§6等直圆杆扭转时的应变能 单元体外力作功dW=(ahy)(rhx)= rydxdydz 2 dw= dy 应变能密度 2 dxdvdz 等直圆杆扭转时的应变能 a=∫ lp ax T dAd P dA 2 2G1, GⅠ§6 等直圆杆扭转时的应变能  x y z dx   dz dy  dW = (dydz)• (dx) 2 1 单元体外力作功  dxdydz 2 1 = dW = dV 应变能密度 dV dV v   = dxdydz  dxdydz 2 1 =  2 1 = 等直圆杆扭转时的应变能  = V V v dV  = l A v dAdx   v  2 1 =  G  =  = l A dAdx G V 2 2    P I T =          = A P dA I T G l 2 2 2  GIP T l 2 2 =