Development of a dynamic true triaxial electromagnetic Hopkinson bar system

Understanding the dynamic behavior of rocks under coupled three-dimensional static and dynamic stresses - conditions commonly associated with seismic, blasting, and vibrational events - is critical to the safety and design of geotechnical engineering. To overcome the critical experimental barrier posed by the lack of a true triaxial dynamic setup, a novel dynamic true triaxial electromagnetic Hopkinson bar (DTEHB) system is developed and presented in this study. It is the first apparatus in the world for studying dynamic responses of rock masses under coupled three-dimensional dynamic disturbances and true triaxial static in situ stresses. The fundamental working principles, system configuration and key technical challenges overcome in the development of the DTEHB are introduced in detail in this paper. By combining electromagnetic energy conversion and synchronous control techniques, the DTEHB achieves highly repeatable (>99%) and precise true triaxial synchronous impact loading, and synchronous six-directional dynamic loading (time error ≤5 μs). The DTEHB system is also capable of simulating coupled triaxial/six-directional impact and static confining pressure loading, replicating 3D in situ stress conditions. Moreover, the system’s reliability and performance are validated through analyzing controlled and adjustable stress waveforms (repeatability, duration, amplitude and arrival time), static true triaxial confining pressures and synchronous generation and arrival six-directional stress pulses. Dynamic true triaxial synchronized impact tests were successfully conducted on rock specimens for the first time. The establishment of the DTEHB could facilitate experimental testing of rock and other materials under a range of dynamic disturbances, thereby advancing the theory of three-dimensional rock dynamic theories.