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基于统一相场理论的早龄期混凝土化-热-力多场耦合裂缝模拟与抗裂性能预测

COMPUTATIONAL MODELING OF SHRINKAGE INDUCED CRACKING IN EARLY-AGE CONCRETE BASED ON THE UNIFIED PHASE-FIELD THEORY

  • 摘要: 受水化反应和热量传输等过程影响, 混凝土在养护阶段会发生受约束收缩变形, 并由此在结构内引发较大的拉应力, 而此时混凝土力学性能往往还处于较低水平, 容易导致建造期混凝土结构即出现裂缝等病害. 这种早龄期混凝土裂缝对核安全壳、桥梁隧道、地下结构、水工或海工结构等重大土木工程和基础设施的全生命周期完整性、耐久性和安全性造成严重影响. 为了准确预测早龄期混凝土抗裂性能并量化裂缝演化对混凝土结构行为的不利影响, 亟需开展化-热-力多场耦合环境下的混凝土裂缝建模与抗裂性能分析研究. 针对这一需求, 本工作在前期提出的固体结构损伤破坏统一相场理论基础上, 考虑开裂过程与水化反应、热量传输等之间的相互影响, 建立裂缝相场演化特征(包括基于强度的裂缝起裂准则、基于能量的裂缝扩展准则和基于变分原理的扩展方向判据等)与混凝土水化度和温度之间的定量联系, 提出混凝土化-热-力多场耦合相场内聚裂缝模型, 发展相应的多场有限元数值实现算法并应用于若干验证算例. 数值模拟结果表明, 上述多场耦合相场内聚裂缝模型合理地考虑了水化反应、热量传输、力学行为以及裂缝演化之间的耦合效应, 揭示了早龄期混凝土热膨胀变形和自收缩变形的相互竞争机理, 且分析结果不受裂缝尺度和网格大小等数值参数的影响, 实现了早龄期裂缝演化全过程准确模拟和抗裂性能定量预测, 有望在混凝土结构早龄期裂缝预测和控制方面发挥重要作用.

     

    Abstract: During curing of concrete, hydration and thermal transfer inevitably result in expansion and shrinkage and hence, large tensile stresses in early-age concrete structures. As the mechanical properties of young concrete are still very low, structures are vulnerable in the construction stage to defects induced by crack nucleation, propagation and evolution, severely threatening the integrity, durability and safety of concrete structures and infrastructures like nuclear containment vessels, bridges and tunnel linings, hydraulic and off-shore structures. In order to predict the fracture property of early-age concrete and quantify its adverse effects on structural performances, it is pressing to investigate the computational modeling of early-age cracking in concrete structures under the chemo-thermo-mechanically coupled environment. To the above end, in this work we propose a multi-physically coupled phase-field cohesive zone model within our previously established framework of the unified phase-field theory. The interactions between the crack phase-field with the hydration reaction and thermal transfer are accounted for, and the dependence of the characteristics of crack phase-field evolution, e.g., the strength-based nucleation criterion, the energy-based propagation criterion and the variational principle based crack path chooser, etc., on the hydration degree and/or temperature, are quantified. Moreover, the numerical implementation of the proposed model in the context of the multi-field finite element method is also addressed. Representative numerical examples indicate that, with the couplings among hydration, thermal transfer, mechanical deformations and cracking as well as the competition between thermal expansion and autogenous shrinkage both properly accounted for, the proposed multiphysical phase-field cohesive zone model is able to reproduce the overall cracking process and fracture property quantitatively. Remarkably, the numerical predictions are affected by neither the phase-field length scale nor the mesh discretization, ensuing its promising prospective in fracture control of early-age concrete structures.

     

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