Study on particle fragmentation evolution characteristics and contact reconstruction response characteristics at the steel–coal–rock interface in compressed structures

The crushing and micro-contact characteristics of powdery particles at the compressed structural steel–coal–rock interface have an important impact on the micro-contact mechanical characteristics of the structural steel surface and the macro-contact and friction characteristics of the interface with coal and rock as fixed supports and sliding bases. In order to explore the fragmentation evolution and microscopic contact mechanism of powdery particles at the compressed structural steel–coal–rock interface, the structural steel and coal–rock models were first reconstructed based on three-dimensional surface topography data and three-dimensional fractional theoretical models. Second, key characteristic parameters, such as ultra-fine powder particle size distribution, were obtained through ultra-fine powder performance measurement tests; a particle fragmentation model was established; and the particle fragmentation parameters were verified and adjusted using the results of constrained compression tests. Furthermore, considering the water content of powder particles, combined with the theory of particle adhesion and fragmentation, a three-body contact model of steel-powder–particle-coal–particle-rock is established by using the finite element–discrete element coupling method. Finally, using the obtained key characteristic parameters as simulation inputs, the time-varying breaking characteristics and microscopic contact characteristics of powder particles under different moisture content conditions were simulated and analyzed. The results show that during dynamic compression, the time period of 0.03–0.20 ms is the main fracture period. When the moisture content is 2%, the original large particle structure basically collapses, producing fine particles with a wide particle size distribution. The remaining grains will show Level 3 crushing characteristics after moisture content crushing. A large amount of the original large-grained structure is retained or only slightly shattered. Among them, when the moisture content is 12%, the dust crushing amount and crushing rate are the largest, while when the moisture content is 6%, the dust crushing amount and crushing rate are the smallest. There is a nonlinear relationship between coal crushing behavior and water content, and the crushing position is persistent and spatial random. After crushing, the contact between particles is redefined. As the water content increases, the time change between particles weakens and the contact direction between particles begins to gradually converge, making the contact behavior more stable and regular.