Adhesive hardening and plasticity in bonded joints

While strain-hardening mechanisms for many metals are well understood, polymers in general, and adhesives in particular, have received less attention. Thin adhesive joints are difficult to characterize, for instance, where the constraint of relatively rigid adherends can mask plastic response. The aim of this work was to quantify adhesive plastic strain hardening and evaluate the effectiveness of a nonlinear hardening model. The plastic response of two structural epoxy adhesives was shown to be dominated by kinematic hardening. A numeric model was developed to describe the shear stress-strain response of scarf and lap shear joints. Experimental adhesive joint responses were compared with linear and nonlinear hardening models. A nonlinear kinematic hardening model described the shear stress-strain response within 3% for a toughened adhesive. Agreement with a second adhesive, using a nonlinear combined hardening model, was within 2%.