Modelling of Stress Evolution and Its Effect on Formability in Tension Under Cyclic Bending Plus Compression

Single point incremental forming (SPIF) and Double-sided incremental forming (DSIF) are two main variants of incremental sheet forming (ISF) processes. Tension under cyclic bending (TCB) have been developed as a means for experimental evaluation and validation of the SPIF process and further extended to DSIF process by adding a compression force (TCBC) in recent years. In this study, an analytical model is proposed to capture the localised deformation and stress evolutions due to bending, reverse-bending and additional compression in TCB and TCBC tests as a simplification of SPIF and DSIF processes. The results show the through-thickness stress variation has determinative influence on fracture initiation. The effects of test parameters and their interactions on formability were evaluated. Although the surface contact deformation and material thinning are simplified in the analytical model, the results obtained are comparable to experimental testing and finite element (FE) simulations. This work shows that the analytical model can be used as an effective means to decouple the complex deformation modes and local stress evolutions of TCB and TCBC and to provide a new insight into SPIF and DSIF processes.