Methods and apparatus for monitoring structural members subject to transient loads

A method of detecting changes in the structural integrity of a structural member comprising:

• (a) detecting the sound transmitted by the structural member along a first linear dimension in response to a transient load at frequencies including the natural fundamental and harmonic frequencies of the structural member along the first linear dimension;
• and
• (b) subjecting the structural member to a first transient load;
• and
• (c) determining a first structural acoustic signature from the detected sounds transmitted along the first linear dimension by the structural member in response to the first transient load, said first signature including the detected fundamental and harmonic frequencies subsequent to the first transient load;
• and thereafter
• (d) subjecting the structural member to a second transient load;
• (e) determining a second structural acoustic signature from the detected sound transmitted along the first linear dimension by the structural member in response to the second transient load, said second signature including the detected fundamental and harmonic frequencies subsequent to the second transient load;
• and
• (f) comparing the second signature and the first signature to determine whether the detected fundamental or harmonic frequencies of the first signature and the second signatures differ by more than a predetermined amount, whereby any such difference corresponds to a change in structural integrity.

An apparatus for detecting changes in the structural integrity of a structural member having a mass and dimension comprising:

• (a) linear motion transducer means for detecting the sonic and infrasonic frequencies transmitted by the structural member in a first linear dimension in response to a transient load including the natural fundamental and harmonic frequencies of the structural member;
• (b) first processing means for converting the detected frequencies into a structural acoustic signatures in the frequency domain;
• (c) second processing means for comparing a first structural acoustic signature corresponding to the frequencies transmitted by the structural member in said first dimension in response to a first transient load to a second structural acoustic signature corresponding to the frequencies transmitted by the structural member in said first dimension in response to a second transient load;
• and
• (d) means for determining that the structural integrity of the structural member has changed when the portion of the second signature corresponding to the second transient load differs from the portions of the first signature by more than a predetermined amount.

An apparatus for detecting changes in the structural integrity of a structural member having a mass and dimension comprising:

• (a) a triaxial accelerometer for detecting the sonic and infrasonic frequencies transmitted by the structural member along more than one direction of the structural member in response to a transient load including the natural fundamental and harmonic frequencies of the structural member;
• (b) first processing means for converting the detected frequencies into a structural acoustic signature in the frequency domain;
• (c) second processing means for comparing a first structural acoustic signature corresponding to the frequencies transmitted by the structural member in response to a first transient load to a second structural acoustic signature corresponding to the frequencies transmitted by the structural member in response to a second transient load;
• and
• (d) means for determining that the structural integrity of the structural member has changed when the portion of the second signature corresponding to the second transient load differs from the portion of the first signature by more than a predetermined amount.

An apparatus for detecting changes in the structural integrity of a structural member having a mass and dimension comprising:

• (a) transducer means for detecting the sonic and infrasonic frequencies transmitted by the structural member by detecting the displacement and acceleration of the transient member in response to a transient load including the natural fundamental and harmonic frequencies of the structural member;
• (b) an esonic transducer device for detecting the airborne sounds generating by the structural member in response to the transient load;
• (c) first processing means for converting the detected frequencies into a structural acoustic signature in the frequency domain;
• (d) second processing means for comparing a first structural acoustic signature corresponding to the frequencies transmitted by the structural member in response to a first transient load to a second structural acoustic signature corresponding to the frequencies transmitted by the structural member in response to a second transient load;
• (e) third processing means for comparing a first esonic signal corresponding to the detected airborne sounds generated by the structural member in response to a first transient load to a second esonic signal corresponding to the detected airborne sounds generated by the structural member in response to a second transient load;
• and
• (f) means for determining that the structural integrity of the structural member has changed when the portion of the second signature corresponding to the second transient load differs from the portion of the first signature by more than a predetermined amount and the first and second esonic signals contain different frequencies.