Detection and monitoring of cracks and fractures using nonlinear response to multimode acoustic signals

A system comprising:

• a controller comprising one or more hardware processors with memory coupled thereto;
• first and second acoustic transducers;
• a signal generator having a control input coupled to the controller and a signal output coupled to the first acoustic transducer;
• and
• a signal processor having a signal input coupled to the second acoustic transducer and a receiver output coupled to the controller;
• wherein the system is configured to perform operations comprising:
• (a) transmitting, with the first acoustic transducer, a broadband first acoustic signal through an interrogation region of a rigid structure;
• (b) receiving, with the second acoustic transducer, a second acoustic signal responsive to the first acoustic signal;
• wherein the first and second transducers are respectively coupled to the rigid structure at first and second locations which define the interrogation region, the interrogation region having an extent at least ten times a largest transverse extent of sensor contact areas of the first acoustic transducer or the second acoustic transducer;
• (c) canceling a linear response from the second acoustic signal to obtain a nonlinear third acoustic signal;
• (d) determining an acoustic nonlinearity of the interrogation region based at least in part on a magnitude of the third acoustic signal;
• and
• (e) outputting an assessment result for the interrogation region of the rigid structure based on the determined acoustic nonlinearity, wherein the outputted assessment result is a defect alert and is further based on modeling of at least a portion of the rigid structure including the interrogation region.

A method for detecting or monitoring a crack or fracture in an elongated rigid structure, the method comprising:

• locating a first acoustic transducer at a first location along a surface of the rigid structure;
• locating a second acoustic transducer at a second location along the surface of the rigid structure;
• locating a third acoustic transducer at a third location along the surface of the rigid structure, wherein the second location is between the first location and the third location, a longitudinal spacing between the first location and the second location defines a first interrogation zone, and a longitudinal spacing between the second location and the third location define a second interrogation zone, and wherein at least one of the longitudinal spacings defining the first interrogation zone or the second interrogation zone is at least ten times a largest transverse extent of an active area of the second acoustic transducer;
• generating, with the second acoustic transducer, a baseline broadband acoustic signal along the rigid structure;
• obtaining, with the first acoustic transducer, a first linear response baseline signal responsive to the baseline broadband acoustic signal in the first interrogation zone;
• obtaining, with the third acoustic transducer, a second linear response baseline signal responsive to the baseline broadband acoustic signal in the second interrogation zone;
• generating, with the second acoustic transducer multiple probing broadband acoustic signals, with respective signal strengths exceeding a signal strength of the baseline broadband acoustic signal, along the rigid elongated structure;
• obtaining, with the first acoustic transducer, multiple first monitoring signals responsive to respective ones of the multiple probing broadband acoustic signals in the first interrogation zone;
• obtaining, with the third acoustic transducer, multiple second monitoring signals responsive to the respective probing broadband acoustic signals in the second interrogation zone;
• determining a plurality of first nonlinear response signals for the first interrogation zone from the first monitoring signals by:
• performing baseline subtraction on each of the first monitoring signals using the first linear response baseline signal, to determine a respective one of the first nonlinear response signals;
• determining a plurality of second nonlinear response signals for the second interrogation zone from the second monitoring signals by:
• performing baseline subtraction on each of the second monitoring signals using the second linear response baseline signal, to determine a respective one of the second nonlinear response signals;
• determining whether microstructural defects exceed a first threshold in the first interrogation zone based on the first nonlinear response signals;
• and
• determining whether microstructural defects exceed a second threshold in the second interrogation zone based on the second nonlinear response signals.