N13A-T011 TITLE: Novel Approaches to Bond Quality Nondestructive Evaluation with Emphasis on Kissing Bond Detection and Bond Line Assessment

TECHNOLOGY AREAS: Air Platform, Ground/Sea Vehicles, Materials/Processes

ACQUISITION PROGRAM: PEO (U&W), PEO (T)

OBJECTIVE: To identify and demonstrate the feasibility of previously unexplored methods for the nondestructive evaluation (NDE) of adhesive bond quality, including in-particular kissing bonds, both as initially fabricated and as a function of service. Bond quality implies at least a semi-quantitative indication of bond strength.

DESCRIPTION: Current state-of-the-art in bondline quality inspection is capable of identifying the location and size of delaminations in bonded joints. These inspection methods, which include ultrasonics, thermography, shearography, and X-ray, are universally used throughout the aerospace community to detect most bondline defects formed during part manufacturing as well as failures that may occur in the operational environment. These systems, however, have proven to be unable to detect weakened (also called "kissing") bonds that may have formed during initial manufacturing. Such bonds may have occurred due to contamination at the bondline surface or in the adhesive, incorrect thermal cure of the adhesive, or poor mixing of the adhesive’s constituents. Bonded joints are used extensively for both civilian and military aircraft applications. Assessing the quality of these bonds is typically performed using NDE techniques such as bulk wave ultrasonics or thermography. These methods cannot reliably differentiate between a good bond and a so-called "kissing" bond, presenting major barrier to the optimum utilization of adhesive bonding as a joining method in primary airframe structures.

This solicitation seeks novel approaches based on bulk or guided wave techniques which provide a semi-quantitative evaluation of bond shear strength sufficient to detect a variety of kissing bond defects ranging from fully to partially adhered bond line flaws. The ability to measure the bond strength of joints of dissimilar materials such as composites bonded to aluminum or titanium is highly desirable, as well as the ability to discern bond strengths of bonds in layered assemblies. Instruments/equipment to be derived from any such new approach must be factory as well as field deployable.

PHASE I: Identify a particular approach to be taken and show feasibility by demonstrating a strong correlation between predicted bond quality for a range of appropriately flawed test specimens and the results of destructive testing of these same specimens. Both initially fabricated and aged conditions should be addressed.

PHASE II: The performer shall demonstrate increased capability by measuring the bond strength on realistic aircraft designs manufactured with bonded structures. Develop and deliver an optimized version of equipment based on the approach demonstrated in Phase I. Conduct both factory and field demonstrations of appropriate prototypes.

PHASE III: Partner with a tech transition small business and/or OEM to scale up and produce the equipment and methodology.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Military application: The advanced bond inspection tool would be beneficial for almost all composite structures and for hybrid assemblies of composite and metal. Commercial application: In addition to almost all DoD systems applications include recreational sporting industry, commercial aircraft, and marine applications.

REFERENCES:
[1] T. Kundu, A. Maji, T. Ghosh, and K. Maslov "Detection of kissing bonds by Lamb waves", Ultrasonics, Volume 35, Issue 8, January 1998, Pages 573–580.

[2] J. Tucker, "Ultrasonic Spectroscopy for corrosion detection and multiple layer bond inspection", Proc 1st Joint DoD/FAA/NASA Aging Aircraft Conference. 1998.

[3] J.K. Chambers and J.R. Tucker, "Bondline analysis using swept frequency ultrasonic spectroscopy", Insight J. British Institute of NDT, Vol. 41, 1999.

[4] Yan, Dawei; Drinkwater, Bruce W.; Neild, Simon A. "Experimental and Theoretical Characterization of Kissing Bonds in Adhesive Joint Using Non-Linear Ultrasonic Measurement" Review of Progress in Quantative Non-destructive Testing, Vol. 29. AIP Conference Proceedings, Volume 1211, pp. 1190-1189 (2010).

[5]. R. Bossi, K, Housen and W. Shepherd, "Application of Stress Waves to Bond Inspection," SAMPE Proceedings, May 16-20, 2004, Long Beach, CA.