A new formulation to model the mechanical behavior of high performance fiber reinforced cement composites with arbitrarily oriented short fibers is presented. The formulation can be considered as a two scale approach, in which the macroscopic model, at the structural level, takes into account the mesostructural phenomenon associated with the fiber-matrix interface bond/slip process. This phenomenon is contemplated by including, in the macroscopic description, a micromorphic field representing the relative fiber-cement displacement. Then, the theoretical framework, from which the governing equations of the problem are derived, can be assimilated to a specific case of the material multifield theory. The balance equation derived for this model, connecting the micro stresses with the micromorphic forces, has a physical meaning related with the fiber-matrix bond slip mechanism. Differently to previous procedures in the literature, addressed to model fiber reinforced composites, where this equation has been added as an additional independent ingredient of the methodology, in the present approach it arises as a natural result derived from the multifield theory. Every component of the composite is defined with a specific free energy and constitutive relation. The mixture theory is adopted to define the overall free energy of the composite, which is assumed to be homogeneously constituted, in the sense that every infinitesimal volume is occupied by all the components in a proportion given by the corresponding volume fraction. The numerical model is assessed by means of a selected set of experiments that prove the viability of the present approach.

中文翻译：

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钢纤维混凝土的微形态模型

提出了一种新的公式来模拟具有任意取向短纤维的高性能纤维增强水泥复合材料的力学行为。该公式可以被认为是一种两尺度方法，其中宏观模型在结构水平上考虑了与纤维-基体界面粘合/滑移过程相关的细观结构现象。通过在宏观描述中包括表示相对纤维-水泥位移的微形态场来考虑这种现象。然后，推导出问题的控制方程的理论框架可以被同化为材料多场理论的特定情况。为该模型推导出的平衡方程，将微应力与微形力联系起来，具有与纤维-基体键合滑移机制相关的物理意义。与文献中针对纤维增强复合材料模型的先前程序不同，在该程序中，该方程已被添加为该方法的额外独立成分，在本方法中，它是从多场理论得出的自然结果。复合材料的每个组分都定义有特定的自由能和本构关系。采用混合理论来定义复合材料的总自由能，假设复合材料是均匀构成的，即每个无穷小的体积都被所有组分以相应体积分数给出的比例占据。数值模型是通过一组选定的实验来评估的，这些实验证明了本方法的可行性。