In rubber processing, particularly laboratory testing, two common parameters often cause confusion, i.e., tensile strength and tear strength. One question we frequently receive from our clients is what the difference between the two types of strength is.
Here are the formal definitions (DU Aihua edited, 2017).
- Tensile strength is the maximum tensile stress reached in stretching a test specimen to its broken state. It means the ultimate capacity of resistance to damage.
- Tear strength refers to the force needed for tearing the sample.
Still confused? Okay, in a simple term, tensile strength is the maximum force needed to break a sample (rubber O-ring or cord), whereas tear strength is the energy needed to tear apart the sample alongside a precut.
Note that for tear strength, there is no such thing about “maximum force”, since the crack is already occurred as a given, and the issue at hand is how much total energy is needed to tear the sample apart alongside the crack. Therefore, it is more accurate to speak of tear energy than tear strength.
Now it should be clearer that tensile strength measures the strength of the sample, while tear strength is more about the ability of a sample to sustain a damage.
The methods of measuring the two parameters also demonstrate their difference. As the following pictures show, tensile strength is tested by pulling a sample apart, whereas tear strength is measured by tearing a trouser-shaped specimen, that is, by pulling apart the two legs.
Basically, tear strength is more relevant to dynamic sealing compared with static sealing since the former is more exposed to the risk of cut and abrasion. In contrast, tensile strength applies equally to both dynamic and static sealing.
Figure 1: Testing of tensile strength
Figure 2: Testing of tear strength