Oneschkow Nadja, Scheiden Tim, Hüpgen Markus, Rozanski Corinna, Haist Michael
Institute of Building Materials Science, Leibniz University Hannover, Appelstraße 9a, 30167 Hannover, Germany.
Materials (Basel). 2021 Sep 28;14(19):5650. doi: 10.3390/ma14195650.
A high-strength concrete subjected to compressive fatigue loading with two maximum stress levels was investigated and the behaviour was evaluated using the macroscopic damage indicators, strain and acoustic emission hits (AE-hits), combined with microstructural analyses utilising light microscopy and scanning electron microscopy (SEM). A clustering technique using Gaussian mixture modelling combined with a posterior probability of 0.80 was firstly applied to the AE-hits caused by compressive fatigue loading, leading to two clusters depending on the maximum stress level. Only a few cracks were visible in the microstructure using light microscopy and SEM, even in phase III of the strain development, which is shortly before failure. However, bluish impregnated areas in the mortar matrix of higher porosity or defects, changing due to the fatigue loading, were analysed. Indications were found that the fatigue damage process is continuously ongoing on a micro- or sub-microscale throughout the mortar matrix, which is difficult to observe on a mesoscale by imaging. Furthermore, the results indicate that two different damage mechanisms take place, which are pronounced depending on the maximum stress level. This might be due to diffuse and widespread compressive damage and localised tensile damage, as the findings documented in the literature suggest.
对承受两种最大应力水平的抗压疲劳荷载的高强度混凝土进行了研究，并使用宏观损伤指标、应变和声发射计数（AE计数），结合利用光学显微镜和扫描电子显微镜（SEM）的微观结构分析来评估其性能。首先，将结合0.80后验概率的高斯混合模型聚类技术应用于抗压疲劳荷载引起的AE计数，根据最大应力水平产生了两个聚类。即使在应变发展的第三阶段，即在破坏前不久，使用光学显微镜和SEM在微观结构中也只能看到少数裂纹。然而，对较高孔隙率或缺陷的砂浆基体中因疲劳荷载而变化的蓝色浸渍区域进行了分析。研究发现，在整个砂浆基体中，疲劳损伤过程在微观或亚微观尺度上持续进行，这在中观尺度上通过成像很难观察到。此外，结果表明发生了两种不同的损伤机制，这取决于最大应力水平而表现明显。正如文献中记载的研究结果所示，这可能是由于弥散和广泛的压缩损伤以及局部拉伸损伤所致。
