Rate-related study on mechanical properties and fracture characteristics in aluminium alloy via electromagnetic ring expansion test

The uniform one-dimensional tension can be easily realized by the electromagnetic ring expansion (EMRE) test at high strain rates of 10³-10⁴ s⁻¹, which utilizes strong pulsed electromagnetic force to deform materials. However, the accurate and rapid acquisition of the time-dependent stress, strain and strain rate in EMRE test has been a bottleneck that hinders its wide application. Based on the electromagnetism and the principle of virtual velocity in plastic dynamics, a stress analytical model considering both the electromagnetic and inertial components is established. The whole EMRE process of deformation, strain localization and fracture for 5052 aluminium alloy (AA5052) which is widely used in the automotive and aerospace industries is collected by a measurement system with microsecond time-resolved imaging, and then the true stress-strain-strain rate relationship is calculated based on the above analytical model. In addition, the dynamic mechanical properties of AA5052 under EMRE test are contrastively analyzed with those under the split Hopkinson tension bar (SHTB) and quasi-static tests. The ductility and formability of AA5052 under EMRE are improved due to the inertial and eddy current effects which is demonstrated by fracture characteristics observed using Scanning Electron Microscopy (SEM).