Lap shear of a soft and elastic adhesive

This paper studies the lap shear, in which both the adhesive and adherends are elastic, but the adhesive is much softer than the adherends. The shear lag model identifies a length, called the shear lag length Ls. The energy release rate of a debond crack is affected by the elasticity of both the adhesive and adherends. Their relative importance is characterized by the ratio of the length of the remaining joint, L, to the shear lag length, Ls. In the short-joint limit, L/Ls→0, the adherends do not deform, and the elasticity of the adhesive gives the energy release rate. In the long-joint limit, L/Ls→∞, the interior of the adhesive does not deform, and the elasticity of the adherends gives the energy release rate. The shear lag model gives an approximate expression of the energy release rate for all values of L/Ls. This expression is in excellent agreement with the results obtained by finite element calculations, so long as the crack is long compared to the thickness of the adhesive. •Lap shear of a soft and elastic adhesive is studied using the shear lag model.•The shear lag model identifies an enormous shear lag length.•The elasticity of both the adhesive and adherends affects the energy release rate.•The ratio between the bonded length and the shear lag length is significant.•The shear lag model gives an analytical expression of the energy release rate.