Research of characteristics of cyclic growth rate of cracks in materials of the critical parts of aviation gas-turbine engines

Аuthors

Potapov S. D.^*, Perepelitsa D. D.^*

Central Institute of Aviation Motors, CIAM, 2, Aviamotornaya St., Moscow, 111116, Russia

*e-mail: potapov_sd@ciam.ru

Abstract

The research aimed to establish the possibility of using the results of sample tests for evaluation of fracture in real detail. The effect on the rate of crack growth in standard samples of different factors: temperature, sample thickness, loading frequency, the asymmetry of loading cycle, the influence of plane stress on the sides of the specimen, crack growth under high stress intensity factor, and so on are determined. The stability of the geometry of the crack front in the standard samples with the development of cracks are investigated. Stability boundaries of the site and the coefficients of Paris for the test results of standard samples using the method developed by the authors are determined. The studies were conducted for aircraft materials: nickel and titanium alloys and steels at the operating temperature range. Based on the results the linear relationship between the coefficients of the equation of Paris and the focal point of presence on the kinetic diagram for all the materials are established. The presence of a focal point confirms the fractographic studies fracture surfaces of samples. The presence of a focal point allows you to set: one value of the exponent of the Paris equation there, and only one, the coefficient of the equation Paris, average coefficients Paris should ensure passage of the averaged characteristics of crack growth rate in the focal point, the average values of the coefficients of Paris can be determined using linear relationship between the coefficients of the equation Paris. For nickel alloys a decreasing dependence of the degree of the equation Paris on temperature was received. For titanium alloys, this dependence is absent.
Developed a special model allows us to investigate the development of semi-elliptical surface cracks. Comparative tests of cross-cutting and surface (semi-elliptical) cracks in standard and special samples were made. These results suggest the influence of fracture type (pass-through or semi-elliptical surface) on the characteristics of the crack growth rate. The results suggest the need to study the development of cracks in the evaluation of different types of longevity of critical aircraft engine parts.

Keywords:

growth rate of a crack, fracture strength, Paris equation, fractography

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