Adhesive geometry dependence of JIS adhesive strength expressed as average stress and countermeasure based on ISSF

Abstract

The Japanese Industrial Standard (JIS) specifies the adhesive strength as an average ultimate tensile stress without considering the size effect. The prescribed JIS specimen has a smaller adhesive area, $A^{JIS}={\left(12.7mm\right)}^2$. In this paper, therefore, the reduction of the average adhesive strength is investigated for large adhesive areas $A\gg A^{JIS}$. The discussion is based on the results that the adhesive strength can be expressed as a constant ISSF (Intensity of the Singular Stress Field), as shown in previous studies. Even for ductile resin, the elastic behavior of the adhesive layer is confirmed, as well as small-scale yielding, showing the validity of the ISSF obtained by elastic analysis. Numerical simulation shows that the average adhesive strength varies depending on the adhesive geometry. With a tenfold increase in the adhesive geometry, the adhesive strength decreases to 50 % of the JIS strength, and with a hundredfold increase, the adhesive strength decreases to 20 % of the JIS strength. For large adhesive areas, the JIS strength can be applied by using the same adhesive thickness as that for the small adhesive area specified by the JIS. This is because the ISSF of the actual product is controlled by the adhesive thickness regardless of the adhesive area.