Abstract
Environment stress cracking (E.S.C.) of polyethylene (PE) is an important performance factor of telephone cables with PE sheath.
The discussed are (1) a test to evaluate the E.S.C. resistance of telephone cable sheath, (2) a method to secure telephone cables from the E.S.C., (3) an estimate of the duration of the E.S.C. danger of bent cables and (4) several interesting physical evidences which were found in the course of the study and considered to be important for the understanding of the E.S.C.
The conclusions are as follows. (1) The test proposed is a modified bent strip test. The specimens should be cut, transversely to the cable length direction, from the outer part of the sheath of naturally curved cable. The channel width should be properly adjusted according to the outer diameter of the cable. (2) In case bent cables are annealed 3min. at 70°C, the bent cables are free from the E.S.C.. (3) In case bent cables are maintained at room temperature about 1 year, they are almost free from E.S.C. as a result of the stress relaxation. (4) The topography of cracked PE surfaces are not affected by the stress magnitude, but affected by the crystalline texture of PE and the concentration of surface active agent. Partial melting of unstable crystalline regions in PE and their recrystallization play an important role in the mechanism of the stress relaxation effect on the E.S.C..
