花岗岩-喷射混凝土梁损伤的声发射可视化表征

Visualized characterization of damagein granite-shotcrete beams based on acoustic emission

摘要:

为研究输水隧洞围岩-喷射混凝土衬砌结构的协同抗弯损伤特性,制备两种花岗岩-喷射混凝土组合梁进行不同加载速率的四点弯曲试验,并采用数字图像相关（DIC）和声发射（AE）两种无损监测技术对花岗岩-喷射混凝土组合梁的四点弯曲试验进行监测。结果表明:在裂缝从喷射混凝土中扩展至花岗岩表面时,荷载-应变曲线在峰后下降段出现明显的拐点,该拐点可以作为花岗岩起裂的标志；通过声发射技术对喷射混凝土中的损伤类型识别发现,剪切损伤所占的比例随着应变率的提高而增加。为实现对组合梁内部损伤的可视化分析,利用声发射损伤定位数据计算了空间b值。结合损伤定位在空间中的密度分布规律,给空间b值附加系数后构建新的Rb值。与空间b值相比,Rb值的云图对不同损伤程度的区分度更高,改善了损伤可视化分析的效果。最后,将Rb值定位的损伤云图与DIC监测到的裂缝云图进行对比,验证了这种利用声发射技术对损伤进行可视化分析方法的有效性。

Abstract:

To study the synergistic flexural damage resistance characteristics of the surrounding rock-shotcrete lining structure of water transportation tunnel, two granite-shotcrete composite beams were prepared for four-point bending tests with different loading rates. The four-point bending tests of the granite-shotcrete composite beams were monitored by two nondestructive monitoring techniques: digital image correlation (DIC) and acoustic emission (AE). Results show that when the crack extended from the shotcrete to the granite surface, the load-strain curve showed an obvious inflection point in the post-peak descending section, which can be a sign of granite crack initiation. Through identifying the damage types in shotcrete by AE technology, we found that the proportion of shear damage increased with the increase in strain rate. For the visual analysis of the internal damage of the composite beam, the spatial b-value was calculated using the acoustic emission damage localization data. Then, a new Rb-value was constructed by attaching coefficients to the spatial b-value in combination with the density distribution law of damage localization in space. Compared with the spatial b-value, the cloud map of Rb-value had a higher differentiation of different damage degrees, which improved the visualization of damage. Finally, the damage clouds localized by Rb-values were compared with the crack clouds monitored by DIC, which verified the effectiveness of the proposed method for damage visualization using AE technology.