  The failure of adhesive bondlines has been studied at the microscopic level
via tensile tests. Stable crack propagation could be generated by means of
samples with improved geometry, which made in-situ observations possible. The
interaction of cracks with adhesive bondlines under various angles to the crack
propagation was the focus of this study as well as the respective loading
situations for the adhesives UF, PUR, and PVAc, which have distinctly different
mechanical behaviors. It is shown how adhesive properties influence the
occurrence of certain failure mechanisms and determine their appearance and
order of magnitude. With the observed failure mechanisms, it becomes possible
to predict the propagation path of a crack through the specimen.
