Search

Fatigue cracks are often a result of incremental stable crack growths that can be described by fracture mechanics. Fatigue crack initiation, however, has been most often described using empirical relationships between an alternating stress or strain and the number of cycles at those loads until either a specimen fails or a crack is observed. There are, however, modern views that consider fatigue crack growth and crack initiation directly related phenomena, the former being repeated instances of the latter, localized at an existing crack tip. Models of this newer class allow for an integrated initiation and crack growth calculation process which is advantageous when dealing with notched details in elastoplastic strain conditions. Recently, Huffman developed such a model which relates Walker-like stress-life relation and fatigue crack growth behaviour. This paper expands upon this new approach in order to account for the expected statistical variation using probabilistic S-N and ε-N fields as per works of Castillo and Fernandez-Canteli. A unified local approach proposed to treat fatigue crack initiation and growth is used on notched geometries with the predicted probabilistic variations being accounted. Notched details made of puddle iron from the Eiffel bridge and P355NL1 pressure vessel steel are considered in this study. [ABSTRACT FROM AUTHOR]

A new proposal of generalization of the fatigue Kohout-Věchet (KV) model for different fatigue damage parameters is proposed. The purpose of this generalized model is to describe all fatigue regimes from very low-cycle fatigue (VLCF) to very high-cycle fatigue (VHCF), and accounting for several fatigue damage parameters, such as, strain parameter, Smith-Watson-Topper (SWT) parameter, Walker-like strain parameter, energy-based parameter in uniaxial loading conditions, among others. The full range of fatigue life responses for all loading regimes of materials and structural components are extremely important in the fatigue design. Engineering structures are subjected to different types of loading that cause fatigue failure. These loadings can range from quasi-static monotonic loading to long term dynamic/cyclic loading. In this paper, a proposal of generalization of the KV model for several fatigue damage parameters was verified and compared with experimental fatigue results under uniaxial loading conditions available in literature. This study validates the importance and applicability of full range fatigue life models for different damage parameters in fatigue life prediction of materials and structural components. [ABSTRACT FROM AUTHOR]

A steel hybrid structural solution for onshore wind turbine towers was proposed in the European project SHOWTIME. This solution is used in the lattice structure for the lower portion of the tower. Recently, a procedure for fatigue life estimation of steel half-pipes bolted connections applied in global structural models using multiaxial Smith-Watson-Topper (SWT) criteria was proposed by Öztürk et al. In this paper a procedure for design S-N curve modelling of steel half-pipes bolted connections is proposed. This procedure is based on a local approach using multiaxial fatigue criteria together with an elastoplastic analysis using the finite element method. The materials to be used in this analysis are the S355 and S690 steels. This evaluation to be performed is calibrated with experimental results of fatigue tests of the connection under consideration. [ABSTRACT FROM AUTHOR]

Maintenance of ancient road and railway metallic bridges has become a major concern for governmental agencies in the past few decades. Indeed, since the construction of these structures, between the end of the 19 th century and the beginning of the 20 th century, traffic conditions have evolved, both in weight and frequency. In the purpose to assess the remaining life of old metallic bridges, some critical structural details have been identified and associated to S-N curves in order to be used in damage estimation (using Palmgren-Miner's rule for cumulative damage, for example). These constructional details are described by design rules of several European and North American standards, such as the Eurocode 3, BS 5400 and AASHTO standards. The particularity of ancient bridges is that hot riveted assemblies, commonly used for their construction, are not represented in most construction standards. Further experiences on the matter by numerous research teams have suggested detail category C71 from the Eurocode 3 as appropriate. In this paper, experimental data from double shear assemblies manufactures from three different metallic ancient bridges is used to identify, through a statistical analysis, the S-N curves that best fit this constructional detail. Portuguese and French puddled iron bridges were considered. [ABSTRACT FROM AUTHOR]

The fatigue life of materials and structural details can be characterized by distinct fatigue regimes. These regimes may range from quasi-static monotonic loading to very high cyclic fatigue. The Kohout-Věchet (KV) fatigue model describes the damage regimes since the limiting tensile strength to the permanent fatigue limit. In this paper, the fatigue S-N response of the P355NL1 steel, using smooth specimens under uniaxial stress states, is characterized based on the original suggestion by Kohout and Věchet. The experimental results related to the fatigue behavior of the P355NL1 steel were obtained through fatigue tests under stress-control conditions, covering distinct stress ratios. This study validates the importance and applicability of the global S-N models to describe the Wöhler S-N curve, from tensile strength to the fatigue limit, in the fatigue life evaluation of structural details. [ABSTRACT FROM AUTHOR]

The fatigue analysis of materials and structural details using local approaches, such as, stress-life, strain-life or energetic approaches, are important to estimate the fatigue crack initiation at notches. Various engineering structures, such as, bridges, wind towers, among others are subjected to cyclic dynamic loading which may substantially reduce the strength of these structures. Nowadays, the structures tend to be more complex and it is necessary to find computationally efficient solutions to perform their fatigue analysis, for dynamic actions corresponding to long complex loading events (e.g. diversity of trains crossing a bridge). Thus, this paper aims at presenting a generalization of a methodology based on modal superposition technique for local fatigue damage parameters evaluation, which could be applied in fatigue analysis using local approaches. This technique was applied recently in the context of fracture mechanics based fatigue crack propagation. But the modal superposition technique can be extended to compute the history of local notch stresses and deformations at notches. In addition, the technique can be explored for the case of local confined plasticity at notches where global elastic behavior of the component still prevails. Local submodeling can be explored with this technique to avoid the necessity of large computational models. Local models are only required to be run only for the selected modal shapes of the structure, the local time history of fatigue damage variable being reconstructed by modal superposition for each loading event. [ABSTRACT FROM AUTHOR]

The current paper presents a research aiming at characterizing the fatigue behavior of adhesively bonded aluminum joints. In particular, Double Cantilever Beam (DCB) specimens and End Notch Flexure (ENF) specimens built using the 6061-T651 aluminum alloy substrate and the Araldite 2015 epoxy adhesive were used to evaluate the pure mode I and mode II fatigue crack propagation rates. Besides the fatigue crack growth rates the monotonic quasi-static fracture behaviors of the adhesive joints are also characterized for both loading conditions. Numerical finite element models of the joints are also proposed for the evaluation of the compliance calibration curves, avoiding the need of direct fatigue crack growth measurements, which is a very complex task mainly for the ENF tests. Critical fracture energies (G Ic and G IIc ) from experimental tests were in the same order of magnitude of the values published in the literature. Concerning the fatigue crack growth behavior, it was verified a higher fatigue crack growth resistance under pure mode II loading. A good agreement was found between the experimental fatigue crack growth data and the modified Paris law that accounts for fatigue crack propagation regimes I and II. [ABSTRACT FROM AUTHOR]

The structural components from structures such as bridge members are subjected to a long operating period of time. The problem of fatigue cracks is more interesting in existing bridge structures with existing cracks. In case of the structures erected at the turn of the 19 th and 20 th centuries, the cracks are natural elements of the old steel metallic structures. The uniaxial fatigue crack growth description lead us often to significant errors in predicting of a residual lifetime. As a good example, it can be a residual lifetime of the riveted joints in such a type of structures. On the other hand, the 19 th century structures were erected with puddled iron or low carbon mild rimmed steel. The experimental results [1,2] obtained by authors, have shown that the fatigue cracks grow much faster than its modern equivalent. This phenomenon is supported by microstructural degradation processes [2] . In this paper some examples of degenerated microstructures have been presented. In order to fill a lack in experimental data in the literature, the results of a mixed mode (I+II) fatigue crack growth have been presented and discussed within the background of Fracture Mechanics models. All the results have been implemented into the Abaqus environment. [ABSTRACT FROM AUTHOR]

A general procedure for fatigue life prediction of structural details based on Fracture Mechanics approach is presented in this paper, taking advantage of the new normalized fatigue crack growth model proposed by Castillo et al., here denoted as CCS model. An extension to the CCS model is proposed by adopting the cyclic J-integral range instead of the stress intensity factor range as reference parameter. This enables the generalized elastoplastic conditions resulting for the cracked geometry of the structural detail to be considered by means of the cyclic J-integral values obtained from a finite element analysis, for different loading levels and crack lengths. As a practical application, the proposed approach is applied to a notched plate made of P355NL1 steel, using the equivalent initial flaw size ( EIFS ) concept. Fatigue crack growth data for CT specimens from the literature is evaluated to estimate the modified CCS crack growth model parameters. The predicted fatigue propagation lifetime prediction is compared with the results and, finally, the goodness of the predictions is analysed and deviations discussed. [ABSTRACT FROM AUTHOR]

Several fatigue cracks growth laws have been suggested over the past 50 years. Recently, a fatigue crack propagation law was proposed by Castillo-Canteli-Siegele (CCS model) based on the assumption that fatigue crack growth takes the form of a Gumbel cumulative distribution function. Besides many physical aspects, the fatigue crack propagation laws need to account for fatigue crack opening and closure effects. Thus, in this paper a modification of the CCS fatigue crack growth law is proposed to account for the crack opening and closure effects, as well as the stress R -ratio effect, R σ . The fatigue crack opening and closure effects are taken into account using a plasticity-induced crack-closure model. Other fatigue crack closure models can also be used in the proposed modification of the CCS crack growth model through the quantitative parameter U = Δ K eff /Δ K . This modified CCS crack propagation model using the effective stress intensity factor range, Δ K eff , is a new version of an explicit fatigue crack propagation model, supported by mathematical and physical assumptions. In this paper, the proposed model is applied using the fatigue crack growth data and mechanical properties that were collected for the 2219-T851 aluminium alloy. Based on the plasticity-induced crack-closure model, which was first formulated by Newman, and in this paper modified with a boundary correction factor, F w , the crack opening stress intensity factor, K op , and quantitative parameter U are determined. The results showed a good agreement between the proposed modification of the CCS fatigue crack propagation model taking into account the plasticity-induced crack-closure model with the boundary correction factor and experimental results of the fatigue crack propagation data for the 2219-T851 aluminium alloy. [ABSTRACT FROM AUTHOR]

Several methods for fatigue life prediction of structural components have been proposed in literature. The fatigue life prediction based on crack growth analysis has been proposed to assess the residual fatigue life of components, which requires the definition of an initial flaw. Alternatively, Fracture Mechanics crack growth-based fatigue predictions may be used to simulate the whole fatigue life of structural components assuming that there are always initial defects on materials, acting as equivalent initial cracks [1,2]. This latter approach is applied to a notched plate made of P355NL1 steel [3]. Fatigue crack growth data of the material is evaluated using CT specimens, covering several stress R-ratios. Also, S-N fatigue data is available for the double notched plate, for a stress R -ratio equal to 0 [3]. An estimate of the equivalent initial flaw size is proposed, using a back-extrapolation calculation [1,2]. The crack propagation model takes into account the elastic–plastic deformations in the crack-tip area within the calculation, based on the cyclic J-integral method. The performances of predictions are analyzed and deviations discussed. [ABSTRACT FROM AUTHOR]

Probabilistic fatigue models are required to account conveniently for several sources of uncertainty arising in the prediction procedures for structural details, such as the scatter in material behaviour. In this paper, a procedure to derive probabilistic S-N fields for structural details [1] is applied to a notched geometry with elliptic central hole made of puddle iron from the Eiffel bridge, based on the local approaches supported by the probabilistic ɛ a –N or Smith–Watson–Topper (SWT)–N fields [1,2]. This procedure suggests an extension of the fatigue crack propagation model proposed by Noroozi et al. [3,4] to structural details, in order to cover both the fatigue crack initiation and fatigue crack propagation, based on local strain approaches to fatigue. Both fatigue crack initiation and fatigue crack propagation mechanisms are accounted for in the proposed approach. The numerical results are compared with available experimental S-N fatigue data for the notched plate under consideration. [ABSTRACT FROM AUTHOR]

The cumulative concept proposed by Palmgren and Miner [1] maintains that the damage level can be expressed in terms of the number of cycles applied at a given stress range divided by the number of cycles needed to produce failure for the same stress range. Failure occurs when the summation of these damage increments at several stress ranges becomes unity. After this formulation, this rule is repeatedly tested for different materials under multi-step and variable amplitude loading programs [2]. Though its applicability has been often questioned, it has been practically adopted by all design codes related to structural and mechanical fatigue design. In this paper, a fatigue damage assessment of a riveted connection made of puddle iron from the Fão bridge [3–6] using the modified probabilistic interpretation technique (MPIT) is applied [7]. This technique is a generalization of the Van Leeuwen and Siemes [8,9] work by considering a probabilistic S-N field providing a statistical distribution of the Miner number although based on a log-normal distribution. This generalization was proposed by Fernández-Canteli [10], based on the probabilistic model developed by Castillo and Fernández-Canteli [11]. [ABSTRACT FROM AUTHOR]

An approach for probabilistic prediction of fatigue crack initiation lifetime of structural details and mechanical components is presented. The methodology applied is an extension of the generalized local model (GLM) to the fatigue case using the fatigue Weibull regression model proposed by Castillo-Canteli. First, the primary failure cumulative distribution function (PFCDF) of the generalized failure parameter is derived from experimental results for a given reference size, taking into account the non-uniform distribution of the generalized parameter (GP) the specimens are submitted to. The adequacy of the GP is presumed, ensuring uniqueness of the derived PFCDF as a material property, irrespective of the specimen shape and size, and the test chosen to this end. Next, the GP distribution is obtained by a finite element calculation and the PFCDF is applied to each finite element, considering the scale effect, to derive the probability of failure for the whole component. The suitability of the proposed approach is illustrated twice: first, assessing simulated data in a theoretical example, and second, evaluating experimental fatigue life results for riveted joints from the historical Fão Bridge. The PFCDF for the puddle iron from the bridge is calculated from standard tensile specimens, from which the initiation fatigue lifetime of the riveted connections is predicted and compared with the experimental results. In this way, the transferability from standard tests to real components is demonstrated. [ABSTRACT FROM AUTHOR]

• Low-cycle fatigue behaviour of nine advanced high-strength steels is studied. • Cumulative strain energy density is applied as fatigue indicator parameter. • Cumulative strain energy density can successfully assess fatigue life. In this paper, the applicability of the cumulative strain energy density is explored as a fatigue indicator parameter for advanced high-strength steels subjected to strain-controlled conditions. Firstly, the cyclic stress–strain responses of nine steels, selected from three multiphase families, encompassing different elemental compositions and different heat treatment routes, were studied. Then, the predictive capabilities of the proposed model were compared with those of other strain-based and energy-based approaches. It was found that the cumulative strain energy density decreases as the strain amplitude increaes. It was also found that the cumulative strain energy density and the fatigue life can be related via a power function. In addition, the relationship between the cumulative strain energy and the fatigue life was not significantly affected by the elemental composition or the heat treatment route. Finally, the fatigue lives computed through the cumulative strain energy density concept were close to those of the other models but were slightly more conservative. [ABSTRACT FROM AUTHOR]

• A finite element model capable of simulating the cyclic flexural behavior of steel members is developed. • A numerical parametric study considering different influencing parameters is conducted. • Empirical equations are proposed to estimate the plastic rotations of steel beams with deep and shallow cross sections. • The proposed rotations provide reasonable estimates compared with experimental data and are recommended for EC8-3. This paper focuses on the characterization of the rotation capacity of steel deep and shallow members made with European profiles subjected to cyclic flexural loading by considering several influencing parameters such as geometrical imperfections, material ductility, lateral unbraced length, and member length. For this purpose, an advanced finite element model, validated with past experimental data, was developed and an extensive parametric study was conducted. The numerical simulations revealed that shallow and deep members have different buckling behaviours and rotation capacity trends. Based on the numerical results and the experimental data collected from the literature, empirical equations are derived to quantify plastic rotation capacity limits. Compared with existing estimations, the proposed empirical equations show a more reasonable estimate. These rotation limits can be useful as modelling parameters for nonlinear static and response-history analysis and for the identification of the damage states in the context of Part 3 of Eurocode 8. [ABSTRACT FROM AUTHOR]

• A probabilistic model for fatigue life prediction under defects. • Damage mechanism modeling of surface initial crack by using Weibull distribution. • Influence of size effect on fatigue life distribution under constant amplitude loading. • Proposed model predictions agree well with the experimental scatter bands. Engineering components made of ductile cast irons and aluminum alloys, show fatigue lives which are normally dominated by crack initiation from defects raised by manufacturing processes. This study presents a probabilistic model to account for the influence of manufacturing defects on fatigue life, based on size and position of those defects. Specifically, a correction factor considering the influence of defect surface position is developed by modeling the damage mechanism of surface initial cracks with Weibull distribution. Experimental data of three cast irons and aluminum alloys are used for model validation and comparison. Moreover, the statistical size effect influence on fatigue life distribution under constant amplitude loading is explored. Fatigue lives of three materials with different sizes are evaluated respectively, and P–S–N diagrams show that proposed model predictions agree well with the probabilistic scatter bands. [ABSTRACT FROM AUTHOR]

Requirements of industrial piping and pipelines to withstand extreme cyclic loading conditions have been motivating increasing interest on a particular extreme fatigue regime: the ultra-low cycle fatigue (ULCF). This damage domain corresponds to a transition between low-cycle fatigue and monotonic ductile damage. Albeit better understanding of this damage regime is required, very few studies are available covering full-scale testing. This study aims at investigating the performance of X60 and X65 piping steels, subjected to extreme cyclic loading conditions resulting in a reduced number of fatigue cycles ( N i < 100). Experimental tests were carried out on full-scale straight pipes subjected to cyclic pure bending, which were performed under the framework of the ULCF RFCS/EU project. Additionally to the large-scale tests, plain material was also tested under monotonic and ULCF conditions, supported by small-scale smooth and notched specimens. Large-scale tests were simulated by means of elastoplastic finite element models in order to reproduce the local plastic instability (buckling) where fatigue cracking was verified. Classical Coffin-Mason relation and a modified Xue relation were calibrated using small-scale testing data, the latter relation accounting for triaxiality and Lode angle stress tensor dependencies. The referred models were applied in the damage prediction of the full-scale pipes and results compared with code based procedures such as the ones proposed in the ASME VIII, Div.2. In general, the incorporation of the stress state parameters in the computation of ULCF damage produced improved predictions with respect to the pure strain range based models as the Coffin-Manson or ASME VIII, Div.2 code. [ABSTRACT FROM AUTHOR]

This paper proposes an experimental study aiming to evaluate stress intensity factors (SIFs) for fatigue cracks propagating under pure mode I and mixed-mode I + II for a S235 structural steel. Compact tension (CT) specimens with a side hole were manufactured in order to generate a stress field, ahead of the crack tip, resulting in mixed-mode fatigue crack propagation. Specimens with distinct side hole locations were submitted to fatigue tests under stress controlled conditions for a stress ratio, R = 0.01. Fatigue tests were coupled with digital image correlation (DIC) to assess mode I and mode II SIF from full-field displacement measurements. Besides, DIC data was used to directly estimate the crack tip location during the test. A validation study was carried out by comparing this approach with regard to conventional optical measurements. Finite element simulations were also performed to validate the crack branching models and direct identification of SIF values. The proposed DIC approach was demonstrated to be an efficient tool for the automation of crack path detection and stress intensity factors computation. Mixed-mode fatigue crack data correlated well with pure mode I fatigue crack propagation data using the Paris law and an effective stress intensity factor as proposed by Tanaka. [ABSTRACT FROM AUTHOR]

• Strain-time history signals of coil spring were measured through road tests. • Fatigue life data was conducted based on 90%, 95% and 100% retained damage. • Durability analysis was performed based on Coffin-Manson, Morrow and SWT life models. • Reliability assessment using the probability Gumbel distribution model. • Hazard rate was obtained for risk assessments based on the fatigue life predictions. This study presents a fatigue reliability assessment of a vehicle coil spring based on random road load conditions for fatigue life characterisation. Fatigue life data characterisation was carried out to accelerate the durability analysis by retaining the higher amplitude cycles in the original strain signals and thus indicate the fatigue damage. To collect experimental data, road testing was conducted using various road profiles, which contributed significantly to the fatigue failure performance of the vehicle coil spring. Fatigue reliability analysis was performed to assess the failure behaviour of the coil spring utilising the probabilistic Gumbel distribution model to forecast the probability distribution of the fatigue life data. Furthermore, the highest and lowest mean-cycles-to-failure (McTF) of 5.44 × 107 and 2.46 × 105 blocks were estimated for the Coffin-Manson and Smith-Watson-Topper models from the highway and rural road profiles. The findings demonstrate that the lowest hazard rate corresponded to the highest McTF, making this an acceptable model to be implemented in reliability assessments of road profiles. Hence, the fatigue reliability assessment provided a hazard rate based on the fatigue life predictions for risk assessments when characterising the fatigue life data. [ABSTRACT FROM AUTHOR]

• Mechanical and magnetic properties characterization of the century-old structure's current state. • Identification of the unknown manufacturing process from an ancient Bridge's component. • Ferritic microstructure of heterogeneous size grains containing numerous coarse non-metallic inclusions that lead to low toughness values at room temperature. • Barkhausen Noise results reveal the distinction of an easy magnetization axis aligned with the forming process direction. • Potential of application of the non-destructive technique for characterization of structural components in loco. In the mid-19th century, with the advent of the industrial revolution, the puddled iron was the main metallic material produced on a large scale to meet the existing demand in the manufacture of large riveted structural components, such as railway bridges, thus representing a technological advance in this period. Due to the incipient metallurgical knowledge of the time and the fact that corrective maintenance may have been carried out during the lifetime of the components, such as localized heating and/or welding that might not be suitable for this type of material, the study of this class of material becomes important since many of the structures made with it are still in operation. Furthermore, its heterogeneous characteristics, inherent to its manufacturing process, make it difficult to characterize it and there is little information about the status of the microstructure and mechanical properties of these structures, making the application of non-destructive characterization techniques appealing in this scenario. Thus, the present work is based on the characterization of the effects of the microstructure on the mechanical and magnetic properties of samples of puddled iron taken from a component in service for approximately 150 years and compared when subjected to a normalizing heat treatment. The results denote a ferritic microstructure of heterogeneous grain size containing numerous coarse nonmetallic inclusions that result in low tenacity values at room temperature both in specimens obtained from samples as received and normalized, although in the thermally treated condition a higher value of ferritic grain size, on average, was obtained which promoted a slight decrease in the hardness values. These phenomena were characterized by magnetic measurements of magnetic Barkhausen Noise (MBN) allowing the distinction of an easy magnetization axis aligned with the conformation direction of the evaluated components. Therefore, a great potential is exhibited in the non-destructive characterization of this class of material, although several standards are required to obtain a calibration curve with the evaluated properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dimple core configuration provide better structural integrity for sandwich panel. • Moderate size of hemispherical dimple provides an optimum bonding strength. • Large dimple size is vulnerable to experience an early delamination between the layer. • Analysis onto dimple hotspot region provide sufficient data for damage plot modelling. • Fatigue assessment via damage analysis provide essential data for dissimilar panel. This paper aims to investigate the effects on metal sandwich panels with different dimple core designs using four-point bending simulation under constant and variable amplitude loading. A core design with cavity and porosity in the body structure was found to reduce the panel structural integrity. This would lead to unstable bonding between the panels and initiate an early delamination process. Sandwich panels consisting of AR500 as the outer layer and magnesium alloy AZ31B as the core material were simulated using dimples of different diameters and depths; 5.0 / 2.5 mm, 6.0 / 3.0 mm, 7.0 / 3.5 mm and 8.0 / 4.0 mm, at a range of 50 % to 90 % of maximum strength, based on the lowest material strength for cyclic loading. The results indicate that the highest fatigue damage of 85 % occurred at the effective region of the dimple area, where force was applied to the panel. A hemispherical dimple core 6.0 mm in diameter and 3.0 mm in depth produced a reduction of failure at the effective zone of more than 85 % and the regression coefficient was over 0.89. This illustrates that a large dimple size was vulnerable to early delamination failure at the dimple region. [ABSTRACT FROM AUTHOR]

• Fatigue models are classified in three classes according with their possible design application. • A new generalized parameter (GRV) is proposed to replace the stress range as driving force. • The probabilistic Castillo-Canteli fatigue model is revisited and improved to include the LCF regime. • The new probabilistic GRV -N field is applied to evaluate experimental results and discussed. In this work, three classes of fatigue models are reviewed according to the fatigue regimes commonly considered in the current components design. Particular attention is devoted to the so-called Class III fatigue models, covering the three fatigue regimes, namely, LCF, HCF and VHCF. The applicability and limitations of the proposed analytical sigmoidal solutions are discussed from the viewpoint of practical design. The compatible Weibull S-N model by Castillo and Canteli is revisited and improved by considering a new reference parameter GP = E· σ M · (dε/dσ)| M as the driving force alternative to the conventional stress range. In this way, the requirement, σ M ≤ σ u , according to the real experimental conditions, is fulfilled and the parametric limit number of cycles, N 0 , recovers its meaning. The probabilistic definition of the model on the HCF and VHCF regimes is maintained and extended to the LCF regime. The strain gradients may be calculated from the monotonic or cyclic stress–strain curve of the material although a direct derivation from the hysteresis loop is recommended. Some Class III fatigue models from the literature and another one improved by the authors are applied to the assessment of one experimental campaign under different stress ratios conditions and the results compared accordingly. Finally, the new probabilistic GP-N field is evaluated. The results confirm the practical confluence of the stress- and the strain-based approaches into a single and advantageous unified methodology. [ABSTRACT FROM AUTHOR]

• A purpose-built fatigue testing setup for full-scale thin-walled profiles was used. • A master S-N curve based on peak elastic maximum principal stresses was generated. • Manufacturing and structural simulations were coupled in elastoplastic FEA. • The TCD was coupled with the modified Morrow model using the PM and LM methods. • Fatigue life predictions including manufacturing residual stresses were suitable. This paper presents experimental research aimed at addressing the fatigue behaviour of thin-walled cold roll-formed steel sections, very commonly used in rack structures. This research is performed under the FASTCOLD-RFCS project, which aims to fill an existing gap on fatigue design rules. A new design S-N curve is derived from an innovative testing methodology, which supports the current revision of the Eurocode 3 (EN 1993-1-9). Additionally, a local fatigue approach, encompassing residual stresses from numerically simulating the manufacturing process and structural elastoplastic stress analysis supported by the Theory of Critical Distances, returned consistent fatigue life predictions for the tested profiles. [ABSTRACT FROM AUTHOR]

• Two PUR materials were tested regarding different hardness level. • Hardness strongly influences mechanical properties. • 90ShA material demonstrated significantly higher fatigue resistance. • 90ShA material presented higher abrasive properties. The paper presents the results of experimental research on polyurethane materials used in car suspension systems. Taking into account the frequency of maintenance and the number of replacement metal-rubber bushings on the market, the authors considered it reasonable to carry out their tests of materials with different hardnesses of 80 and 90 ShA used in conventional applications as well as in sports vehicle suspensions. Two types of PUR material were produced for this purpose. The materials were subjected to mechanical tests; tearing, tensile, compression, abrasive wear. Finally, a model of the polyurethane bushing was created and subjected to fatigue tests. As a result, several significant findings were made regarding the influence of hardness on selected mechanical properties. As evidenced by the results of the investigations, even a small increase in material hardness significantly affects changes of fatigue parameters and material fracture-related parameters in general. The pilot results can serve as reference values in the design of anti-failure bushing systems. [ABSTRACT FROM AUTHOR]

• ULCF/LCF is characterized for X52 pipeline steel by smooth and notched specimens. • The theory of critical distances is applied with point, line and area methods. • Point method revealed to be the most appropriate for correlating ULCF and LCF data. • Proposed TCD/PM successfully predicted notch bending ULCF test data. The cyclic failure observed in structural components such as pipelines subjected to extreme loading conditions highlights some limitations concerning the application of existing fatigue damage models. The evaluation and prediction of this type of failure in these steel components under large-scale plastic yielding associated with high levels of stress triaxiality are not sufficiently known nor explored. This fatigue domain is conventionally called ultra-low-cycle fatigue (ULCF) and damage features are representative of both low-cycle fatigue (LCF) and monotonic ductile fracture. Thus, in order to understand the ULCF damage mechanisms both monotonic and LCF tests are required to get representative bounding damage information to model the material damage behaviour under such extreme loading conditions. This paper aims at exploring the Theory of Critical Distances (TCD) in the LCF and ULCF fatigue regimes, including the application of the point, line and area methods. The application of the TCD theories has not been explored so far in the ULCF fatigue regimes, despite its promising results in the LCF and high-cycle fatigue. An experimental program was carried out on several specimens' geometries made of X52 piping steel. In detail, smooth plane specimens and notched plane specimens were cyclic loaded under tension/compression loading in order to obtain fatigue lives within the range of 101–104 cycles. In addition, cyclic bending tests on notched plane specimens were also incorporated in this study. Finite element simulations of all small-scale tests were conducted allowing to derive elastoplastic stress/strain fields along the potential crack paths. The numerical data were subjected to a post-processing in order to find characteristic lengths that can be treated as a fatigue property according to the TCD. A unified strain-life relation is proposed for the X52 piping steel together with a characteristic material length, consisting of a practical relation for pipeline strain-based design under extreme cyclic loading conditions. [ABSTRACT FROM AUTHOR]