Fractures of Structural Steels (Part 3)

The second part of group II of fractures (in accordance with the classification presented in the first paper [1]) is considered in detail. The deviations in the structure of these fractures from the fiber and crystalline patterns are caused by the action of high temperatures on the metal. The characteristics of fractures, the causes and conditions of their formation, and the interconnection with the mechanical properties of the metal are considered. Each kind of fracture is illustrated.     

Protecting the anode foil of a high-current electron accelerator against arc-discharge damage

The mechanism of anode foil damage during the extraction of a high-power pulsed electron beam from a high-current diode has been experimentally studied on a TEU-500 electron accelerator [1]. It is established that the breakage of the anode foil is caused by the appearance of cathode spots on its surface, the intense electron emission from these spots during positive voltage pulses (postpulses following the main negative pulse of accelerating voltage), and the formation of arc discharge in the interelectrode gap. The improvement of diode matching to the pulse-forming line of the accelerator and the use of an auxiliary electrode (anode) forming additional vacuum discharge gap (crowbar) with the cathode practically excludes the anode foil breakage by arc discharge and significantly increases the working life of the foil (up to ∼10⁵ electron beam pulses).     

Influence of the modes of operation and structural factors on the crack propagation in 12Cr–2Ni–Mo steel

We study the influence of temperature, specimen sizes, loading frequency, and the time of holding under long-term static loading on the crack growth rate in 12Cr–2Ni–Mo steel. It is shown that the influence of these factors on the crack growth rate is insignificant. A numerical-experimental model is proposed for the evaluation of the time of subcritical crack growth with regard for the duration and cyclic character of loading. Translated from Problemy Prochnosti, No. 3, pp. 66–77, May–June, 2009.     

Estimating working life for aircraft gas turbine engine disks at the stage of fatigue crack development. Part 2

It is shown that the cyclic cracking resistance in turbine disk materials is substantially affected by temperature, frequency, loading-cycle shape, and specimen thickness. Formulas describing fatigue crack growth rates are considered and calculations are done on the periods needed for fatigue cracks to grow to critical sizes from stress concentrators at various temperatures. Deceased. Translated from Problemy Prochnosti, No. 12, pp. 3–15, December, 1994.     

Aberration properties and performance of a new diffractive-gradient-index high-resolution objective

We present what we believe is a new hybrid objective consisting of a gradient-index optical element that has external flat refracting surfaces and is made of two different inhomogeneous materials separated by a cemented spherical surface. Microstructures of diffractive lenses are placed on the flat external surfaces of the objective. The most surprising property of this objective is that even calculation in the area of the third- and the fifth-order aberrations yields an efficient design for imaging with a Rayleigh resolution of 1 mum.     

Analysis of the Deformation Process in Ni<Subscript>3</Subscript>(Al,Fe) Intermetallic under Longitudinal Bending

The structure and magnetic properties of an Ni₃(Al, Fe) single crystal after high-temperature rolling deformation have been studied. It has been shown that high-temperature rolling deformation induces longitudinal bending in Ni₃(Al, Fe), which is accompanied by the nonuniform distribution of stresses along the length of the sample. It has been found that longitudinal bending leads to change in either the mechanical or physical properties of the metal. Dynamic recrystallization has been found to occur at high degrees of deformation (starting at 40%). Local change in the distance between nickel and aluminum atoms, as well as the chemical composition, that takes place in the bending zones (distortions) of a crystal lattice of Ni3Al intermetallic compound is accompanied by change in the saturation magnetization and Curie temperature.     

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.Translated from Problemy Prochnosti, No. 1, pp. 70–81, January, 1993.