The Tearing Strength Tester works on the principle of measuring the Internal tearing resistance, which is the force perpendicular to the plane of the fabric required to propagate a single-rip or tear of a defined length from a cut in the fabric when a sudden force is applied. The force required to continue a slit previously cut in a fabric is determined by measuring the work done in tearing the fabric through a fixed distance.
The apparatus consists of a pendulum carrying a clamp which is in alignment with a fixed clamp. The pendulum is in raised, starting position with maximum potential energy. The tear force is computed from scale reading and pendulum capacity. Specimens in warp direction and 5 in weft direction shall be cut. No two test specimen shall contain the same warp and weft threads, and no specimen shall be cut within 150 mm of the edge of the fabric.