Tensile testing is one of the most common mechanical tests carried out to measure and verify the properties of plastic and rubber materials. Properties measured include the ultimate tensile strength, yield strength, elongation, percent elongation, Modulus of Elasticity, and more.
During a tensile test, the test specimen is pulled and stretched. Most tests require the specimen to be pulled apart completely to calculate the force capacity at failure. Units of force calculated is expressed in lbf (imperial) or kN (metric) and this property is noted as the tensile strength at break or the ultimate tensile strength. In addition to force calculations, the amount of stretch in the specimen is another property that provides information on the material characterization and on product verification. The length of the specimen will increase with the applied tensile force. How much the sample stretches before failure is expressed as the elongation of the material. Depending on the followed format, the unit of elongation is often in inches (imperial) or in millimeters (metric).
Noting the percent elongation may be a better expression of results for certain materials. Percent elongation takes into account the initial length of the specimen in addition to the final length after it is stretched. Several hundred percent elongation for rubber and elastomers are common as they are high-stretch materials. Percent elongation of rigid plastics, on the other hand, is often under five percent.
Modulus of Elasticity or Tensile Modulus (E) measures the stiffness, it is calculated based on the ratio of the normal stress component in phase with the normal strain, to the normal strain. The modulus of rigid plastics is often high as more stress is required to produce a given amount of strain.
Poisson’s Ratio measures the relationship between how far the specimen stretches and how its thickness changes during the process.
Note that some measurements such as the measurement of stress and strain at yield applies only to some thermoplastic rubbers and certain other compounds.