Portable Impulse Measurements to Non-Destructively Predict the Integrity of Adhesive Joints.

摘要

The impulse-frequency response technique discussed in this report, successfully detected the presence of both macroscopic (debond) and microscopic (pores) flaws as reflected by a pronounced increase in damping (loss factor) with an increase in size, number and severity of the flaws tested. The presence of both macroscopic and microscopic flaws resulted in a degradation in the shear strength of the adhesive joint. The observed change in damping (loss factor) with cure time at the accelerated cure temperature was attributed to several competing mechanistic processes involving: a). shrinkage; b) chemical and physical characteristics of the adhesive; and c) thermal stresses. The pores and voids coupled with changes in the reaction kinetics of the adhesive mixture caused a large change in damping which was detected by the technique. Debond areas within an adhesive joint were observed to cause a marked increase in.., damping with concomitant reduction in strength of the adhesive joint. The damping was observed to increase exponentially with an increase in debond area. For different types, degree and intrinsic severity of flaws, a relationship was developed to predict strength of an adhesive joint from its dynamic properties. The actual fracture strength or. load accords reasonably well with the predicted value obtained using this relationship.