Method for the evaluation of adhesive bond strength via swept-frequency ultrasonic phase measurements
Inventors
Haldren, Harold A. • Perey, Daniel F. • Yost, William T. • Cramer, K. Elliott • Gupta, Mool C.
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-11519881-B2
Publication Date
2022-12-06
Expiration Date
2041-03-23
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Abstract
A method and system for ultrasonic testing of adhesion within a sample, which provides ultrasonic bursts of different frequencies to the sample and maintains a predetermined phase difference between echoes returned from the sample and representative reference signals of the bursts supplied to the sample until a spectrum of the phase differences versus frequency is obtained and from which properties of the adhesion at an interface reflecting the echoes are derivable.
Core Innovation
The invention provides a method and system for ultrasonic testing of adhesion in samples by generating bursts of ultrasonic waves at different frequencies and maintaining a predetermined phase difference between echoes returned from the sample and reference signals representative of these bursts. This process continues until a spectrum of phase differences versus frequency is obtained, from which properties of adhesion at an interface reflecting the echoes are derivable.
The problem being solved relates to the nondestructive evaluation of adhesive bond strength, particularly for bonded joints in various applications such as aerospace and automotive design. Conventional methods for assessing adhesion often rely on destructive techniques or are insensitive to weak interfacial bonding like "kissing" bonds, leading to potential failures. Prior ultrasonic methods are complex, bulky, time-consuming, and lack reliable sensitivity for industrial use. Therefore, there is a need for a reliable, accurate, and non-destructive ultrasonic method for quantifiably measuring adhesion strength that is applicable in manufacturing and repair settings.
The present invention addresses these limitations by employing an ultrasonic phase-based method that uses swept-frequency measurements to detect interfacial bond strength. By maintaining a predetermined phase difference or quadrature between the echoes and reference signals over a range of frequencies, the system can produce a high-resolution spectrum of phase versus frequency. This approach enables accurate, robust, and rapid quantitative non-destructive bond strength measurements compatible with production environments. Analytical models and experimental data demonstrate that measuring the zero-crossing frequency and slope of the phase response correlates strongly with mechanical tensile strength, enabling prediction of bond quality.
Claims Coverage
The patent includes several independent claims directed to methods and systems for ultrasonic testing of adhesion using swept-frequency phase measurements maintaining a predetermined phase difference between echoes and reference signals.
Phase difference maintenance across frequency sweep for adhesion evaluation
A method of ultrasonic testing wherein bursts of ultrasonic waves at incrementing frequencies are supplied to a sample, echoes from an interface are measured, and a predetermined phase difference between each echo and a respective reference signal is maintained until obtaining a phase spectrum versus frequency.
Frequency and phase adjustment to maintain quadrature
Maintaining quadrature between echoes and reference signals either by adjusting frequency or by adding phase shifts to the reference signals to uphold the predetermined phase difference, enabling calculation of the ultrasonic wave reflection phase across the frequency spectrum.
Identification and locking of echo timing for selective phase measurement
Using timing from echoes to identify a portion of the echo attributed to the reflective interface, locking this timing, and recording the adjustments made during frequency sweeps to produce the phase spectrum.
Correction of instrumental effects and calculation of bond properties
Correcting for instrumental frequency responses in obtaining the phase spectrum and calculating from the spectrum anti-resonance frequency and tensile strength based on a single lap joint model and bondline reflection coefficient.
System configured with ultrasonic wave generator, transducer, detector and processor
A system comprising an ultrasonic wave generator, transducer, and detector configured to generate, deliver, and measure ultrasonic bursts at varying frequencies, with a processor maintaining a predetermined phase difference between echoes and reference signals, continuing to obtain a phase spectrum versus frequency.
Tracking cavity resonance with amplitude variation
A system where bursts of varying pulse widths, amplitudes, and frequencies are supplied, with the processor tracking cavity resonance shifts as burst amplitude increases to identify frequency shifts associated with bond characteristics.
The claims cover inventive methods and systems that utilize swept-frequency ultrasonic bursts and controlled phase difference maintenance between echoes and reference signals to derive high resolution phase spectra from bonded interfaces. These spectra allow quantitative evaluation of adhesive bond strength, incorporating frequency or phase adjustments, selective echo timing, instrumental corrections, and cavity resonance tracking.
Stated Advantages
Provides quick and accurate measurement of interfacial bond strength.
Enables nondestructive, quantitative evaluation compatible with assembly line and repair facility environments.
Exhibits superior sensitivity to weak interfacial bonding and kissing bonds compared to prior methods.
Achieves high signal-to-noise ratio and low phase measurement noise using narrowband filtering and phase-locked loop techniques.
Correlates ultrasonic phase response features directly to mechanical tensile strength for predictive capability.
Documented Applications
Nondestructive evaluation of bonded joints and coatings in aerospace structures.
Quality assurance of adhesive bonds in automotive composite and aluminum structures.
Assessment of bond strength during manufacturing and repair of structural adhesive joints.
Measurement of adhesive curing progression in UV-curable and other adhesive systems.
Potential use in medical and dental adhesive bonding research to evaluate bond strength under moist conditions.
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