Design and development of a novel electromagnetic-driven composite expansion ring system to test dynamic tensile fragmentation for brittle material

The electromagnetic-driven composite expansion ring technique provides an effective means of generating one-dimensional tensile loading at high strain rates for brittle materials. In this method, a low-resistivity pusher drives a high-resistivity specimen, thereby minimizing the influence of the specimen’s electrical properties. To clarify the underlying loading mechanisms and guide test design, this study establishes a coupled electromagnetic-mechanical theoretical framework together with a simplified formulation for insulating specimens. Based on these equations, a systematic parametric analysis is conducted to evaluate the effects of pusher material, capacitance, discharge voltage, solenoid configuration, and ring geometry on the loading response. Using polymethyl methacrylate (PMMA) as a representative brittle material, two dynamic expansion ring experiments were performed, reaching maximum strain rates of 2912 and 1142 s⁻¹. High-speed imaging captured the expansion and fragmentation processes, while photon Doppler velocimetry measured the expansion velocity. The results show that fragmentation consistently initiates during the deceleration phase and becomes increasingly severe with rising strain rate. These findings, together with the validated theoretical framework and the developed test methodology, demonstrate that the proposed system provides a reliable and effective approach for characterizing the dynamic tensile fragmentation behavior of brittle materials. (Figure presented.)