冲击载荷下脆性空心颗粒破碎机理

Breaking mechanisms of brittle hollow particles under impact loading

为考察脆性空心颗粒在冲击载荷作用下的应变率效应和破碎行为的细观机理,以粉煤灰漂珠为研究对象,基于低速冲击实验和有限元数值模拟,对比了典型空心颗粒材料在不同加载速率下的力学响应特性和细观压溃行为,阐释了材料宏观应变率效应产生的细观机理,获得以下结果。(1)在0.001~300 s~(-1)应变率范围,漂珠颗粒的破碎率和Hardin破碎势平均提升了约21%和10%~30%,材料比吸能提升了50%~125%,比吸能的额外增加主要与动态颗粒滑移产生的摩擦耗能相关。颗粒平均尺寸较大的试样体现出更强的应变率效应。(2)初始压溃阶段的应力应变响应特征的数值模拟结果与实验结果较吻合,低速冲击下动态二次压溃现象产生的细观机理为动态颗粒滑移和压紧行为对加载速率的依赖性。(3)数值模拟表明,冲击加载下产生相同应变时颗粒的损伤程度和范围大于准静态加载,这与实验所得破碎势随应变率增加的结果一致。对比低速冲击实验的相对破碎势分析和细观数值模拟结果可知,脆性颗粒堆积材料在动态冲击下表现出的宏观应变率效应主要归因于颗粒压溃行为的率敏感性和动态加载下颗粒破碎能量利用率的降低。

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.By 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.