Tear resistance

Tear resistance (or tear strength) is a measure of how well a material can withstand the effects of tearing. It is a useful engineering measurement for a wide variety of materials by many different test methods.
Discussion.
For example, with rubber, tear resistance measures how the test specimen resists the growth of any cuts when under tension, it is usually measured in kN/m. Tear resistance can be measured by the "ASTM D 412" method (the same used to measure tensile strength, modulus and elongation). ASTM D 624 can be used to measure the resistance to the formation of a tear (tear initiation) and the resistance to the expansion of a tear (tear propagation). Regardless of which of these two is being measured, the sample is held between two holders and a pulling force applied until the aforementioned deformation occurs. Tear resistance is then calculated by dividing the force applied by the thickness of the material.
Materials with low tear resistance sometimes have poor resistance to abrasion and when damaged will quickly fail (this includes hard materials, since hardness is not related to tear resistance).
Tear resistance of different materials.
Substances with high tear resistance include epichlorohydrin, natural rubber and polyurethane. In contrast, materials such as silicone and fluorosilicone have low tear resistance.
Tear-yield ratio.
The ratio of tear resistance to the yield strength is called the tear-yield ratio. It is a measure of notch toughness.