Gradient Effects at Macro, Micro, and Nano Scales
Gradient Effects at Macro, Micro, and Nano Scales
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宏观、微观和纳米尺度的梯度效应
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
E. Aifantis
中科院分区：
文献类型：
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作者：
E. Aifantis
讨论了梯度对从毫米（宏观尺度）到纳米（纳米尺度）的各种尺度的变形的局部化和图案化的影响。在纳米尺度下，变形的主要机制是自由纳米体积的重新排列以及体与晶界空间之间的动量交换。在微观尺度上，最常见的变形机制是位错运动。在宏观尺度上，通过将应变从变形材料的一个区域传输到另一个区域而发生变形图案化。在每种情况下，相应的纳米、微观或宏观变量的高阶梯度必须包括在本构方程中。这导致了各种类型的材料行为，包括弹性梯度理论，缺陷动力学梯度理论和宏观塑性梯度理论。在这样的“内部长度”的理论，它是可能的讨论发生的变形模式在不同的尺度，确定的宽度，间距和速度的变形带，以及裂纹尖端的结构和相关的应变或应力奇异性的去除。
The effects of gradients on the localization and patterning of deformation at various scales ranging from the millimeter (macroscale) down to the nanometer (nanoscale) are discussed. At the nanoscale, a dominant mechanism of deformation is the rearrangement of free nano volume and exchange of momentum between bulk and grain boundary space. At the microscale, a most common mechanism of deformation is dislocation motion. At the macroscale, deformation patterning occurs by the transport of strain from one region of the deforming material to another. In each case, higher order gradients of the respective nano, micro or macro variables are essential to be included in the constitutive equations. This leads to various classes of material behavior including a gradient theory of elasticity, a gradient theory of defect dynamics, and a gradient theory of macroscopic plasticity. Within such "internal-length" theories it is possible to discuss the occurrence of deformation patterns at various scales, the determination of width, spacing and velocity of deformation bands, as well as the structure of the crack tip and the removal of associated strain or stress singularities.