或(,)=(1-55)(1+mn)(i=12,34) N10:N,0:N20:N0 0N10N20N30N4 思考题:这种单元是收敛的单元吗?为什么? 2.单元应力与应变 0/ax0 /a·a/a50 =00/0y=01/b。0/0n 0/00/axl/b-a/n1/a./02 s}=[4[N(5,n)P =[4[N[4N…by IB][B…[B1]o =BS       T e  = A N(,)            T T e = A N 1 A N 2   或 (1 )(1 ) ( 1,2,3,4) 4 1 Ni (,) = − i  +i  i =         = 1 2 3 4 1 2 3 4 0 0 0 0 0 0 0 0 ( , ) N N N N N N N N N   思考题:这种单元是收敛的单元吗?为什么? 2.单元应力与应变   A d T  =                     =                   =     1/ / 1/ / 0 1/ / 1/ / 0 / / 0 / / 0 b a b a y x y x A T        = N 1 N 2  N 4         e = B 1 B 2  B 4     e = B 