Carle Illinois College of Medicine, Beckman Institute for Advanced Science and Technology, The University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Kennesaw State University, Kennesaw 30144, Georgia, USA.
Ultrasonics. 2018 Aug;88:64-71. doi: 10.1016/j.ultras.2018.03.006. Epub 2018 Mar 16.
This research conducts in situ nonlinear ultrasonic (NLU) measurements for real time monitoring of load-induced damage in concrete. For the in situ measurements on a cylindrical specimen under sustained load, a previously developed second harmonic generation (SHG) technique with non-contact detection is adapted to a cylindrical specimen geometry. This new setup is validated by demonstrating that the measured nonlinear Rayleigh wave signals are equivalent to those in a flat half space, and thus the acoustic nonlinearity parameter, β can be defined and interpreted in the same way. Both the acoustic nonlinearity parameter and strain are measured to quantitatively assess the early-age damage in a set of concrete specimens subjected to either 25 days of creep, or 11 cycles of cyclic loading at room temperature. The experimental results show that the acoustic nonlinearity parameter is sensitive to early-stage microcrack formation under both loading conditions - the measured β can be directly linked to the accumulated microscale damage. This paper demonstrates the potential of NLU for the in situ monitoring of mechanical load-induced microscale damage in concrete components.
本研究进行了原位非线性超声（NLU）测量，以实时监测混凝土在载荷作用下的损伤。对于圆柱形试件在持续载荷下的原位测量，采用了先前开发的具有非接触检测的二次谐波产生（SHG）技术来适应圆柱形试件的几何形状。通过证明所测量的非线性瑞利波信号与平面半空间中的信号等效，从而可以定义和解释相同的声非线性参数β，验证了这个新设置。在一组混凝土试件中，无论是进行 25 天的徐变，还是在室温下进行 11 个循环加载，均测量声非线性参数和应变，以定量评估早期损伤。实验结果表明，在这两种加载条件下，声非线性参数都对微裂纹的早期形成很敏感——所测量的β可以直接与累积的微尺度损伤相关联。本文展示了 NLU 用于原位监测混凝土构件中机械载荷引起的微尺度损伤的潜力。
