· Simple structures with uniform stresses
Pressure vessels, piping, man-lift booms
· Structures where working stresses can be artificially stimulated
Pressure vessels, piping, man-lift booms.
·Redundant structures with non-uniform stresses.
Bridges, Offshore platforms, Aircraft
· Structures containing mechanically clamped joints and resulting frictional movement.
Most structures with the exception of pressure vessels and piping fall into this category.
The motivation for designing and using Smart AE transducers and instrumentation came about after recognizing that the AE signals created in plates by extraneous noise, differs from those created by crack growth.
Extraneous noise such as impact and friction are out-of-plane (OOP) sources. These type of sources create primarily low frequency flexure waves and high frequency shear waves in plates with very little extensional wave component.
Crack growth is an in-plane (IP) source of AE signals, which creates primarily high frequency extensional and shear waves with small low frequency flexure wave components depending on crack depth.
The SE9125-M transducer and AESMART 2000 instrument combination are designed to recognize the difference between AE signals generated by an OOP source and an IP source. This is accomplished by first designing the transducer to be equally sensitive to AE signals generated by both OOP and IP sources. The signals from this transducer are split into two frequency ranges, the peak amplitude of the signals in both frequency ranges are detected and the ratio of the high frequency (HF) to low frequency(LF) peak amplitudes is calculated. The value of this ratio can be used to determine if the source of the AE signal is OOP or IP. The ratio can also be used to estimate the depth in the plate where the signal originates. A ratio filter in the instrument can be activated to eliminate AE signals from extraneous noise (OOP sources), before they enter the data base.
The ratio of the peak amplitudes of the AE signal created by IP sources can be used to estimate crack depth.