The inspection of crack initiation in mid-plane by means of ultrasonic

Ultra-sonic is one of the major methods to inspect and locate the damage or flaws of materials in the components or structures in engineering¹. The technique to inspect the crack initiation in mid-plane by ultrasonic in real time is presented and developed upon the requirement of detecting the initiation of cracks for thick compact tension specimen (CTS) to set up the I-II mixed mode fracture criterion. The paper is concerned with the application of an ultra-sonic scheme to detect initiation or growth of through-thickness crack at mid-plane from the surface during the loading. The technique in relation to the inspection of crack initiation in mid-plane by ultra-sonic is described in detail. The principles of the technique, and the equipment required to facilitate it are reviewed. The verification of the technique which is supported by a specific example of a CTS inspection performed on an I-II mixed mode fracture test shows that the method is valid and the technique can be capable of detecting delaminations, disbonds and lack-of-adhesion in a wide diversity of coated and uncoated materials. It is also capable of assessing the quality of composites.