Scientists at Perm National Research Polytechnic University have developed a methodology for accelerated assessment of multi-cycle fatigue resistance of typical gas turbine engine elements made of polymer composite materials based on their self-heating during cyclic loading.
According to PNRPU, traditional tests of real composite elements can take weeks or months, whereas with the new methodology, the endurance limit can be assessed in a few hours.
The problem is related to the specifics of polymer composite materials. Their fatigue resistance characteristics can vary significantly depending on the reinforcement scheme, part shape, manufacturing technology features, and other structural and technological factors. Therefore, the results of standard sample tests cannot always be directly used to evaluate a finished engine element.
Perm researchers proposed to monitor not only mechanical load but also surface temperature. During cyclic loading, fatigue damage develops in the composite, accompanied by self-heating. By changing the heating parameters with increasing load, the endurance limit can be determined.
The experiments used a Testronic-50 electro-resonant testing machine and a V-850-440 electrodynamic vibration stand, and the temperature field was recorded by a NEC TH9100 WR ProNew thermal imager. For testing shells with an L-shaped flange and a stiffening rib, a frequency of about 80 Hz was used.
The methodology was tested on three typical structural elements of a gas turbine engine made of layered carbon fiber reinforced plastic: a plate with a free hole, a shell connection with an L-shaped flange, and a shell connection with a stiffening rib.
The values obtained by the thermographic method were compared with the results of standard fatigue tests. For the typical elements studied, the discrepancy in the endurance limit was within 9–18.8%, which the abstract evaluates as acceptable given the characteristic scatter of multi-cycle fatigue characteristics for composites.
However, this does not mean a complete abandonment of standard tests. The dissertation states that the thermographic method significantly reduces the labor intensity, duration, and number of tested samples compared to traditional fatigue tests. The methodology is intended for accelerated assessment of the endurance limit of typical gas turbine engine elements.
The results of the work, according to Danil Solomonov's abstract, have been implemented at JSC ODK-Aviadvigatel and are used in the development and strength refinement of gas turbine engines.
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