Negative Mode I Loading During Buckling-Induced Delamination and Its Impact

In modern engineering, combinations of substrate structures and thin coatings is ever present. Be it in protective applications, microelectronics, or with micro-electromechanical systems, the adhesion between the substrate material and thin film is crucial, and delamination is often the reason for the failure of the components. Therefore, the thin-film adhesion measurement is extremely important for the longevity and reliability of micro-scale components. One of the available methods is the buckling-induced delamination technique, using the compressive residual stresses in thin films to cause the films to delaminate and form a buckle. This method is well established within the material science community; however, one misconception still persists, that of discarding the negative mode I loading at the delamination crack front. The practice has led to assuming some buckling to be under pure mode II loading, but new analysis shows that the negative mode I loading pushes crack surfaces towards each other, increasing friction and apparent adhesion energy. This work presents the first description of the negative mode I influence in the case of buckling-induced delamination and the possibilities it could open for more investigation.