Introduction. The results of multiple tests of liquid rocket engines indicate that the engine with cracks in blades can "safely" work within a few launchings. Therefore, the resource estimation of the nozzle blade with a crack becomes highly relevant, especially for reusable rocket engines. The objective of this work was to determine the residual life of nozzle diapgragm blades with cracks. Method. For reliable residual life estimation of the blade with a crack the comprehensive approach was used: fractographic and material science studies on the one hand and fracture mechanics propositions on the other hand. Results. Fractographic and material science studies have shown that blade destruction occurs through the countergrowth of fatigue surface cracks from the blade pressure side and the blade suction face, which interconnects to form a "main" crack, whose growth is controlled by growth of surface cracks from the blade pressure side. Using the fracture mechanics propositions and the results of finite element calculations of the stress-strain state of nozzle diaphragm blades under gas and thermal loads in elasto-plastic formulation, equations of crack growth in nozzle blades were obtained. Finally the scheme of blade unstable fracture is proposed; the blade guaranteed residual life under certain conditions is evaluated and the maximum tolerable crack length in the blade suction face is determined. Conclusion. The method offered in this work makes it possible to evaluate the blade residual life as the number of loading cycles while fatigue crack propagation and as the tolerable number of firing tests. The method also enables the maximum permissible crack lenth to be determined.
liquid rocket engine, nozzle diaphragm, blade, surface crack, edge crack, residual life
1. Polyanskiy A. M., Polyanskiy V. M. Trudy NPO Energomash [Proc. of NPO ENERGOMASH]. 2010, no. 27, pp. 223-243 (in Russ.).
2. D. Broek. Elementary Engineering Fracture Mechanics. Springer Science & Business Media, 1982, 469 p.
3. Polyanskiy A. M., Polyanskiy V. M. Trudy NPO Energomash [Proc. of NPO ENERGOMASH]. 2011, no. 28, pp. 79-93 (in Russ.).
4. Murakami Yu. Spravochnik po koeffitsientam intensivnosti napryazheniy, Tom 2 [Stress Intensity Factors. Reference Book. Vol. 2]. Mir, 1990, 1013 p. (in Russ.).
5. Polyanskiy A. M., Polyanskiy V. M. Trudy NPO Energomash [Proc. of NPO ENERGOMASH]. 2014, no. 31, pp. 310-352 (in Russ.).
6. Razrabotka rekomendatsiy po snizheniyu maksimal´nykh napryazheniy v soplovom apparate i rabochem kolese turbiny dvigatelya RD 180 [Recommendations Development for Reducing the Maximum Stresses in the Nozzle Diaphragm and the Turbine Wheel of the RD 180 Engine]. Мoscow, TsVNT TsIAM, 2006, 99 p. (in Russ.).
