TC12 Programme


Tuesday, 14 July 2020

Timetable (Time zone is CEST) - ROOM: LINK

09.00-09.45: Risk based assessment of pressure vessel integrity and life

Aleksandar Sedmak, Full Professor, Faculty of Mechanical Engineering, University of Belgrade, Serbia,; Snezana Kirin, Associate Professor, Innovation Center of the Faculty of Technology and Metallurgy, Belgrade, Serbia, (Presentation)

10:00 - 10:45: Overview on the generalization of fatigue models based on local damage parameters

José António Correia, Researcher, INEGI & CONSTRUCT, Faculty of Engineering, University of Porto, Porto, Portugal,; Abílio de Jesus, Associate Professor, INEGI, Faculty of Engineering, University of Porto, Porto, Portugal, (Presentation)

11.00 - 11.45: Reliability and safety of complex technical systems

Vladimir Moskvichev, Full Professor, Director of the Special Design and Technological Bureau "Nauka" of the Institute of Computational Technologies of the Siberian Branch of the Russian Academy of Sciences (ICT SB RAS), Russia, (Presentation)

11.45 - 12.30: Fatigue crack growth rate description – experimental and theoretical approach

Grzegorz Lesiuk, Associate Professor, Department of Mechanics, Materials and Biomedical Engineering, Faculty of Mechanical Engineering, Wrocław University of Science and Technology, Poland, PL-50370 Wrocław, Smoluchowskiego 25 St., (Presentation)

14.00 - 14.45: A probabilistic framework for evaluation the probabilistic S-N fields for riveted joints

Abílio de Jesus, Associate Professor, INEGI, Faculty of Engineering, University of Porto, Porto, Portugal,; José António Correia, Researcher, INEGI & CONSTRUCT, Faculty of Engineering, University of Porto, Porto, Portugal, (Presentation)

15.00 - 15.45: Failure behavior of protective coatings and oxide scales for energy and aircraft applications

Elena Fedorova, Associate Professor of Department of Applied Mechanics, Polytechnic Institute of Siberian Federal University, 79, Svobodny Pr., Krasnoyarsk, 660041, Russia, (Presentation), (Paper), (Paper), (Paper), (Paper), (Paper)

16.00 - 16.45: Fatigue reliability design and assessment under uncertainty

Shun-Peng Zhu, Full Professor, School of Mechanical and Electrical Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China; &, Center for System Reliability & Safety, University of Electronic Science and Technology of China, Chengdu 611731, China, (Presentation)

16.45 - 17.15: Online evaluation

Risk based assessment of pressure vessel integrity and life

Risk based assessment of structural integrity and life is presented and applied to pressure vessels. Risk is evaluated according to risk matrix, i.e. it is defined as the product of the consequence and probability. The approach adopted here uses simple engineering methods, based on fracture mechanics concept, such as Failure Assessment Diagramme (FAD), to estimate probability. Consequence is estimated by simple reasoning of what would happen if pressure vessel fails, which is typically a catastrophic event. Therefore, focus here is on probability, estimated using the position of operating point in FAD, corresponding to a given stress state for a cracked component.

Risk based analysis of structural integrity is presented using an example of the reverse hydro power plant penstock. To assess its structural integrity, extensive testing of the full-scale prototype had been performed, including hydrostatic over-pressurizing, during the design phase. More recently, the Failure Assessment Diagramme has been used to evaluate probability of failure, whereas phenomenological analysis has been used to estimate consequence, in the scope of common risk estimation. Probability was estimated as the ratio of distance of operating point from zero point and distance between corresponding point on limit curve and zero point. It is shown that over-pressuring has potential detrimental effect on pipeline safety, i.e. structural integrity.

Risk assessment of structural life estimation has been applied to oil drilling rig welded pipe. Oil drilling rig welded pipe life has been estimated by integration of the Paris law, and also by xFEM simulation of fatigue crack growth. Probability of failure is then taken as the ratio of the number of cycles for a given crack length and the number of cycles for the critical crack length, estimated by using the basic linear elastic fracture mechanics concept.

This approach is also useful for managers to make decision about further use of damaged pressure vessels, based on data provided by engineers. The procedure for risk assessment of structural integrity and life is a general one, applicable to any component with known geometry, including crack, material properties and loading data.

Overview on the generalization of fatigue models based on local damage parameters

Fatigue models that have been proposed for use in global and local approaches to fatigue are based on fatigue damage parameters. In current design codes, the global approaches are based on fatigue Wohler's or S-N curves originally proposed by Basquin. Regarding the local approaches, these are based on fatigue damage parameters, mainly in stress, strain and energy. In the design codes, the fatigue Wohler's or S-N curves have been used to describe the structural details/connections fatigue behaviour. Single power and combined power laws have been proposed to describe fatigue curves for global and local approaches. Kohout and Věchet suggested the full-range S-N curve based on stress fatigue damage parameter covering all fatigue regimes, low- (LCF) and high-cycle fatigue (HCF) regimes. A first adaptation of the Kohout-Věchet model to the local strain parameter was proposed by Karunananda. Later, Correia generalized the Kohout-Věchet model for various damage parameters considering simple power laws and combined power laws. The expressions proposed by several authors were developed taking into account uniaxial fatigue loading conditions. The same can be considered for multiaxial fatigue criteria based on stresses, strains and energy. Global fatigue approaches applied to the structural details and/or connections are generally based on stress criteria, such as structural stresses, notch stresses and hot-spot stresses. The latter is complemented with linear-elastic and/or elastoplastic numerical analyses of the local stresses and/or strain history of structural details and/or connections. A review of the global and local approaches used for fatigue analysis of metallic materials and structural details under uni- and multi-axial loading conditions is presented. In this lecture, some examples of applications, such as notched details from metallic bridges, pressure vessels, among others, are used.

Reliability and safety of complex technical systems

The development of complex technical systems (CTS) with a high level of danger is associated with problems of CTS safety and reliability. Conventional methods for ensuring the strength and the service life of CTS do not exclude the probability of accidents and disasters.

The lecture aims to provide an overview on analytical and experimental methods for ensuring the safety of CTS based on the criteria of Deformation and Fracture Mechanics, on the evaluation algorithms of damaged structures residual life, on the models of the Theory of Reliability and Risk Analysis.

The lecture presents examples of large technological disasters of CTS based on cause/effect analysis of failures, the defect parameters of welding joints, and the limit states of CTS. The results of fracture toughness characterisation of stainless steels and welding joints under static and cyclic loading will be presented.

The lecture discusses applied problems of Fracture Mechanics and Safety of CTS using different examples such as: resource design; reliability and risk assessment of failure of welding structures; stress-strain state and fracture toughness of space truss structures and the Launch Complex of Baikonur; assessment of the technical state and life cycle of hydro turbines of the Sayano-Shushenskaya and Krasnoyarskaya hydroelectric power stations.

In conclusion, the lecture indicates promising directions for future research in the area of Fracture Mechanics and Safety of CTS.

Fatigue crack growth rate description – experimental and theoretical approach

Fatigue and fracture are the two main (more than 70% of all failures) phenomena responsible for the structural damage in steel structures subjected to cyclic loads. The main difficulty in describing of the fatigue crack growth rate in mathematical terms is the incomplete understanding the nature of this process in various material groups under different loading conditions (constant amplitude, random loads, single and multi-axial loads, etc.). One of the reasons for this inadequacy is the effect of mean stress expressed by, e.g. by the R-stress ratio. The main goal of this lecture is to understand the physical Crack Driving Force (CDF) meaning in terms of the experimental and theoretical approach. During the lecture, it will be discussed, and reviewed new methods for description of fatigue crack growth regarding mixed-mode loading condition (I+II, I+III) in the range of elastic and elastic-plastic fracture mechanics based on new strain energy density parameters. The next aim of the presentation is to show the significance and complexity of fatigue fracture process in long term operated structures as well as the potential influence of several factors on fatigue lifetime (i.e. new technologies, degradation of materials etc.) of cracked components. During the presentation will be presented the technical recommendations for fatigue fracture testing under mode I and mixed-mode loading condition as well as mathematical models linked with the numerical tool for fatigue lifetime predictions.

A probabilistic framework for evaluation the probabilistic S-N fields for riveted joints

The availability of probabilistic fatigue strength S–N data for riveted connections is essential to carry out reliability analysis of ancient riveted bridges. This lecture aims at presenting a procedure to derive probabilistic S–N fields for riveted connections, using material fatigue data and detailed finite element modelling of the joints. Strain-life fatigue data of the plain material as well as fatigue crack growth data can be used to compute the total fatigue life of a riveted connection, integrating both the Local and Fracture Mechanics fatigue approaches, in a so-called two stages fatigue approach. The basic fatigue data is inputted in the probabilistic form as well as some relevant parameters of the model which are subjected to higher uncertainty. Three-dimensional finite element modelling of riveted joints is discussed in order to assess the local stresses/strains at the critical location, as well as the stress intensity factor history, for a postulated growing fatigue crack. The proposed approach allows for the assessment of the effects of both clamping stresses on rivets and friction coefficient, on local stress/strain values and stress intensity factors. The clamping stresses on rivets and friction coefficient are assumed random variables. The inputs, in the probabilistic form, are accounted for in the fatigue strength assessment procedure using the Monte Carlo sampling technique.

The lecture will include a case study to illustrate the feasibility of the proposed methodology. A p–S–Nf field is computed for a simple riveted joint and compared with experimental data, illustrating the agreement of the model. In addition, a sensitivity analysis is presented regarding some model parameters

Failure behavior of protective coatings and oxide scales for energy and aircraft applications

In the first part, the lecture aims to provide the basic concepts and methods used to protect the surface integrity of Ni-based alloys and heat-resistant stainless steels against degradation under high-temperature oxidation environment.

Regarding the second part, the lecture combines practically relevant insights and examples from current research and experimental observations.

Special attention is given to structure-property relationships of protective coatings and oxide scales and techniques used to characterize materials properties including aspects of interfacial adhesion quantification and hardness measurement by nanoindentation.

Lecture also explores the role of modeling and numerical simulation in understanding the failure behavior. The numerical analysis of factors governing the magnitude and the distribution of residual thermal stress in oxide/metal systems are presented regarding the industrial application of Ni-based superalloys protected by the thermal barrier coatings (TBCs) in the hot section of gas turbines

Damage mechanisms of TBCs system including microstructural changes, crack initiation, and crack propagation under thermal cycling will be discussed.

Fatigue reliability design and assessment under uncertainty

In order to ensure the safety and reliability of power and energy systems, including gas/steam turbines, power plants, etc., failure mechanism and reliability assessment have becoming a recent development in integrity analysis of these systems/components. For many countries, currently facing a potential future mismatch from energy production and transformation, currently increasing interests are being paid on new techniques to discover and understand the lifing and reliability assessment of power and energy systems. Due to unexpected ageing related fatigue damaging, mechanical properties, microstructures and structural resistance of components often require stochastic considerations related to failure mechanism modelling and analysis. In addition, various sources of uncertainty/variability arising from a simplified representation of the actual physical process (often through semi-empirical or empirical models) and/or sparse information on manufacturing, material properties, and loading profiles contribute to stochastic behavior under operation.

The aim of the presentation is to show how to improve structural fatigue reliability through the accurate modelling of failure mechanisms by introducing advanced mathematical approaches/tools, from the aspects of design and assessment in engineering practice. Particularly, through combining the deterministic and probabilistic modelling techniques, researches on failure mechanism and reliability are provided for new structures at the design stage and ensure the integrity in the construction at the fabrication phase. Specifically, an engineering case on power system failure under multi-sources of uncertainty/variability will be elaborated, which results from load variation in usages, material properties, geometry variations within tolerances, and other uncontrolled variations.

In this presentation, advanced methods and applications for theoretical, numerical, and experimental contributions that address these issues on failure mechanism and reliability analysis are introduced, including the influence of notch, size effects and defects on fatigue strength and life prediction, which attempts to prevent over-design and unnecessary inspection and provide the tools to enable a balance between safety and economy to be achieved.