Detection of Disbonded Regions in Bonded Aluminum Plates Using an Ultrasonic 7.5 MHz Linear Array Medical Imaging System

Abstract

INTRODUCTION Current concern for ensuring the air-worthiness of the aging commercial air fleet has prompted the establishment of broad-agency programs to develop NDT technologies that address specific aging-aircraft issues.[l, 2] One of the crucial technological needs that has been identified is the development of rapid, quantitative systems for depot-level inspection of bonded aluminum lap joints on aircraft.[l-3] Research results for characterization of disbond and corrosion based on normal-incidence pulse-echo measurement geometries are showing promise, but are limited by the single-site nature of the measurement which requires manual or mechanical scanning to inspect an area. [4-7] One approach to developing efficient systems may be to transfer specific aspects of current medical imaging technology to the NDT arena. Ultrasonic medical imaging systems offer many desirable attributes for large scale inspection. They are portable, provide real-time imaging, and have integrated video tape recorder and printer capabilities available for documentation and post-inspection review. Furthermore, these systems are available at a relatively low cost (approximately $50,000 to $200,000) and can be optimized for use with metals with straightforward modifications. As an example, ultrasonic phased-array and linear array imaging technology, which was first developed for use in the medical industry, has been successfully implemented for some NDT applications by other investigators. [8-1 0] In this paper we explore the feasibility of implementing medical linear array imaging technology as a viable ultrasonic-based nondestructive evaluation method to inspect and characterize bonded aluminum lap joints. We present an image, obtained using an unmodified medical ultrasonic imaging system, of an epoxy-bonded aluminum plate specimen with an intentionally disbonded region. This image is compared with corresponding conventional ultrasonic contact transducer measurements in order to assess whether this image can detect disbonded regions and provide information regarding the nature of the disbonded region. The results of this investigation may provide a step toward the development of a rapid, real-time, and portable method of adhesive bond inspection and characterization based on linear array technology. BACKGROUND