应力应矩平衡微分方程、斜截面上的应力应矩及边界条件

In this paper, from the balance of a unit body under the action of the stress and MPUA, 6 new equilibrium differential equations and 6 comprehensive equilibrium differential equations are deduced. The new equilibrium differential equations connect 9 stress quantities with 9 MPUA quantities, which is not like the now-used elastics mechanics that transform the torsion and bending moment into shear stress and normal stress. The new equilibrium differential equations pointed out that the shear stress reciprocal theorem works only on the conditions of pure pulling and pure shearing. The stress state of a unit body is developed. 3 boundary conditions of stress and 3 boundary conditions of MPUA are developed.