y64 F(L+6 O=△= EA 三EA B L δ-L eAs B A EA N E O E=200GPa o=200MPa 6/L=1/1000例题 6.4 A B L EA B A L EA   = L ( ) EA FN L + =   L L EA FN  = L E  = E = 200GPa  L =1 1000  = 200MPa