Whereas various simplistic microplane models of limited applicability, defined by stress–strain curves on the microplane, can function as either explicit or implicit, the explicit‐to‐implicit conversion of realistic versatile microplane models for plain or fiber‐reinforced concrete, shale and composites has remained a challenge for quarter century. The reason is that these realistic models use microplane stress–strain boundaries defined by inequalities. Here, we show how the conversion can be easily achieved on the microplane level and then transferred to a tangent stiffness tensor or an inelastic stiffness tensor to be used in Newton–Raphson iterations within a loading step. To ensure convergence, a minor adjustment in the M7 algorithm is introduced to achieve continuity. Power‐law convergence, almost quadratic in most cases, is also demonstrated. Seven examples of crack‐band finite element simulations of challenging laboratory tests document nearly identical implicit and explicit results, as well as good match of test data. Three of them, including the vertex effect in compression‐torsion tests, pure Mode II shear fracture, and the “gap test” of the crack‐parallel compression effect on Mode I load‐deflection curve, have not been reproduced by other models before. The coding of implicit M7 subroutine, usable in, for example, UMAT of ABAQUS, is posted for a free download.

中文翻译：

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带有边界的显式微平面模型到隐式有限元程序的本构子程序的转换

有限的适用性的各种简单的微平面模型（由微平面上的应力-应变曲线定义）可以作为显式的或隐式的，而对于普通或纤维增强的混凝土，页岩和复合材料的现实通用微平面模型的显式到隐式转换四分之一世纪以来一直是一个挑战。原因是这些现实模型使用了由不等式定义的微平面应力-应变边界。在这里，我们展示了如何轻松地在微平面水平上实现转换，然后将其转换为切线刚度张量或非弹性刚度张量，以在加载步骤中用于Newton-Raphson迭代中。为了确保收敛，引入了M7算法中的细微调整以实现连续性。幂律收敛在大多数情况下几乎是平方的。挑战性实验室测试的裂纹带有限元模拟的七个示例记录了几乎相同的隐式和显式结果，以及测试数据的良好匹配。其中三个模型，包括压缩扭力试验中的顶点效应，纯模式II剪切断裂，以及裂纹平行压缩效应对模式I载荷-挠度曲线的“间隙试验”，以前其他模型均未复制。发布了可在例如ABAQUS的UMAT中使用的隐式M7子例程的编码，以供免费下载。之前，其他模型均未复制裂纹对模式I载荷-挠度曲线的平行压缩效应的“间隙测试”。发布了可在例如ABAQUS的UMAT中使用的隐式M7子例程的编码，以供免费下载。之前，其他模型均未复制裂纹对模式I载荷-挠度曲线的平行压缩效应的“间隙测试”。发布了可在例如ABAQUS的UMAT中使用的隐式M7子例程的编码，以供免费下载。