Investigation of applicability of tin fatigue gauges for monitoring operational load of cultivator spring strut
2020
Tyutrin, S., Kurgan State Univ., (Russian Federation)
The problem of increasing the reliability of agricultural machinery is considered. To prevent fatigue failure of the most loaded parts, it is proposed to monitor their operational load with the help of fatigue gauges. As a result, the amplitude of cyclic stresses is determined, which is equivalent in terms of the damaging effect to the spectrum of operational stresses. If the actual loads are significantly higher than the design values, it is necessary to increase the strength of the overloaded parts or reduce the operating loads. Fatigue gauges, which are fragments of copper or aluminium foil, are widely known. Fatigue gauges made of stannum with addition of antimony are used in this work. Tin fatigue gauges were proposed by the author; they have high sensitivity and they quickly react to relatively low stresses. The evaluation of the applicability of tin fatigue gauges for monitoring the operational load of the cultivator spring strut was carried out experimentally in laboratory conditions. Test specimens of the same material as the spring strut were used. These specimens were tested according to the symmetrical bending scheme. One specimen was subjected to a load that reproduced the operational load spectrum. This spectrum is known from the results of measurements by resistive-strain sensors. The sequence of application of the load was determined by random sampling. Another specimen was tested under symmetrical bending conditions with constant amplitude. The fatigue gauges were monitored visually with a microscope at 100x magnification. Calibration specimens and the scheme of the testing stand are shown. Photos of surfaces of fatigue gauges after tests are presented. The Palmgren-Miner linear damage theory was used. It is shown that the use of highly sensitive fatigue gauges made of tin foil together with the linear damage theory provides sufficient accuracy of the results: the discrepancy was less than 3 %.
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