O Vosikovsky

Bio: O Vosikovsky is an academic researcher. The author has contributed to research in topics: Corrosion fatigue & Stress intensity factor. The author has an hindex of 2, co-authored 2 publications receiving 77 citations.

Frequency, Stress Ratio, and Potential Effects on Fatigue Crack Growth of HY130 Steel in Salt Water

Abstract: Fatigue crack growth rates over wide ranges of stress intensities (from threshold to nearly critical stress intensity) were measured on HY130 steel in 3.5% sodium chloride aqueous solution at several cyclic frequencies, stress ratios, and potentials. The growth rates are compared with reference data measured in laboratory air. The growth rate curves for both environments can be approximated by two linear sections converging at low stress intensity ranges to the same threshold, which depends only on the stress ratio. The upper parts of the lines with lower slopes converge again to the point where maximum stress intensity approaches its terminal value. As a result, the maximum environmental acceleration of crack growth appears at intermediate stress intensities, and it increases with decreasing frequency and potential. Data indicate a relatively low susceptibility of HY130 steel to corrosion fatigue. With increasing stress ratio R the fatigue crack growth threshold is shifted to lower stress intensity ranges by the same amount in both air and salt water environments. The effect of R on growth rate can be introduced into a power law expression.

Effects of Stress Ratio on Fatigue Crack Growth Rates in X70 Pipeline Steel in Air and Saltwater

Abstract: Fatigue crack growth rates in an X70 pipeline steel were measured over a wide range of stress intensities in laboratory air and in 3.5% sodium chloride solution under free corrosion and cathodic (coupled to zinc) potentials. The effects of stress ratio in all these environments and of cyclic frequency in the sodium chloride solution were studied. The results are compared with fatigue crack growth rates measured previously in lower strength X65 steel. The stress ratio strongly influences the fatigue crack growth thresholds and close-to-threshold growth rates. With increasing stress intensity range, the stress ratio effect decreases similarly in both air and aqueous environments. The lower cyclic frequency enhances corrosion fatigue crack growth rates at intermediate stress intensity ranges, as was observed earlier in X65 steel.

Near-threshold fatigue-crack propagation in steels

Abstract: The characteristics of fatigue-crack propagation in metals and alloys have been the subject of several extensive reviews in recent years, but in very few instances have the details of ultralow growth rate, nearthreshold fatigue-crack propagation been similarly discussed. In this review the effects are examined of various mechanical, microstructural, and environmental factors which influence fatigue-crack propagation in steels at growth rates less than 10-6 mm/cycle, where the alternating stress intensity ∆K approaches the so-called threshold stress intensity ∆K0 below which crack growth cannot be experimentally detected. The marked influences of load ratio, material strength, and microstructure on such near-threshold growth are analysed in detail and rationalized in terms of possible environmental contributions and crackclosure concepts. These effects are contrasted with crack-propagation behaviour in other engineering materials and at higher growth rates.

Review of corrosion fatigue in offshore structures: Present status and challenges in the offshore wind sector

Abstract: Offshore wind has been identified as one of the emerging sustainable energy sources in the United Kingdom. Offshore wind turbine support structures are mainly fabricated of welded tubular members, similar to structures used for oil and gas applications, and are exposed to highly dynamic, harsh marine environments. However, their structural details and design requirements are significantly different due to the magnitude and frequency of operational and environmental loadings acting on the support structures. These conditions would significantly affect their structural dynamic response characteristics due to the magnitude of the applied load. This may therefore have some significant effects on the crack growth behaviour and the extent to which corrosion can be associated with damage to the support structures. However, the magnitude of the applied load might depend on turbine size, water depth, soil conditions and type of support structures. It is therefore essential to design wind turbine support structures against prescribed limit states to ensure economical and safe operation. This paper presents a review of corrosion fatigue in offshore structures as regards the effects of seawater, environment and mechanical loading. Existing literature which documents results from previous campaigns is presented, including works referring to oil and gas structures, highlighting the significant difference in the aspects of loading and use of modern fabrication processes, with a view to illustrating the requirements for an update to the existing corrosion fatigue database that will suit offshore wind structures׳ design requirements.

The cyclicJ-integral as a criterion for fatigue crack growth

Abstract: The definition of the cyclic J-integral is offered and its physical significance for fatigue crack growth is discussed using the Dugdale model on the assumption that the crack closure, cycle dependent creep deformation, and crack extension under cycling can be neglected. It is shown that the cyclic J-integral for small scale yielding is equivalent to theJ-integral for linear elastic crack independent of loading processes, while the value for large scale yielding varies with the loading processes. However, in both cases, the cyclicJ-integral remains constant during the reversal of loading under a constant stress range, if the first monotonic loading stage is excluded. In this situation, the cyclicJ-integral can be applied as a criterion for fatigue crack growth, since it is evaluated as a generalized force on dislocations to be moved or the energy flow rate to be dissipated to heat by the dislocation movements in an element just attached to the fatigued crack tip during one cycle of loading. It is suggested that the available experimental data of different materials for fatigue crack growth can be generalized to a unified formulation on the basis of the energy criterion. It is also deduced that the threshold ΔJ corresponding to ΔKth should be larger than 4γ where γ is the surface energy of the material. Finally the operational definition of the cyclicJ-integral on single loadversus displacement curves is given for center cracked plate with wide uncracked ligaments in tension.