Some Peculiarities of Fatigue Crack Growth at Various Stages of Its Development

The author considers some peculiarities of fatigue crack growth in metals at the stages of its initiation and initial development, and stable and unstable growth that precedes final fracture. It is shown that at the stage of initial growth of fatigue cracks, the stress state, nonlocalized fatigue damage that precedes initiation of the main fatigue crack, residual surface stresses, surface manufacturing and in-service defects, and contact interactions are the factors that determine the crack paths. Stable growth of a fatigue crack is primarily determined by the stress-strain state of a structure as a whole and by the stress-strain state at the crack tip with allowance for its variation due to crack propagation, which is evaluated by the criteria of fracture mechanics. The author also studied peculiarities of fatigue crack development in compressor blades of marine gas turbines. It is shown that for embrittled steels, when fatigue cracks develop under plane strain conditions, final fracture occurs at very small crack sizes. In this case, the characteristics of fatigue fracture toughness are appreciably lower than the static values. The paper also considers peculiarities of unstable fatigue crack propagation.     

Effect of interstitial impurities on the crack resistance of ductile titanium alloys. 2

We have investigated the failure ductility of a 2V-type ductile titanium alloy with a nitrogen and oxygen impurity content ranging from 0.05 to 0.35%. Here we have employed approaches that are based on utilization of the J integral. We have established the optimum values for nitrogen and oxygen impurity concentrations to ensure an adequate level of crack resistance and stress. We have proposed relationships for the calculation of microspall resistance, based on the geometric parameters of the structure when the a phase is laminar in form. The analytical determination of microspall resistance made it possible to estimate the crack resistance of the alloy to a high degree of accuracy over the entire range of variations in impurities, based on empirical relationships.Translated from Problemy Prochnosti, No. 8, pp. 30–36, August, 1991.     

Automatic system of programmed control of parameters of vibration and thermal tests of gas turbine engine blades (ASPC VTT)

The article describes the automated system of programmed control of the parameters of vibration and thermal tests of gas turbine engine blades, designed at the Special Design and Technological Bureau of the Institute of the Strength of Materials, Academy of Sciences of the Ukrainian SSR, and intended for the control of different types of electrodynamic vibration test stands and heating installations; they make it possible to test the life and the ultimate state of turbine blades under conditions of the simultaneous effect of cyclically changing vibration and thermal loads in a broad range of vibration frequencies of blades.Translated from Problemy Prochnosti, No. 1, pp. 102–105, January, 1990.