ASTM D751

ASTM D751 includes two primary procedures for evaluating fabric tearing strength:

Pendulum Method (Based on Test Method D1424)

This method uses a falling pendulum to tear the material. It measures the energy absorbed during tearing and is suitable for specific coated fabrics. It works best when yarns do not bunch together and when tear initiation is consistent.

Tongue Tear Method

This widely used method measures the force required to continue a tear initiated by a central slit. ASTM D751 outlines requirements for jaw size, pulling speed (commonly 5.00 ± 0.2 mm/s), and specimen orientation relative to warp and fill direction. The test continues until the tear travels between 76–102 mm. Any specimen that slips or tears outside the intended path must be discarded and replaced.

Many laboratories prefer the tongue tear method because it provides a stable, repeatable measurement of tear propagation under tension.

Trapezoidal Tear Strength Test

The trapezoidal tear strength test—another critical keyword and testing method—uses an isosceles trapezoid-shaped marking on the fabric with a small cut at the center. During testing, clamps pull the specimen in a way that concentrates stress along the cut. The operator records the tearing force as the fabric tears across the trapezoid.

This method is especially useful for coated textiles and woven materials that do not tear uniformly. ASTM D751 requires the tearing force to fall within 15–85% of the testing machine’s capacity to ensure accuracy. If breakage occurs near the jaws, padded jaws or adjusted clamping may be needed.