Multiscale modelling of the degradation progress in the localised fracture zone of carbon fibre reinforced high-performance concrete subjected to high-cycle tension and flexural tension fatigue loading - phase 2: damage accumulation and degradation predic

为了将来能够用相应的数值模拟代替复杂的疲劳试验，对高性能混凝土的退化机理进行了研究。使用的高性能混凝土通过混合定向短碳纤维实现了非常高的拉伸和弯曲强度，并且可以作为未来其他具有更复杂成分的高性能混凝土疲劳行为建模的起点。在第一个资助阶段，为此目的结合了在不同规模水平上起作用的多种测量方法。在宏观层面上，在周期性单轴拉伸试验中，除了数字图像相关等常规测量方法外，还使用声发射分析和尾波干涉测量来表示内部损伤。此外，碳纤维的导电性使得通过测量电阻来确定试样的损伤程度成为可能。在细观和细观水平上，借助计算机断层扫描和显微检查，记录了试件在受弯拉伸试验中空载时的微观结构和微裂纹的发展情况。基于所获得的数据，研究人员开发了面向微观结构的单晶胞（RVE），其中碳纤维通过滑移位移条件与周围基体连接。第一次裂缝开发模拟计划将持续到第一个融资阶段结束。在第二个资助阶段，必要的调查将由经过验证的紧密联网的项目小组继续进行，该小组将两个实验研究机构在不同规模水平上的优势结合起来，用高度专业化的非破坏性测量方法补充它们，并导致数值多尺度模型。一个特别的重点放在疲劳行为和退化预测的描述。特别是，必须回答碳纤维本身的微观失效（纤维提取或纤维断裂）的问题。因此，在微观和宏观层面上应用的测量方法将得到补充或进一步发展，从而从根本上研究从疲劳阶段II到疲劳阶段III的转变。除了第一阶段使用的系统外，还使用了透射电子显微镜（TEM）。数字图像相关和电阻测量将进一步发展，以便更好地了解内部和外部的损伤。此外，还将集中研究损害累积方面的问题。在所有考虑的尺度水平上对序列效应进行了研究和评估，以确定它们对材料降解的影响。以这种方式获得的知识直接流入模型中数学模拟的验证。

In order to be able to replace complex fatigue tests with corresponding numerical simulations in the future, the mechanisms leading to degradation are investigated on a high-performance concrete. The high performance concrete used achieves very high tensile and flexural strength by mixing in oriented short carbon fibres and can serve as a starting point for the future modelling of the fatigue behaviour of other high performance concretes with a more complex composition. In the first funding phase, multiple measuring methods acting on different scale levels were combined for this purpose. At the macro level, in cyclical, uniaxial tensile tests, sound emission analysis and coda wave interferometry were used in addition to conventional measurement methods such as digital image correlation to represent the internal damage. In addition, the conductivity of the carbon fibres made it possible to determine the damage in the test specimen by measuring the electrical resistance. On the micro and meso level, the microstructure of unloaded test specimens on the one hand and the development of microcracks on the other hand were recorded in flexural tensile tests with the aid of computer tomography and microscopic examinations. On the basis of the data thus obtained, microstructure-oriented unit cells (RVE's) were developed in which the carbon fibres were connected to the surrounding matrix via slip-displacement conditions. First crack development simulations are planned until the end of the first funding phase.In the second funding phase, the necessary investigations are to be continued by the proven closely networked project group, which combines the strengths of two experimental research institutions on different scale levels, supplements them with highly specialized non-destructive measurement methods and leads to numerical multi-scale modelling. A special focus is placed on the description of fatigue behaviour and degradation prognosis. In particular, the question of microscopic failure (fibre extraction or fibre crack) of the carbon fibres themselves has to be answered. Therefore, the applied measuring methods on micro- as well as on macro-level will be supplemented or further developed to the extent that the transition from fatigue phase II to phase III can be fundamentally investigated. In addition to the systems used in the first period, transmission electron microscopy (TEM) is used. The digital image correlation as well as the resistance measurement will be further developed in order to better understand the damages inside and outside.In addition, the aspect of damage accumulation will be intensively examined. On all considered scale levels sequence effects are investigated and evaluated in order to work out their influence on material degradation. The knowledge gained in this way flows directly into the validation of the mathematical simulation in the models.