Heterogeneous Mechanical Response And Multi-scale Catastrophic Failure Of Iron Tailings

The heterogeneous microstructure and its multiscale features determine the macroscopic mechanical response and failure characteristics of materials.The accurate description of the multiscale driving mechanisms and mechanical response is a direct requirement for safety assessment and practical engineering design.However,there is currently a lack of effective mechanical models.This study aims to characterize the microstructural features at different scales and develop a mechanical model that connects the driving mechanisms and response principles at different scales.Based on this,the relationship between microstructural features and macroscopic mechanical response are revealed,elucidating the mechanisms and processes underlying multiscale failure.This provides a theoretical foundation for understanding the multiscale heterogeneous processes in solids.This study focuses on the analysis of three different scales of characteristics in the original iron tailings.The particle size,aspect ratio,and roundness of the tailings particles were analyzed based on CT scanning and quantitatively characterized.Three types of tailings samples with different microstructural states were designed and prepared.The experiments demonstrated the corresponding characteristics of significant differences in mechanical response caused by microstructural variations.Based on the mechanics of granular materials,a stress-force-fabric relationship corresponding to tailings was derived.This relationship was verified through discrete element simulations,and the internal fabric evolution and characteristics of tailings during the loading process under different aspect ratio conditions were analyzed.The results indicate that as the loading progresses,the structural units and force chain paths within the samples undergo collapse and reconfiguration,ultimately resulting in the formation of a macroscopic shear band and leading to differences in macroscopic mechanical response.Starting from the microstructure of tailings,a strength theory model considering the influence of microstructural features was established.Firstly,by constructing simplified models of linear force chains and arching force chains,the stable characteristics of different force chain structures under anisotropic conditions were analyzed.The microstructural and force characteristics on the sliding surface of the tailings were studied,and the arrangement characteristics of tailings particles were analyzed.A quantitative relationship between the direction of the particle’s major axis and the contact normal vector direction was established.Based on the anisotropic distribution of contact normal vectors on the sliding surface,an improved strength criterion expression considering the anisotropic effect was proposed.Finally,the reliability of the improved strength criterion was validated through laboratory triaxial tests and discrete element numerical simulations.The results demonstrate that the improved strength criterion can effectively predict and evaluate the peak strength of tailings with different structures.A multi-scale catastrophic failure model was developed to investigate the multi-scale catastrophic failure process and its mechanism.The model described the characteristics and driving principles of damage events at different scales.Numerical simulations revealed four levels of damage events leading to overall catastrophe failure: micro-damage and cracking,small-scale catastrophe damage,large-scale catastrophe damage,and macro-catastrophe damage.The formation of large-scale catastrophe damage involves local small-scale catastrophe damage and random micro-damage in other regions.Macro-catastrophe damage occurs due to the cascade of small-scale catastrophe damage.The release of local elastic energy drives small-scale catastrophe damage,while the elastic energy corresponding to the entire damaged body drives macro-catastrophe damage.Based on numerical simulations using the model,an analysis was conducted to examine the correlation characteristics among damage events at different scales.The findings revealed the constitutive features of precursor events for catastrophe damage at each scale.It was elucidated that the macroscopic catastrophe failure process involves damage events at various scales.However,it was observed that the precursor process does not encompass all events.Instead,it was found that the precursor process of this catastrophe failure event is formed by the cascade of lower-level catastrophe damage events.