Experimental investigations of concrete at a very high number of load cycles as basis for modeling of concrete fatigue taking into account viscous and damage-induced strains

在大量载荷循环下对混凝土进行实验研究，作为混凝土疲劳建模的基础，考虑粘性应变和损伤引起的应变

• 批准号: 504102079
• 负责人: Professor Dr.-Ing. Frank Dehn
• 金额: --
• 依托单位: Abteilung Baustoffe und Betonbau
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/504102079?language=en
• 关键词: Experimental; investigations; concrete; very; number

The service life of civil engineering structures is dominated apart from static actions more and more by cyclic actions which can cause fatigue failure. Concrete is the most used building material in civil and building engineering and therefore of considerable importance. Well-founded knowledge concerning the number of load cycles endurable by concrete under cyclic compression loading is currently limited to the so called Low Cycle-Fatigue (LCF) range up to N = 10^5 load cycles as well as the so called High-Cycle-Fatigue (HCF) range up to N = 10^7 load cycles. Fatigue scenarios with a number of load cycles N > 10^7 are classified as belonging to the Very-High-Cycle-Fatigue (VHCF) range, for this fatigue range currently no significant research work exists.The research project includes a detailed and fundamental examination of fatigue behaviour for very high numbers of load cycles under consideration of an additive strain model approach. Elastic, viscous, damage-induced and thermal strain components are quantified on the basis of cyclic load tests in the VHCF range in combination with specifically coordinated creep and shrinkage tests as well as temperature measurements. The strain components are considered taking into account interaction effects, as the recorded specimen heating in the VHCF tests are explicitly taken into account as the external ambient temperature in the HCF and creep and shrinkage tests. By using a high-frequency testing technique, fatigue tests are obtained in a temporally condensed manner so that load cycle numbers N > 10^7 can be realised. A detailed investigation of the fatigue behaviour of concrete is carried out at three different stress levels with test frequencies from f = 1 Hz to f = 150 Hz with a significant number of test results. To connect the test results to fatigue processes in concrete subjected to low-frequency stress, specific investigations in the HCF range are supplemented. Possible influences of scaling effects are recorded by the parallel investigation of two different specimen sizes. For the first time extensive tests make it possible to obtain basic knowledge in the VHCF range of concrete and to realise the connection between test results from time-related, high-frequency and low-frequency fatigue tests. This is the basis for understanding the fatigue behaviour of concrete on the basis of the respective strain components in the VHCF range, for anchoring it in a modelling based on test engineering and for using it for design in the future.

土木工程结构的使用寿命除受静力作用外，越来越多地受到循环作用的影响，循环作用会引起疲劳破坏。混凝土是土木和建筑工程中最常用的建筑材料，因此具有相当重要的意义。关于混凝土在循环压缩载荷下可承受的载荷循环次数的有根据的知识目前仅限于所谓的低周疲劳（LCF）范围（N = 10^5载荷循环）以及所谓的高周疲劳（HCF）范围（N = 10^7载荷循环）。载荷循环数N > 10^7的疲劳情况被归类为超高循环疲劳（VHCF）范围，因为目前还没有针对该疲劳范围的重要研究工作。该研究项目包括在考虑附加应变模型方法的情况下对超高循环载荷下的疲劳行为进行详细和基本的检查。根据VHCF范围内的循环载荷测试，结合专门协调的蠕变和收缩测试以及温度测量，对弹性、粘性、损伤诱导和热应变分量进行量化。应变分量考虑到相互作用的影响，因为在HCF和蠕变和收缩试验中，明确考虑了在VHCF试验中记录的试样加热作为外部环境温度。通过使用高频测试技术，以时间压缩的方式获得疲劳测试，从而可以实现载荷循环次数N > 10^7。混凝土的疲劳性能进行了详细的调查，在三个不同的应力水平与测试频率从f = 1 Hz到f = 150 Hz的大量的测试结果。为了将测试结果与混凝土在低频应力下的疲劳过程联系起来，对HCF范围内的具体调查进行了补充。标度效应的可能影响记录的两个不同的试样尺寸的平行调查。广泛的测试首次使人们能够获得VHCF混凝土范围的基本知识，并实现与时间相关的高频和低频疲劳测试的测试结果之间的联系。这是理解混凝土疲劳性能的基础，基于VHCF范围内的相应应变分量，将其锚定在基于测试工程的建模中，并将其用于未来的设计。