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| ASTM D638 | |
|---|---|
| Title | ASTM D638 |
| Status | Active |
| Year | 2014 |
| Organization | ASTM International |
| Domain | Materials testing |
| Type | Standard test method |
ASTM D638 is a standardized test method specifying tensile properties for plastics, widely used by manufacturers, laboratories, and regulatory bodies to determine strength, elongation, and modulus. It connects material selection in industries such as automotive, aerospace, and packaging with certification frameworks and product liability considerations by providing repeatable measurement protocols. Practitioners use it alongside complementary standards and test methods to inform design decisions and compliance with procurement specifications.
ASTM D638 delineates geometry, conditioning, and procedure for tensile testing of molded and extruded plastic specimens to obtain tensile strength, tensile modulus, and elongation at break. The scope addresses comparisons among thermoplastics, thermosets, and reinforced polymers for engineering and quality assurance in contexts involving Society of Automotive Engineers, European Space Agency, National Institute of Standards and Technology, Underwriters Laboratories, and procurement specifications from agencies like Department of Defense (United States). Its purpose is to reduce variability among laboratories and provide data for finite element inputs, failure analysis, and material selection alongside standards such as those from International Organization for Standardization and American Society for Testing and Materials committees.
Specimen types include "Type I" through "Type V" dumbbell shapes molded or cut per the standard, with exact dimensions specified to control stress distribution during testing. Specimens are typically produced in molds or by extrusion and may be machined from molded parts; production methods reference practices used by manufacturers like General Motors and Boeing when qualifying materials. Conditioning prior to testing often follows standardized environmental exposures—temperature and relative humidity control—aligned with climate-controlled laboratories such as those at National Research Council Canada or Fraunhofer Society facilities. For hygroscopic plastics, preconditioning is coordinated with materials databases maintained by organizations like MatWeb.
The procedure prescribes gripping, alignment, strain-rate selection, and extensometry to minimize slippage and bending, with strain rates chosen relative to specimen gauge length to control strain-rate sensitivity for polymers used by companies like Ford Motor Company and Airbus. Extensometer attachment or non-contact methods such as digital image correlation are permitted; equipment selection often references measurement protocols in research from Massachusetts Institute of Technology, Stanford University, and ETH Zurich. Operators document test temperature and humidity, and record force-displacement data to generate stress-strain curves used in fracture and creep analysis across sectors including Lockheed Martin and Siemens.
Required apparatus includes a universal testing machine with load cell and grips capable of specified alignment and stiffness, calibrated according to national metrology institutes such as NIST or Physikalisch-Technische Bundesanstalt. Calibration intervals and verification use reference materials traceable to standards maintained by institutions like National Physical Laboratory (UK) and proficiency programs run by entities like ASTM International. Extensometers and strain-measurement systems are calibrated with gauge blocks, optical comparators, or interferometry techniques developed in laboratories at Caltech and Imperial College London to ensure measurement uncertainty is quantified.
Raw force and elongation data are converted to engineering stress and strain using specimen cross-sectional area and gauge length, then reported as tensile strength at yield, tensile strength at break, tensile modulus, and percent elongation at break. Data reduction practices align with statistical treatment taught in courses at Harvard University and University of Cambridge; results feed into material property catalogs used by industries including Toyota and NASA. Reported values include test conditions, specimen type, and measurement uncertainties compatible with reporting frameworks from International Electrotechnical Commission and accreditation bodies like American Association for Laboratory Accreditation.
Precision and bias are influenced by specimen preparation, machine stiffness, grip method, and operator technique; interlaboratory studies coordinated by committees within ASTM International and academic consortia quantify repeatability and reproducibility. Limitations include sensitivity to specimen geometry for anisotropic composites, rate- and temperature-dependent behavior for amorphous polymers studied at Princeton University and University of Michigan, and potential mismatch with in-service stress states in components used by Raytheon Technologies. Complementary tests such as impact, fatigue, and creep are often required for comprehensive characterization.
ASTM D638 is applied in material selection for automotive components, consumer goods, medical devices, and packaging, used by companies like Johnson & Johnson, 3M, ExxonMobil, and Dow Chemical Company. The standard is periodically revised through ASTM committee ballots and stakeholder input, reflecting advances in measurement such as digital image correlation and novel composite architectures developed at institutions including Rensselaer Polytechnic Institute and Delft University of Technology. Ongoing revisions consider harmonization with ISO test methods and emerging regulatory expectations from agencies like European Chemicals Agency.
Category:Standards