Reliably testing fatigue behavior
Reliable material parameters are essential if simulation models are to make safe predictions – especially when durability of the service life is being calculated. Structures in automotive engineering, medicine and energy technology are exposed to load changes of more than ten million cycles over the course of their expected lifetime –due to either high-frequency stress or a long operating time of up to 30 years. This range is referred to as the very high cycle fatigue (VHCF) range and extends far beyond the range of classic S-N curves. Extensive knowledge of the fatigue behaviour of the materials used is thus of vital importance if these high-performance components are to operate reliably in the VHCF range. To be able to go through the high load changes of 1010 in a reasonable time period of less than one month, the samples are offset in resonance vibration at frequencies in the kHz range.
Measuring stress and strain and Eigen modes
With regard to verifying the simulated sample model, Polytec 3D Scanning Vibrometers provide a direct way of measuring the true fatigue sample’s Eigen modes and Eigen frequencies. Another potential application lies in the field of high-frequency stress and strain analysis, since contact measurement methods such as strain gages are not suitable for this type of endurance stress. This method also comes into play for operational reliability testing of high-stress train components (wheel rims), wind turbines and ultrasonic scalpels (medical technology).
Fatigue testing of high-voltage terminal blocks
Using laser Doppler vibrometry, we carry out non-contact testing of AC connection terminals in high-voltage electric motors during resonance dwell tests, and monitor natural frequencies and frequency decay as indicators of damage.
Particularly in the case of fatigue-prone laminations, natural frequency measurement using LDV is the only reliable method, as the additional mass of conventional sensors would distort the results.
This enables non-destructive assessment of crack formation, failure risk and service life, and allows material and geometric optimisations to be derived for reliable high-voltage drives.
Precisely detecting the onset of damage
[Translated from the original German]
MAHLE International GmbH
Vibration - Laboratory Testing - R&D Services - Corporate Research (CRREL2)
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