Energy dissipation-based approach to stochastic fatigue of concrete considering interacting time and temperature effects

大幅度降低材料消耗，提高工程结构的使用寿命，迫切需要更高的材料利用率，同时伴随着智能维护、维修和回收的理念。研究计划的总体目标是通过加深对结构在整个生命周期内相互作用载荷和环境攻击情景下的材料和结构行为的了解，支持结构混凝土设计中必要的创新发展。虽然金属的高周疲劳已经得到了深入的研究，并通过提供可靠的疲劳寿命预测将科学成果推进到工程实践中，但混凝土中的疲劳损伤传播机制尚未得到充分的了解。尽管近年来在混凝土疲劳行为的建模和表征方面取得了显著的进展，但为了对混凝土疲劳现象学有一个深入而普遍的认识，仍然需要从根本上解决许多悬而未决的问题。这项研究的科学目标是开发先进的、热力学一致的数值模拟方法和表征方法，这些方法可以在比目前更广泛的基础上捕捉控制疲劳行为的耗散机制的相互作用。为了实现这一目标，现有的以局部累积应变演变来反映疲劳行为的通用中宏建模平台将被扩展到包括温度、加载速率和随时间变化的材料变化的影响。理论和数值的发展将通过系统的实验程序进行验证，为所研究的现象提供多种观察视角。为了最大限度地提高研究与工程实践的相关性，将使用先进的概率建模方法捕获疲劳载荷和局部材料特性固有的随机性，该方法将用于根据S-N曲线、疲劳裂纹扩展准则、加载顺序的影响和疲劳蠕变发展对疲劳行为进行统计表征。这种特性将作为工程规范中精细设计和评估规则的基础。

The need to drastically reduce material consumption and increase the service life of engineering structures urgently requires higher material utilization, accompanied with intelligent maintenance, repair and recycling concepts. The overall objective of the research proposal is to support the necessary innovative development in structural concrete design by deepening the knowledge of the material and structural behavior in the whole range of interacting loading and environmental attack scenarios during the structure’s lifetime. While high-cycle fatigue of metals has been thoroughly studied and scientific results have progressed to engineering practice by providing reliable predictions of fatigue lifetime, the fatigue damage propagation mechanisms in concrete are yet to be fully understood. In spite of a remarkable progress in recent years made in modeling and characterizing the concrete fatigue behavior, many open questions remain that need to be fundamentally addressed in order to develop a deep and general insight into the phenomenology of concrete fatigue. The scientific goal of the research is to develop advanced, thermodynamically consistent numerical modeling approaches and characterization methods that can capture the interplay of dissipative mechanisms governing fatigue behavior on a broader basis than currently possible. To achieve this goal, the existing common meso-macro modeling platform, which reflects fatigue behavior in terms of local cumulative strain evolution, will be extended to include the influence of temperature, loading rate, and time-dependent material changes. The theoretical and numerical developments will be validated by a systematic experimental program providing multiple observation perspectives to the studied phenomena. To maximize the relevance of the research for engineering practice, the randomness inherent to fatigue loading and local material properties will be captured using advanced methods of probabilistic modeling that will be used for statistical characterization of fatigue behavior in terms of S-N curves, fatigue crack propagation criteria, effect of loading sequence and fatigue creep development. This characterization will serve as a basis for refined design and assessment rules in engineering codes.