Mechanical wave measurement and gas excitation for bondline inspection

A method for determining a strength of a bond in a bonded structure, the method comprising:

• producing a gas pulse that is directed normal to a target area on a front free surface of the bonded structure, the gas pulse having an energy sufficient to excite a compression wave;
• activating a light source to generate a first light beam;
• splitting the first light beam into second and third light beams;
• directing the second light beam toward the target area on the front free surface;
• directing the third light beam toward a stationary mirror;
• capturing fringes produced by interference of reflected light of the second light beam which has been reflected by the target area on the front free surface with reflected light of the third light beam which has been reflected by the stationary mirror;
• converting analog data representing the captured fringes to digital data representing the captured fringes;
• and
• calculating an estimated surface velocity of the target area on the front free surface during a period of time subsequent to production of the gas pulse, using the digital data.

A system for testing a strength of a bond in a bonded structure, the system comprising:

• a gas gun positioned and configured to produce a gas pulse directed normal to a target area on a front free surface of the bonded structure, the gas pulse having an energy sufficient to excite a compression wave;
• an interferometer located and configured to generate a first light beam in response to activation, split the first light beam into second and third light beams, direct the second light beam toward a target area on a back free surface of the bonded structure, direct the third light beam toward an internal mirror, and then capture fringes produced by interference of reflected light of the second light beam which has been reflected by the target area on the back free surface with reflected light of the third light beam which has been reflected by the internal mirror;
• an interferometer control unit connected to the interferometer and configured to control activation of the interferometer;
• a signal analyzer connected to receive analog data representing captured fringes from the interferometer and configured to convert the analog data to digital data representing the fringes captured by the interferometer;
• a synchronization gated circuit connected and configured to synchronize operation of the gas gun, the interferometer control unit, and the signal analyzer;
• and
• an electronic image processor connected to receive the digital data from the signal analyzer and configured to calculate an estimated surface velocity of the target area on the back free surface during a period of time subsequent to production of the gas pulse, using the digital data.

A method for determining a strength of a bond in a bonded structure, the method comprising:

• producing a gas pulse that is directed normal to a target area on a front free surface of the bonded structure, the gas pulse having an energy sufficient to excite a compression wave;
• activating a light source to generate a first light beam;
• splitting the first light beam into second and third light beams;
• directing the second light beam toward a target area on a back free surface of the bonded structure;
• directing the third light beam toward a stationary mirror;
• capturing fringes produced by interference of reflected light of the second light beam which has been reflected by the target area on the back free surface with reflected light of the third light beam which has been reflected by the stationary mirror;
• converting analog data representing the captured fringes to digital data representing the captured fringes;
• and
• calculating an estimated surface velocity of the target area on the back free surface during a period of time subsequent to production of the gas pulse, using the digital data.