Investigating Loading Path–Dependent Fatigue Behavior of Nonlinear Viscoelastic Adhesive Bonding Butt Joints Under Tension–Torsion Multipath Cyclic Loading

The tension–torsion multipath cyclic loading experiments of the nonlinear viscoelastic adhesive bonding butt joints were conducted with the asymmetric strain-control mode, and the effect of loading path and strain strength on the mechanical behavior of the joint was observed through the dissipated energy and the cyclic stress response. It was found that the loading path had influences on the fatigue damage and nonproportional strain loading path had additional fatigue damage to the joints. Meanwhile, the initial decline rate of dissipated energy and cyclic stress increased with the increase of equivalent mean strain (EMS) and equivalent strain amplitude (ESA) have been observed. In addition, the uniaxial cyclic damage model was extended to a tension–torsion fatigue damage model by adding a path factor into the tensile and torsional cyclic damage model. The model calculated results showed that the proposed model could better predict the loading path–dependent fatigue behavior of the joint.