Introduction:
ASTM D 790 is a crucial standard used in the plastics industry to determine the flexural properties of various materials, both reinforced and unreinforced. Understanding this standard is essential for engineers, manufacturers, and researchers involved in material testing and product development.
What is ASTM D 790?
ASTM D 790 outlines the procedures for testing the flexural properties of plastics and electrical insulating materials. Flexural properties include modulus of elasticity, flexural stress, flexural strain, and flexural modulus. These properties are vital for assessing a material’s behavior under bending or flexural loading, which is common in many applications.
Testing Procedure: The testing procedure outlined in ASTM D 790 specifies precise conditions for specimen preparation, test setup, and data collection to ensure accurate and reproducible results.
Specimen Preparation: Before testing, specimens are prepared according to specific dimensions outlined in the standard. The standard provides guidelines for specimen size based on the material type and intended application. For example, specimens for rigid plastics typically have rectangular cross-sections with dimensions of 127 mm (5 inches) in length, 12.7 mm (0.5 inches) in width, and a thickness ranging from 3.2 mm to 13 mm (0.125 inches to 0.5 inches), depending on the material’s flexibility.
Test Setup: Once specimens are prepared, they are positioned on supports within a universal testing machine (UTM) according to the specified span length. The span length typically ranges from 16 mm to 64 mm (0.625 inches to 2.5 inches), depending on the material’s thickness and modulus of elasticity. The standard allows for both three-point and four-point bending configurations, with the choice depending on the material’s stiffness and the desired sensitivity of the test.
Testing Speed: ASTM D 790 recommends a testing speed of 1.3 mm/min (0.05 inches/min) for materials with moduli of elasticity less than 7 GPa (1 × 10^6 psi) and 2.5 mm/min (0.1 inches/min) for materials with moduli of elasticity greater than or equal to 7 GPa (1 × 10^6 psi). This controlled testing speed ensures uniform deformation rates across different materials and allows for accurate determination of flexural properties.
Data Collection: During the test, the specimen is subjected to a constant rate of loading until failure or a predetermined strain is reached. Load and corresponding deflection data are continuously recorded throughout the test using the UTM’s load cell and displacement transducer. These data are then used to calculate various flexural properties.
Interpretation of Results: The results obtained from ASTM D 790 testing provide valuable insights into the material’s flexural behavior, including its ability to withstand bending loads without permanent deformation or failure. Engineers and researchers use these results to assess material performance, optimize material selection for specific applications, and ensure product quality and reliability.
Applications:
The flexural properties determined by ASTM D 790 testing are crucial for a wide range of industries and applications, including:
- Automotive: Assessing the structural integrity of plastic components in vehicles.
- Aerospace: Evaluating the performance of composite materials used in aircraft structures.
- Construction: Determining the suitability of plastic materials for use in building and infrastructure projects.
- Electronics: Testing the reliability of electrical insulating materials under bending stress.
Conclusion:
ASTM D 790 plays a vital role in the characterization and evaluation of the flexural properties of plastics and electrical insulating materials. By adhering to this standard, manufacturers and researchers can ensure consistency, reliability, and performance in their materials and products.
References:
- ASTM International. “ASTM D790 / D790M – 20: Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials.” ASTM International, West Conshohocken, PA, 2020, www.astm.org/cgi-bin/resolver.cgi?D790.