Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India.
Special and Multi-functional Structures Laboratory (SMSL), CSIR-Structural Engineering Research Centre, Chennai 600113, India.
Ultrasonics. 2021 Aug;115:106472. doi: 10.1016/j.ultras.2021.106472. Epub 2021 May 26.
In reinforced concrete (RC), material nonlinearity is evident even in its undamaged state due to the inherent microstructure. In the present work, damage progression in RC structure at different levels of damage is investigated using linear and nonlinear ultrasonic techniques. The primary focus of this study is to monitor the structure from its initiation stage(s) of damage to advanced stages. Ultrasonic velocity tomography is first implemented to identify the weaker regions and map any damage occurring at various levels of loading. Two critical regions are identified from ultrasonic tomography and further damage characterization is carried out using various ultrasonic techniques to quantitatively assess the progression of damage in these two regions. The linear ultrasonic techniques such as time-of-flight (TOF) and attenuation, and the nonlinear ultrasonic techniques such as sub- and super- harmonic, energy distribution, etc. are employed to detect the damage progression. It is found that the changes in linear parameters due to damage progression in RC structure are often insignificant and inconsistent. However, some of the nonlinear ultrasonics-based techniques are found to be very efficient to monitor the damage progression. A relatively new and promising nonlinear ultrasonic technique, namely the sideband peak count-index (or SPC-I) provides a very clear and consistent indication of damage at the early stage. The present study shows that during the initial stages of damage, SPC-I based nonlinear technique performs significantly better (at both regions as identified through ultrasonic tomography) than other linear and nonlinear techniques, whereas at higher damage stage the superiority of this nonlinear ultrasonic technique slowly diminishes. The present study also shows that out of all nonlinear ultrasonics-based techniques considered here, SPC-I technique provides the highest sensitivity to the damage progression and can be effectively used as a very robust nonlinear ultrasonic tool for identifying the onset and progression of damage in RC structures.
在钢筋混凝土 (RC) 中，由于其固有微观结构，即使在未损坏状态下也明显存在材料非线性。在本工作中，使用线性和非线性超声技术研究了 RC 结构在不同损伤水平下的损伤进展。本研究的主要重点是从损伤的初始阶段开始监测结构，并一直监测到高级阶段。首先实施超声速度层析成像以识别较弱区域，并映射在各种加载水平下发生的任何损伤。从超声层析成像中识别出两个关键区域，并使用各种超声技术进一步进行损伤特征描述，以定量评估这两个区域中损伤的进展。采用线性超声技术，如飞行时间 (TOF) 和衰减，以及非线性超声技术，如次谐波和超谐波、能量分布等，来检测损伤进展。结果发现，由于 RC 结构损伤进展导致的线性参数变化通常不显著且不一致。然而，一些基于非线性超声的技术被发现非常有效地监测损伤进展。一种相对较新的、很有前途的非线性超声技术，即边带峰值计数指数 (或 SPC-I)，可在早期阶段非常清晰和一致地指示损伤。本研究表明，在损伤的初始阶段，基于 SPC-I 的非线性技术的性能明显优于其他线性和非线性技术（在通过超声层析成像识别的两个区域中均如此），而在更高的损伤阶段，这种非线性超声技术的优势逐渐减弱。本研究还表明，在所考虑的所有基于非线性超声的技术中，SPC-I 技术对损伤进展的灵敏度最高，可有效地用作识别 RC 结构中损伤的起始和进展的非常可靠的非线性超声工具。
