Recently

torsion cracking was found on some new optical fibre cables.In order to solve this problem

the characteristic of torsion cracking was summarized by test

and the mechanics of torsion was analysed in theory

and the cause of cracking was concluded.It shows the cause of cracking is not only the squeezing from steel tape

but also the stress concentration from step on sheath innner wall.Finally

the result of trial reveals that the most effective method to improve torsion cracking is applying hot melt near steel tape overlap.