Fatigue Testing at 1000Hz Testing Frequency

Abstract

There is no infinite fatigue life. In the recent decades we learned that fatigue testing with higher number of load cycles is required in some areas. The development of faster testing techniques e.g. Ultrasonic systems testing on 20kHz have allowed the conduction of many research activities in the giga cycle regime in the recent decades. In 2014 RUMUL could present a new resonant fatigue testing machine, with a testing frequency of 1000Hz. The dynamic load of maximum 50kN peak-peak is produced with an electromagnetic system. The static portion of the load is provided by two mechanical spindles, the maximum load of the system is +/- 50kN. Any load ratio can be selected. Flat and round specimen types that are normally used in fatigue testing can be used. The actually tested material volume is larger than the material volume that is tested on ultrasonic systems. The new testing machine offers new possibilities for investigations of material properties in the very high cycle fatigue (VHCF) regime.In the past years the new testing machine was intensively used in several laboratories in Germany for example at the laboratory of the Fraunhofer institute IWS Dresden in Germany. Some effects of the 1000Hz testing frequency on the fatigue behavior of the material have been observed. This paper provides a summary how the frequency of an alternating load affects fatigue life of a material. And it highlights some of the found frequency related effects on fatigue strength. Some examples of heating up of the specimen related to the 1000Hz testing frequency are shown. Normally continuous fatigue testing is possible, without stopping for cooling down the specimen.