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D5947-24 – Standard Test Method Technical Guide
ASTM D5947-24, issued under the fixed designation D5947, provides standardized test methods for determining the physical dimensions of solid plastic specimens. These measurements are critical input data for calculating the results of common mechanical, thermal, and physical property tests. Developed by Subcommittee D20.10 on Mechanical Properties, this standard establishes a clear framework for accuracy and precision in dimensional measurement.
📐 Overview and Scope of D5947-24
The scope of D5947-24 specifically targets solid plastic specimens where the measured dimensions are used directly to determine test results, such as cross-sectional area for tensile modulus or thickness for flexural strength. The standard mandates the use of SI units as the primary unit system. It encompasses five distinct procedural pathways, identified as Test Methods A through D, and H, each designed to accommodate different specimen geometries and material responses. The selection of a specific method is typically dictated by the material specification for the plastic being tested.
⚠️ Multinational Standardization: As per Note 1 of the standard, D5947-24 and ISO 16012 address the same subject matter but differ in technical content. Users should verify compliance with the specific jurisdictional requirements of their testing program.
⚙️ Test Methods, Apparatus, and Operational Selection
The standard defines a “micrometer” as an instrument capable of measuring with an absolute uncertainty of 25 µm (0.0010 in.) or smaller. The test methods vary primarily in the contact pressure exerted by the micrometer anvil and the duration of that pressure, ensuring compatibility with both rigid materials and softer, more compressible plastics. Understanding these nuances is essential for accurate data generation.
The table below summarizes the primary applications and fundamental requirements for each of the defined test methods outlined in the D5947-24 Summary of Test Methods.
| 🟦 Feature | 📐 Test Method A | 📐 Test Method B | 📐 Test Method C | 📐 Test Method D | 📐 Test Method H |
|---|---|---|---|---|---|
| Application | Thickness of sheet & plate | Width of sheet & plate | Length of specimen | Diameter of rods & tubing | Thickness for durometer |
| Geometry | Flat, parallel surfaces | Flat, parallel edges | Flat, parallel ends | Cylindrical / round | Flat, thick block |
| Typical Anvil | Flat, planar anvils | Flat, parallel anvils | Flat face + depth rod | V-anvil or ball anvil | Flat, small diameter |
| 🎯 Uncertainty | 25 µm or smaller | 25 µm or smaller | 25 µm or smaller | 25 µm or smaller | 25 µm or smaller |
💡 Method Selection Criteria: When testing materials that creep or deform easily under pressure (e.g., soft foams or elastomers), ensure the selected method specifies a lower contact pressure and a shorter dwell time to minimize measurement error. Refer to the referenced conditioning standard D618 before measurement.
📊 Key Terminology and Measurement Traceability
The standard provides critical definitions to ensure uniformity in measurement practices. Adhering to these definitions is mandatory for compliance with D5947-24. The concept of traceability through calibration and verification is a cornerstone of the procedure.
| 📏 Term | 🎯 Definition per D5947-24 | ⚡ Operational Significance |
|---|---|---|
| Absolute Uncertainty | Smallest division that may be read directly on the instrument. | Limits the resolution of the measurement. If the instrument reads to 0.01 mm, uncertainty is ±0.01 mm. |
| Micrometer | Instrument for measuring within an absolute uncertainty of 25 µm or smaller. | Defines the class of allowable measurement equipment. |
| Calibration | Operations establishing the relationship between measured/indicated values and reference standards. | Ensures the instrument reading matches a known standard length. |
| Verification | Proof, using calibrated standards, that the instrument operates within requirements. | An ongoing check that the instrument has not drifted out of tolerance. |
| 1 mil | A dimension equivalent to 25 µm (0.0010 in.). | Common imperial unit conversion used in the plastics industry. |
The standard references several other key ASTM documents, including D618 (Conditioning), D638 (Tensile Properties), D790 (Flexural Properties), D2240 (Durometer Hardness), and D883 (Terminology). Together, these form a comprehensive framework for quality control and material characterization in the plastics industry.
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D5947-24?
The standard provides standard test methods for measuring the physical dimensions of solid plastic specimens, specifically when those dimensions are required to calculate results for other property tests (e.g., tensile strength, flexural modulus, hardness).
💡 How does D5947-24 differ from ISO 16012?
As stated in Note 1 of the standard, D5947-24 and ISO 16012 address the same subject matter—determination of linear dimensions of test specimens—but they differ in technical content, including specific procedural steps and apparatus requirements.
⚡ What is the maximum allowable absolute uncertainty for a micrometer used under this standard?
The standard explicitly defines a micrometer as an instrument capable of measuring any dimension within an absolute uncertainty of 25 µm or smaller. The absolute uncertainty is the smallest division that can be read directly on the instrument.
📌 What does the term “1 mil” represent in the context of D5947-24?
Section 3.2.5 of the standard defines “1 mil” as a dimension equivalent to 25 µm (0.0010 in.). It serves as a common unit of thickness measurement in imperial systems for films and coatings.