misalignment angle of the detected waviness was 7.4°. The effectiveness of the probe and physical background of the obtained signals were verified by finite element method analyses.

Liquid composite molding (LCM) is a method to manufacture fiber-reinforced composites, where dry fabric reinforcement is impregnated with a resin in a molding apparatus. However, the inherent process variability changes resin flow patterns during mold filling, which in turn may cause void formation. We propose a method to reconstruct three-dimensional resin flow in LCM, without embedding sensors into the composite structure. Capacitance measured from pairs of electrodes on molding tools and the stochastic simulation of resin flow during an LCM process are integrated by a sequential data assimilation method based on the ensemble Kalman filter; then, three-dimensional resin flow and permeability distribution are estimated simultaneously. The applicability of this method is investigated by numerical experiments, characterized by different spatial distributions of permeability. We confirmed that changes in resin flow caused by spatial permeability variations could be captured and the spatial distribution of permeability could be estimated by the proposed method.

We experimentally test a previously reported lightning protection sheet (LPS) sensor to detect impacts within a short collision interval. The exact loading position is achieved using a two-step method. Our sensor sheet is flexible and can easily be attached to different shaped structures. Current flows in the sensor only during loading and our quick switching system identifies the real-time x, y coordinates of the loading position. Using this method multiple impacts can be detected when the time difference between two impacts is larger than 10 ms. The position of a single impact is estimated within 16 mm. This means that detailed inspection needs to be conducted only over a circular area with a radius about a few centimeters. Our method is ideally suited for aircraft components and it reduces costs and saves time as only small specific areas require inspection using ultrasonic or electrical resistance techniques.

Rapid and automatic inspection of composite aircraft after every flight would reduce the safety factor and allow for more flights. Although, an electrical resistance change method (ERCM) has been proposed, there are many problems with its practical application. In this study, a new diagnostic method, impact-damage visualization, was developed. Indentation damage increases fiber–fiber contact at the interlaminar interface and electrical conductivity. Consequently, electrical current applied to the material will concentrate around the damaged area, and lead to selective and intense resistive heating. This temperature increase can be observed by thermography or detected as a change in electrical resistance caused by the temperature difference. The proposed method had sufficient reliability and sensitivity for practical application as a damage inspection method.