或(,)=(1-55)(1+mn)(i=12,34) N10:N,0:N20:N0 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 7-1=0 4(-1,1) 3(1,1) 0/ax0 /a·a/a50 =00/0y=01/b。0/0n 1=0 0/00/axl/b-a/n1/a./02 1(-1,-1) 2(1 同理,有 (2)=(5+1)(1-m) 4 N3(5,m)=,(5+1)(1+7) N1(5,m7)=:(5-1)(7-1 N4(52m)=(1-5)(1+m)( 1)( 1) 4 1 ( , ) N1   =  −  − 或 (1 )(1 ) ( 1,2,3,4) 4 1 Ni (,) = − i  +i  i = 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         = 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          = N 1 N 2  N 4 同理,有 ( 1)(1 ) 4 1 ( , ) N2   =  + − ( 1)(1 ) 4 1 ( , ) N3   =  + + (1 )(1 ) 4 1 ( , ) N4   = − + 4   1 2 3 (-1,-1) 1 1 1 1 (1,-1) (1,1) (-1 ,1)  −1 = 0  −1 = 0