The elongation of elastomers is critically important to tire manufacturers, as this property helps predict how tires may behave during use. This property, however, can create challenges in testing.
Tire Rubber Tensile Test
While extensometers are not required by the most common standards (ASTM D412 and ISO 37), a strain measurement device is recommended to ensure the most accurate and repeatable results. Traditional clip-on extensometers do not provide sufficient travel for elastomeric testing.
In addition, for many customers testing elastomeric tire materials at varying temperatures is critical.
The Advanced Video Extensometer (AVE 2) is a non-contacting extensometer which is ideal for elastomeric materials. The AVE 2 is capable of measuring strain up to 2400% with a 1-inch gage length and can also measure strain up to break. It does not require contact with the specimen and therefore does not produce pinch points which may cause a premature failure and an invalid test. The AVE 2 can be used to measure strain inside of an environmental chamber when testing at non-ambient conditions.
Instron's XL long travel extensometers can also be used through break and are designed to work for elastomeric materials. The adjustable clamping force on the knife edges reduces premature failure of the specimen. Strain can be measured up to 3000% with a 1-inch gage length.
Gripping of Elastomers
During testing, rubber materials can typically see significant thinning as they experience high elongation. This can cause extrusion from the grips and result in slipping and non-valid test results. Over tightening the grips, however, can result in jaw breaks and premature failure.
The 2712-04x series pneumatic side action grips are capable of maintaining a constant pressure throughout the test. The adjustable inlet pressure ensures that the pressure can be optimized to eliminate both slipping and jaw breaks. The patented quick-change jaw faces make it easy to change faces to best suit your material.
Alternatively, a self-tightening eccentric roller grip can be used. These grips use a serrated eccentric roller to clamp the specimen throughout the test. As the load increases on the elastomeric material, the off-center nature of the roller increases clamping force preventing the specimen from slipping out of the grips.
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