Mathematical Modeling of the Process of Reduction of the Material Consumption of Gas Transmission System Elements

The new method for a comprehensive assessment of the strength, durability and material capacity of the critical elements of the main gas pipelines, taking into account the combined impact of factors causing damage (environment, corrosion, random loading, geometry variation, material defects, etc.), which are changing the bearing capacity and material capacity of these structures, is proposed. As the main damaging factor, the process of corrosion fatigue is accepted, the qualitative and quantitative assessment of which are realized by applying a set of equations of comparable fatigue lines obtained by fatigue tests carried out in air and in corrosive environment. By the joint solution of these equations, the functions of the corrosion action coefficients are obtained in a wide range of cyclic strength and durability, which in standard calculation procedures are performed only for cyclic strength and only at the inflection point of the fatigue lines (NG 5  106 cycles).The issues of reducing the material consumption and ensuring the cost-effectiveness of structures, by using relatively cheap materials for pipelines - low-carbon and low-alloy structural steels subjected to surface hardening in stressed sections of pipes (edge welds) in order to significantly increase the physical and mechanical characteristics of the used steel grades are considered. In order to increase the corrosion resistance of these sections, contemporary polymer anticorrosive coatings are used.

Tools and Methods for Analysis of Fatigue High-Cycle Stochastic Loading for Evaluating the Accuracy and Reliability of Numerical Solutions

The article presents methods of processing and the results of the analysis of the accuracy of solutions obtained when calculating the structure fatigue life in the case of random loading using domestic and foreign computer systems. Unlike foreign analogues, domestic software products for calculating the fatigue life of a product under random loading are based on the regulatory documents of the Russian Federation, which are proposed along with methods adopted abroad.

Assessment of the probability of the fatigue fracture of structural components subjected to deterministic and stochastic loading taking into account the scatter in the initial crack size

An analytical approach which provides conservative estimates of the probability of fatigue brittle fracture of structural components of technical systems taking into account the scatter of the initial dimensions of crack-like defects described by the exponent probabilistic distribution is presented. The operational loading is considered both as deterministic (with loading cycles of constant amplitude and frequency) and random (stationary narrow-band Gaussian random loading) process. The crack growth kinetics is described by the modified Paris equation that takes into account the stress ratio effects. The parameters of the Paris law are considered deterministic values. An example of the assessment of the probability of fatigue failure of tubular structural component with an axial crack on the inner surface of a tube subjected to internal pressure is presented. A comparative analysis of the results obtained with and without taking into account the random nature of the operational loading is carried out. It is shown that neglection of the random nature of the operational loading leads to non-conservative estimates of the fatigue failure probability, which may differ by an order of magnitude compared to the calculation data obtained with allowance for the stochastic nature of the loading process. The developed method can be used in the implementation of probabilistic and risk-based approaches to ensuring strength, service life and safety of technical systems in real operation conditions and in adjusting standard operation programs in terms of choosing the frequency and scope of non-destructive testing.

Dirlik and Tovo-Benasciutti Spectral Methods in Vibration Fatigue: A Review with a Historical Perspective

The frequency domain techniques (also known as “spectral methods”) prove significantly more efficient than the time domain fatigue life calculations, especially when they are used in conjunction with finite element analysis. Frequency domain methods are now well established, and suitable commercial software is commonly available. Among the existing techniques, the methods by Dirlik and by Tovo–Benasciutti (TB) have become the most used. This study presents the historical background and the motivation behind the development of these two spectral methods, by also emphasizing their application and possible limitations. It further presents a brief review of the other spectral methods available for cycle counting directly from the power spectral density of the random loading. Finally, some ideas for future work are suggested.

Theory of Uncertainty Analysis with Application to Naval Hydrodynamics

The modern methodology for quantifying the quality of experimental data is uncertainty analysis. Current methods are reviewed with some examples primarily from naval hydrodynamics. The methods described are applicable to fluids engineering. The history of uncertainty analysis, US and international standards on uncertainty analysis, verification and validation standards for computational fluid dynamics, and instrument calibration are discussed. One important result is that random loading in force calibration can produce a lower uncertainty estimate than sequential loading. Statistically, the calibration results for the slope and intercept are the same for the two methods in the example thrust calibration, but the uncertainty in random loading is factor of three smaller than sequential loading.