Material composition influenced damage development in high-strength concrete under cyclic loading

与普通强度混凝土相比，高强混凝土表现出更致密和改善的微观结构。高强混凝土在单调递增外荷载作用下的材料行为与普通强度混凝土的材料行为有很大的不同。它主要受水泥或粘结剂和界面过渡区性能优化的影响。关于高强混凝土和普通混凝土的疲劳性能，由于它们的微观结构不同，目前还不清楚它们的损伤过程是如何不同的。因此，在这个项目中，将检查、描述和模拟循环荷载下高强混凝土的退化机理。特别是，将研究裂纹在退化的不同阶段的形核和扩展。采用逐步分析的方法，系统分析了生产高强混凝土的典型混凝土工艺措施对疲劳性能的影响。退化机制将使用不同的损害指标来确定。将详细阐述和量化差异，同时将调查和评估实验-虚拟实验室内损害指标的应用。此外，还将应用高分辨率成像技术来观察不同的裂纹状态，并将它们与疲劳过程中损伤指标的发展联系起来。在这个联合项目中，计划了一个实验/建筑材料子项目和一个理论/计算子项目。这两个次级项目将在内容和方法方面密切合作。发生在非常小的尺度上的破坏过程有时只能在大得多的尺度上通过实验观察到。关于这些破坏过程的知识将通过由实验结果校准的尺度转换模型来获得，该模型允许在精细尺度上得出关于过程的结论。为实现这一点，将采用多尺度投影法，结合交叉有限元和非局部损伤，在多尺度上模拟裂纹的形核和动态裂纹扩展。为了在合理的模拟时间内捕捉几千个载荷循环的计算过程，将采用基于小波的多时间尺度方法WATMUS。对于微结构部件，将假定为弹粘塑性材料模型。试验和模拟的结合将对高强混凝土的损伤机理有新的认识，最终将导致新的和改进的混凝土组成的疲劳性能的可预测性。

Compared to normal-strength concrete, high-strength concrete exhibits a denser and improved microstructure. The material behaviour of high-strength concrete under monotonically increasing external loads is significantly different compared to the material behaviour of normal-strength concrete. It is mainly influenced by optimized properties of the cement or the binder agent and the interfacial transition zone. Concerning fatigue properties of high-strength concrete and normal-strength concrete until now it is unclear how the damage processes differ due to their different microstructures.As a consequence, within this project the degradation mechanisms of high-strength concrete under cyclic loading will be examined, described and modelled. In particular, the nucleation and propagation of cracks within the different phases of degradation will be investigated. Based on a stepwise methodology the influence on the fatigue behaviour of typical concrete technology measures to produce high-strength concrete will be analysed systematically. The degradation mechanisms will be determined using different damage indicators. Differences will be elaborated and quantified while the application of the damage indicators within an experimental-virtual-lab will be investigated and evaluated. In addition, high resolution imaging processes will be applied to observe different crack states and to relate them to the development of the damage indicators within the fatigue process.Within this conjoint project an experimental/building material subproject and a theoretical/computational subproject are planned. The two subprojects will cooperate intensively regarding contents and methodology. Damage processes happening on a very small scale can sometimes be observed experimentally only on a much larger scale. Knowledge about these damage processes will be gained by a scale transitioned modelling calibrated by experimental results which allows for drawing conclusions about processes on the fine scale. To realize this, the multiscale projection method in combination with the XFEM and non-local damage for the simulation of crack nucleation and dynamic crack propagation on multiple scales will be used. To capture the progress computationally for a couple of thousand load cycles within reasonable simulation times, the wavelet based multi timescale method WATMUS will be applied. For the microstructural components an elastic-viscoplastic material model will be assumed. The combination of experiment and simulation will lead to new insight into the damage mechanisms of high strength concrete and eventually it will lead to the predictability of the fatigue properties of new and improved concrete composition.