Ultrasonic attenuation effects associated with the physical modeling of adhesive bonds

The purpose of this work is to examine the effects of selected attenuation functions in adhesive bond modeling problems so that the attenuation in signal processing and interpretation can be treated adequately, and also to determine the significance of attenuation in evaluating bond integrity. Bond models are presently being used to study such problems as improper substrate surface preparation, improper adhesive cure, and chemical segregation of the adhesive. Specific attenuation functions used include some experimentally measured values for real materials, such as polystyrene, Lucite, and rubber, and also a few hypothesized resonant functions based on observed attenuation phenomena in polymeric materials. Results indicate that attenuation effects do not substantially alter the ultrasonic reflection at frequencies lower than 7 MHz. As a result of the study, however, it becomes possible either to eliminate or to amplify attenuation effects by selecting processing techniques for bond inspection. It is also possible to study more sophisticated adhesive bond models with more accurate attenuation functions that could ultimately lead to improved criteria for transducer and signal-processing selection.