Thadd C. Patton

Apparatus for acoustically inspecting a workpiece

An apparatus for acoustically inspecting a workpiece has a tubular member with a membrane sealing an end of the tube to form a first chamber. An acoustic transducer assembly is mounted in the tubular member. An adapter secured to the tubular member is adapted to contact the workpiece and space the membrane from the workpiece and form a second chamber. In operation, the transducer generates an acoustic wave that travels through coupling fluid disposed in the chambers to strike the workpiece. The acoustic wave is reflected from the workpiece, received by the transducer assembly, and a corresponding electrical signal is sent to a processor for evaluation. Additional features include a fluid conduit providing the independent coupling fluid, a spacer that accommodates workpiece surface variations while maintaining acoustic coupling with the workpiece, and a vacuum housing that removes excess coupling fluid from around the inspection apparatus and workpiece mating surface.

The elastic moduli of a thick composite as measured by ultrasonic bulk wave pulse velocity

One thick filament-wound composite in the form of a large thick-walled cylinder with locally orthorhombic symmetry has been measured by ultrasonic velocity to calculate its elastic moduli. The basic assumption was that small sections of the composite could be treated as a homogeneous body analogous to a crystal for ultrasonic propagation. The experimental work and the results as best expressing homogeneous body theory are presented. Because of the high anisotropy with the normal to the layers (the three-direction) much different from the axial and hoop directions, it was necessary to calculate slowness surfaces with approximate values of c13 and c23 in order to find the directions of the Poynting vectors to use in making actual measurements on c12 and c13.

Recent Developments with the Dripless Bubbler Ultrasonic Scanner

In keeping with the requirements of the air carrier maintenance community, we have developed a closed-cycle, water-coupled, ultrasonic method using a focused-beam broadband pulse for the nondestructive inspection (NDI) of adhesively bonded aluminum and composite aircraft fuselage structures. This approach, known as the “Dripless Bubbler” technique, is a combination of focused-beam immersion ultrasonics with portable ultrasonic scanners[1–4]. The Dripless Bubbler retains the high quality associated with focused-beam immersion ultrasonics, eliminates uncontained couplant water; and more importantly, it provides the capability to ultrasonically scan the exterior of an aircraft over surface protrusions such as button-head rivets and lap splice edges.

Fatigue-induced disbonds in adhesive lap splices of aluminum and their ultrasonic detection

This paper describes an experimental study of inducing disbonds in adhesively bonded aluminum lap splices by flexural fatigue and the use of ultrasonic methods for detecting such disbonds.Disbonds were imaged using focused beams of high frequency (15MHz) and low frequency (1 MHz) ultrasound. Detectability of disbonds above and below scrim cloth in the adhesive bond was investigated. Ultrasonic NDE results were compared with optical edge-on observations of disbond propagation during mechanical testing and also to other NDE methods such as thermal wave imaging and electronic speckle pattern interferometry. Methods for exploiting focused ultrasonic beam for inspection are discussed.

FIELD DEMONSTRATIONS OF THE DRIPLESS BUBBLER ULTRASONIC SCANNER

During the months of March and April of 1994, a motorized (hands-off) version of the Dripless Bubbler ultrasonic scanner was field tested at the FAA-Aging Aircraft Nondestructive Inspection Validation Center (AANC) in Albuquerque, NM and at Northwest Airlines (NWA) in Minneapolis, MN. The purpose of the field demonstrations was to validate the effectiveness of the Dripless Bubbler for ultrasonic nondestructive inspection (NDI) of fuselage lap splices, tear straps, and composite repair patches for the presence of disbond and corrosion.

Correlation of NDE Parameters with Fatigue Lifetime of Aircraft Adhesive Bonds

Various NDE methods and techniques have recently been developed to characterize adhesive bonds. These techniques simply detect voids. However, information about the presence of voids does not necessarily reflect the strength of the joints [1]. Moreover, it has been shown by Schonhorn [2] that the static failure load of joints is not largely affected by the size of a defect. Although this may be true for monotonic loading, it may not be the case under fatigue loading which is more representative of the in-service conditions. Under fatigue loading, inherent voids, cracks etc. can coalesce and form a considerably larger flaw which will eventually consume a very large portion of the bonded area. Fatigue failures account for a large number of in-service material failures of joints. Therefore, it is important to relate the size and number of defects detected by NDE methods to a quantity such as fatigue lifetime; this is the focus of the present work.

Response of a Thick Orthotropic Composite Material to Dynamic Surface Line Loads and the Application to Elastic Constant Determination

Thick composites are used in many primary structures. The determination of the elastic moduli of thick composites is important not only in characterizing ultrasonic waves for NDE, but also in prediction of load-carrying capacity of the structures. For a sufficiently thick composite, the attenuation of waves often makes echoes too weak for practical measurements. Therefore, surface measurement becomes an important method for determining the elastic moduli of a thick composite.

The Elastic Moduli of Thick Composites

Thick composites are in use in critical applications and are proposed for still others. It is important to measure the elastic moduli of thick composites for two reasons: (1) for design data on stiffness, and (2) for prediction of feasible wave paths for ultrasonic waves for NDE. Previously only relatively thin composites of relatively simple symmetries have been measured for their elastic moduli. Now, it is becoming necessary to measure thick composites of feasible engineering lay-ups. These generally provide the complexity of orthorhombic symmetry locally in a specimen combined with curvature in the gross structure. In this work, specimens cut from thick structures will be treated in the same way as crystals to measure the elastic moduli by means of ultrasonic wave velocities. Results on one structure will be presented. Difficulties will be analyzed.

Quantitative Measurement of Metal Loss Due to Corrosion in Aluminum Aircraft Skin

The detection and characterization of corrosion is one of the many challenges in the nondestructive inspection (NDI) of aging aircraft. A number of groups are pursuing ultrasonic techniques for the detection and evaluation of corrosion in such aluminum fuselage structures such as lap splices and tear straps [1]. Under the FAA-Aging Aircraft Research Program, Patton and Hsu [2–4] at Iowa State University have developed the capability to apply high resolution, water-coupled, focused-beam ultrasonic NDI to aircraft fuselage structures in a maintenance hangar environment. The method, known as the “Dripless Bubbler” technique, is a combination of focused-beam immersion ultrasonics with a portable ultrasonic scanner. With the Dripless Bubbler, B- and C-scan images of the aircraft fuselage may be acquired using both high frequency and low frequency immersion ultrasonics typically only reserved for the laboratory. In this paper, we present results on corrosion detection in the outer aluminum skin of a fuselage lap splice section using high frequency (15 MHz nominal center frequency) immersion ultrasonics, and compare these results against those obtained from collimated-beam X-ray attenuation measurements. This comparison has been quite instructive and revealed several important considerations in the interpretation of both ultrasonic and X-ray data when applied to the quantitative measurement of metal skin thickness.

Development of a portable, focused‐beam ultrasonic scanner for the NDI of adhesively bonded aircraft fuselage skin structures

In keeping with the requirements of the air carrier maintenance community, a closed‐cycle, water‐coupled, focused‐beam ultrasonic method for the NDI of adhesively bonded aircraft fuselage structures has been developed. This approach, known as the ‘‘dripless bubbler’’ technique is the combination of focused‐beam immersion ultrasonics with protable ultrasonic scanners. Because a focused ultrasonic beam is used during the scan, the spatial resolution is much greater than that obtainable with conventional flat contact transducers. The improved spatial resolution is necessary for the detection of localized corrosion pits and surface roughness associated with active corrosion sites in aluminum skin structures. The dripless bubbler allows for the capability to ultrasonically scan the exterior of an aircraft over surface protrusions such as button‐head rivets in any orientation without the problem of uncontained couplant water. Recently the dripless bubbler has been involved in a technology deployment and transit...