Stress wave-regulated dynamic friction loading with precise interfacial stress control at high sliding speed

Traditional friction loading methods fail to replicate transient, high-speed conditions commonly encountered in engineering applications, primarily owing to uncontrollable loading parameters, and non-uniform pressure distribution across contact interfaces. In this work, we developed a novel dynamic friction loading system which functions by controllably guiding stress waves. The system is based on the Hopkinson pressure bar, and its components were optimally designed to control loading specifications through guiding the stress wave propagation. Experiments were performed for verifications via high-speed friction tests involving Ti6Al4V, Cu and SUS304 sliding against SUS304. Precise control was achieved experimentally, with adjustable loading durations lowered to 80 μs, and sliding speeds varied from 1 to 40 m/s and even higher. Specific pressure fixture was elaborately designed along with the tribo-pairs, enabling improvement of stress uniformity over contact interfaces. Other loading configurations were obtained by cyclic and micro sliding controls, and wider sliding speed range and sliding displacement could be facilitated by adjusting the components and the guiding stress wave propagation. Friction and wear responses were evaluated as functions of sliding speed. Surface and EBSD analyses revealed material-dependent wear and microstructural evolution, including transfer-layer formation, recovery-related lattice distortion reduction in Cu, microstructural refinement and possible α/β phase redistribution in Ti6Al4V, and strain-induced α′-martensitic transformation in SUS304. These results demonstrate the capability of the proposed method to investigate transient tribological and near-surface microstructural responses under high-speed sliding.