Bulk directional enhancement factors are determined for axisymmetric (girdle and single-maximum) orientation fabrics using a transversely isotropic grain rheology with an orientation-dependent non-linear grain fluidity. Compared to grain fluidities that are simplified as orientation independent, we find that bulk strain-rate enhancements for intermediate-to-strong axisymmetric fabrics can be up to a factor of ten larger, assuming stress homogenization over the polycrystal scale. Our work thus extends previous results based on simple basal slip (Schmid) grain rheologies to the transversely isotropic rheology, which has implications for large-scale anisotropic ice-flow modelling that relies on a transversely isotropic grain rheology. In order to derive bulk enhancement factors for arbitrary evolving fabrics, we expand the c-axis distribution in terms of a spherical harmonic series, which allows the rheology-required structure tensors through order eight to easily be calculated and provides an alternative to current structure-tensor-based modelling.

中文翻译：

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取向相关的非线性晶粒流动性对体积方向增强因子的影响

使用具有与取向相关的非线性晶粒流动性的横向各向同性晶粒流变学来确定轴对称（腰围和单最大）取向织物的体积方向增强因子。与简化为与取向无关的晶粒流动性相比，我们发现，假设多晶尺度上的应力均匀化，中等强度到强轴对称织物的体应变率提高可高达 10 倍。因此，我们的工作将基于简单基底滑移 (Schmid) 晶粒流变学的先前结果扩展到横向各向同性流变学，这对依赖于横向各向同性晶粒流变学的大规模各向异性冰流建模具有影响。为了推导出任意演化织物的体积增强因子，