What Is High Cycle Fatigue?
The high-cycle fatigue test applies a repeated stress below the elastic limit to a specimen and determines the number of cycles to failure. Repeated at different stress amplitudes, this produces the stress-cycle (S-N) curve. Loading is usually stress-controlled.
Purpose of High Cycle Fatigue
The purpose is to determine the material's life under repeated loads far below the static strength. For parts subjected to many low-amplitude cycles, such as those from vibration and rotation, design relies on this data.
Which Products Is High Cycle Fatigue Applied To?
- Rotating parts such as crankshafts, axles and shafts
- Springs and fasteners
- Aerospace structural components
- Welded structural details
- Automotive suspension parts
In Which Sectors Is High Cycle Fatigue Used?
Standards Related to High Cycle Fatigue
- ISO 1099 (metallic materials — fatigue testing under axial force control)
- ASTM E466 (constant amplitude axial fatigue tests)
- ASTM E739 (statistical analysis of fatigue data)
- ISO 12107 (statistical planning of fatigue data)
High Cycle Fatigue Conditions
- Loading type
- Stress-controlled, constant amplitude
- Stress ratio (R)
- From the specification; selected as tension-tension or tension-compression
- Frequency
- Selected so as not to cause heating in the specimen
- Termination
- Fracture, or reaching the cycle count defined in the specification (run-out)
Equipment for High Cycle Fatigue
- Servohydraulic or resonance fatigue machine
- Load cell and alignment fixture
- Cycle counter and data acquisition system
- Specimen temperature monitoring equipment
- Stereo microscope for fracture surface examination
Sample Requirements for High Cycle Fatigue
- The specimen surface must be machined and polished per the standard; surface roughness directly affects life.
- Specimen geometry must minimise stress concentration.
- Many specimens at multiple stress levels are required for the S-N curve.
- Sampling location and orientation must be recorded.
- For welded specimens, weld geometry and grinding condition, if any, must be reported.
Duration of High Cycle Fatigue
High-cycle fatigue is inherently long: a single specimen can reach millions of cycles and take days. Together with the number of specimens needed for a full S-N curve, the study spans weeks.
High Cycle Fatigue Procedure
- 1Specimens are machined, measured and their surface condition recorded.
- 2Machine alignment is checked.
- 3Stress level and stress ratio are set.
- 4The specimen is cycled at the defined frequency.
- 5The cycle count at fracture is recorded; specimens that do not fracture are marked as run-outs.
- 6The test is repeated at different stress levels.
- 7The S-N curve is constructed and assessed statistically.
High Cycle Fatigue Acceptance Criteria
The method standard defines how the test is performed, not what the result should be. The acceptance limit comes from the material standard, the product specification or the customer's technical drawing; this page therefore gives no numerical limit.
Evaluation of Results
Results are interpreted as a distribution, not individually; fatigue data is inherently scattered. Statistical approaches such as ASTM E739 are used in the assessment, and a design curve is derived for a given confidence level.
High Cycle Fatigue Report
- Specimen identification, material type and cast/batch number, if any
- Specimen geometry, dimensions and preparation method
- Standard and test conditions applied
- Test temperature and ambient conditions
- Measured values and calculated quantities
- Fracture surface or indentation photographs (where applicable)
- Measurement uncertainty (if requested)
- A statement that the result applies only to the specimen submitted for testing
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- EN 10204 (inspection documents for metallic products)
- EU 305/2011 Construction Products Regulation (for products used in construction)
- Harmonised standards applied according to the product family
Mekanik Testler — What Does This Testing Field Cover?
The section below describes the field that the High Cycle Fatigue test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Mechanical testing measures how a material or a part behaves under force. The family ranges from static loading (tension, compression, bending) to time-dependent behaviour (fatigue, creep), and from hardness and wear to fracture toughness.
What these tests have in common is that the result is reported as a MATERIAL PROPERTY. Yield strength or hardness is not a conformity decision; it is numerical data against which the design and the product standard will compare. Mechanical test reports are therefore usually an input to an engineering decision rather than to a product approval — material selection, safety factor, life prediction.
The distinction between static and dynamic behaviour is the key to understanding the field. A part may appear entirely unstressed under a static load yet break under repeated loading; fatigue fracture occurs at stresses well below the yield strength and gives no warning. For rotating, vibrating or cyclically loaded parts, a tensile test alone is therefore not sufficient evidence.
Test conditions determine the result, and this is critical for the readability of the report: specimen geometry, loading rate, temperature, conditioning and the gripping arrangement. The same material gives different values under different conditions. In plastics the rate effect is very pronounced, in metals the temperature effect; in composites the specimen orientation changes the result entirely.
Hardness is the most misused measurement in the field. Because it is fast, close to non-destructive and inexpensive, it is often used in place of strength. Conversion tables from hardness to strength exist, but they are APPROXIMATE and depend on the material group; using them as the sole evidence in material acceptance is wrong.
The fracture mechanics side requires a specific competence. Fracture toughness and fatigue crack growth rate measurements make it possible to calculate how long a cracked structure will last; they are the basis of damage-tolerant design in fields such as pressure equipment, aircraft structures and pipelines.
Method groups in this field
Static tests
Tension, compression, bending, shear and torsion. Yield and tensile strength, elongation and modulus of elasticity are obtained.
Impact tests
Charpy and Izod notch impact; the brittle-to-ductile transition behaviour of the material is determined as a function of temperature.
Hardness
Brinell, Vickers, Rockwell, Shore and micro hardness. Valuable for surface treatment depth and local differences in strength.
Fatigue
Force- and strain-controlled axial fatigue, fatigue in bending; S-N curves and the endurance limit.
Creep and stress relaxation
Behaviour under long-term load at high temperature; decisive for boiler, turbine and pressure equipment materials.
Fracture mechanics
Plane-strain fracture toughness, the J integral, CTOD and fatigue crack growth rate.
Wear and friction
Taber and rotating drum abrasion, coefficient of friction measurements.
Commonly confused in this field
- Calculating strength from hardness is approximate; it cannot be used as the sole evidence in material acceptance.
- Adequate static strength does not demonstrate fatigue strength; a cyclically loaded part requires a separate test.
- If test rate and temperature are not reported, the result cannot be compared — especially for polymers and composites.
- A test specimen and the actual part may not give the same value; moulding orientation, weld lines and differences in surface treatment all have an effect.
- A strength value given for a composite without stating the specimen orientation is meaningless.
- ASTM and ISO counterparts measure the same quantity but use different specimen geometries; the results are not treated as directly equivalent.
Which decisions these results support
- Design verification and material selection
- Incoming material control and supplier approval
- Meeting the mechanical requirements of the product standard
- Failure analysis, life prediction and damage tolerance calculation
- Verifying heat treatment and surface treatment processes
Related Tests
Frequently Asked Questions About High Cycle Fatigue
What is the difference between high-cycle and low-cycle fatigue?
In high-cycle fatigue, stress stays in the elastic region and life is hundreds of thousands to millions of cycles; the test is stress-controlled. In low-cycle fatigue, plastic strain dominates, life is much shorter, and the test is strain-controlled.
What does run-out mean?
It means the specimen reaches the cycle count defined in the specification without fracturing. This is not a failure data point and is treated separately in the statistical assessment.