A. V. Prokopenko

Characteristics of fracture toughness of metals during cyclic loading. I

Conclusions1.A detailed experimental investigation has been made of the fracture toughness characteristics of various structural steels (10GN2MFA, 15G2AFDps, 45) and Armco iron over a wide range of low temperatures with static, dynamic, and cyclic load application. It has been shown that the materials investigated may be divided into two groups according to the nature of the influence of the loading system. The first group includes the type 10GN2MFA and 15G2AFDps steels for which the fracture toughness characteristics obtained during cyclic and dynamic loading are significantly lower than the fracture toughness characteristics obtained during static loading by the standard method. The second group includes type 45 steel and Armco iron. For this group the fracture toughness characteristics are almost independent of the type of loading system.2.An analysis of the effects of various factors on the fracture toughness characteristics has been made.

Evaluation of the life and methods of ensuring reliability of large blades of an axial compressor. Report 1

Calculations were carried out to determine the life of a large compressor blade of DIT alloy with a crack at the inlet edge in the root section with the specified probability of nonfailure under the conditions corresponding to the service conditions. Special attention is given to examining the feasibility of producing this blade from VT6S alloy instead of DIT alloy with an allowance made for the mechanical properties of materials, cracking resistance, and service conditions. Investigations were carried out into the cracking resistance characteristics of DIT and VT6S alloys with an allowance made for the statistical properties of the experimental results obtained at temperatures of 363, 293, 173, and 77 K and different stress ratios. The results were then compared. The data obtained in service loading were used to calculate the period of the crack growth in blades of DIT and VT6S alloys at a nonfailure probability of 0.5 and 0.999. Analysis of life calculations showed that D1T alloys are more suitable than VT6S alloys for producing blades of compressors of a wind tunnel.

Probabilistic prediction of the fatigue life of gas-turbine engine compressor blades under two-level programmed loading

Conclusions1.It was shown that with statistical modeling of the normal distribution of the crack resistance characteristics of a material, the endurance of GTE compressor blades in programmed loading by the two-level schema has log-normal distribution.2.A combined theoretical and experimental method was worked out for the probabilistic prediction of the fatigue life of GTE compressor blades for determinate programmed cyclic loading according to the results of laboratory fatigue crack resistance tests of standard specimens with a crack.3.The suggested algorithm is universal, and it may be applied in different cases of determinate programmed loading using modeling of the Weibull, Johnson, and other distributions of the parameters of fatigue crack resistance.

Fracture toughness characteristics of metals in fatigue. Report no. 2

Conclusions1.Based on an analysis of the experimental data obtained and the results of fractographic studies of fracture surfaces, we have proposed a model of fatigue crack growth under cyclic loading and the transition to unstable crack growth, based on a consideration of the crack growth rate in a zone damaged during cyclic loading and explaining the above-noted test results.2.It has been shown that, together with strain-rate sensitivity, characteristics of the cyclic strain of metals may be used as bases for classifying materials according to the degree to which the cyclicity of load application effects a reduction in fracture toughness. The reduction is greatest for materials sensitive to strain rate and steels which do not strain-harden under cyclic loads. There is no such effect for materials not strain-rate sensitive and for steels which strain-harden under cyclic loads, as well as for steels with very small cyclic strains.

Determining fracture toughness from the results of fatigue tests in circular bending

Conclusions1.A method has been proposed for determining the stress concentration factor in a cylindrical specimen with unilateral crack loaded in cantilever bending, based on the method of measuring the elastic ompliance of a specimen. Results obrained by this method for 15G2AFDps steel and boiler steel are in good agreement with test data for specimens in eccentric tension.2.It was es tablished that the value of the dimensionless, coefficient Y2 at one and the same relative crack length

A study of the influence of service operating time and a corrosive medium on the life of gas-turbine engine compressor blades

\bar l

Effect of high temperature and load cycle asymmetry on the growth rate of fatigue cracks in stainless steel, nickel, and titanium alloys

has little dependence on the relative area