ASTM D790-17 PDF

Full title and description

Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials — ASTM D790-17. This document specifies procedures (three-point bending) for measuring flexural strength, flexural stress, flexural strain and flexural modulus of rectangular specimens of plastics, composites and insulating materials used for quality control, specification and material characterization.

Abstract

ASTM D790-17 defines two procedures for three‑point bend testing of solid rectangular specimens of unreinforced and reinforced plastics and electrical insulating materials. It provides test geometry, measurement methods (crosshead or deflectometer), formulas for flexural stress and strain, guidance on span‑to‑depth ratios and limitations (notably a 5% outer‑fiber strain limit for determination of flexural strength). The standard is intended for both rigid and semi‑rigid materials and is commonly used for routine quality control and comparative testing.

General information

• Status: Active (designation D790-17).
• Publication date: 2017 (published July 2017; ASTM record shows last update July 24, 2017).
• Publisher: ASTM International (formerly American Society for Testing and Materials).
• ICS / categories: 29.035.20 (Plastics and rubber insulating materials).
• Edition / version: D790‑17 (2017 revision).
• Number of pages: 12 pages (typical published PDF/Book of Standards extract).

(Bibliographic details summarized from the ASTM specification entry and standard metadata.)

Scope

These test methods determine flexural properties of unreinforced and reinforced plastics, high‑modulus composites and electrical insulating materials using a three‑point loading system on a simply supported beam. Specimens are solid, rectangular cross section, and may be molded or cut from sheets, plates or shapes. The method is applicable to rigid and semi‑rigid materials but cannot determine flexural strength for materials that do not break or yield in the outer surface within the 5.0% strain limit of the test. The standard specifies two procedures (A and B) to cover materials with relatively small deflections (Procedure A) and materials that undergo large deflections (Procedure B).

Key topics and requirements

• Three‑point bending test setup: simply supported beam with center loading nose (loading at midspan).
• Two procedures: Procedure A (recommended for modulus and small‑deflection materials) and Procedure B (for large‑deflection materials; may be used for strength measurements).
• Specimen geometry and conditioning: rectangular solid specimens prepared by molding or cutting from extruded/molded stock; dimensions and support span-to-depth ratios specified.
• Measurement methods: deflection may be measured via crosshead position or a deflectometer (method used must be reported).
• Calculations: equations provided for flexural stress, flexural strain and modulus (including guidance on tangent modulus and span‑to‑depth effects).
• Limits and notes: outer‑fiber strain limit of 5% for valid flexural strength; shear and orthotropy considerations for composites; SI units are the standard units of record.
• Relation to other tests: four‑point bending (ASTM D6272) discussed for materials not suitable for three‑point bending; ISO 178 noted as a related but not technically equivalent method.

Key technical elements and limitations are drawn from the official test method text.

Typical use and users

Common users include materials testing laboratories, plastics and composite manufacturers, R&D engineers, quality control and specification authors, and certification bodies. Typical uses are routine QC of production lots, material comparison, verification of supplier claims, and research into mechanical behavior (modulus, strength and strain under bending). Test houses and industrial labs frequently quote ASTM D790 results when specifying parts or materials.

Related standards

Standards commonly referenced with or as alternatives to D790-17 include ASTM D6272 (Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials by Four‑Point Bending), ISO 178 (Determination of Flexural Properties of Plastics — comparable method but not technically equivalent), and other ASTM mechanical property methods such as D638 (tensile) and D256 (impact). The D790 text explicitly references D6272 and ISO 178 in explanatory notes.

Keywords

flexural properties, flexural strength, flexural modulus, three‑point bend, plastics testing, composites, electrical insulating materials, Procedure A, Procedure B, span‑to‑depth ratio, deflectometer.

FAQ

Q: What is this standard?

A: ASTM D790‑17 is the ASTM standard that provides test methods for measuring flexural properties (strength, stress, strain and modulus) of unreinforced and reinforced plastics and electrical insulating materials using a three‑point bending configuration.

Q: What does it cover?

A: It covers specimen preparation (solid rectangular specimens), test fixtures and spans, measurement techniques (crosshead or deflectometer), calculation methods for flexural stress/strain/modulus, two procedures to accommodate small and large deflections, and limitations such as the 5% outer‑fiber strain limit for flexural strength determinations.

Q: Who typically uses it?

A: Materials and test laboratories, plastics and composite manufacturers, R&D and materials engineers, quality managers and standards authors use D790 results for specification, acceptance testing and comparative material characterization. Third‑party test houses commonly run D790 for client materials.

Q: Is it current or superseded?

A: As published, D790‑17 is the 2017 ASTM designation and is listed as active in the ASTM catalog (last updated July 2017). Revision activity/work items have been recorded by ASTM committees to update the standard (indicating planned revisions), but D790‑17 remained the current published designation at the time of the cited records. Users should confirm the most recent status directly with ASTM if they require the latest revision after 2017.

Q: Is it part of a series?

A: D790 is part of the suite of ASTM test methods covering mechanical properties of plastics and composites (Book of Standards Volume 08.01, committee D20 and subcommittee D20.10). It is commonly used alongside complementary ASTM tensile, impact and four‑point bending methods.

Q: What are the key keywords?

A: Flexural properties, three‑point bend, flexural modulus, flexural strength, plastics, composites, deflectometer, Procedure A, Procedure B, span‑to‑depth ratio.