88-2 Basic Equations under Rectangular Coordinate One Differential Equations of equilibrium Consider an arbitrary point inside the body and fetch a small parallel hexahedron, which 中 stress components on each side are shown as fs gure ay If ab denotes the line which joins the centers of two faces of the hexahedron, then from ∑ m=0 ve get d+x2a空 2 2 T+ dz ldxdv-=T dxdy=0 az 2 2 Canceling terms and neglecting higher order small variables, we get 77 §8-2 Basic Equations under Rectangular Coordinate One. Differential Equations of Equilibrium Consider an arbitrary point inside the body and fetch a small parallel hexahedron, which stress components on each side are shown as figure. If ab denotes the line which joins the centers of two faces of the hexahedron, then from we get mab = 0 2 2 dy dxdz dy dy dxdz y yz yz yz    +           + 0 2 2 − =           − + dz dxdy dz dz dxdy z zy zy zy    Canceling terms and neglecting higher order small variables,we get