)2+1 q q 显然 (压) 4+”拉 (b/a)2+1 emax (b/a)2-1 rmax 0r a q a abrb q abrb ( ) 1 ( ) 1 , ( ) 1 ( ) 1 22 22 −+ = −−  = −  q a   r 显然  r " −（压）， "  “+”拉 r r r a a a σ σ | q q b a b a = = −−+ = max = 22 max ( / ) 1 ( / ) 1  