Abstract
The prediction of springback angle for ultra-thin metallic sheets becomes extremely difficult with the existence of size effects. In this study, size effects on the springback behavior of CuZn20 foils are investigated by experiments and analytical methods. The experimental results reveal that the springback angle first decreases gradually and then increases markedly with the decrease of foil thickness, which cannot be analyzed by current theoretical models. Then, an analytical model based on the Taylor-based nonlocal theory of plasticity is developed, in which the drastic increases of both the proportion of surface grains and the strain gradient are taken into account. Moreover, the influence of strain gradient is modified by the grain-boundary blocking factor. The calculation results show that the springback angle of foils is determined by the intrinsic competition between the decrement angle caused by surface grains and the increment angle caused by the strain gradient. Besides, the relative error of predicted springback angle by the model is less than 15%, which means that the developed model is very useful for improving the quality of micro sheet parts with high accuracy of springback prediction.
Highlights
Nowadays, multiple fields such as medical equipment, aircraft, and micro electro mechanical systems show growing trends in miniaturization and lightweight, which leads to a big increase in the demand for micro-bending parts [1,2]
The surface grain theory holds that, compared with internal grains, surface grains have less constraint owing to the presence of free surface, so the deformation of surface grains is much easier than that of internal grains [5]
Classical bend forming theory; Surface grain theory; Strain gradient theory; The analytical model (calculation with ∆θcla + ∆θsg, ω is calculated as Equation (9) in ∆θsg )
Summary
Multiple fields such as medical equipment, aircraft, and micro electro mechanical systems show growing trends in miniaturization and lightweight, which leads to a big increase in the demand for micro-bending parts [1,2]. For most of the micro-bending parts, in particular, heart stent, corrugated sheet, lead frames, and so on, the final shapes have an important influence on their functions [3,4]. Because of complicated size effects, the springback behavior of foils is difficult to predict, which leads to the lack of theoretical support for designing the foil bending process. Research on the size effects on foil forming can be roughly divided into two fields. Some researchers focus on the weakening material deformation behavior caused by surface grains. In the micro-compression test of copper performed by Geiger et al., Materials 2020, 13, 4929; doi:10.3390/ma13214929 www.mdpi.com/journal/materials
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
