This International Standard specifies three test methods for the determination of the tear strength of vulcanized rubber, namely
— Method A, based on the use of a trouser test piece;
— Method B, based on the use of an angle test piece, with or without a nick of specified depth;
— Method C, based on the use of a crescent test piece.
The value of tear strength obtained depends on the shape of the test piece, speed of stretching and temperature of test. It may also be susceptible to grain effects in vulcanized rubber.
Method A : using trouser test piece
Method A, using the trouser test piece, is preferred because it is not sensitive to the length of the cut, unlike the other two test pieces in which the nick has to be very closely controlled. In addition, the results obtained are more easily related to the fundamental test properties of the material and are less sensitive to modulus effects (provided that the leg extension is negligible) and the rate of propagation of the tear is directly related to the rate of grip separation. However, all the methods are reasonably satisfactory in respect of reproducibility and practicability.[1].
Method B : Procedure (a) : Using angle test piece without nick
The test is a combination of tear initiation and propagation. The stress is built up at the base of the angle until it is sufficient to initiate a tear and then further stresses propagate this tear. But it is only possible to measure the overall force required to rupture the test piece, and therefore, the force cannot be analysed into two components producing (1) initiation and (2) propagation. [3]
Method B, procedure (b) : Using angle test piece with nick
This test measures the force required to propagate a nick already produced in the test piece. The rate of propagation is not directly correlated with the jaw speed.［2］
Method C : Using crescent test piece
This test also measures the force required to propagate a nick already produced in the test piece and the rate of propagation is not correlated with the jaw speed.
NOTE — A separate method for the determination of tear strength of small test pieces of vulcanized rubbers (Delft test pieces) is specified in ISO 816.
DS/ISO 34:1980 history
1980DS/ISO 34:1980 Rubber, vulcanized. Determination of tear strength (trouser, angle and crescent test pieces)