On energetic and dissipative gradient effects within higher-order strain gradient plasticity: Size effect, passivation effect, and Bauschinger effect

The size effect, the passivation effect, and the plastic behavior under non-proportional loading in the context of bending and tension of thin foils, and a combination of compression and shear of constrained layers, are studied using Gudmundson?s higher-order strain gradient visco-plasticity theory. Bending experiments on thin nickel foils with and without passivation are performed with a load-unload technique. The passivated layer increases the flow stress significantly. Finite element simulations are carried out on elasto-viscoplastic foils under bending and tension, and on constrained layers under combined compression and shear. The simulation results are generally in agreement with the experimental observations. Implications for higher-order boundary conditions and the roles of energetic and dissipative gradient terms are highlighted. The dissipative gradient terms contribute to the increased yield strength, whereas the energetic gradient terms lead to increased strain hardening and an anomalous Bauschinger effect. The modeling of the deformation of constrained layers suggests that compressive stress has a significant influence on the shear flow stress, reducing it compared with the shear flow stress under pure shear.

Automated summary

This study investigates the mechanical properties of thin foils in bending, tension, and constrained layers through experiments and simulations. The passivated layer significantly increases the flow stress of the foil, while the dissipative gradient terms contribute to the increased yield strength and the energetic gradient terms lead to increased strain hardening and an anomalous Bauschinger effect.