我现在需要使用constant-strain 能量最小化的方法研究一个复合材料体系的机械性能,通过摸索,已经大致确定需要使用Forcite模块中的Mechanical功能,但是文献要求在体系X方向施加一个应变,我在这个Mechanical中没有找到如何在一个方向施加应变,有没有Forcite模块的大神 或者用过constant-strain方法的 求教啊!!!
本人新手一枚,头疼好几天了就为这个东西...... 如有相助,万分感谢!!!!(我没金币...希望大神能够伸出援助之手)
以下是我help中的叙述以及文献要求的截屏,或者有大神帮我解读一下,我读不懂......
Constant strain approach
Forcite Mechanical Properties calculations use the "Constant strain" approach. The process starts by removing symmetry from the system, followed by an optional re-optimization of the structure, where the cell parameters can be varied. Optimization at this stage is always advised as incorrect results can be obtained if the structure is far from its lowest energy configuration.
For each configuration, a number of strains are applied, resulting in a strained structure. The resulting structure is then optimized, keeping the cell parameters fixed. For example:
Number of steps for each strain = 4
Max. Strain amplitude = 0.003
Strain patterns 100000, 010000
This defines a range of values {-0.003, -0.001, 0.001, 0.003} which are applied to each strain pattern:
strain pattern 100000 gives e={-0.003, 0,0,0,0,0}, {-0.001, 0,0,0,0,0}, {0.001, 0,0,0,0,0}, {0.003, 0,0,0,0,0}
strain pattern 010000 gives e={0,-0.003,0,0,0,0}, {0, -0.001,0,0,0,0}, {0, 0.001,0,0,0,0}, {0, 0.003,0,0,0,0}
Each strain pattern represents the strain matrix in Voigt notation. It is converted to the strain matrix E, such that E(0,0)=e(0), E(1,1)=e(1),E(2,2)=e(2),E(2,1)=E(1,2)=0.5*e(3), ...
These are then used to generate the metric tensor G;
G = H0'[2E+I]H0
Where H0 are formed from the lattice vectors; I is the identity matrix and H0' is the transpose of H0. From G the new lattice parameters can be derived, these are then used to transform the cell parameters (fractional coordinates are held fixed). Following these steps the structure is optimized and the stress is calculated.
A stiffness matrix is built up by from a linear fit between the applied strain and resulting stress patterns. In the case of a trajectory this is averaged over all frames.
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