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D623-07 – Standard Test Method Technical Guide
📏 Scope and Apparatus Overview
ASTM D623-07 (Reapproved 2019) provides standardized methods for comparing the fatigue characteristics and rate of heat generation of different rubber vulcanizates when subjected to dynamic compressive strains. The methods utilize rapidly oscillating compressive stresses under controlled conditions to accelerate the generation of heat and fatigue within a vulcanized test specimen of definite size and shape.
The standard covers two distinct types of apparatus for testing:
- Test Method A — Goodrich Flexometer: A widely recognized apparatus for measuring temperature rise and blowout resistance.
- Test Method B — Firestone Flexometer: An alternative apparatus for evaluating fatigue characteristics and dimensional stability under compressive load.
| 🟦 Feature | 📏 ASTM D623-07 Specification |
|---|---|
| Standard Designation | D623 −07 (Reapproved 2019)´1 |
| Test Objective | Compare fatigue characteristics and rate of heat generation under dynamic compressive strains |
| Primary Measurement | Temperature rise (to equilibrium or fixed time interval) |
| Secondary Measurements | Permanent set, dimensional changes, time to fatigue failure (blow out) |
| Apparatus Methods | Method A: Goodrich Flexometer; Method B: Firestone Flexometer |
| Unit System | SI units (standard); inch-pound values in parentheses for information only |
| Applicable Samples | Any vulcanized rubber compound (excluding hard rubber); lab compound, production sample, or finished article |
⚙️ Procedure and Key Measured Properties
The test procedure defined in Section 3 outlines two primary ways the temperature rise is captured:
- Equilibrium Temperature: The test runs until the specimen reaches an equilibrium point where the heat generated by flexing equals the heat dissipated.
- Fixed-Time Temperature Rise: The temperature increase is recorded over a strict, predetermined time interval while the specimen is under dynamic load.
In addition to temperature data, the standard requires the measurement of the specimen’s degree of permanent set and other dimensional changes caused by the flexing. For specific test conditions, the procedure is continued until the specimen experiences a fatigue failure by internal rupture or “blow out”, and the time to failure is documented.
⚠️ Critical Interpretation Note: Section 4.1 explicitly states: “Because of wide variations in service conditions, no correlation between these accelerated tests and service performance is given or implied.” These methods are strictly intended for comparative compound quality estimation and research and development studies.
📊 Sample Preparation and Reference Standards
According to Section 5, the sample may consist of any vulcanized rubber compound except those generally classed as hard rubber, provided it is of sufficient size to permit preparation of the test specimen. Acceptable sources include compounds mixed experimentally in the laboratory, samples taken during the manufacturing process, or specimens cut from a finished article of commerce.
In accordance with Section 1.2, the values stated in SI units are to be regarded as the standard. Values given in parentheses are for information only. The standard references several companion ASTM standards for proper testing execution, including D395 (Compression Set) and D1349 (Standard Conditions for Testing).
💡 Required Reference Materials: For accurate implementation of Test Method A, the Goodrich Flexometer Anvil Drawings (ASTM Adjunct) are required. Users should also consult Practice D3182 for standard mixing procedures and Practice D4483 for evaluating precision of the method.
❓ Frequently Asked Questions
🔍 What is the main purpose of ASTM D623-07?
The primary purpose is to compare the fatigue characteristics and rate of heat generation of different rubber vulcanizates when they are subjected to dynamic compressive strains under controlled laboratory conditions.
💡 Can ASTM D623-07 results be used to predict actual product lifespan?
No. The standard explicitly states that no correlation between these accelerated tests and actual service performance is given or implied due to wide variations in service conditions. Results are best used for relative compound comparison and R&D evaluations.
⚡ What are the two types of flexometer apparatus defined in the standard?
The standard covers Test Method A, which utilizes the Goodrich Flexometer, and Test Method B, which specifies the Firestone Flexometer. Both apparatus types subject the specimen to rapidly oscillating compressive stresses.
📌 What specific measurements must be taken in addition to temperature rise?
The standard requires the measurement of the degree of permanent set, other specimen dimensional changes, and under specific conditions, the time required for a fatigue failure by internal rupture or blow out.