Non-Contact and Contact Ultrasonic Detection of Fiber Orientation in Orthotropic Composite Laminates

Abstract

Since layup orientation of the laminates greatly influences its properties, an NDE technique for layup orientation determination would be very beneficial. It is desirable to perform contact-less nondestructive evaluation to assess material properties and defects of composites because of permeation of coupling medium such as water. An ultrasonic technique would be very useful, which could be used to test the part after and before curing laminates and requires less time than the optical test. First of all, conventional ultrasonic experimentations were conducted using water as a transmitting medium. In contrast, air-coupled ultrasound is non-contact and has clear advantages over water-coupled testing. Therefore ultrasonic systems for air-coupled and conventional ultrasound were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. Firstly, a manual scanner was built for making transmission measurements using a pair of normal-incidence shear wave transducers to find the effect of fiber misorientations of orthotropic composite laminates. With the transmitter and receiver on the same side of a laminates, Lamb waves were generated and used for the amplitude magnitude. As a result, it was confirmed that the influence of fiber direction in the laminates could be detected by the non-contacting or contacting inspection from one-side and the detectability was improved by using shaped tube for reducing the specular reflection on transmitting. Furthermore, a vector decomposition model was utilized for lay-up error of the orthotropic laminates. Finally, aircoupled results well corresponded somewhat to those of contact ultrasonic examination in the orthotropic laminates.