Analysis of core instability in the plastic forming of honeycomb sandwich panels

Core instability poses a major obstacle to the advancement of plastic forming technology for honeycomb sandwich panels. To address this issue, the article performs an in-depth analysis of the core instability defect during plastic forming utilizing multi-point forming (MPF) experiments and numerical simulations of brazed aluminum honeycomb panels (BAHP). By simplifying the stress conditions experienced by the core during the BAHP plastic forming process, and using MATLAB for curve fitting analysis of the horizontal and vertical cross-sectional lines of the unstable core cell walls, the bending-shear coupling analytical model for core instability is established. Numerous MPF numerical simulations and experiments have been carried out on saddle-shaped and spherical BAHPs with different core parameters. The results indicate that the bending-shear coupling analytical model is suitable for the plastic forming of honeycomb sandwich panels, and that the height and thickness of the core are the main factors affecting core instability. Finally, the article constructs the relationship diagram between the critical forming radius of the honeycomb sandwich panel and the critical shear stress of the core based on the bending-shear coupling analytical model and numerical simulation results.