Summarization Sheet is different from thick board Generally if the ratio of the thickness of the board and the minimal dimension of the board face satisfies 80100b(58 We call the board sheet We call the plane halves 三==== the thickness of the board middle pl ane Choose the ordinate origin as a point of the middle plane and y axes of x and y in the middle plane, z perpendicular to it which are shown in fig5 Summarization Sheet is different from thick board。Generally,if the ratio of the thickness of the board and the minimal dimension of the board face satisfies:             8 1 ~ 5 1 100 1 ~ 80 1 ＜ ＜ b t We call the board sheet. Choose the ordinate origin as a point of the middle plane, and axes of x and y in the middle plane, z perpendicular to it, which are shown in fig. . x y z o We call the plane halves the thickness of the board middle plane