高强混凝土动态压缩试验分析

准确测量混凝土动态压缩性能及其应变率强化效应一直是冲击动力学研究领域的重点和难点之一。针对混凝土大口径SHPB实验,分析探讨了其中几个主要问题:应力均匀性问题、恒应变率问题和端面接触问题。研究表明:对于此次试验中混凝土试件而言,应力均匀性假设限制试验最大应变率小于166 s^-1;杆和试件端面接触不平和接触不良使得测算出的杨氏模量和屈服强度明显小于实际值;在此基础上,给出了五步测试法和预应力法;利用复合整形技术实现了近似恒应变率加载。利用以上所发展和改进的技术得到了C110混凝土动静态应力应变曲线,结果显示,在试验范围内混凝土杨氏模量并没有应变率效应,其单轴压缩屈服强度与应变率对数呈线性正比关系,其唯象应变率强化因子为0.10。理论分析表明,大口径SHPB试验所得混凝土应变率效应是一种唯象效应,对于混凝土类压力敏感屈服材料而言,应该根据其屈服面方程对其进行校正,从而得到其本构方程中材料的应变率强化因子,分别利用Tresca屈服准则和K&C本构中屈服面方程对其进行校正,得到C110材料的真实应变率强化因子分别为0.015和0.038。

Analysis of the dynamic compressive test of high strength concrete

Accurate measurement of the dynamic compressive performance of concrete and its strain rate enhancement effect is a key point in impact dynamics research.In this study,aiming at the dynamic compressive behavior test of concrete C110,we examined the stress uniformity,constant loading strain rate and interface contact in the large-size Split Hopkinson Pressure Bar test and found that the upper-limit strain rate in consideration of the stress uniformity hypothesis was less than 166 s.1 for the concrete specimens in this test and that,owing to the imperfect contact of the interface between the rod and the end surface of the specimen,the experimental young modulus and yield strength were obviously smaller than the actual value.Then we developed the five-step test method and prestress method,by which the approximate constant strain rate loading was realized using the combined pulse shaping technology.Using the above technologies the dynamic and static stress-strain curves the concrete C110 were presented.The results showed that the strainrate effect of the young's modulus of the concrete C110 was not observed and the yield strengths of the uniaxial compression were linearly proportionate to the logarithmic strain rates,with the experimental strainrate enhancement factor to be 0.10,and that the concrete-like pressure-sensitive material should be calibrated using the yield criteria.In this research,the strain-rate enhancement factor of the concrete material,respectively,were calibrated using the Tresca yield criterion and the K&C yield criterion,and then the strainrate enhancement factor of the concrete material were found to be 0.015 and 0.038 respectively.