The synergistic action and interplay of hydrogen embrittlement mechanisms in steels and iron: Localized plasticity and decohesion

The paper reviews recent research and development activities in the field of hydropower technology. It covers emerging and advanced technologies to mitigate flow instabilities (active and passive a ...

Analysis of emerging technologies in the hydropower sector

Hydro turbine failure mechanisms: An overview

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http://comjnl.oxfordjournals.org/content/25/3/337-c.full.pdf

Practical Reliability Engineering

There is a general need to change hydropower operational regimes to balance the growing contribution of variable renewable energy sources in power systems. Quantifying the burden on generation equipment is increasingly uncertain and difficult. Here, we propose a framework combining technical and economic indicators to analyze primary frequency control (PFC) on a timescale of seconds. We develop a model integrating hydraulic, mechanical, and electrical subsystems to characterize efficiency loss, wear and fatigue, regulation mileage, and frequency quality. We evaluate burden relief strategies under three idealized remuneration schemes for PFC, inspired by those used in Sweden, the USA, and China, respectively. We show how burden and compensation vary under future scenarios of renewable power systems. Our framework can be used by producers to develop favorable operation strategies that reduce burden and increase economic value, and by transmission system operators to provide insights on the relation between incentive structures and regulating performance.

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Burden on hydropower units for short-term balancing of renewable power systems

Failure analysis of hydraulic turbine shaft

Bearing in mind the multiple effects of hydrogen in steels, the specific mechanism of hydrogen embrittlement (HE) is active, depending on the experimental conditions and numerous factors which can be grouped as environmental, mechanical and material influences. A large number of contemporary studies and models about hydrogen environment assisted cracking and HE in steels are presented in the form of critical review in this paper. This critical review represent the necessary background for the development of a multiscale structural integrity model based on correlation between simultaneously active HE micro-mechanisms: the hydrogen-enhanced localized plasticity (HELP) and the hydrogen-enhanced decohesion (HEDE) - (HELP+HEDE) and macro-mechanical response of material, unevenly enriched with hydrogen during service of boiler tubes in thermal fossil fuel power plant. Several different experimental methods and techniques were used to determine the boiler tube failure mechanism and afterwards also the viable HE mechanisms in the investigated ferritic-pearlitic low carbon steel, grade 20 - St.20 (equivalent to AISI 1020). That represent a background for the development of a structural integrity model based on the correlation of material macro-mechanical properties to scanning electron microscopy fractography analysis of fracture surfaces of Charpy specimens, in the presence of confirmed and simultaneously active HE micro-mechanisms (HELP+HEDE) in steel. The aim of this paper is to show how to implement what we have learned from theoretical HE models into the field to provide industry with valuable data and practical structural integrity model.

Towards a unified and practical industrial model for prediction of hydrogen embrittlement and damage in steels

The load distribution in machine elements is the first step in the analysis of their operating condition. Because of influence of many various factors, constructional and technological, it is very difficult to determine precisely a real condition – real load distribution without the approximations – hypotheses. The load distribution is basic input in mechanical and mathematical modelling with the purpose of the analysis of machine parts operating conditions from different relevant aspects: durability, stiffness, reliability and stability. Because of that, the modelling of load distribution is a very responsible and difficult task. The existing models of load distribution in rolling bearings [1], gear transmissions, chain transmissions etc. contain many approximations and empirical coefficients, which have no the appropriate physical basis. Load distribution in rolling bearings, which operate in condition of the time limited endurance, has a dominant influence on bearing durability. The small vibrations, noise and friction losses are required from the rolling bearings. The large operational safety, load carrying capacity, durability, and accuracy of rotation are required, as well. Hence, developed mathematical models of rolling bearings, their technology of manufacturing and assembly, as well as design optimization were improved. The special place at designing and optimization of rolling bearings has load distribution between rolling elements. The mathematical model developed in this paper establishes correlation between elastic deformations of the bearing parts in contact, internal radial clearance and external radial load distribution between rolling elements of the ball bearing. Developed mathematical model can be used for more exact analysis of load distribution between rolling elements, and for more reliable determination of the bearing carrying capacity, durability and power losses.

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Mathematical model of load distribution in rolling bearing

This paper aims to present the methodology to determine Archard’s wear coefficient. By applying this coefficient into the numerical simulation of wear, it is possible to predict wear without long lasting and usually expensive experiments.,To determine necessary particles of Archard’s equation and calculate wear coefficient K, an experimental investigation is proposed. Afterwards, the wear simulation is executed in FEM software ANSYS 18.1. Analytical method is offered to determine worn volume for cylinder-in-cylinder contact, based on “inclination” of inner cylinder.,Comparing the value of Archard’s coefficient obtained by this experimental investigation with the values from the literature for the similar materials, high correlation is noted. Furthermore, numerically calculated contact pressure is confirmed with analytical method. Trend of pressure decrease due to wearing process, as well as due to increase of contact surface is observed.,Since the prediction of the wear is closely related to the life cycle assessment of bearings, and the machines in general, it has significant practical importance for designers.,Determination of Archard’s coefficient is usually performed by conventional pin-on-disk tribometers. This methodology offers a different approach for the determination of Archard’s wear coefficient for cylinder-in-cylinder contact, which is convenient for shaft-sliding bearing contact.

Determination of Archard’s wear coefficient and wear simulation of sliding bearings

Abstract The advanced development of additive technologies over the past years led to the fact that parts made by these technologies have been increasingly used in the most diverse engineering applications. One of the most famous and the most applied additive technology is 3D printing. In this paper the influence of the material type on the operational characteristics of spur gears manufactured by the 3D printing technology is analyzed, after the experimental testing performed on a back to back gear test rig, in the predefined laboratory conditions.

https://sciendo.com/pdf/10.2478/scjme-2018-0039

Radivoje Mitrovic

Papers

Failure analysis of hydraulic turbine shaft

Towards a unified and practical industrial model for prediction of hydrogen embrittlement and damage in steels

Mathematical model of load distribution in rolling bearing

Determination of Archard’s wear coefficient and wear simulation of sliding bearings

The Influence of Material on the Operational Characteristics of Spur Gears Manufactured by the 3D Printing Technology