ASTM D2991-84 PDF

Full title and description

ASTM D2991-84 — Recommended Practice for Testing Stress-Relaxation of Plastics. This practice describes procedures for determining the time-dependence of stress (stress relaxation) in plastic materials held at constant strain under controlled environmental conditions.

Abstract

Practice D2991-84 provides guidance on specimen preparation, conditioning, gripping, test environment, instrumentation and data recording for stress‑relaxation measurements on plastics. The document outlines methods to minimize eccentric loading and environmental variability so that long‑duration constant‑strain tests yield reproducible stress‑vs‑time data. The edition was published in 1984 and later withdrawn.

General information

• Status: Withdrawn / superseded (withdrawal recorded by ASTM, see withdrawal information).
• Publication date: 1984 (Designation D2991-84; published November 1984 in the ASTM Annual Book).
• Publisher: ASTM International (formerly American Society for Testing and Materials).
• ICS / categories: 83.080.01 — Plastics in general.
• Edition / version: D2991-84 (1984 edition).
• Number of pages: 3 pages (short practice).

Scope

This practice covers the determination of the time‑dependence of stress (stress relaxation) of plastics subjected to long‑duration, constant strain under approximately constant temperature and humidity, with negligible vibration. It is intended for laboratory measurements that evaluate how stress decays with time at fixed deformation and controlled environment; specimen type, conditioning time, gripping techniques and environmental control are addressed to ensure comparability.

Key topics and requirements

• Specimen geometry and preparation — recommended shapes and gauge lengths for tension specimens.
• Preconditioning and conditioning time — control of temperature and relative humidity before testing.
• Gripping and fixturing — use of grips, swivel or universal joints to minimize eccentric loading and slippage.
• Constant‑strain application and measurement — instrumentation for maintaining and monitoring fixed deformation.
• Data recording and interpretation — stress‑vs‑time curves, typical test durations and reporting conventions.
• Safety and material‑handling considerations for some polymers.

Typical use and users

Used by materials testing laboratories, plastics and polymer R&D groups, quality control teams, and product developers who need to characterize long‑term stress relaxation behavior of polymer parts and formulations (for sealing, load‑bearing, and dimensional‑stability assessments). It is primarily a laboratory practice rather than a manufacturing acceptance specification.

Related standards

ASTM E328 includes general stress‑relaxation methods for materials and at one time referenced methods that relate to plastics; responsibility for plastic stress‑relaxation practice has been associated with D2991 historically. Standards for stress relaxation of elastomers and rubbers (ISO 3384 series, ISO 13145, ISO 6914, and newer ASTM methods such as D8363 for specific rubber tests) cover related test methods for non‑plastic elastomeric materials and complementary measurement techniques. Users commonly consult these documents for comparable procedures or when testing non‑thermoplastic materials.

Keywords

stress relaxation, plastics, constant strain, conditioning, grips, ASTM D2991-84, time‑dependent stress, materials testing

FAQ

Q: What is this standard?

A: ASTM D2991-84 is a short practice document that provided recommended procedures for testing stress relaxation of plastics — measuring how stress decays with time when a specimen is held at constant strain.

Q: What does it cover?

A: It covers specimen preparation and conditioning, environmental control (temperature and humidity), gripping/fixturing to avoid eccentric loading, instrumentation for constant‑strain tests, and data recording/reporting for stress‑vs‑time results.

Q: Who typically uses it?

A: Laboratory technicians, materials scientists, polymer R&D engineers, and quality/control personnel in industries that evaluate long‑term mechanical relaxation behavior of plastic components.

Q: Is it current or superseded?

A: D2991-84 has been withdrawn by ASTM (withdrawal information is recorded; users should confirm current, accepted methods for stress relaxation in the latest ASTM or ISO literature).

Q: Is it part of a series?

A: It was developed under ASTM Committee D20 (Plastics), Subcommittee D20.10 (Mechanical Properties). While not a numbered series, it relates to other ASTM and ISO practices for stress‑relaxation and mechanical testing of polymers and elastomers.

Q: What are the key keywords?

A: stress relaxation, plastics testing, constant strain, specimen conditioning, grips, ASTM practice, time‑dependent stress.