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ASTM D882 - Thin Plastic Film Tensile Testing Fixture

Standard Test Method for Tensile Properties of Thin Plastic Sheeting - PDF

 

ASTM D882 is a widely recognized standard used to determine the tensile properties of thin plastic sheeting, typically with a thickness of 0.25 mm (0.010 in) or less. It is an essential method for evaluating the mechanical behavior of flexible plastics under tensile stress, which includes important properties like tensile strength, elongation, modulus of elasticity, and stress-strain characteristics. This test method provides insight into the performance of plastic films and sheeting when subjected to mechanical forces, which is crucial for applications where plastic materials are used in packaging, construction, and other industries.

1. Scope

The standard outlines a procedure for measuring the tensile properties of thin plastic materials, specifically focusing on:

  • Tensile strength

  • Elongation at break

  • Modulus of elasticity (tensile modulus)

  • Stress-strain behavior

This test is conducted by pulling a sample of the plastic sheet between two grips in a tensile testing machine, measuring how the material deforms as stress is applied.

2. Test Specimen Preparation

The specimens should be prepared with dimensions appropriate for the testing equipment. The sample is generally cut to specific sizes, commonly in a dumbbell shape, with standardized lengths and widths, ensuring uniformity across tests.

  • Dimensions: Typically, the specimen is cut into a rectangular or dumbbell shape. The most common length is 150 mm (6 in), with widths between 10 and 25 mm (0.4 to 1 in).

  • Thickness: For thin plastic films, the material thickness is often around 0.25 mm or less.

The specimens should be conditioned to the appropriate temperature and humidity, as plastic materials' behavior can vary significantly under different environmental conditions.

3. Testing Equipment

To perform ASTM D882, the following equipment is typically used:

  • Universal Testing Machine: This machine is capable of applying tensile stress to the sample, measuring force, and elongation during the test.

  • Load Cell: The load cell measures the force applied during the tensile test.

  • Extensometer: Used to measure elongation, especially at higher precision.

  • Tensile Testing Grips: Proper grips are essential to securely hold the plastic sheeting during testing without causing premature failure due to improper handling.

The test must be conducted at a consistent rate of elongation, typically between 50 to 500 mm/min, depending on the type of material.

4. Test Procedure

The test procedure involves the following steps:

  • Mounting the Sample: The specimen is securely mounted between the machine's grips.

  • Application of Force: The grips pull the specimen at a constant rate of elongation.

  • Measurement: As the specimen is pulled, force and elongation are measured simultaneously. These values are used to generate a stress-strain curve for the material.

    • Stress is calculated by dividing the force by the initial cross-sectional area of the specimen.

    • Strain is calculated by measuring the elongation (increase in length) relative to the original length of the specimen.

5. Results and Calculations

Once the test is completed, the data collected from the test machine is analyzed, and the following key tensile properties are determined:

  • Tensile Strength: This is the maximum stress the material can withstand before it breaks.

  • Elongation at Break: This is the amount of strain the material undergoes before failure, expressed as a percentage of the original length.

  • Modulus of Elasticity (Tensile Modulus): This is a measure of the material's stiffness, calculated from the initial slope of the stress-strain curve in the elastic deformation region.

  • Stress-Strain Curve: A plot of stress versus strain, which provides insight into the material's mechanical behavior. The curve is used to assess the material’s elastic and plastic behavior.

6. Precision and Accuracy

The precision of the test method is influenced by several factors, including the alignment of the specimen, the rate of elongation, and the condition of the testing equipment. It is important to maintain consistent test conditions and ensure proper calibration of testing machines to ensure accurate and repeatable results.

7. Applications

ASTM D882 is used in various industries where thin plastic materials are used, including:

  • Packaging: To evaluate the strength and flexibility of plastic films used in food, medical, and industrial packaging.

  • Textiles: For testing the properties of thin polymer sheets used in fabrics and textiles.

  • Engineering and Manufacturing: To determine the suitability of materials for applications requiring flexibility, such as coatings, films, and laminates.

8. Considerations

  • The testing environment, including temperature and humidity, can affect the results. Specimens should be conditioned before testing.

  • The choice of specimen size and shape may vary depending on the equipment used, but the principles of the test remain the same.

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9. Similar ASTM Methods

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10. Conclusion

ASTM D882 is an essential standard for evaluating the tensile properties of thin plastic sheeting. It provides critical information about the mechanical behavior of plastic films under stress, which is invaluable in assessing their suitability for specific applications. This test method is widely used across various industries to ensure the quality, durability, and performance of plastic materials in real-world conditions.

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