High Cycle Fatigue Testing
Typically, High Cycle Fatigue (NCF) Testing is performed in the elastic region (i.e. before yielding) of a material. HCF Testing is useful for simulating specific scenarios and investigating real world failures. This type of testing can be performed on many different types of conventional and additively manufactured materials.
Test specimens preparation is critical for fatigue testing. When machining fatigue test specimens, any operations performed on the specimen should minimize the chances of imparting residual stresses or undesirable machining marks into the specimen surface. Prior to testing smooth fatigue specimens, each specimen is low stress ground and then longitudinally polished to remove all circumferential machining marks. Any transverse flaw, such as a machining mark or scratch, can cause a premature failure in the material.
Testing is conducted in an axial test frame with the capability of applying both tensile and compressive forces. Typically, the test will run with a sinusoidal wave form at a frequency of 10 Hz to 100 Hz. The stress amplitude and loading ratio are prescribed by the customer. Testing continues until specimen failure or until a predetermined number of cycles are reached. Most cases involve the creation of an S-N Curve. This curve will provide engineers with the fatigue specific coefficients to apply to their particular application. The curve will also provide an endurance limit, based on the test environment and alloy systems, which defines the maximum stress that can be applied for an infinite number of load cycles without exhibiting failure.
Once testing is complete, each specimen data set is analyzed and reported to the customer. Typical analysis value given are as follows:
Total Cycles to Failure
S-N (Stress vs. Life Cycle) Curve
Most Common Testing Specifications:
ASTM E466 - Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Test of Metallic Materials
Entry Originally Posted July 2021