Air Fingers and Cavitation - Analysis of Wood Bonding Failures that Initiated Before Adhesive Solidi

TITLE: Air Fingers and Cavitation - Analysis of Wood Bonding Failures that Initiated Before Adhesive Solidification

PRESENTED BY:  FAS, the Failure Analysis Society

SPEAKER: Dirk Lukowsky – Senior Scientist - Fraunhofer Institute for Wood Research 

DESCRIPTION: If the bond line is opened while the adhesive is still viscous (i.e. liquid or paste-like), characteristic marks are left. Air fingers and cavitation develop on the surface of the adhesive when the joint parts separate, either fully or partially, before the adhesive has solidified. Therefore, observing air fingers or cavitation can provide important clues as to the root cause of bond line failure. To improve our understanding of adhesive structures, we conducted some experiments on this phenomenon. Air fingers dominate when air can easily penetrate the adhesive, when the adhesive is thick and when it has a low viscosity (i.e. early in the process). Cavitation dominates when the adhesive layer is thin or when the viscosity is high (i.e. late in the process), or when air ingress is restricted. These insights will improve the future analysis of failing bond lines in wood, but they can also be applied to other materials.