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NASA's Method of Evaluating Adhesive Bond Strength is an accurate, robust, quantitative, and nondestructive bond strength measurement method that meets an immediate need in composite manufacturing. Even with careful control of the bonding procedure, destructive testing has shown that bonded joint strength shows substantial variation. Prior art in the field is insensitive to weak interfacial bonding, which leads to poor service life and potential catastrophic failure. Using NASA's method, phase measurements are acquired at a single frequency and then swept to obtain measurements at other frequencies. Narrowband filtering removes extraneous frequencies, which allows for much lower phase measurement uncertainty than other methods. Digital sine wave generation allows for better phase measurement resolution. The resultant system is a phase-based ultrasonic measurement tool for interrogating bonded joints and detecting weak adhesion with superior sensitivity than the state of the art. This new method models adhesive interfaces as a distributed spring system, where the interfacial stiffness constants of the joint can be determined from the zero- crossing frequency of the phase response and the "sharpness" or slope of the phase response. Previous theoretical research has shown that a linear correlation exists between interfacial stiffness constants and mechanically-measured interfacial bond strength. As such, the ultrasonic phase measurement method identifies intermediate bond strengths, rather than simply detecting good or bad bonds. This technique verifies bond quality in metal and composite joint systems, including those commonly found in aerospace, automotive, and many other transportation and infrastructure designs. The demonstrated ultrasonic phase method is applicable to a variety of bonding material systems.

X-ray radiography is commonly used for the detection of cracks in metal parts such as those used in the aerospace industry. A typical application is for weld inspection where volumetric flaws such as pores, inclusions and flaws resulting in volumetric features such as suck-back, and under-cut are detected. The x-ray inspection of welds is also meant to detect cracklike or tight flaws and cracks that provide linear indications. X-ray inspection reliability is based on POD of the desired minimum size cracks in suitable crack specimens. The demonstrated x-ray technique is then assumed to provide the same level of POD in actual part inspection. However, in many cases the POD demonstration specimens and setup are not similar to that used for x-ray inspection of actual parts due to the lack of appropriate demonstration crack verification toolsets. The ideal demonstration toolset shall match the parts to be tested in alloy type, part geometry, thickness and expected crack morphology, target crack size, locations, and orientations. If a qualified CIQI tool is available at the time of part inspection, x-ray technique sensitivity for crack detection can be verified for the part inspection setup. A CIQI toolset could provide simulated known crack sizes and have the same material and geometry for x-ray inspection to that of the actual part. Ideally, the appropriate crack specimen can be used to make a CIQI tool but manufacturing specimens with cracks of controlled morphology and size for different x-ray applications with different material alloys and thicknesses may be impractical and cost prohibitive. Therefore, cheap CIQI toolsets with representative cracklike discontinuities may be desired by industry. The Crack Image Quality Indicator (CIQI) is a technology readiness level (TRL) 6 (system/sub-system model or prototype demonstrated in an operational environment). The innovation is now available for your company to license. Please note that NASA does not manufacture products itself for commercial sale.

NASAs software technology uses an Image Quality Indicator (IQI)-based model that can predict whether cracks of a certain size can be detected, as well as a model that can provide appropriate conditions to optimize x-ray crack detection setup. Because this modeling software can predict minimum crack sizes that can be detected by a particular X-ray radiography testing setup, users can test various setups until the desired crack detection capabilities are achieved (predicted) by the modeling system. These flaw size parameter models use a set of measured inputs, including thickness sensitivity, detector modulation transfer function, detector signal response function, and other setup geometry parameters, to predict the minimum crack sizes detectable by the testing setup and X-ray angle limits for detecting such flaws. Current X-ray methods provide adequate control for detection of volumetric flaws but do not provide a high probability of detection (POD), and crack detection sensitivity cannot be verified for reliable detection. This results in reduced confidence in terms of crack detection. Given that these cracks, if undetected, can cause catastrophic failure in various systems (e.g., pressure vessels, etc.), verifying that X-ray radiography systems used for NDE can detect such cracks is of the utmost importance in many applications.