A new peel test method has been developed for allowing debonding of adhesively bonded, thin metallic substrates. The rolling of the substrates on rollers allows control of the plastic dissipation during substrate bending and prevents dissipation associated with substrate unbending. The measured debonding toughness is shown to be independent of substrate thickness when proper account is taken of the work required for straining the adhesive layer. Mechanical analysis shows that control of plastic dissipation in substrates remains effective, as long as the ratio of the plate thickness to the roller radius is large enough to prevent wound-up. Mode mixity during debonding can be conveniently modified by changing the radii of the rollers. This possibility of altering mode mixity allows a better control of the occurrence of the cohesive, or near-interfacial debonding mechanisms. Evidence is given for the fact that the debonding mechanism is not governed by the minimum in the debonding toughness. A significant increase of debonding toughness with increasing mode mixity is observed only when the substrate roughness is high.