Speed Matters--Or Does It?
Due to the fact that resonance fatigue testing machines are capable of very high test frequencies of up to 1100Hz (typically 50 – 200 Hz for component testing) the question might arise whether the test frequency affects the material fatigue performance. If working faster makes you feel exhausted why should it be different for the samples you are testing?
Fig. 1: 1100Hz resonance fatigue test set-up for steel specimen
Generally speaking, when performing fatigue tests at frequencies exceeding 20 Hz we highly recommend a static-dynamic calibration. Without this calibration, the acting inertia forces from masses such as the specimen fixture will lead to a measurement error. This inertia effect is neutralized when calibrating the equipment transducer (load cell) with a strain gage signal on the component itself. First, several static load steps are applied, then the same dynamic loads at test frequency are applied. The ratio of transducer signal to strain gauge signal is your calibration factor. This has to be done only once for a specific test setup.
Concerning the material fatigue properties themselves it goes without saying that a significant specimen temperature increase will lead to lower fatigue strength. Because of the good heat dissipation of metals this problem usually does not arise in linear or bending resonance fatigue test setups for these materials. With torsion loads however, it may be a good idea to keep an eye on the temperature when testing at load levels significantly higher than the fatigue strength. But even this can be resolved with the installation of a relatively simple cooling system if necessary. People may get hot headed quickly, metals don’t!
Except for extremely low-test frequencies when evaluating characteristics like stress crack corrosion performance (SCC), the test frequency itself has no influence on the material fatigue performance when operating at typical test speeds ranges of a resonance fatigue test machine. Literature indicates that for steels and other body centered cubic (BCC) metals, testing at less than 1000 Hz does not impact the fatigue performance. Its influence on light alloys (face centered cubic materials – FCC, such as Aluminum) can be slightly more pronounced and varies with the material microstructure. However, no influence in fatigue performance is to be expected for these types of alloys at frequencies up to 250 Hz.
In conclusion, there is no frequency influence on fatigue performance to be expected in the typical frequency range of resonance fatigue testing applications for metals. If this topic still gives you a headache, don’t hesitate to contact SincoTec USA with any questions you may have. We can cure your headache and provide fast and efficient solutions for any dynamic testing problem you are dealing with
Concerning the material fatigue properties themselves it goes without saying that a significant specimen temperature increase will lead to lower fatigue strength. Because of the good heat dissipation of metals this problem usually does not arise in linear or bending resonance fatigue test setups for these materials. With torsion loads however, it may be a good idea to keep an eye on the temperature when testing at load levels significantly higher than the fatigue strength. But even this can be resolved with the installation of a relatively simple cooling system if necessary. People may get hot headed quickly, metals don’t!
Except for extremely low-test frequencies when evaluating characteristics like stress crack corrosion performance (SCC), the test frequency itself has no influence on the material fatigue performance when operating at typical test speeds ranges of a resonance fatigue test machine. Literature indicates that for steels and other body centered cubic (BCC) metals, testing at less than 1000 Hz does not impact the fatigue performance. Its influence on light alloys (face centered cubic materials – FCC, such as Aluminum) can be slightly more pronounced and varies with the material microstructure. However, no influence in fatigue performance is to be expected for these types of alloys at frequencies up to 250 Hz.
In conclusion, there is no frequency influence on fatigue performance to be expected in the typical frequency range of resonance fatigue testing applications for metals. If this topic still gives you a headache, don’t hesitate to contact SincoTec USA with any questions you may have. We can cure your headache and provide fast and efficient solutions for any dynamic testing problem you are dealing with
