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

为了能够在未来用相应的数值模拟取代复杂的疲劳试验，在高性能混凝土上研究了导致退化的机理。所使用的高性能混凝土通过掺入定向短碳纤维获得了非常高的拉伸和弯曲强度，并可以作为未来模拟其他成分更复杂的高性能混凝土疲劳行为的起点。在第一个供资阶段，为此目的结合了作用于不同比额表级别的多种衡量方法。在宏观层面上，在循环单轴拉伸试验中，除了数字图像相关等常规测量方法外，还使用了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件中的损伤成为可能。在细观和细观水平上，借助计算机层析成像和显微镜观察，一方面记录了未加载试件的微观结构，另一方面记录了弯曲拉伸试验中微裂纹的发展过程。在此数据的基础上，发展了微结构取向的单胞(RVE)，其中碳纤维通过滑移条件与周围的基质相连。在第二资助阶段，必要的调查将由经过验证的紧密联系的项目组继续进行，该项目组结合了两个不同规模的实验研究机构的优势，用高度专业化的无损测量方法补充它们，并导致数字多尺度建模。特别关注疲劳行为和退化预测的描述。特别是，碳纤维本身的微观失效(纤维拔出或纤维断裂)的问题必须得到回答。因此，将补充或进一步发展微观和宏观层面上的实用测量方法，以从根本上研究从疲劳阶段II到阶段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)。为了更好地了解损伤内部和外部的情况，将进一步发展数字图像相关和阻力测量。此外，还将深入研究损伤累积方面。在所有考虑的尺度上，对顺序效应进行了调查和评估，以确定其对材料降解的影响。通过这种方式获得的知识直接流入模型中的数学模拟的验证。

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.