应用非线性高阶谐波衰减和尾波干涉监测高温作用后水泥制品的损伤演化

非线性高阶谐波和尾波波速变化均能够反映水泥材料内部微结构的应力变化。利用高阶谐波和尾波干涉实验测量系统，对引入高温作用后的3类不同粒径共6块水泥试样进行单轴加载的损伤演化实验，并与无高温作用的完整试样的实验结果进行对比。结果表明，从初始状态到25%抗压强度的过程中，高温作用后的试样的谐波幅值和尾波波速变化出现明显增强的现象（谐波幅值最大增幅约20%），而无高温作用的完整试样的谐波幅值和尾波波速变化较为平稳（谐波幅值最大增幅约5%）；在达到65%抗压强度的过程中，高温作用后的试样的谐波幅值和尾波波速变化急剧增大（谐波幅值最大增幅约100%），且粒径较大的试样的增幅高于粒径较小的试样，而无高温作用的完整试样的谐波幅值和尾波波速变化的增幅较小（谐波幅值最大增幅约10%）；当抗压强度超过75%以后，高温作用后的试样的谐波幅值和尾波波速变化急剧衰减（谐波幅值最大衰减幅度约140%），而无高温作用的完整试样的谐波幅值和尾波波速的最大衰减幅值在40%以内。基于以上观测结果对高温作用后水泥制品损伤演化的物理机制以及这两类监测方法的适用性进行了讨论。

Application Nonlinear High Order Harmonics and Coda Wave Interferometry on Monitoring Damage Evolution of Cement Specimens Subject to Elevated Temperature

Nonlinear high order harmonics and ultrasonic coda waves are both stress sensitive to very small changes of cement based materials. Damage evolution on cement based specimens with three distinct aggregate size after heating at elevated temperature are investigated by applying measurement of nonlinear high order harmonics and velocity change by coda wave interferometry under uniaxial loading. The results show that the specimens subject to elevated temperature at early damage stage, then a rapid increase in increase in the amplitude of high order harmonics (about 100%) and velocity change before 65% of failure force, as a comparison, the stable increase (about 20%) of intact specimens which did not suffer hearting are observed at this stage. Comparing to the slightly increase (about 5%) in intact specimens which did not suffer hearting, apparent increase in the amplitude of high order harmonics (about 20%) and velocity change are observed. The rapid attenuation in high order harmonics (about 140%) and decrease in velocity change are observed after 75% of failure force at final stage, while only 40% attenuation in high order harmonics are observed subject to intact specimens. Based on the above results, the mechanism of damage evolution of cement specimens after heating at elevated temperature and the advantage of the two methods is discussed.