能念法 ②变形能: U= N2(x) dx+ M(x) dx t dx 2EA JL 2GIP L2EI P2R(sin p)Rdg rr P2R2(1-cos()Rdo o 2EI 0 2GIp 3P2R3xP2R丌 4( P 4EI ③外力功等于应变能 21=U P 3PR'T PR'I 2GI2El③外力功等于应变能 ②变形能：    = + + L L P L x EI M x x G I M x x EA N x U d 2 ( ) d 2 ( ) d 2 ( ) 2 2 n 2   + − =   j j j j 0 2 2 2 0 2 2 2 d 2 (sin ) d 2 (1 cos ) R EI P R R GI P R P EI P R GI P R 4 P 4 3 2 3 2 3   = + f U P W = A = 2  EI PR GI PR f P A 2 2 3 3 3    = +