R,<r<R2Wm-22兀r 8兀 22 2 W= wdv= d m 8兀2r 单位长度壳层体积 2R --- dⅣ=2πrdr.1 R R dr n R14兀r 4πR L1/L=u R R 2元R R wm 2 ) 2π ( 2 1 r I =  2 2 2 8π r I R1  r  R2 = V r I W w V V V d 8π d 2 2 2 m  m  = =  R2 r dr 单位长度壳层体积 dV = 2π rdr1 r r I W R R d 4π 2 1 2 m  =  1 2 2 ln 4π R I R = 2 m 2 1 W = LI 1 2 ln 2π R R L  =