求翻译：梁发生纯弯曲时，横截面上只有正应力，所有微小内力(σ、d A)构成空间平行力系，而横截面上无轴力，所以只有xy平面内弯矩M是什么意思？

Liang Fasheng pure bending, the cross section of only the normal stress parallel to the tiny internal forces (σ, da) constitute a space force system, the cross section of the axial force, so only the xy-plane bending moment m

When LEUNG in purely bend, the cross-section is the only strain of all minor (d A), should be a parallel effort, space, and a cross-sectional axis force, therefore, it is only in XY plane squirrel trap M

When Liang has the pure bending, in the lateral section only then the normal stress, all small endogenic forces (sigma, d A) constitutes the spatial parallel system of forces, but in the lateral section does not have the axle strength, therefore only then in xy plane bending moment M

Beam pure bending occurs, only normal stress in the cross section, all the small force (σ, and d a) constitutes a spatial parallel force system, and no axial forces on the cross, so only in the XY-plane bending moment m

正在翻译，请等待...