VHCF- variable Amplitude

FKM 2012
Issue number 317
Project no. 292

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Abstract:
Vibration and fatigue strength tests were carried out on the quenched and tempered steel 50CrMo4 (Rm = 919 MPa) and the aluminum alloy EN AW-5083 (Rm = 323 MPa) on smooth and notched specimens (Kt = 2.06) at R = -1 on conventional testing machines (NG = 108)
and an ultrasonic vibration testing system (NG = 1 09). The tests on the conventional testing machines were carried out at a frequency of f 106 up to the limit number of cycles. Specimen fractures were observed in the aluminum alloys up to NG = 109 and were predominantly caused by hard intermetallic particles. The influence of the
test frequency and testing technique on the fatigue strength behavior was investigated.
A two-stage and a Gaussian-like collective were used for the fatigue strength tests. The test results were compared with the damage accumulation calculations according to the variants of the Palmgren-Miner rule and with crack propagation calculations using an elastic-plastic crack propagation model.
With the consistent form of the Palmgren-Miner rule and a damage sum D = 0.3, using the experimentally determined picker lines for a survival probability Pü = 50 % and maximum collective values slightly above the fatigue strength at the bending point of the picker line, lifetimes are predominantly estimated that lie in the average of the test results or also tend to be conservative. The investigations were carried out with relatively complete collectives. The results of the crack propagation calculations are largely comparable with the results of the damage accumulation calculations with the consistent form of the Palmgren-Miner rule for a damage sum of D=0.3 or D = 1.
The Wöhler lines and the Gassner lines in accordance with the FKM guideline are conservative in comparison with the results from the tests, in some cases only taking into account the basic safety factor jD.
The objective of the research project has been achieved.