Introduction to ASTM D638 and ASTM D882
The tensile test describes how a material will react under tension. ASTM D638 and ASTM D882 are two commonly used ASTM specifications for plastic tensile testing. Both standards measure tensile property data, tensile strength, elongation at break, and modulus, but both apply to different materials. ASTM D638 applies to rigid and semi-rigid plastics; ASTM D882 applies to thin plastic films and sheets. The choice of the appropriate standard is crucial, as the geometry of the specimen, the experimental conditions, and the conclusions drawn from the results differ markedly between the two standard methods.
Scope of ASTM D638 and ASTM D882
- ASTM D638 is a standard for determining tensile properties of rigid and semi-rigid plastics.Â
- ASTM D882 is a standard that tests the tensile properties of thin plastic films and sheeting.Â
- Dog bone type specimens are molded or machined for ASTM D638.Â
- The rectangular strip specimens from thin films are cut in accordance with ASTM D882.
- Both standards ensure quality control, material development, and product qualification.Â
- The standards provide a means of comparing material performance under tensile loading.Â
- The standards help manufacturers compare material performance under tensile loading.Â
Principle of ASTM D638 and ASTM D882
The basic principle of both ASTM D638 and ASTM D882 is the same. A testing machine is used to apply a controlled amount of tensile force to a specimen until it deforms or breaks. The equipment measures the applied load and the corresponding deformation during testing to obtain the tensile properties. The major difference is the material being tested. ASTM D638 tests thicker pieces of plastic that can be molded or cut into standard dog-bone shapes. These specimens allow even stress patterns when tested. The ASTM D882 method, on the other hand, tests thin plastic films and sheets that are not suitable for dog-boning. The standard, therefore, adopts rectangular strip specimens, which are particularly suitable for thin, flexible materials. ASTM D882 provides testing conditions specific to thin films to obtain accurate and repeatable results, since they may have different stretching properties than rigid plastics.
Test Procedure Overview of ASTM D638 and ASTM D882
| Step | ASTM D638 | ASTM D882 |
| Instrumentation | Employs a universal testing machine with appropriate grips, load cells, and extensometers to determine tensile properties of plastics. | Accurately measures tensile properties using a universal testing machine with thin film and sheeting grips. |
| Sample Preparation | Molds, machines, or cuts standardize dogbone-shaped specimens from plastic sheets. | Cut rectangular strip samples from thin plastic film/sheeting without wrinkling or edge damage. |
| Measurement Process | Applies tensile force at a predetermined crosshead velocity until the specimen stretches or snaps, while measuring the force and elongation. | Applies tensile force at a controlled speed until film failure while continuously recording force and extension. |
| Results Obtained | Reports tensile strength (MPa), tensile modulus (GPa or MPa), and other relevant tensile properties. | Reports tensile strength (MPa), modulus (MPa), elongation at break, and other characteristics of film performance. |
| Environmental Conditioning | Prepare specimens in the controlled environment (temp and humidity) and test for uniformity before testing. | Precondition film specimens for measurement under defined conditions. |
| Thickness | Typically used for plastics ≥ 1.0 mm thick | Used for plastics < 1.0 mm thick |
Significance of ASTM D638 and ASTM D882
The mechanical properties of plastics are important, and these standards provide basic information on their mechanical behavior. ASTM D638 is the test standard for tensile properties of structural plastics used in automotive applications, consumer products, electrical enclosures, and industrial machinery. The standard defines the resistance of materials to service loads for the useful life. In the packaging and film fields, ASTM D882 is helpful. The manufacturers use this test to identify the strength and flexibility of plastic films used in protective wrapping, medical packaging, agricultural films, and packaging of foods. These findings enable ensuring the integrity of the test during handling, transport, and end-use conditions. Laboratories can obtain accurate tensile property data with the proper standard to aid in material selection, product development, and quality assurance decisions.
Applications of ASTM D638 and ASTM D882
ASTM D638 Applications
- Measures the tensile characteristics of solid and semi-solid plastics.Â
- Supports materials selection for engineering and structural applications.Â
- Checks molded plastic products/parts for quality.Â
- Assists in product development and material comparison studies.Â
- Assists in failure analysis and investigations into performance.Â
- Automotive, electrical, consumer goods, and industrial plastic products.Â
ASTM D882 Applications
- Tests the tensile characteristics of thin plastic films and sheets.
- Confirms the quality and uniformity of packaging materials.Â
- Â Enables packaging solutions for food, medical, and industrial packaging.Â
- Assesses the performance of films after aging or environmental exposure.Â
- Packaging, agricultural films, shrink film, stretch film, and laminates.
