Dynamic shearing banding and fracturing in unsaturated porous media is a significant problem in engineering and science. This article proposes a multiphase micro-periporomechanics (uPPM) paradigm for modeling dynamic shear banding and fracturing in unsaturated porous media. Periporomechanics (PPM) is a nonlocal reformulation of classical poromechanics to model continuous and discontinuous deformation/fracture and fluid flow in porous media through a single framework. In PPM, a multiphase porous material is postulated as a collection of a finite number of mixed material points. The length scale in PPM that dictates the nonlocal interaction between material points is a mathematical object that lacks a direct physical meaning. As a novelty, in the coupled uPPM, a microstructure-based material length scale is incorporated by considering micro-rotations of the solid skeleton following the Cosserat continuum theory for solids. As a new contribution, we reformulate the second-order work for detecting material instability and the energy-based crack criterion and J-integral for modeling fracturing in the uPPM paradigm. The stabilized Cosserat PPM correspondence principle that mitigates the multiphase zero-energy mode instability is augmented to include unsaturated fluid flow. We have numerically implemented the novel uPPM paradigm through a dual-way fractional-step algorithm in time and a hybrid Lagrangian-Eulerian meshfree method in space. Numerical examples are presented to demonstrate the robustness and efficacy of the proposed uPPM paradigm for modeling shear banding and fracturing in unsaturated porous media.

翻译：非饱和多孔介质中的动态剪切带与断裂是工程与科学领域的重要问题。本文提出了一种多相微观近场多孔力学（uPPM）范式，用于模拟非饱和多孔介质中的动态剪切带与断裂。近场多孔力学（PPM）是经典多孔力学的非局部重述，旨在通过统一框架模拟多孔介质中的连续与非连续变形/断裂及流体流动。在PPM中，多相多孔材料被假定为有限个混合材料点的集合。PPM中控制材料点间非局部相互作用的长度尺度是一个缺乏直接物理意义的数学对象。作为创新点，在耦合的uPPM中，通过引入基于微结构的材料长度尺度，并遵循固体Cosserat连续体理论考虑固体骨架的微转动。作为新贡献，我们重新定义了用于检测材料失稳的二阶功、基于能量的裂纹准则及用于模拟断裂的J积分，将其纳入uPPM范式。同时，我们扩展了可缓解多相零能模式不稳定的稳定化Cosserat PPM对应原理，使其涵盖非饱和流体流动。通过时间域的双向分数步算法和空间域的混合拉格朗日-欧拉无网格方法，我们数值实现了这一新型uPPM范式。数值算例展示了所提出的uPPM范式在模拟非饱和多孔介质剪切带与断裂方面的鲁棒性与有效性。