k 2.形函数的性质 若l1=1;v 0 则(x,y)=N(x,y) ①.N(x,y)=1;N2(x,y)=N(xk,yk)=04=1 2. N(x,y)+N (x, y)+NK(x,y)=l 若 则(x,y )=N,+N,+N k N,0:N:0:N,0 0N,0N0N4 x,[[N] INIS [N]-形函数矩阵N(x,y)--形函数  e k k j j i i i j k i j k v u v u v u N N N N N N v u d                           =       = 0 0 0 0 0 0 2.形函数的性质              e k j i i j Nk I N I N I           =       e = N  N ---形函数矩阵 N (x, y) i ---形函数 若 ui =1;vi = u j = vj = uk = vk = 0 u(x, y) N (x, y) 则 = i i j k =1 i u ①. Ni (xi , yi ) =1;Ni (xj , y j ) = Ni (xk , yk ) = 0 ②. Ni (x, y) + Nj (x, y) + Nk (x, y) =1 若 ui = u j = uk =1 Ni N j Nk 则 u(x, y) = + +