抄録
Since adhesive bonded joints generally possess a considerable scatter in their strength, elucidation of the strength distribuion properties of these joints is important for better utilization of these joints.
In this study, to investigate the change in strength distribution of adhesive joints due to the size effect, tensile and tensile shear strengths of adhesive bonded butt and lap joints were statistically evaluated. The probability of failure was calculated for butt joints with a different diameter and for lap joints with a different lap length. Each data set was then plotted using normal, Weibull and doubly exponential functions. Furthermore, the effect of adhesive area on the mean and coefficient of variation of the joint strength was investigated. First, the strength distributions of butt and lap joints were simulated by the weakest link model based on the strength distribution of the butt joint having the smallest diameter and stress distribution of the adhesive layer obtained by FEM analysis. Then, the mean and coefficient of variation of these joints were compared with the simulation results. The main results obtained are summarized as follows;
(1) The strength distribution of adhesive bonded butt joint was nearly approximated by a normal distribution. However, for lap joint the strength distribution was fitted for an extreme distribution rather than a normal ditribution.
(2) The relationship between the mean strength and adhesive area plotted on a logarithmic graph paper showed experimental curves of butt and lap joints with a convex shape. However, the mean strength of the butt joint simulated by the weakest link model decreased linearly with increasing adhesive area, while the shape of the simulated curve of the lap joint was concave.
(3) The coefficient of variation of the butt joint was independent of the adhesive area, as predicted from the model, whereas the coefficient of variation of the lap joint decreased with increasing adhesive area contrary to the prediction of the model. This discrepacy may have been caused by a variation in shear strength due to a measurement error in the lap length.
