Fracture in concrete at high temperatures involves complex thermo-mechanical couplings and arbitrary crack evolution, imposing great challenges to its computational modeling. This work addresses a length scale insensitive phase-field cohesive model for fully coupled thermo-mechanical fracture in concrete at high temperatures. Both the thermal expansion and transient creep strain are accounted for in the kinematics. Based on the underlying phase-field cohesive model for fracture in solids at ambient temperature, the temperature-dependent mechanical properties of concrete, that is, Young's modulus, tensile and compressive strengths and fracture energy, and so forth, are all incorporated. In addition to the cracking-induced mechanical damage mechanism represented by the crack phase-field, the thermal deterioration mechanism is also considered by a temperature-dependent thermal damage variable. The numerical implementation of the proposed model into the multi-field finite element method is then briefly addressed. Several representative numerical examples, for example, thermally induced cracking in energy storage structures, thermal shock in quenched concrete plates, mode-I and mixed-mode failure of notched beams at high temperatures, and so forth, are presented for the validation. The effects of various expressions for the transient creep strain (TCS) on the global behavior of concrete structures are also studied. As in those purely mechanical problems, both the predicted crack pattern and global responses for all examples are insensitive to the incorporated phase-field length scale. Being able to capture the fully coupled thermo-mechanical fracture in concrete, the proposed phase-field cohesive model, combined with a reliable hydro-chemo-thermal analysis, is promising in assessing the integrity and safety of concrete structures at high temperatures like fire scenarios.

中文翻译：

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高温下混凝土全耦合热力断裂的长度尺度不敏感相场模型

混凝土高温断裂涉及复杂的热力耦合和任意裂纹演化，对其计算建模提出了巨大挑战。这项工作解决了高温下混凝土中完全耦合的热机械断裂的长度尺度不敏感相场内聚模型。运动学中考虑了热膨胀和瞬态蠕变应变。基于环境温度下固体断裂的基本相场内聚模型，将混凝土的温度相关力学性能，即杨氏模量、拉伸和压缩强度以及断裂能等全部纳入。除了以裂纹相场为代表的裂纹诱发的机械损伤机制外，热劣化机制也可以通过与温度相关的热损伤变量来考虑。然后简要介绍了所提出的模型在多场有限元方法中的数值实现。提出了几个具有代表性的数值例子，例如储能结构的热致开裂、淬火混凝土板的热冲击、高温下缺口梁的模式I和混合模式破坏等，以供验证。还研究了瞬态蠕变应变 (TCS) 的各种表达式对混凝土结构整体行为的影响。与那些纯机械问题一样，所有示例的预测裂纹模式和全局响应都对合并的相场长度尺度不敏感。