A novel methodology for affecting the strain paths during hydraulic bulge tests by means of laser heat treatments

Nowadays, the design of manufacturing processes is supported by numerical simulations, that require an understanding of the material forming limits under the process conditions. The hydraulic bulge test represents an effective and well-established experimental procedure to evaluate critical strains of a material. However, it relies on using different elliptical die geometries to vary strain paths, introducing limitations in experimental flexibility. This work aims to evaluate the feasibility of achieving different strain paths during hydraulic bulge tests only using a circular die, by pre-softening certain zones of the testing blank using laser heating. The laser heat treatments (LHTs) were designed using a numerical/experimental approach. Two LHT strategies using different laser power values were performed to locally modify the material properties. Then, hydraulic bulge tests were conducted on the LHTed specimens and the resulting strain paths were analysed. The strain paths acquired during hydraulic bulge tests confirmed the possibility to affect the slope of the strain path at the dome by changing the LHT strategy, designed with the proposed methodology.