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donggaomin金蟲 (正式寫手)
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[求助]
關(guān)于彈性常數(shù)的一個基本問題
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c11,c22,c33 是不是分別對應著笛卡爾坐標的xyz三個方向? 那么,xyz分別對應著晶體的哪一個晶向(或者基矢a1,a2,a3)?有規(guī)定嗎? [任意一種晶類,元胞的基矢不一定是正交的,如何規(guī)定哪個晶向就是x方向呢? 這個問題是我在計算Cc空間群的晶體時引起的,我把它的元胞變成一個大的晶胞(通過Redefine lattice變成大晶胞,new lattice{[-1 1 1] [1 -1 1] [1 1 -1]},這個結(jié)構(gòu)體積是原胞的4倍)后計算彈性常數(shù),發(fā)現(xiàn)不知道怎么定義它的xyz方向了(即我應該在哪一個方向加應變可以計算c11等?)。我的那個帖子在http://www.gaoyang168.com/bbs/viewthread.php?tid=4462753] 不知道我說清楚了沒? 祝好! |

新蟲 (初入文壇)
木蟲 (著名寫手)
木蟲 (正式寫手)
金蟲 (正式寫手)
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但,按您說的任意定X方向的話,彈性常數(shù)c11就是不確定的了。不符合一個所謂的國際標準,這個國標是我剛查到的,但沒有理解,您可以說說對這個國標的理解不?謝謝! 在這篇文章中:Reconciliation of ab initio theory and experimental elastic properties of Al2O3,提到:elastic constants are defined in terms of a Cartesian coordinate system with axes x1, x2, and x3, and the values of the elastic constants may depend on how the Cartesian axes are aligned with the crystal axes. Prior to 1952, two alignments (referred to as obverse and reverse) were in use for trigonal crystals, and these gave different signs for one of the elastic constants. With standards set in 1949 (Ref. 5) and 1952 (Ref. 6), there is now no ambiguity as to how Cartesian coordinate axes are to be fixed to a trigonal structure: x3 along the three-fold axis and one of the crystal’s primitive lattice vectors must have a positive x3 component, a negative x2 component, and no x1 component. Consequently, there should be no ambiguity in the values (and signs) of elastic constants. 上面提到的standard應該就是了。 |

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