Tensile Test for Thin Plastic Strips

As a delicate challenge, thin plastic sheeting can be difficult to test without bending and slipping. Plastic sheeting is commonly tensile tested using methods found in ASTM D882. ASTM D882 pulls the plastic until it breaks in order to measure elongation, tensile modulus, tensile yield strength, and tensile strength at break.

ASTM D882

ASTM D882 is very similar to ASTM D638, but D882 is designed specifically for thin sheeting and film less than 1 mm (0.04 in.). Another difference is that in D882 samples can be cut into simple rectangular strips rather than the typical dumbbell shape. Tensile properties of the plastic can be measured with grip separation, extension indicators, or displacement of gage marks.

The tensile modulus of elasticity is an indicator of the stiffness of thin plastic sheeting. Make sure to maintain precise control over all test conditions to increase the chance of test result reproducibility. The tensile energy to break (TEB) is the total energy absorbed per unit volume of the specimen up to the breaking point. Sometimes the TEB is referred to as toughness. It is used to evaluate materials that are subjected to heavy abuse or that can stall web transport equipment in the event of a machine malfunction in end-use applications. However, the rate of strain, specimen parameters, and especially flaws can cause large variations in the results. In that sense, we advise caution in utilizing TEB test results for end-use design applications.

Testing Procedure

For ASTM D882, a few trial runs may be necessary to select a proper combination of load range and specimen width. To begin, place the test specimen in the grips of a testing machine, taking care to align the long axis of the specimen with an imaginary line joining the points of attachment of the grips to the machine. Tighten the grips evenly and firmly to the degree necessary to minimize slipping of the specimen during testing.

Next, start the machine and record the load versus extension. When total length measurements between grips are used as the test area, record load versus grip separation. When an extensometer is used, record load versus extension of the test area measured by the extensometer. If modulus values are being determined, select a load range and chart rate to produce a load-extension curve of between 30 and 60 degrees to the X axis. For maximum accuracy, use the most sensitive load scale for which this condition can be met. If tensile energy to break measurements is being determined, provision must be made for integration of the stress-strain curve.

A universal testing machine can be used for ASTM D882. There are also many options for special line contact jaws that are used to establish gage length. By means of our plastic testing expertise and modular product design, we will help find the testing solution that is right for you. Give one of our application engineers a call today for help with creating the best budget and testing plan according to ASTM D882.

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