混凝土类材料SHPB实验若干问题探讨

ISSUES OF SHPB TEST ON CONCRETE-LIKE MATERIAL

分离式霍普金森压杆(SHPB)实验是研究混凝土类材料动态力学性能的主要方法。该文简要回顾了当前混凝土类材料SHPB实验中存在的若干问题(如端面摩擦、骨料大小、惯性效应、温度效应等)的研究进展;通过对混凝土SHPB实验的精细化数值模拟,进一步分析了惯性效应产生机理,提出了材料的塑性流动引起的横向加速度是产生围压的关键原因,围压波在试件中心的反射和边缘的卸载形成试件中围压从中心向四周逐渐减小的抛物线型分布;利用该文所提的SHPB实验惯性效应产生机理,较好地解释了SHPB实验的尺寸和主动围压的影响规律;基于自主研制的可进行围压和温度共同加载的SHPB实验装置TSCPT-SHPB,对在5MPa^25MPa围压作用下以及在40℃~80℃温度下盐岩动态力学性能进行实验研究,结果表明,高围压下应变率效应不如低围压下显著,温度越高,强度越低;基于考虑粗骨料大小、形状及空间随机分布的三维混凝土细观模型,对混凝土各细观组分对动态效应影响进行了研究,结果表明:各组分材料静态强度越高,混凝土动态强度也越高;在相同骨料粒径条件下,骨料体积率越高,混凝土动态强度也越高;而相同骨料体积含量条件下,骨料尺寸越大,混凝土动态强度越低。

The split Hopkinson pressure bar test is the major method in studying the dynamic properties of concrete-like materials. Firstly, we briefly reviewed the progresses of some issues of the SHPB test of concrete-like materials, i.e. the end friction effect, the aggregate effect, the temperature effect and the inertia effect. Secondly, some mechanism analyses of the inertial effects were performed based on the detailed FE simulation of numerical SHPB tests. It was found that the lateral acceleration caused by the plastic flow of the material model determines the lateral inertia and the parabolic distribution of the confining pressure is caused by the wave propagation in the specimen. And based on the mechanism analysis of the inertial effect, we explained the size effect and actively confining pressure effect in the SHPB test well. Thirdly, in order to explore the dynamic properties of salt rock under confining pressure and temperature, a new SHPB instrument(TSCPT- SHPB) was designed. And the salt rock specimens with the confining pressure ranging from 5 to 25MPa and the condition of temperature ranging from 40 to 80 were tested on the TSCPT℃ ℃-SHPB. It was observed that the strain-rate effect is not obvious under a higher confining pressure condition. Finally, the effects of the mesoscopic components on the dynamic properties of concrete were discussed based on a 3-D mesoscale concrete model. The simulation results indicated that the dynamic strength of concrete increases with the static strength of the mesoscopic components and the volume fraction of aggregate, but decreases with aggregate size.