混凝土单轴循环加卸载试验及声发射特性

利用10 MN大型多功能液压伺服静动力三轴试验系统和SAEU2S声发射信号采集系统, 研究了单轴循环荷载作用下混凝土强度变化及声发射特征。结果表明:混凝土在单轴循环荷载作用下，其抗压强度与回弹值的比值随应变速率的增加而增大，通过线性拟合发现混凝土抗压强度与回弹值的比值率效应表现明显；混凝土在单轴循环加卸载过程中，声发射定位研究揭示了混凝土开裂位置及发展状况，并将混凝土变形分为4个阶段进行研究，结合每个阶段声发射累积定位数情况，分析了混凝土损伤变化；对循环加卸载过程中声发射累积定位数的分析发现，卸载后再次至最大历史应力水平前大量声发射信号产生说明混凝土不满足Kaiser效应；基于声发射定位数与应力随时间变化关系的研究认为，混凝土强度与应力水平有关，与内部结构也有关。

Concrete under uniaxial cyclic loading and unloading test and acoustic emission characteristics

Strength variation and acoustic emission characteristics of concrete under the conditions of uniaxial cyclic loading and unloading are studied by using a 10-MN large multifunctional hydraulic servo static and dynamic triaxial test equipment and a SAEU2S acoustic emission acquisition system. Testing analysis results show that under the uniaxial cyclic loads, the ratio of concrete compressive strength to rebound values increases with the increase of a strain rate. Through linear fitting, it is found that the ratio of the concrete compressive strength to the rebound values concering the rate effect is apparent. During the uniaxial cyclic loading and unloading process of concrete, experimental studies of the acoustic emission location are carried out to reflect the position and development of concrete cracks. Then 4 deformation stages of concrete are divided; with each stage of the acoustic emission cumulative number of positioning, analysis of the damage of concrete is made; the acoustic emission cumulative fixed number of the cyclic loading and unloading process is analysed. Unloading again to the maximum stress level before a large number in history shows that the acoustic emission signal generated under such conditions does not meet the Kaiser effect; based on the relationships between the number of the acoustic emission and the time variation of the stresses, the concrete strength not only relates to the stress level, but also to the internal structure.