Investigation on influence of time on tear behaviour of airship envelope

An experimental investigation on tearing behaviour of a coated fabric used in aerostat/airship has been undertaken. The tear tests have been conducted on bi-axial set up and pressurised cylinder. Tear propagation was studied by inducing dynamic tear on a bi-axially stressed coated fabric through a falling dagger. The influence of traverse rates, 1–500 mm/min, on tear strength under uniaxial loading was also studied. Thiele’s empirical equation has been found to fit the data of bi-axial tests and cylinder tests. The instantaneous tear on a bi-axially stressed fabric when left under constant stress for some duration lead to failure of fabric at even 15% lesser than critical tear slit length in about 15 min. The tear strength of the coated fabric was found to be less at 1 mm/min traverse rate while remaining nearly constant for higher rates of traverse. The critical tear length not only depends upon inherent tear strength of material, diameter and pressure of envelope but also on the time for which the tear remains under creep.