Characterization of Bonding Agent Durability in Fatigue Monitoring Applications Utilized in NDT

Choosing the appropriate bonding agent for fatigue monitoring applications is critical considering bond reliability is an important aspect for reliably detecting signals over time and in structural health monitoring applications. The purpose of this study was to characterize several bonding techniques used in the laboratory environment to better understand the durability of various bonding agents. A Krouse testing machine was used with a triangular beam specimen designed to provide constant stress/strain on the surface throughout the beam test section when deflected. Piezoelectric sensors were bonded by various methods to the specimens and cycled. A Pencil lead break (PLB) was performed before the test began and at intervals of 100,000 cycles up to a total of 500,000 cycles to track the deterioration of the bond. The amplitude of the recorded pencil lead break waveforms was the main characteristic used for evaluation in this study. The results indicated that across all the bonding agents there was an observable difference in the amplitude of the signal between the initial pencil lead break at 0 cycles and 100,000 cycles. The signal’s amplitude remains somewhat constant after the first 100,000 cycles to 500,000 cycles. However, the effect on the amplitude was different across bonding agents and varying amplification would be needed for the waveform to be distinguishable. The results from this study demonstrated that not only is it important to pick a bonding agent that demonstrates good amplitude for signals, but also one that performs well after long periods of fatigue.



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