Variation of adhesive strength prescribed by JIS depending on the adhesive geometries

Abstract

The Japanese Industrial Standards (JIS) specify the adhesive strength σ_C^JIS as an average ultimate tensile stress by using a small specimen with adhesive area. For the adhesive specimen, singular stress field appears at the bonded interface end, and the uneven stress concentration in the adhesive area must be considered. Therefore, the bond strength σ_C^JIS varies depending on the adhesive geometory. As the authors have recently pointed out, if the intensity of the singular stress field (ISSF) at the interface end is taken into account, the adhesive strength can be expressed as ISSF = constant. However, this average adhesive strength σ_C^JIS is straightforward, easier to understand than the ISSF, and is widely recognized as adhesive strength. Therefore, this study discusses the validity of obtaining the adhesive strength σ_C^W from σ_C^JIS specified in JIS when the geometric dimensions of the bonded area are changed, such as when the bonded area is larger than the JIS bonded area. The bond strength decreases when the bond area is increased in a similar shape specimen. This can be explained in terms of ISSF. In the case of butt joints, σ_C^JIS is applicable when h in the JIS specimen is equal to h in the actual product, and in the case of lap joints, it is shown to vary depending on the adherend thickness and bond length.