A Study on the Crack Propagation of Composite Materials Using a Planar Piezo Sensor

As fiber-reinforced composite materials are widely used in aircraft, space structures, and robot arms, studies that investigate NDT methods are growing in importance as they seek to improve the reliability and safety of these methods. It is very important to measure the defect sizes and to decide their tolerance ranges. Acoustic emission (AE) can evaluate these defects by detecting the emitting strain energy when the elastic waves are generated by the initiation and growth of a crack, plastic deformation, fiber breakage, matrix cleavage, or delamination. In this paper, 8 × 8 planar piezo sensors were manufactured and the crack initiation and propagation of the AE signals were experimentally investigated using these sensors. An electronic circuit able to amplify and control the 64 channel AE signals was designed and manufactured. The amplified 64 channel AE signals were output into light emitting diodes (LEDs) and stored on an optical film. From the ensuing tests, it was demonstrated that the initiation location and transmitting path of AE signals in composite materials could be detected effectively by the planar piezo electric sensor.