Patent Document ID: 5408881
Application ID: 08121367
Patent Flag: 1

Claim One:
1. A method of characterizing interfacial adhesion strength between layers in a multilayer composite having at least three layers, comprising the steps of: a) irradiating the multilayer composite with an ultrasonic pulsed signal for interaction therewith, the duration of a pulse of the ultrasonic pulsed signal being approximately less than or equal to 100 nanosecond.sub.p to obtain an interaction signal characteristic of the interfacial adhesion strength at the interface of the at least three layers; b) detecting the interaction signal from the irradiated multilayer composite; c) storing amplitude and phase information corresponding to the detected interaction signal; d) convening the stored amplitude and phase information from the time domain to the frequency domain to obtain a frequency spectrum related to the stored information; e) comparing the frequency spectrum with a spectrum derived from a model of a multilayer composite that includes at least two additional layers that model the interfacial adhesion strength of the interface between the composite layers, the at least two additional layers including viscoelastic properties expressed in terms of a complex modulus M.sub.i.sup.* ; and f) obtaining a viscoelastic stiffness value characteristic of interfacial adhesion strength between layers of the composite from the model of the multilayer composite having a spectrum that most closely matches the spectrum of the detected interaction signal, the at least two additional layers each having a thickness d.sub.i, and whereby the viscoelastic stiffness value is characterized by a parameter S=M.sub.i.sup.* /d.sub.i.