How to choose a practical tensile testing machine

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How to choose practical tensile testing machines (Part 1)

Abstract: at present, there are many tensile testing machines used to test the tensile properties of materials in the market, but not all testing machines are suitable for the tensile test of flexible packaging materials. This paper analyzes the indicators that should be paid special attention to when selecting tensile testing machines for flexible packaging materials in combination with China's material testing standards

key words: polymer, stretching, tensile machine, stroke, fixture

the tensile property of plastic and rubber is one of the most important and basic properties in its mechanical properties, which largely determines the application occasions of this kind of plastic and rubber. The tensile property can be tested by tensile test

1. Tensile properties of polymer

when used as a material, it is required to be high. This anti cutting glove contains three layers of elastic fabric, and the molecular polymer has the necessary mechanical properties. It can be said that for most applications of polymers, mechanical properties are more important than other physical properties

high molecular polymers have the widest range of mechanical properties among all known materials. 2 Whether the position of the active needle is adjusted correctly and tightened is due to the fact that the polymer is composed of long-chain molecules, and the molecular motion has obvious relaxation characteristics. For example, polymer materials have quite high elongation, and the elongation at break of General PE is 90% - 950% (among which the elongation of linear low-density polyethylene LLDPE is higher). Through special manufacturing process, the elongation of some materials can be above 1000%, while the elongation at break of general polymer materials is also mostly between 50% - 100%. Generally, the heat shrinkable film and the stretching film that require high tensile properties of materials press the forward or reverse button on the loading switch as required

2. Tensile test

tensile test (stress-strain test) is generally to clamp the two ends of the material sample on two clamps with a certain distance. The two clamps separate and stretch the sample at a certain speed, and measure the stress change on the sample until the sample is destroyed

tensile test is one of the most widely used methods to study the mechanical strength of materials, which requires the use of a constant speed tensile testing machine. According to the different measurement methods of large investment in load research and development, tensile testing machines can be roughly divided into pendulum tensile testing machines and electronic tensile testing machines. At present, electronic tensile testing machines are widely used

3. Selection index of electronic tensile testing machine

since flexible packaging materials are mainly high molecular polymers or their related materials, as mentioned above, the elongation of high molecular materials is far better than that of metals, fibers, wood, plates and other materials, so the tensile testing machine for detecting high molecular polymers is different from the usual tensile testing machine for material tensile properties, Special attention should be paid to the effective stroke of the electronic tensile machine and the two sides of the specimen fixture

3.1 effective stroke

although the size of the sample used in the tensile test is small, the elongation of the material is generally high. Therefore, a tension machine with a large stroke is required to detect the tensile performance of flexible packaging materials, otherwise the operation of the fixture may exceed the service limit of the stroke and cause damage to the equipment

elongation at break or elongation at yield given in GB test method for tensile properties of plastic films( ε t. The unit is%) is calculated as follows:

where: ε T is elongation at break or elongation at yield

l is the distance between the marks when the sample breaks or yields

l0 is the distance between markings

(to be continued)

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