Experimental study and probabilistic bond strengths of adhesively-bonded steel butt joints under mixed-mode loadings

To study the bond behavior of adhesive-steel bonded interfaces under mixed-mode loading, a tension-torsion testing arrangement was adopted to subject adhesively bonded steel butt joints to various combinations of shear and tensile stresses. It was observed that failure mode transitions from shear cohesive with subsequent adhesive-steel interface debonding to pure tensile cohesive failure as the ratio of tensile to shear stresses increases. The interfacial tensile strength exhibits greater variability than the shear strength. For combined loading scenarios the variability of the strength increases as the normal stress to shear stress ratio increases. Statistical tests demonstrate that the shear and tensile bond strengths can each be represented using a two-parameter Weibull distribution. A superelliptical interaction relationship is presented to predict the capacity of joints that are subjected to combined shear and tensile stresses. Finally, the difference between normal and Weibull distributions in determining the characteristic and guaranteed strengths are highlighted. These comparisons indicate that normal distributions can yield non-conservative bond strengths. The research findings can provide guidance in the design of bonded joints in metallic components.