Sergey Panin

Structural levels of the nucleation and growth of fatigue crack in 17Mn1Si steel pipeline after long-term service

AbstractThe majority of modern gas pipelines in Ukraine, Lithuania and Russia have been operating for more than 30–40 years. The problem of forecasting residual life-time of materials comprising such gas pipelines calls for study of their degradation kinetics as well as requires to determine its relationship with the strain-force loading parameters. The aim of the paper is to study the kinetics of fracture in order to range mechanisms of cyclic deformation of 17Mn1Si steel at nucleation and growth of a fatigue crack. Flat specimens were cut out from a fragment of 17Mn1Si steel pipe after 40 years of service. Microstructures of specimens were examined. In the paper, an attempt was made to apply the combined approach to study of deformation and fracture based on the following research parameters from nonlinear fracture mechanics: physical mesomechanics and numerical fractography.

Effect of temperature-force factors and concentrator shape on impact fracture mechanisms of 17mn1si steel

The influence of the notch shape on the impact fracture of 17Mn1Si steel is investigated at different temperatures with the focus placed on the low-temperature behavior. An approach towards fracture characterization has been suggested based on the description of elastic-plastic deformation of impact loaded specimens on the stage of crack initiation and growth at ambient and lower temperatures. The analysis of the impact loading diagrams and fracture energy values for the pipe steel 17Mn1Si revealed the fracture mechanisms depending on the notch shape. It was found that the testing temperature reduction played a decisive role in plastic strain localization followed by dynamic fracture of the specimens with differently shaped notches. A classification of fracture macro- and microscopic mechanisms for differently notched specimens tested at different temperatures was proposed which enabled a self-consistent interpretation of impact test results.

Improvement of Wear Resistance of UHMWPE by Adding Solid Lubricating Fillers

For estimating effectiveness of adding solid fillers for composites with ultra-high molecular weight polyethylene matrix tribotechnical characteristics of UHMWPE mixture with graphite, molybdenum disulfide and polytetrafluoroethylene were investigated under dry friction, boundary lubrication and abrasion. The optimum filler weight fraction was determined in terms of increasing wear resistance. Permolecular structure and surface topography of wear tracks for UHMWPE composites with different weight fraction of the fillers was studied. The mechanisms of wear of polymeric composites “UHMWPE-graphite”, “UHMWPE-PTFE” and “UHMWPE-MoS2” under dry sliding friction and abrasive wear are discussed.

Structural and mechanical defects of materials of offshore andonshore main gas pipelines after long-term operation

Abstract The study has established the main regularities of a fatigue failure of offshore gas steel pipes installed using S-lay and J-lay methods.We have numerically analyzed the influence of preliminary deformation on the fatigue life of 09Mn2Si steel at different amplitudes of cyclic loading. The results have revealed the regularities of formation and development of a fatigue crack in 17Mn1Si steel after 40 years of underground operation. The quantitative analysis describes the regularities of occurrence and growth of fatigue cracks in the presence of a stress concentration.

Segmentation and Statistical Processing of Geometric and Spatial Data on Self-Organized Surface Relief of Statically Deformed Aluminum Alloy

The methods of segmentation and statistical processing of the data on the relief formation on the self-organized surface of the statically deformed alloy D16chT are used. This allowed determining the signal parameters, segment structure and morphological peculiarities of self-organization as the data of the cyclic random process model. The mathematical methods are proposed, which allow increasing the accuracy, reliability and informative value of the profilometric data processing in diagnostic systems of control of the surface condition.

Detecting acoustic-emission signals with fiber-optic interference transducers

Results of the analysis of acoustic-emission signals generated due to ultrasonic waves propagating in a polymer composite material and registered with piezoelectric and fiber-optic sensors are presented. The fiber-optic sensors were arranged into an adaptive interferometer based on using a dynamic hologram formed in a photorefractive crystal. Reducing the setpoint fading has made it possible to improve the noise immunity and sensitivity of the measurement system when using an adaptive interferometer on a photorefractive crystal. Optical fibers in the interferometer’s measurement system served as sensors of ultrasonic waves and were built into a polymer composite material when the sample was manufactured. The sample was a rectangular plate made of a multilayer fiberglass material. It has been discovered that the sensitivity of the adaptive interferometer makes it possible to detect acoustic- emission signals generated by a Hsu–Nielsen source. When determining the speed of sound in the polymer composite material, peculiarities of registering a group wave by fiber-optic sensors have been established that are due to the anisotropy of the medium the wave propagates in and the distributed character of sensor placement in the studied composite material. The wavelet transform has been used to separate the informative component of the wanted signal.

Effect of notch shape on strain localization in steel under shock loading: Hybrid CA simulation

A hybrid discrete-continuum Excitable Cellular Automata (ECA) approach is proposed to study the vector character of the mass and energy transfer flows in a solid under high-rate loading. Based on the torsion energy calculations, the model of generation and accumulation of defect structures is proposed. Numerical simulations of uniaxial shock loading of specimens with three typical notch shapes are performed to validate the proposed approach. It is shown that stress relaxation occurs most effectively when the modulation of various components of the force moment takes place at various scales. This offers the possibility to reduce the stress concentration substantially by tailoring the materials microstructure.

Lamb Wave Based Ultrasonic Technique for AA2024 Fatigue Evaluation

Experimental results of Lamb wave technique investigation for evaluation of fatigue state of AA2024T3 specimens under cyclic loading conditions are presented. Analysis of acoustic signal data obtained by the piezoelectric transducers network was done through the calculation of two parameters: maximum envelope and 2nd central moment. Understanding of relations between acoustic signals features and emergent damages will provide the ability to determine the state of the structure and evaluate the defects, therefore assume the preventative measures and avoid accidents.

Influence of Preliminary Deformation on Micromechanisms of Failure of Offshore Gas Pipeline Material

The S and J - methods of pipe laying tend to increase the brittle fracture component in the material, however, they have practically no effect on the residual life-time of metal under low amplitude cyclic loading (260 MPa). An increase in the stress range up to 320 MPa enhances the negative effect of preloading, which is more pronounced in case of using the S - method of pipe laying as compared to the J - one. Within the high amplitude range (420 MPa) the process of preliminary deformation causes the activation of relaxation processes and longitudinal splitting in the material, giving rise to an abnormal increase in the cyclic life of the plastically deformed material.

Structural Aspects of Zr+ Ion-Beam Surface Modification and Mechanical Properties of 12CrMoV Steel

Surface modification is an effective way both to protect structural materials and to improve their mechanical properties. However under mechanical loading the distinction of elastic moduli of a modified surface layer and adjacent bulk material causes the stress concentrators to occur, whose relaxation may give rise to localized development of plastic deformation or fracture [1]. Under cyclic loading such distinction of the properties brings to multiple microcracking of strengthened surface layer, to act as structural micronotches [2, 3]. Therefore, optimized modes and parameters for surface layer modification are to be determined being a certain compromise between strength/ductility of the layer and its thickness etc.