Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
ASME B29.26-2013 — Fatigue Testing Power Transmission Roller Chain
🔬 ASME B29.26-2013 is the authoritative method standard for fatigue testing of power transmission roller chains. It establishes uniform requirements for testing equipment, test chains, test loads, testing procedures, fatigue data analysis, and presentation of test results, and applies to precision power transmission roller chains (the ANSI B29.1 family), multiple-strand roller chains, and leaf chains. The Standard grew out of a 1982 ISO effort on motorcycle chain standards that introduced dynamic (fatigue) strength requirements; at the time, several different test procedures and analysis methods were in use and could produce significantly different fatigue strength results for the same chain sample, so a uniform testing and analysis procedure was clearly needed. The first edition, ASME B29.26M, was approved by the American National Standards Institute on December 9, 1996. The 2001 revision added a conformance test for dynamic strength requirements in related B29 product standards, increased the number of tests required for four- or five-level staircases, and added appendices describing Probit analysis for step size and a method for adjusting fatigue strength from a short test specimen (five pitches) to a longer drive chain (100 pitches). The 2013 revision incorporates new specimen drawings and a revised section on step size covering multiple-strand roller and leaf chains, and corrects two editorial errors from the 2001 edition.
💡 Fatigue testing is one of the most service-relevant quality checks for chain: the load at which a chain fails under cyclic loading is far below its Minimum Ultimate Tensile Strength (M.U.T.S.). Only standardized fatigue testing turns “dynamic strength” into an acceptance criterion and a design input.
1. Scope and Purpose 📌
The body of the Standard has ten sections: Scope, Purpose, Definitions and Nomenclature, References, Testing Equipment, Test Chains, Test Loads, Testing Procedures, Analyzing Fatigue Testing Data, and Presentation of Test Results, supported by figures such as the typical load cycle, test specimens and fixtures, the Johnson-Goodman diagram, the staircase data plot, and a typical fatigue test data plot. Nonmandatory appendices cover the survival method with abridged Probit analysis, additional “phantom” data points, adding one step to the minimum fatigue strength, and adjusting laboratory fatigue strength for applications.
- Uniformity: provides a comparable platform for fatigue data from different laboratories and manufacturers.
- Conformance verification: since 2001, a conformance test evaluates whether a chain meets the dynamic strength requirements of related B29 product standards.
- Engineering conversion: Appendix D gives a method for adjusting a chain’s fatigue strength from a short test specimen to a longer drive chain for application use.
⚠️ Fatigue results are highly sensitive to test details: specimen length, fixture design, load frequency, and loading waveform all matter. Following the equipment and procedures of this Standard exactly is the prerequisite for comparable data; simplified, non-standard procedures cannot be used for cross-manufacturer comparison.
2. Testing Equipment and Test Chains 🔧
The Standard requires test machines capable of applying stable cyclic axial loads with accurate recording of load and number of cycles. Figures show typical fatigue test specimens and fixtures for single-strand roller chains, double-strand roller chains, leaf chains, and typical fixtures for endless chains tested on sprockets or sheaves. Fixtures must transmit load uniformly along the chain’s longitudinal axis and avoid eccentric loading.
Selection of test chains should consider:
- Specimen form: open chain segments (usually specified in pitches) or endless chains mounted on sprockets or sheaves.
- Specimen length: short specimens (e.g., 5 pitches) versus longer chains (e.g., 100 pitches); the difference is addressed by the adjustment method in the appendices.
- Chain condition: new chains should be made by the manufacturer’s normal process; testing of used chains requires separate provisions.
💡 Specimen length matters: short specimens measure higher fatigue strength than long chains. Using short-specimen results directly for selection is unconservative — always apply the Appendix D adjustment to the application-length fatigue strength.
3. Test Loads and Procedures 📊
A typical load cycle (Fig. 1) subjects the chain to alternating tension between a minimum load Pmin and a maximum load Pmax; the mean load Pm and load amplitude Pa define the fatigue condition. The staircase method is the core recommended strategy:
| Item | Requirement | Notes |
|---|---|---|
| Load-amplitude steps | Raised/lowered by a preselected step size | Step size affects statistical precision |
| Number of levels | 4 to 5 levels (tightened since 2001) | More levels require more tests |
| Number of data points | Meets the minimum in Table 1 | Corresponds to the staircase levels |
| Data analysis | Survival method / abridged Probit analysis | Determines fatigue strength at a given survival probability |
The procedures also require specifying the reference number of cycles (run-out criterion, e.g., 10⁷ cycles), recording the failure location and cycles for each specimen, and plotting the staircase results and the Johnson-Goodman diagram. The Johnson-Goodman diagram plots mean load on the horizontal axis and load amplitude on the vertical axis, connecting the fatigue limits at different mean loads in a Goodman-type line that defines the fatigue boundary under combined steady and alternating stress.
🚨 Load frequency and specimen temperature must be controlled: excessively high frequencies heat the chain joints and change material behavior, distorting results. The Standard requires monitoring specimen temperature and, when necessary, reducing frequency or applying cooling.
4. Data Analysis and Presentation 📈
The data-analysis section establishes the following:
- Survival method: the 50% survival probability (median fatigue strength) is the common characterization; other survival probabilities (e.g., 99%) may be computed per Appendix A.
- Abridged Probit analysis: used to set a rational step size and estimate the mean and standard deviation of the fatigue strength.
- Presentation: report chain specification, pitch, specimen length, load conditions (Pm/Pa), number of cycles, survival probability, number of data points, and the Johnson-Goodman diagram or staircase plot so results are reproducible and auditable.
💡 A complete test report is more than a “strength number” — it is traceable quality evidence: state the step size and number of levels, the run-out criterion, the specimen batch and heat-treatment state so third-party review and engineering selection can be trusted.
5. Engineering Practice Essentials 🛠️
- Acceptance testing: include the conformance test in supplier incoming inspection to verify dynamic strength claims.
- Design selection: use fatigue strength (not only M.U.T.S.) for chains under pulsating loads, frequent starts and stops, or shock loading.
- Inter-laboratory comparison: with a uniform procedure, fatigue strength differences between laboratories on the same sample should shrink; residual gaps point to machine calibration or fixture issues.
- Documentation: keep full staircase data and Goodman diagrams as inputs for reliability design and life prediction.
6. Frequently Asked Questions ❓
❓ Q: What is the difference between fatigue strength and M.U.T.S.?
A: M.U.T.S. is the one-time static breaking load; fatigue strength is the maximum load amplitude the chain can endure for a reference number of cycles (or indefinitely) without failure. Fatigue strength is usually much lower than M.U.T.S., and both must be considered in design.
A: M.U.T.S. is the one-time static breaking load; fatigue strength is the maximum load amplitude the chain can endure for a reference number of cycles (or indefinitely) without failure. Fatigue strength is usually much lower than M.U.T.S., and both must be considered in design.
❓ Q: Why is the staircase method recommended?
A: The staircase method estimates the center of the fatigue strength distribution with relatively few specimens by building a statistical sample from adjacent “fail/pass” results, making it more efficient than conventional group testing.
A: The staircase method estimates the center of the fatigue strength distribution with relatively few specimens by building a statistical sample from adjacent “fail/pass” results, making it more efficient than conventional group testing.
❓ Q: How are short-specimen results converted to long-chain fatigue strength?
A: Use the Appendix D adjustment, which accounts for length effects (defect distribution and stress non-uniformity grow with length), converting a short-specimen (e.g., 5-pitch) result to the actual drive chain length (e.g., 100 pitches).
A: Use the Appendix D adjustment, which accounts for length effects (defect distribution and stress non-uniformity grow with length), converting a short-specimen (e.g., 5-pitch) result to the actual drive chain length (e.g., 100 pitches).
❓ Q: Does the Standard apply only to roller chains?
A: It is primarily for power transmission roller chains, but the 2013 edition explicitly extends the specimen and fixture content to multiple-strand roller chains and leaf chains, which follow the same uniform methodology.
A: It is primarily for power transmission roller chains, but the 2013 edition explicitly extends the specimen and fixture content to multiple-strand roller chains and leaf chains, which follow the same uniform methodology.
