关于规定曲率弯矩方程弯矩正负号的问题

The problem of designating the sign of bending moment in the curvature-bending moment equation

阐明了曲率弯矩方程的物理概念及用此方程建立梁(柱)弯曲微分方程的思路,论述了在建立梁(柱)弯曲微分方程中规定弯矩正负号(简称这种规定)引起的问题:1)这种规定破坏了曲率弯矩方程所反映的物理概念及用曲率弯矩方程建立梁(柱)弯曲微分方程的思路;2)这种规定导致了梁(柱)截面内力矩与梁(柱)曲率正负号无关的错误概念;3)按这种规定建立梁(柱)弯曲微分方程须记住弯矩正负号的规定,与此种规定对应的坐标系,不考虑梁(柱)曲率的正负号等3条内容,否则得出错误结果。建议材料力学在阐述梁(柱)弯曲微分方程中删去这种规定,以避免上述问题。

The physical meaning of curvature- bending moment equatian and the procedure for the construction of differential equation for beam（column）bending by this equation was pointed out. The problems arising from the formulation of differential equation for beam（column）bending were discussed during designating the sign for bending moment. 1 ）This sign convention has conflicted with the physical meaning of curvature- bending moment equation. 2）The incorrect concept may be directly obtained that the cross- sectional resisting moments are independent of the sign for the curvature. 3）The sign convention itself, the arrangement of corresponding coordinate systems and the sign for the curvature should not be taken into account, otherwise the incorrect resuhs may be obtained. It is strnngly recommended that this sign convention should be cancelled in the canstruetion of the differential equation for beam（column） bending.