It is important to note that
We begin by analysing an infinitesimal LDC1267 of a DCB specimen adherend at x≥a ( Fig. 1 and Fig. 4). The shear force V and the bending moment M act on the cross-sections, while the lower surface is subjected to the normal stress σa transmitted by the adhesive layer. This can therefore be viewed as a beam on elastic extensional foundation problem. The σa stresses do induce local effects on the adherend beam displacements and cross-section rotations. Those effects were modelled by Williams  through extensional and rotational foundations in the composite DCB specimen. However, the author showed in  that the rotational foundation should be discarded, because it would imply shear stresses that cannot exist in the DCB specimen. Moreover, the metal adherends of the DCB specimen considered in the present work are much stiffer than the polymeric adhesives. Therefore, thorns seems reasonable to assume that the vertical beam displacements w are practically identical to those experienced by the adhesive layer. Assuming small uniform εz≈2w/ha ( Fig. 1) strains in the adhesive layer,equation(8)σa=2Easwhawhere Eas=Ea(1−νa)/(1−νa−2νa2) is the uni-axial strain adhesive layer modulus, in view of the stress state observed in the above FEA. The effect of the adhesive layer on the specimen compliance is thereby taken into account and its relevance is assessed below.