Static Strength of Structural Adhesive Joints: Statistical Analysis and Design Parameter Correlation Based on an Extensive Experimental Campaign

The goal of the present research was to find reference surfaces that would interpolate the results of a vast test campaign, performed on several epoxy adhesives, varying numerous parameters, and estimate static failure load values of joints characterized by identical geometries, but different dimensions. Results obtained from static shear tests of single-lap and double-lap specimens were statistically processed using Student’s unilateral test with confidence level of 99%. A multivariate regression was then applied in order to obtain polynomial functions able to describe the interpolation surface. In order to test the validity of the model, failure loads were calculated for two geometrical configurations within the dimensional range used in the experimental test campaign. These values were compared with those obtained from additional experiments, relative to the same geometries. The comparison confirmed the reliability of the developed model. Tendencies that could be translated into geometries characterized by different dimensions of the tested joints were sought, thanks to the experimental data for as much as 4 adhesives and 2 adherends. Scale factors were calculated that allow, in initial design phases, to estimate realistic failure loads based on initial indications, limited to a single geometry used by producers of adhesives in mechanical characterization.