九面体是指由9个平面组成的多面体，而边长全部等长的九面体是七角柱是一种半正多面体。在九面体中，四角锥柱和它的对偶多面体都是九面体。九面体可以是七角柱、八角锥、双三角锥柱等多面体。
它们被称为应力的九个分量，均示于图1。2中一点附近的无限小的平行六面体单元上。
These are known as the nine components of stress and are illustrated with reference to an infinitesimal rectangular element about a point in figure1.2.
它们被称为应力的九个分量，均示于图1.2中一点附近的无限小的平行六面体单元上。
These are known as the nine components of stress and are illustrated with reference to an infinitesimal rectangular element about a point in Figure 1. 2.
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