A novel method based on eddy‐current equilibrium for improving the sensitivity of fiber orientation detection

Abstract

AbstractFiber orientation deviation is a typical defect type in carbon fiber reinforced polymer composites (CFRPs) manufacturing process. Unlike other defect types, fiber orientation deviation has minimal influence on the local conductivity of CFRPs, so it is difficult to be detected by eddy current (EC) detection methods. Based on the principle of eddy‐current equilibrium, a new method is proposed in this paper to improve the sensitivity of fiber orientation detection. In this method, an EC field with eddy‐current equilibrium distribution inside the specimen is excited by means of a special double D‐shaped probe. When there is a deviation from the fiber orientation, the eddy‐current equilibrium state is broken, resulting in a rapid increase in the intensity and distribution range of the induced EC inside the specimen, and finally lead to a drastic change in the probe signal. The experimental results show that the double D‐shaped probe with an eddy‐current equilibrium effect can detect the fiber orientation of CFRPs, and the changes in fiber orientation can cause up to a 423.1% variation in the probe signal. Compared with the traditional rectangular probe, the designed probe is more sensitive than the former to small changes in fiber orientation in the range of −20° to 20° under high frequency excitation above 3 MHz. In addition, the proposed method can also be used for rapidly identifying fiber waviness with a deviation angle of 7.4° inside unidirectional CFRPs, which can be achieved effectively and intuitively through defect imaging.