| Abstract | The growth of application using multi-material assemblies in the transportation industry has resulted in structural adhesive becoming increasingly used. These assemblies, in addition to be subjected to mechanical stresses, are also exposed to harsh environments throughout the life of vehicles with temperature variations, high humidity and exposure to de-icing salts and fluids. While such assemblies are tested for mechanical strength and fatigue resistance, it is also critical to identify the failure mode of adhesive bonds to ensure that proper actions are taken to prevent catastrophic failure. Despite the obvious need to qualify the adhesive failure modes, this task is typically relegated to a semi-quantitative analysis of cohesive/adhesive failure ratios based on the visual inspection of an experienced eye, which along with the use of adhesives of various colors, inevitably introduces variability in the qualifying process. Moreover, the characterization of adhesive performance typically involves analysing hundreds of coupons and while the general failure types are known: bulk of the adhesive (cohesive failure), substrate/adhesive interface (adhesive failure) and near-interface; quantification on each coupon suffers from inaccuracy and better means are needed. In this work, we introduce the use of pulsed thermography (PT) as a repeatable and objective solution to quantify failure modes of metal-adhesive-metal assemblies by harnessing the fundamental differences in thermal properties of the two materials. It is shown that the inspection performed in through transmission mode allows for the distinction of the various adhesion failures. |
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