Adhesion tests stress wave

Finally, non-destructive tests have been developed based upon the phenomenon of acoustic emission. Such an emission is a stress wave derived when some materials undergo an internal change induced by local stress. The basic idea behind using acoustic emission as a quantitative test is that some of the energy expended in rupturing an adhesive joint is converted into the energy of acoustic emissions which arise prior to failure at low applied stress levels. Thus, if there are sufficient, characteristic emissions at an acceptably low applied... 

In stress wave adhesion tests, a stress wave is propagated through the system and the reflection of the stress wave at the interface results in a tensile stress at the interface. The stress wave can be injected into the solid from a flyer plate, a flyer foil, or a laser pulse.f ° ° Conceptually, the stress wave technique could be used to initiate and then stop an interfacial fracture in order to study the fracture initiation. The onset of the fracture might be detected by acoustic emission. A small area, low thickness flyer plate can be generated by depositing a film on the end of an optical fiber, a then spalhng the film off with a laser pulse. 

Variable energy ultrasonic cleaners (Sec. 13.4.5) may also be used to test film adhesion. The collapse of the cavitation bubble forms a jet, which impinges on the film and introduces a stress wave. This test can be used as a comparative test or as an acceptance test by specifying energy density and time. 

---