材料力学第四章弯曲内力 §4-3剪力和弯矩 矩 ∑F=0:F+FB-F=0→F ∑M=0:M-Fx+F(-x)=0→M=FBx-F材料力学 第四章 弯曲内力 §4-3 剪力和弯矩 y A S 0 S A F = 0: F − F =  F = F M M F x M F x C A 0 A  = 0: − =  = x FA FS C M F FS M FB C y S B 0 S B A F = 0: F + F − F =  F = F − F = F M M F x F(l x) M F x F(l x) F x C B 0 B A  = 0: − + − =  = − − = F l l a FA − = F l a FB =