Numerical and experimental investigations for the modeling of the time-dependent deformation characteristics of concrete on the mesoscale with coupled models for mechanical and hygric effects

利用机械和湿度效应耦合模型对介观尺度上的混凝土随时间变形特性进行建模的数值和实验研究

基本信息

批准号：
252766671
负责人：
Dr.-Ing. Jörg F. Unger
金额：
--
依托单位：
Abteilung 7: Bauwerkssicherheit
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/252766671?language=en
关键词：
Numerical experimental investigations modeling time

项目摘要

The modeling of time-dependent deformations of concrete is commonly performed with pure phenomenological approaches, where usually additional deformations due to creep and shrinkage are introduced. However there is experimental evidence that these effects are coupled in a nonlinear way (Picket effect) and are strongly related to mechanically induced damage and the moisture distribution within the specimen.The purpose of the project is the development and implementation of a numerical model for concrete that is able to simulate the coupled effects of mechanical loading and time-dependent local moisture distribution. The simulation will be performed with an explicit representation of the heterogeneous mesoscale structure based on a geometry model for concrete developed by the author. Concrete is modeled as a three phase composite with aggregates, cement paste and the interfacial transition zone (ITZ) as an additional weak link. The nonlinear behavior of the cement paste including the softening is modeled with a combined damage-plasticity model, which is regularized with a gradient damage formulation. This reduces the numerical effort compared to the nonlocal approach used in previous versions for large nonlocal radii. The viscous character of concrete is modeled with an extension of the plasticity model using a Perzyna-type creep model with hardening. This allows for a direct coupling between the mechanically induced damage and viscous creep deformations. The development of the time-dependent macroscopic properties (strength, stiffness) as a function of the moisture content during hardening of the cement paste is modeled with a modified solidification theory while ensuring to satisfy thermodynamic principles. The interaction between the mechanical model and the moisture content is realized by modeling concrete as a porous medium with a decomposition of the macroscopic stress components related to the skeleton and the capillary pressure. In addition, the moisture content influences the solidification rate. The ITZ is modeled using a cohesive interface approach that is extended to accurately describe the moisture transport as a function of the crack opening.The objective of the project is the development of a physics-based numerical model for creep and shrinkage that is able to accurately capture the complex macroscopic effects. It should be investigated if the modeling of coupled physical effects (viscous cement matrix, moisture transport, cement hydration) and the direct representation of the mesostructure are able to explain the complex phenomenological properties and interactions. As a result, the interpretation of experimental results with a realistic understanding of the physical processes on the mesoscale is facilitated. Additionally, the calibration process of the model is simplified due to clear physical meaning of the constitutive parameters.

混凝土时间依赖性变形的建模通常是通过纯粹的现象学方法进行的，通常引入蠕变和收缩引起的额外变形。但是，有实验证据表明，这些作用是以非线性方式（纠察效应）耦合的，并且与机械诱导的损伤和样品内的水分分布密切相关。该项目的目的是开发和实施混凝土的数值模型，该模型能够模拟机械载荷和时间依赖于时间依赖于局部水分的耦合效应。模拟将以基于作者开发的混凝土的几何模型的异质性中尺度结构的明确表示。混凝土被建模为具有聚集体，水泥糊和界面过渡区（ITZ）的三相复合材料，作为附加的弱环节。包括软化在内的水泥糊的非线性行为是用损伤塑性模型建模的，该模型以梯度损伤公式进行了正则化。与大型非局部半径的先前版本中使用的非局部方法相比，这减少了数值努力。混凝土的粘性特征是使用带有硬化的Perzyna型蠕变模型对可塑性模型进行建模的。这允许在机械诱导的损伤和粘性蠕变变形之间直接耦合。时间依赖性的宏观特性（强度，刚度）作为水泥糊化过程中水分含量的函数的发展，以修饰的凝固理论进行建模，同时确保满足热力学原理。机械模型与水分含量之间的相互作用是通过将混凝土建模为多孔介质的，其分解与骨骼和毛细管压力相关的宏观应力成分。另外，水分含量会影响凝固速率。 ITZ是使用粘合界面方法进行建模的，该方法扩展以准确描述水分传输是裂纹开口的函数。如果耦合物理效应（粘性水泥基质，水分传输，水泥水合）的建模以及介质结构的直接表示能够解释复杂的现象学特性和相互作用，则应研究。结果，对实验结果的解释促进了对中尺度上物理过程的现实理解。此外，由于本构参数的明确物理含义，简化了模型的校准过程。