In simpler terms tear resistance (or tear strength) is a measure of how well a material can withstand the effects of tearing. More specifically however it is how well a material (normally rubber) 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 uniform pulling force applied until the aforementioned deformation occurs. Tear resistance is then calculated by dividing the force applied by the thickness of the material.
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Materials with low tear resistance tend to 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. At the opposite, 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.