so as to;in order to

so as to;in order to
in order to; so…as to 二者均表示“以便；为了”，后接动词不定式作目的状语，可以换用；但so as to引导的目的状语不能置于句首，而in order to则可以。如： He stopped working in order to／so as to take a rest．他停止工作以便休息。 In order to make a living, he had to work day and night．为了谋生，他不得不日夜工作。  
“so＋形容词／副词＋as的意思是“如此的……以致于”，引导表示结果的状语。
如： He ran so fast as to get a pain in his side．他跑得太快，结果导致腹侧疼痛。