Nondestructive inspection of adhesive bonds in composite and metallic materials

One of the major responsibilities of the Aging Aircraft NDI Validation Center (AANC) established by the Federal Aviation Administration Technical Center (FAATC) at Sandia National Laboratories is to support nondestructive inspection (NDI) technology development and assessment. This paper describes several AANC projects related to the inspection, production, and utilization of disbond specimens. Conventional and advanced NDI techniques are being applied by the AANC to aid NDI development or to perform formal validation of new composite inspection technologies. The application of existing inspection techniques for adhesive bond integrity will be reviewed in light of recent advances in adhesive inspection devices. The AANC has a project intended to introduce the use of composite doublers to the commercial aircraft industry. Primary among inspection requirements for these doublers is the identification of disbonds, between the composite laminate and aluminum parent material, and delaminations in the composite laminate. The development of NDI techniques for composite doublers and the results from test specimens which were loaded to provide a changing flaw profile are presented here. The AANC has also begun a project with the Commercial Aircraft Composite Repair Committee (CACRC) which hopes to develop a set of 'generic' composite calibration standards for use by aircraft operators in setting up their inspection equipment. The standards will support damage assessment and post repair inspection of all commercial aircraft composites. Specific tasks include NDI characterizations of existing solid laminate reference standards and the identification of the important variables which should be included in composite honeycomb reference standards. The detail of this program and the progress to-date is discussed in the paper.