The tensile properties of plastics and rubbers are one of the most important and basic properties of their mechanical properties, which largely determine the use of such plastics and rubbers. The quality of the tensile properties can be checked by a tensile test.
1. The tensile properties of macromolecule polymers are used as materials to require them to have the necessary mechanical properties. It can be said that for most applications of high molecular polymers, mechanical properties are more important than other physical properties.
High molecular polymers have the widest range of mechanical properties among all known materials. This is due to the fact that polymers are composed of long-chain molecules, and the molecular motion has obvious relaxation properties. If the polymer material has a relatively high elongation, the break elongation of PE is generally 90% to 950% (including the linear elongation of low-density polyethylene LLDPE is higher), through special manufacturing process, some materials The elongation rate can be above 1000%, and the elongation at break of ordinary polymer materials is mostly between 50% and 100%. Generally, the heat-shrinkable film and stretched film are required to have higher tensile properties.
2. Tensile test Tensile test (stress-strain test) generally clamps the two ends of the material sample on two fixtures at a certain distance. The two fixtures separate and stretch the sample at a certain speed to determine the sample The stress on the surface changes until the specimen fails.
Tensile test is one of the most widely used methods to study the mechanical strength of materials. It requires the use of a constant-speed tensile testing machine. According to the different load measurement methods, the tensile testing machine can be roughly divided into two types of pendulum tensile testing machine and electronic tensile testing machine. At present, the electronic tensile testing machine is mostly used.
3. Selection index of electronic tensile testing machine Since flexible packaging materials are mainly high molecular polymers or its related materials, as mentioned above, the elongation of high polymer materials is far superior to metals, fibers, wood, plates and other materials, so There is a certain difference between the tensile machine for detecting high molecular polymers and the conventional tensile machine for material tensile properties. In particular, it is necessary to pay attention to the effective stroke of the electronic tensile machine and the sample fixture.
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