钢-聚丙烯混杂纤维混凝土细观疲劳损伤机理及本构关系研究

The fatigue constitutive relation of fiber reinforced concrete serves as a significant basis in accurate estimation of the structural fatigue performance and failure progress, uncovering the formation mechanism of the entire structural fatigue reliability as well as controlling of the fatigue damage evolution and the catastrophic process of major engineering structures. This proposal aims to conduct a systematic investigation on the mesoscopic fatigue damage mechanism and damage constitutive relation of steel-polypropylene hybrid fiber reinforced concrete (HFRC) by means of experimental, theoretical and numerical approaches. The objective is to (1) explore the evolution laws of fatigue strength and deformation for HFRC and develop a nonlinear fatigue cumulative damage model through uniaxial constant and variable amplitude fatigue tests for different stress levels and fiber characteristic parameters, (2) unravel the fatigue damage mechanism and damage evolution rule of HFRC by constructing a stochastic mesoscopic numerical model, (3) develop a fatigue damage theoretical model of HFRC within the framework of thermodynamics by coupling the theory of damage and elastoplasticity, (4) establish fatigue life prediction methods for HFRC material and railway sleeper elements based on the parametric analyses results from the proposed constitutive modeling outputs. This research can lead to a better understanding of the entire process and physical essence of the fatigue damage evolution of HFRC. The research outcome can play a significant role in the anti-fatigue design, fatigue catastrophe evolution analysis and fatigue life prediction of momentous engineering structures.

纤维混凝土的疲劳本构关系是正确评价结构疲劳性态及破坏规律，发现结构整体疲劳可靠性形成机制，实现重大工程结构疲劳损伤发展及灾变过程控制的重要基础。本项目采用试验研究、理论分析和数值模拟相结合的方法，对钢-聚丙烯混杂纤维混凝土(HFRC)的细观疲劳损伤机理及疲劳损伤本构关系开展系统的研究。通过单轴等幅与变幅疲劳试验，重点考虑不同应力水平、纤维特征参数的影响，研究HFRC疲劳强度与变形演变规律并建立非线性疲劳累积损伤模型；构建HFRC随机细观数值模型，揭示细观疲劳损伤机理及损伤演化规律；基于不可逆热力学框架，融合损伤力学与弹塑性理论，建立HFRC疲劳弹塑性损伤本构模型；运用本构模型进行参数化扩展分析，提出HFRC材料及轨枕构件的疲劳寿命计算方法。本课题的研究将有助于揭示HFRC疲劳损伤演化全过程及物理本质，研究成果将在重大工程结构抗疲劳设计、疲劳灾变行为分析、疲劳寿命预测等方面发挥巨大作用。

纤维混凝土的疲劳本构关系是正确评价结构疲劳性态及破坏规律，发现结构整体疲劳可靠性形成机制，实现重大工程结构疲劳损伤发展及灾变过程控制的重要基础。本项目采用试验研究、理论分析和数值模拟相结合的方法，对钢-聚丙烯混杂纤维混凝土(HFRC)的细观疲劳损伤机理及疲劳损伤本构关系开展了系统的研究。（1）重点考虑不同应力水平、纤维特征参数的影响，揭示了HFRC疲劳强度与变形演变规律并建立了非线性疲劳累积损伤模型；（2）构建了HFRC随机细观数值模型，揭示了细观疲劳损伤机理及损伤演化规律；（3）基于不可逆热力学框架，融合损伤力学与弹塑性理论，建立了HFRC疲劳弹塑性损伤本构模型并进行了数值实现；（4）运用本构模型进行参数化扩展分析，提出了HFRC材料及轨枕构件的疲劳寿命计算方法。研究结果表明：钢-聚丙烯混杂纤维具有多层次、逐级阻裂的特点，显著地提高了混凝土的疲劳性能，从而能够大幅度延长混凝土的使用寿命；相比于普通混凝土，HFRC的疲劳强度和变形最大可提高37.18%和63.29%，且混杂纤维在提高混凝土疲劳强度方面优于单一钢纤维和单一聚丙烯纤维混凝土，体现出正混杂效应；钢纤维作为一种具有高杨氏模量的宏观纤维，对宏观裂纹的扩展起到了非常大的抑制作用。聚丙烯纤维是一种粘弹性微观纤维，不仅能够延缓微裂纹的发展，也能够在疲劳加卸载过程中能够不断消耗机械能；HFRC综合了PFRC和 SFRC的优点，在疲劳加载过程中更具优势。研究成果对揭示HFRC疲劳损伤演化全过程及物理本质，在重大工程结构抗疲劳设计、疲劳灾变行为分析、疲劳寿命预测等方面具有重要的科学意义和工程应用价值。