Deformation and fracture behaviors of copper sheet in laser dynamic flexible forming. (January 2019) - Shen, Zongbao
Graphical abstract: Highlights: Strain localization occurs at the bulge edge under laser flexible shock loading. The variation laws of roughness in bulge and compression regions are investigated. The variation of fracture modes in LDFF are characterized. The serrated fracture boundaries and filaments are formed on the fracture surfaces. Abstract: Laser dynamic flexible forming (LDFF) is a novel high velocity forming (HVF) technology, in which the high-energy laser shock waves act on the workpiece via a flexible medium. Dynamic bulge tests of copper sheet are performed to investigate the deformation and fracture behaviors in LDFF in this paper. The laser ablation states on K9 glass surfaces under different laser energies were characterized. The samples after LDFF were characterized by optical microscopy and scanning electron microscopy. For laser energy ranging from 1020 mJ to1380 mJ, as laser energy increases, the average surface roughness (Ra) in bulge region rapidly increases due to surface free forming. However, the Ra in laser shock compression region slowly decreases due to shock flattening. Strain localization occurs around the bulge edge, and the composition of oxygen element in this region is increased with laser energy. When laser energy is equal to or greater than 1690 mJ, localized deformation evolved into the dynamic failure. Apart from the elongated micro-voids, three interesting phenomena were observed: the melting marks, the serrated fracture boundaries and filaments. As the laser energy increases, the fracture mode varies from a tensile fracture mode to a shear fracture mode, then to a filament fracture mode. The filament fracture mode indicates that superplastic flow of material may exist until fracture, and oxidation behaviors make a great contribution to the superplastic flow.