Breaking mechanisms of brittle hollow particles under impact loading

Abstract

To investigate the strain rate sensitivity of mechanical properties and the breaking mechanisms of brittle hollow particles (BHPs) at mesoscopic level, low-velocity impact tests and the corresponding numerical simulation using finite element method (FEM) were performed on the fly ash cenospheres (CPs). Characteristics of the mechanical response and the mesoscopic crushing behavior of brittle hollow particles under dynamic loadings were observed and discussed based on the impact tests. Additionally, the mechanism of producing strain rate sensitivity of cenosphere was interpreted through the mesoscopic numerical simulations. The results are as follows. (1) At the strain rate of 0.001-300 s-1, the breaking ratio and the Hardin relative breaking potential was improved by 12% and 10～30%, respectively. Meanwhile, the specific energy absorption of two types of cenospheres increased 50%～125%. The extra improvement of energy absorption should be attributed to the increase of the friction energy dissipation which was caused by the dynamic slipping rearrangement of BHPs. Also, the cenosphere specimens with larger particles size distribution exhibited more remarkable strain rate sensitivity. (2) The stress-strain response of BHPs at the initial collapse stage obtained from the numerical simulation coincided well with the experimental results. It was suggested that the dynamic secondary collapse stress was mainly caused by the particle slippage and its dependence on the loading velocity. (3) In addition, the numerical simulation shown that the damage extent of packing particles under dynamic loadings was much higher than that under static loadings at the same compression strain level. This was in good agreement with the experimental results that the relative breaking potential, characterizing the crushing extent of particles, increased with the strain rate. Combining the potential analysis of the testing cenosphere specimens and the mesoscopic simulation, it can be concluded that the intrinsic mechanism of the macro strain rate effect of BHPs is the decrease in energy utilization of particle breaking and the rate-dependence of the particles crushing behavior.