ASTM E328-21 PDF

Full title and description

ASTM E328-21 — Standard Test Methods for Stress Relaxation for Materials and Structures. This standard provides standardized procedures for measuring the time dependence of stress (stress relaxation) in materials and structural elements under approximately constant constraint and controlled test environment; methods are described for tension, compression, bending and torsion test geometries and include guidance on test apparatus, specimen preparation and analysis of relaxation data.

Abstract

ASTM E328-21 specifies test methods to determine how stresses in a constrained material or structural component decay with time when the constraint is held constant. The standard details parts for different loading modes (tension, compression, bending, torsion), gives recommendations for equipment and instrumentation, and describes data-reduction and reporting practices used to generate stress-relaxation curves and characteristic parameters for design and acceptance.

General information

• Status: Active (current ASTM standard).
• Publication date: Published January/February 2021 (E328‑21 edition approved early 2021).
• Publisher: ASTM International (formerly American Society for Testing and Materials).
• ICS / categories: 19.020 — Test conditions and procedures in general; Mechanical testing (ASTM Committee E28 jurisdiction).
• Edition / version: E328‑21 (edition / revision year 2021).
• Number of pages: 15 pages (typical published PDF length for the E328‑21 edition).

Key bibliographic and administrative details above are taken from listings of the ASTM E328‑21 edition and distributor metadata.

Scope

These test methods cover determination of the time dependence of stress (stress relaxation) in materials and structures where the specimen or assembly is held under approximately constant constraint, constant test environment and negligible vibration. Specific procedures are provided for tension (Part A), compression (Part B), bending (Part C) and torsion (Part D) test configurations, and the standard includes recommendations for test apparatus, instrumentation, specimen preparation, test conditions, and analysis/reporting of relaxation data. The standard notes that the plastics stress‑relaxation method has been withdrawn from this document and assigned to Practice D2991.

Key topics and requirements

• Definitions and fundamentals of stress relaxation and its significance for joint integrity and long‑term component performance.
• Part A–D methods addressing tension, compression, bending and torsion stress‑relaxation tests respectively.
• Specimen preparation, fixture and restraint design to maintain approximately constant constraint during testing.
• Instrumentation and measurement recommendations (load cells, displacement/strain measurement, temperature control) and data acquisition practices.
• Data reduction and reporting: generation of relaxation curves, characteristic relaxation values, and methods for fitting or interpolating relaxation behavior for design use.
• Notes on limitations and optional procedures (e.g., elevated‑temperature testing, multiple‑specimen arrangements) and transfer of plastics testing responsibility to Practice D2991.

Typical use and users

ASTM E328‑21 is used by materials engineers, mechanical test laboratories, design engineers and quality/acceptance teams who need standardized stress‑relaxation data for metallic and other structural materials. Typical applications include assessing long‑term preload loss in bolted or riveted joints, evaluating spring and fastener behavior, validating shrink‑fit and interference assemblies, and generating input data for durability or relaxation‑sensitive designs. Test laboratories producing material property data for suppliers, OEMs and regulatory compliance frequently adopt these methods.

Related standards

Relevant and related documents include the previous edition ASTM E328‑13 (superseded by E328‑21), ASTM Practice D2991 (responsibility for plastics stress‑relaxation procedures), and other mechanical testing standards that address tensile, compressive and elevated‑temperature testing (for example ASTM E8 for tensile testing of metallic materials as commonly referenced in mechanical test programs). Users should consider companion ASTM test methods and practices when assembling a test plan.

Keywords

stress relaxation; relaxation test; tension relaxation; compression relaxation; bending relaxation; torsion relaxation; bolted joint preload; springs; long‑term preload loss; ASTM E328; mechanical testing.

FAQ

Q: What is this standard?

A: ASTM E328‑21 is the 2021 edition of the standard test methods that define procedures for measuring stress relaxation in materials and structures under approximately constant constraint. It provides methods for tension, compression, bending and torsion test configurations and guidance on equipment, data collection and analysis.

Q: What does it cover?

A: It covers how to perform stress‑relaxation tests, maintain controlled test conditions, measure the decline in stress over time while constraint is held constant, and how to report and analyze the resulting relaxation data for engineering and quality uses.

Q: Who typically uses it?

A: Materials and mechanical engineers, test laboratories, researchers, OEMs and suppliers involved in fastening/joining design, spring and fastener qualification, interference fits, and any application where time‑dependent relaxation of stress affects performance or safety use these methods.

Q: Is it current or superseded?

A: The E328‑21 edition (approved in early 2021) is the current ASTM edition replacing previous editions (for example E328‑13). Users should verify they hold the E328‑21 document for the latest procedures and any editorial or technical changes.

Q: Is it part of a series?

A: E328 is a standalone ASTM standard that contains multiple parts (A–D) addressing different stress states. It is maintained under ASTM Committee E28 (Mechanical Testing) and is typically used alongside other ASTM mechanical testing practices and standards applicable to the materials and test conditions in question.

Q: What are the key keywords?

A: stress relaxation; relaxation testing; tension/compression/bending/torsion; preload loss; bolted joints; springs; ASTM E328‑21.