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donggaomin金蟲(chóng) (正式寫手)
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[求助]
關(guān)于彈性常數(shù)的一個(gè)基本問(wèn)題
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c11,c22,c33 是不是分別對(duì)應(yīng)著笛卡爾坐標(biāo)的xyz三個(gè)方向? 那么,xyz分別對(duì)應(yīng)著晶體的哪一個(gè)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(gè)晶向就是x方向呢? 這個(gè)問(wèn)題是我在計(jì)算Cc空間群的晶體時(shí)引起的,我把它的元胞變成一個(gè)大的晶胞(通過(guò)Redefine lattice變成大晶胞,new lattice{[-1 1 1] [1 -1 1] [1 1 -1]},這個(gè)結(jié)構(gòu)體積是原胞的4倍)后計(jì)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(yīng)該在哪一個(gè)方向加應(yīng)變可以計(jì)算c11等?)。我的那個(gè)帖子在http://www.gaoyang168.com/bbs/viewthread.php?tid=4462753] 不知道我說(shuō)清楚了沒(méi)? 祝好! |

金蟲(chóng) (正式寫手)
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但,按您說(shuō)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(gè)所謂的國(guó)際標(biāo)準(zhǔn),這個(gè)國(guó)標(biāo)是我剛查到的,但沒(méi)有理解,您可以說(shuō)說(shuō)對(duì)這個(gè)國(guó)標(biāo)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(yīng)該就是了。 |

木蟲(chóng) (著名寫手)
木蟲(chóng) (正式寫手)
新蟲(chóng) (初入文壇)
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