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In this paper, hip implants made of Ti-6Al-4V titanium alloy are analyzed numerically using Extended Finite Element Method XFEM. The combined effect of corrosion and fatigue was considered here since this is a common cause of failure of hip implants. Experimental testing of Ti-6Al-4V alloy was performed to determine its mechanical properties under different working environments, including normal, salty, and humid conditions. The integrity and life of the hip implant were assessed using the Linear Elastic Fracture Mechanics (LEFM) approach. For this purpose, the conditional fracture toughness Kq using CT specimens from all three groups (normal, humid, salty conditions) were determined. This provided insight into how different aggressive environments affect the behavior of Ti-6Al-4V alloy; i.e., how much its resistance to crack growth would degrade depending on conditions corresponding to the real exploitation of hip implants. Next, analytical and XFEM analyses of fatigue behavior in terms of the number of cycles were performed for all three groups, and the obtained results showed good agreement, confirming the validity of the integrity assessment approach shown in this work, which also represented a novel approach since fatigue and corrosion effects were investigated simultaneously. [ABSTRACT FROM AUTHOR]

Risk based analysis of reverse hydro power plant penstock structural integrity is performed using fracture mechanics parameters. 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 Diagram has been used to evaluate probability, whereas phenomenological analysis has been used to estimate consequence, in the scope of common risk estimation. It is shown that over-pressuring has potential detrimental effect on pipeline safety, i.e. structural integrity. [ABSTRACT FROM AUTHOR]

• Proposing a procedure for assessment in the designing phase of an existing rivetted steel bridges. • Risk under control using the assessment procedure presented in the paper. • Structural integrity assessment of existing steel bridges by means of fracture mechanics. • The results of in-depth XFEM analysis with different crack size in the area of a riveted joint are also presented, in order to validate the algorithm. Numerous roads and railways network steel bridges exist with more than 100 years in service, often of great historical value. The in-service safety assessment of these structures is a complex problem which requires interdisciplinary approaches – from civil engineering application of Eurocodes or European recommendation for fatigue life estimation, up to an in-depth assessment by means of fracture mechanics. This article emphasizes the importance of rehabilitating the structure of existing steel bridges, considering the historical monument character of these structures, as well as the reuse of existing structures. Toward this aim, the study case for a historical riveted steel bridge build in the beginning of the twentieth century is presented, with an assessment method considering the structural integrity by means of fracture mechanics. Based on this case study, the paper is proposing an algorithm to assess historical steel bridges. The results of in-depth XFEM analysis with different crack size in the area of a riveted joint are also presented, in order to validate the algorithm. [ABSTRACT FROM AUTHOR]

Abstract In this paper, numerical analyses of fatigue crack growth in integral skin-stringer panel produced by means of laser beam welding (LBW) are presented along with fatigue results verified by previously conducted experiments. Skin-stringer panel is fail-safe structure widely used in aircraft industry, which requires a good estimate of fatigue life after crack initiation. In the past, experimental work was the only successful method for fatigue life estimation of complex damaged structure, but nowadays researches have powerful numerical tools, such as extended finite element method (XFEM), for three-dimensional crack growth analysis. In research presented here, XFEM was initially used for crack growth simulation in simple flat plate made of aluminium 6156 T6 and 6156 T4 for the purpose of procedure verification, since fatigue life for simple plate was known from experiment. Then, XFEM was used to simulate fatigue crack growth in the panel reinforced with four stringers. Fatigue life obtained on the basis of calculated stress intensity factors (SIFS) along the crack fronts on LBW skin-stringer panels was, as expected, significantly longer than experimentally measured life of simple flat plate. Finally, several numerical simulations were performed in order to analyse the influence of mesh size on accuracy of estimated fatigue life of damaged LBW skin panels. For that purpose, average element sizes of 1, 2 and 4 mm were used. Highlights • XFEM may play a significant role in structure fatigue life estimation. • Effect of mesh size on fatigue life estimation is evident, but not dominant. • Coarser mesh provides better agreement with experimental results. • Small changes in material properties significantly change fatigue life. [ABSTRACT FROM AUTHOR]

This paper presents results of experimental examinations of stress concentration influence to fatigue life of butt welded joints with K-groove, produced from the most frequently used structural steel S355J2+N. One group of experiments comprised examinations carried out on the K-groove specimens with stress concentrators of edged notch type. Specimens with short cracks (limited length of initial crack), defined on the basis of the experience from fracture mechanics by the three points bending examinations, have been examined according to standard for the determination of S-N curve, and aimed to determine fatigue strengths for different lengths of initial crack and Relationship between fatigue strength and crack length. Other group of experiments comprised examinations of specimens with edge notch, prepared in accordance with ASTM E 399 for three points bending, in order to establish regularity between crack growth and range of exerted stress intensity factor aimed to determine resistance of welded joint to initial crack growth, namely fatigue threshold (ΔKth). [ABSTRACT FROM AUTHOR]

• Fatigue life of Ti6Al4V orthopedic plates is assessed by xFEM crack growth simulation. • Five different geometries of plates were analysed by xFEM to obtain the optimal one. • Experimental investigation was performed to determine mechanical properties, including crack resistance. • Relatively short fatigue life in each of five geometries is attributed to low crack resistance of Ti6Al4V used here. This study is aimed to analyse fatigue life of orthopedic plates due to cracks initiated in the stress concentration areas. Material used for this analysis was typical orthopedic alloy, Ti-6Al-4V, strong but not very ductile, meaning also sensivite to cracking, as indicated by its mechanical properties, such as tensile strength, impact toughness and fracture toughness, as well as by high fatigue crack rate, all of them tested and analysed here. Extended finite element method (XFEM) in ANSYS software was used for simulating the fatigue crack growth in 5 orthopedic plates with different geometries. Results for crack length and stress intensity factor vs. number of cycles are given, indicating plate D as the best option regarding residual life. Crack paths are analysed in all 5 plates to explain such a behaviour, indicating benefits of initial crack growth into length, followed by growth into depth. Also, the effect of geometry of plates is considered to explain differences in life predictions for 5 different plates. [ABSTRACT FROM AUTHOR]

Finite element modelling of steady state creep process has been described. Using an analogy of visco-plastic problem with a described procedure, the finite element method has been used to calculate steady state stresses and strains in 2D problems. An example of application of such a procedure have been presented, using real life problem - cylindrical pipe with longitudinal crack at high temperature, under internal pressure, and estimating its residual life, based on the C* integral evaluation. [ABSTRACT FROM AUTHOR]

The 1st Virtual European Conference on Fracture (VECF1) has gathered more than 300 researchers from all over the world. They have presented more 320 papers, including 9 plenary lectures in the scope of the main VECF1 topics. Starting with 1800 views on the first day, there were 9300 views in the "hottest period" (June 20–July 2), making this event a great success. Conference was organized through number of Symposia, managed by ESIS Technical Committees. In the scope of these topics number of papers dealt with damage, cracks and related failures, including large structures like bridges, aircrafts, pressure vessels, large rotational equipment, pre-stressed and reinforced concrete constructions. As guest editors, we hope the Damage, Cracks & Failure Special Issue provides a remarkable impact in the research related to residual life assessment, modelling of failure and crack growth analysis. We also would like to express our gratitude to all authors for their contributions and to all reviewers for their generous work to guarantee the excellence of the papers. Finally, the guest editors would like to express a special thanks to Professor Richard Clegg, Editor-in-Chief of Engineering Failure Analysis journal, and to Elsevier staff for their support during the preparation of this issue. [ABSTRACT FROM AUTHOR]

• Numerical simulation of fatigue crack growth through different welded joint regions. • Comparison of steels with significantly different microstructures and applications. • Development of a methodology which could be used for a wide variety of materials, in a relatively simple manner s. Fatigue crack growth through different welded joint regions was investigated, in terms of welded joint geometry and fatigue crack position. In the first phase of investigation, numerical simulation of crack growth in a welded joint made of steel P460NL1 was performed using extended Finite Element Methods (xFEM). Numerical models employed Paris law, using experimentally determined coefficients for each welded joint zone. Weld geometry was varied by using different heat affected zone (HAZ) widths, i.e. fatigue crack lengths. The second stage involved similar numerical models with different material (Protac 500). Fatigue lives for regions in both models were then compared. [ABSTRACT FROM AUTHOR]

• Analysis of the largest pre-stressed concrete structure in the world. • Numerical simulations comparison with analytical results obtained during the construction of the Hall. • Structural integrity analysis of one of the load-bearing elements in the presence of a crack. This paper involves the analytical and numerical calculations of the the largest pre-stressed concrete free-standing structure in the world – the Dome of the "Hall 1 of the Belgrade Fair", designed by a well-known Serbian scientist and engineer Branko Žeželj, one of the founders of the Institute for testing of materials IMS in Belgrade, conveniently positioned just across the street, best known for coming up with a concrete pre-stressing system, which is still widely used today. As a part of this research, this large and unique structure will be analyzed from point of view of structural integrity, including numerical simulation of crack growth in one of its support columns. Presented analyses also include the calculation of forces and moments in the structure as a whole, while also taking into account foundation displacements in the columns. [ABSTRACT FROM AUTHOR]

• Simple engineering analysis is presented, based on calculation of fracture mechanics parameters. • Numerical and experimental approach is needed for complex geometries and material behaviour. • Risk based analysis is useful method to provide gap between engineers and managers. • The best approach would be to adopt two-phase decision making process. Fracture mechanics parameters are used for experimental, numerical and analytical risk assessment of structural integrity and life of oil drilling rig welded pipe with a crack. As a simple analytical tool, the Failure Assessment Diagramme (FAD) has been applied to assess probability of pipe failure, using the ratio of linear elastic fracture mechanics parameter, K I , and its critical value, K Ic , in relation to the ratio of applied stress and its critical value. Alternatively, the ratio of J integral, evaluated experimentally and numerically, and its critical value, J Ic , has been used to estimate probability of failure. Risk was then assessed for all three approaches, in combination with the estimated consequence. Results are given in the form of risk matrix, indicating the effects of the most (analytical) and the least (experimental) conservative estimates. In the case of risk based structural life assessment, number of cycles, obtained analytically and numerically, are related to the number of cycles to the critical crack length, to assess risk due to fatigue. [ABSTRACT FROM AUTHOR]

• Simple engineering approach has been used as efficient method to assess risk by fracture mechanics. • The simple engineering analysis tends to be over-conservative, even in relatively simple case study. • More complex approach, based on FEM, is inevitable for more complex geometries. • Risk based analysis is useful method to provide gap between engineers and managers. Risk assessment procedure based on structural integrity and life estimation has been introduced and applied to oil drilling rig welded pipe. The new concept based on application of structural integrity and life estimation to assess risk level according to probability and consequence of failure was used. Oil drilling rig welded pipe integrity has been assessed by simple application of the Failure Assessment Diagramme (FAD), i.e. by using the ratio of linear elastic fracture mechanics parameter, K I , and its critical value, K Ic , in relation with the ratio of applied stress and its critical value, to define the point in FAD. Probability of failure is then taken according to the position of the point in the FAD, corresponding to oil drilling rig welded pipe data. Then, the FEM has been applied to calculate more precisely the strain and stress state and to get another, less conservative, risk assessment. Oil drilling rig welded pipe life has been estimated by simple integration of the Paris law, as well as by more complex simulation of fatigue crack growth, using the extended Finite Element Method (xFEM). 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. These analyses are useful for managers to make decision about further use of damaged pipes, based on data provided by engineers. Also, the procedure introduced here for risk assessment is not limited to oil drilling rig pipes, but it is rather a general one, applicable to any component with known geometry, material properties and loading data. [ABSTRACT FROM AUTHOR]

• High potential of XFEM in analysing fatigue crack growth in complex 3D geometries. • Results for the equivalent stress intensity factor can indicate point of unstable crack growth. • Initail crack dimensions are assumed according to the experience with failures of hip implants. • Estimation of number of cycles for active person walking pattern before implant failure. • Possible to recommend a certain lifestyle for patients with crack defect implants. Fatigue crack growth in hip implant has been analysed using the extended finite element method. Toward this aim, the three-dimensional finite element model is created and used in ABAQUS and Morfeo/crack add-in for ABAQUS to simulate fatigue crack growth from initial value up to the critical point. Initial crack dimensions are assumed according to the experience with failures of hip implants, whereas the final, critical value was estimated using data for fracture toughness obtained by experimental testing of hip implant made of Ti-6Al-4V alloy. Results for the equivalent stress intensity factor and number of cycles in each of 40 steps of fatigue crack growth are presented and analysed, indicating the point of unstable crack growth. [ABSTRACT FROM AUTHOR]

• The search for optimum shape and size of wing spar cross-section was presented. • The optimum design is based on fatigue life related to the fatigue crack propagation. • Several different shape and sizes of the wing spar cross-section were analysed. • The XFEM was used to simulate crack growth in complex wing spar geometry. Shape optimisation is a nowadays-standard requirement in the design of lightweight structural components. In this paper, optimisation of I-beam cross-section of integral aluminium 2024-T3 wing spar is presented, taking the maximum fatigue life as the criterion. Toward this aim, the extended finite element method (XFEM) was used to simulate crack growth in complex I-beam geometry. The computations were carried out using Morfeo/Crack add-on based on XFEM implementation in Abaqus software. Fatigue lives of wing spars with different sizes of cross section but constant area were compared. Conducted analysis has shown that XFEM seems to be efficient tool for complex three-dimensional configurations optimisation. [ABSTRACT FROM AUTHOR]

• Brief historical overview of studies concerning ductile-to-brittle transition of ferritic steels. • Problems emphasized as a consequence of using fracture mechanics concepts to ductile-to-brittle characterization. • Review on statistical modeling of cleavage fracture in transition region. • Brief outlines of two new developed approaches to ductile-to-brittle characterization of ferritic steels. • The criticisms of all presented methods are oriented mostly on the application domain and capability to predict fracture toughness. The phenomenon of ductile-to-brittle transition in ferritic steels has been a ubiquitous research challenge for the last 50 years. The characterization of this problem using the fracture mechanics concept, from the earliest studies based on the linear-elastic fracture mechanics to the application of the elastic–plastic fracture mechanics, has become inevitable over time. The fracture toughness is not an intrinsic material property but depends on geometrical factors (such as the specimen shape, thickness, and surface roughness), defect type and distribution, loading mode, and environmental conditions. The pronounced scatter of experimental data on fracture toughness, characteristic of all ferritic steels in the ductile-to-brittle transition temperature region, necessitated the use of statistical methods for data processing. That approach, which emerged in the 1970 s, can still be found today as the basis for interpreting fracture toughness data in ductile-to-brittle transition problems. This paper presents a brief historical overview of such studies along with the problems that have arisen as a consequence of using fracture mechanics concepts, such as constraint effects, as an example. In the time-honored research tradition, all the proposed methods and models, as well as their criticisms, provided the basis for the development of new approaches to the ductile-to-brittle characterization of ferritic steels. Specifically, these include size effects and scaling of geometrically similar samples, with the aim of predicting material behavior beyond experimental limits. Brief outlines of two new approaches are provided in this succinct review. The criticisms of all presented methods are oriented mostly on the application domain, as well as their capability to predict fracture toughness, with short overview of their most conspicuous advantages and disadvantages. [ABSTRACT FROM AUTHOR]

• Fatigue Remaining life of high pressure turbine casing with unacceptable defects predicted. • Separating Morphing and Adaptive Remeshing Technology used in the scope of FEM. • The response surface optimization was applied to obtain Paris' coefficients, based on the real data for crack growth. Remaining life of a high-pressure turbine (HPT) casing of aircraft turbofan engine with cracks was determined. Cracks were detected during regular inspection and found out to be initiated by scratches made by non-skilled use of Electrical Discharge Machining (EDM). In total, 9 visible surface marks were made. Keeping in mind that this component is not repairable, and its replacement might be time-consuming and/or too expensive, it was essential to evaluate the remaining life and prevent failure if this component was to be used with cracks. Toward this aim, numerical methods had to be used, since testing of samples or component itself was not possible due to geometry restrictions. To get a reliable estimation of the remaining life, it was necessary to evaluate Paris coefficients C and m. Use of available data for fatigue crack growth was not an option, since coefficients are determined for virgin material and could not provide acceptable predictions for the used material. To overcome these difficulties, an innovative technique in two steps, based on finite element method, has been introduced. First step was to simulate fatigue crack growth. Then, response surface optimization (RSO) was used to obtain Paris' coefficients that predict accurately the number of loading cycles to reach detected crack lengths, provided by the maintenance, repair, and operations (MRO) company's workshop. Coefficients C and m, determined in this way, were then used to evaluate remaining life of the HPT casing and estimate the risk of its further use. [ABSTRACT FROM AUTHOR]

• The size-effect study is aimed at estimation of the J c CDF in the transition region. • A scaling algorithm is derived under constraint of a small statistical-sample size. • Experimental data for 20MnMoNi55 ferritic steel at −60 °C is used in example. • This novel alghoritm provides very good estimates in the intepolation range. • It also provides reasonably conservative lower bounds for extrapolation of data. Ever since the 1980s there is a sustained interest in the size effect, as one of the most pronounced consequences of fracture mechanics. In the present study, the investigation of the size effect is focused on estimation of the Weibull cumulative distribution function (CDF) of the critical value of the J -integral (J c) in the transition temperature region under constraint of a small statistical sample size. Specifically, the J c experimental data correspond to the C(T) specimen testing of the reactor pressure-vessel steel 20MnMoNi55 at only two geometrically-similar sizes. Thus, a simple approximate scaling algorithm has been developed to tackle the effect of the C(T) specimen size on the J c CDF under these circumstances. Due to the specific form of the two-parameter Weibull CDF, F (J c | β, η), the scaling procedure is applied according to a two-step scheme. First, the J c -scaling is performed to ensure the approximate overlap of the points that correspond to the CDF value F (J c = η) = 1 − 1/e ≈ 0.632 for different C(T) specimen widths (W), which assumes η·Wκ = const. Second, the F -scaling is performed to ensure the equality of the slopes of the CDF in the scaled (F·Wξ vs. J c ·Wκ) space. The objective of the sketched approach is to obtain a size-dependent J c CDF that encapsulates a reasonably conservative data extrapolation. [ABSTRACT FROM AUTHOR]

The ESIS Executive Committee decided to nominate a new team for the leadership and management of the TC12/ESIS technical committee (TC), as well as update the TC name as "Risk Analysis and Safety of Large Structures and Components". In this paper, the new organization of the TC12/ESIS as well as the objectives and tasks, and forthcoming events are presented. In addition, this document has editorial purposes regarding the selected and published papers from the International Symposium on Risk Analysis and Safety of Large Structures and Component s (ISRAS-TC12) organized within of the "2nd International Conference of Structural Integrity (ICSI)", which took place at Madeira Island, Portugal, on 4–7 September 2017. As guest editors and TC12/ESIS members, we hope the ISRAS-TC12 Special Issue provides a remarkable impact in the research related to fatigue, fracture, structural integrity, risk analysis and safety of complex structures and components. We also would like to express our gratitude to all authors for their contributions and to all reviewers for their generous work to guarantee the excellence of the papers. Finally, the guest editors would like to express a special thanks to Professor Richard Clegg, Editor-in-Chief of Engineering Failure Analysis journal, and to Elsevier staff for their support during the preparation of this issue. [ABSTRACT FROM AUTHOR]

• The damaged jet engine exhaust nozzle's inner sleeve was analyzed. • Analyzed structure was subjected to thermo-mechanical cyclic loading. • Crack propagation in repaired inner sleeves were simulated and analyzed. • It was determined which type of repair gives longer fatigue life for damaged part. The exhaust nozzle, made of titanium, is the part of a jet engine where the final expansion of the hot gas from the turbine occurs and where the speed of the exhaust gas is further increased to create thrust. During the work, it is exposed to elevated temperatures and compressive and hoop stresses, which makes the cracks' occurrence in the exhaust nozzle's inner sleeve unavoidable, making repairs during maintenance necessary. In this study, crack growth in the repaired inner sleeve was analyzed. The aim of the study was to evaluate the fatigue life of the damaged inner sleeve when a new method of repair is applied and to compare obtained number of cycles with the number observed in the maintenance workshop after the old method of repair was used. Developing the numerical model and conducting simulations using the extended finite element method (XFEM) and finite element method (FEM), it was concluded that a new type of repair should be used to provide longer fatigue life of the damaged exhaust nozzle. [ABSTRACT FROM AUTHOR]