2.形函数的性质 k 若 则L(x,y)=N(x,y) ①.M(x2)=1;N(x,y)=N(xy)=O4 2. N, (x,y)+N, (x,y)+N(x,y)=1 若 k 则(x,y)=N+N,+N N,0:N0:,0 k [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) = + +