CONCLUSIONS
The notch effect of head checks is similar to milled notches with respect to lifetime as a function of loading within the C-N curve in Fig. 6. The investigation verifies the result in [5] that transverse cracks caused by head checks propagate according to the rules of linear- elastic fracture mechanics. The asymmetry of the notch had no bearing on the crack development. The reason was the dominant mode l loading. The following two aspects seem to be important to come closer to real loading, especially at the beginning:
- taking into account the thermal-induced stresses
- implementation of a non-stationary load application
The service fatigue test performed was a preliminary test. It enabled the conclusion that the major part of damage was caused by the maximum amplitude of every individual roll-over. Based on the number of roll-overs and the obtained crack depth to failure, the amplitude of an assumed constant loading test was found to be ±115 and ±110 MPa, respectively, using the C-N curve. So a practical damage equivalent to the load spectrum was found. Further tests with different load spectra are necessary to obtain data that can be generalized.
The test rig has proved for the alternating bending load tests with constant and variable amplitude loading and enables the investigation of fatigue properties of different rail qualities with and without pre-arranged damage.