On the thick-adherend tensile shear test of adhesive technology -: Limitations and correction methods

The thick-adherend lap shear test is numerically investigated. It is shown that the adhesive stiffness influences significantly the uniformity of the adhesive stress distribution and the substrate deformation. Both effects determine the validity of the evaluated shear modulus of the adhesive. Two methods for the substrate deformation correction, i.e., a simple method based on Hooke's law, and a method based on a finite element simulation of a reference specimen, are compared. The correction method based on the finite element method reveals not only better results for the substrate deformation correction in comparison with the simple method based on Hooke's law, but also incorporates the non-uniformity of the adhesive stress distribution for higher stiffness of the adhesive in a considerable way. The possible error of this test method on the determination of the adhesive shear modulus is generally quoted as a function of the stiffness ratio between the adhesive and the substrates.