Investigating deformation and work hardening behaviour of stacked sheet metal specimens in compression test: Influence of friction and interfacial shear resistance

This study specifically investigated the impact of interfacial shear resistance between stacked sheets and friction on work hardening during through-thickness compression testing. The experimental findings indicate that the strain measurement technique influences the measured work hardening. The work hardening measured for the stacked sample differs from the bulk one despite using the same measurement technique. In the presence of severe friction, the stacked sample experiences a more significant reduction in flow stress than the bulk sample in comparison with that under low friction condition when a cross extensometer is employed. The FE analysis illustrates that when the frictional shear stress at the tool-sample contact is comparable to the interfacial shear resistance between stacked sheets, sliding may result in stress relaxation and a decrease in deformation load. A weaker interfacial shear resistance produces more sliding, which leads to a less inhomogeneous distribution of strains and stresses within the sample than that of a bulk sample. This analysis marks the first time that interfacial shear has been taken into account when assessing the material behaviour during compression testing of adhesively bonded samples. Following the current sample preparation and testing protocol, the measured flow stress is underestimated by approximately 1% in oiled condition and 2% in dry condition within a strain range of 0.20 when using a cross extensometer. Friction has a minor influence on the biaxial strain ratio. This research provides valuable insights into the intricate factors influencing work hardening measurements in adhesively bonded samples during compression testing.