A cyclic fatigue test is used to determine crack initiation and to determine fatigue life as well as to validate new materials and processes.
ASTM E466 – Axial Fatigue – Constant Stress Amplitude
This test method determines stress versus fatigue life data by the use of uniaxially loaded test specimens under constant stress amplitudes. Typically 15 to 20 specimens are tested to generate the SN Curve. Common R ratios are -1.0 and 0.1.
ASTM E606 – Axial Fatigue – Constant Strain Amplitude
This test method determines the fatigue properties and crack initiation for nominally homogeneous materials by the use of uniaxially loaded test specimens under constant strain amplitudes. Typically 15 to 20 specimens are tested using a fully reversed strain amplitude. Test specimens have a uniformed gage section. Strain amplitudes typically range from 0.015 strain to .002 strain. In addition to developing the Strain versus Life plot, the cyclic and monotonic Stress versus Strain plots are obtained.
- Fatigue Strength Coefficient, sf’ (ksi)
- Fatigue Strength Exponent, b
- Fatigue Ductility Coefficient, ef’
- Fatigue Ductility Exponent, c
- Cyclic Strength Coefficient, K’
- Cyclic Strain Hardening Exponent, n’
The customer may dictate the R ratio, strain levels, and the test frequency.