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Although several old riveted bridges served more than 100–150 years in the world, some of them are still in the application, generally limited by the economic budget or cultural relic protection reason. Hence, the status of those bridges needed to be evaluated to support the bridge management and rehabilitation, especially with the increasing traffic flow along with their service life. Nowadays, fatigue detail class 71 in the EN 1993-1-9 is generally recommended to evaluate the fatigue behaviour of the riveted joints. But the predicted fatigue behaviour of riveted connection using the recommended S-N curves is excessive conservative because the differences of connection geometries and materials are not fully considered using the global nominal stress methods. Therefore, in this paper, a two-phase fatigue performance approach based on local strain and Paris law, respectively, fatigue crack initiation and propagation phases, combined with numerical simulation, is an effective surrogate method to predict the fatigue performance of riveted connections, considering the material and geometry effects. A good agreement is observed when compared to numerical simulation with experimental observations.

Together with the development of numerical tools for stress-strain analysis, approaches to deal with fracture mechanics problems have been the object of continuous improvement. For linear-elastic fracture mechanics problems, the determination of Stress Intensity Factors (SIF) is available as a post-processing possibility in most commercial finite element software packages such as Ansys and Abaqus, allowing the users to perform straightforward assessments of cracked mechanical parts or structures. However, available techniques for SIF determination in post-processing of these commercial solutions are almost limited to the so-called displacement extrapolation and J-integral techniques. In the present work, the implementation of the J-integral technique is revised considering a new finite element software, labeled as Omicron. Furthermore, a more recent technique, the modified Virtual Crack Closure Technique (mVCCT) is also implemented and evaluated. For results assessment, finite element models were built in Omicron and SIFs were determined considering the J-integral and mVCCT approaches. From this study, it is concluded that the mVCCT implementation is simpler than the J-integral and it allows to determine accurately SIFs. Nevertheless, this technique is not straightly available in the current versions of the commercial packages for finite element modeling, which require separate post-processing for SIF determination.

Modeling of the notch and size effects on fatigue behavior of materials is vital for ensuring structural integrity and reliability of engineering components. This study presents a methodology considering both effects of notch and size to analyze the fatigue life distribution of specimens with different geometries using the highly stressed volume approach. Specifically, a dynamic model coefficient considering the influence of different maximum local stresses is developed by modeling the size effect of highly stressed volumes with Weibull distribution. Experimental data of three aluminum and titanium alloys are utilized for model validation and comparison. Fatigue lives of three materials with different geometries are evaluated respectively, and predicted P-S-N curves indicate that proposed model predictions agree well with the probabilistic scatter band of experimental results.

Fatigue failures are a concern for old riveted steel bridges since most of them were not originally designed taking into account fatigue. The usual fatigue assessment approach for riveted joints consists of using the fatigue class 71 S-N curve proposed in Eurocode 3, part 1–9. However, this approach may lead to excessive conservative predictions since it is applied indistinctly for different riveted connection geometries and materials. Riveted joints fatigue classification according to the proposal of Taras and Greiner produce more consistent description of the experimental data rather than the Class 71 S-N curve as proposed in the EC3. Local approaches are an alternative methodology to perform fatigue characterization of any type of joints, made of any material, providing that material fatigue properties are available as well as accurate numerical models of the joints. This paper presents an experimental campaign and a numerical analysis concerning down-scale riveted specimens. The fatigue behaviour of these riveted joints was also modelled using standard and extended finite element methods. The different models produced diverse predictions, depending on the failure modes considered.

This paper presents a fatigue analysis of a type of fillet welded joint representative of one main joint of the steel box girder of the Alcacer do Sal railway bridge. From previous studies, it was found that the welded joint between the box girder diagonal and the central hanger gusset is one of the most stressed details of the bridge. This welded joint was not fully manufactured according to current construction procedures, as regards the fillet weld end configuration. In order to assess the fatigue behaviour of such welded joint, the present study combines an experimental campaign and numerical analysis. A total of four welded joint series were produced in order to allow the comparison of the fatigue performance of similar type of welded joint of the Alcacer do Sal bridge with welded joints produced according to existing recommendations, such as EC3. Since scale-down specimens were considered, two different thicknesses were included in this study for each joint configuration, to allow the verification of any thickness effect. Concerning the numerical analyses, two main numerical tools were used: the standard Finite Element Method (FEM) with ANSYS and the eXtended Finite Element Method (XFEM) with ABAQUS. Fatigue life predictions were performed including both fatigue crack initiation and fatigue crack propagation phases. The number of cycles to initiate a fatigue crack was computed using local notch strain-life approaches, and the number of cycles for fatigue crack propagation was computed by integrating the Paris fatigue crack growth law with stress intensity factors computed with ANSYS (virtual crack closure technique) and ABAQUS (contour integral method, 3D XFEM model). Experimental tests demonstrated little influence of fillet weld end geometry on fatigue behaviour of welded joints and plate thickness effects were also reduced as also confirmed by the similar fatigue crack propagation rates. Both numerical simulations provided very accurate predictions of the experimental S-N curves, however the XFEM modelling opens new possibilities for mix-mode fatigue crack propagation simulations.

In this work, the yielding response of high-density polyethylene (HDPE) under different stress states and strain rates was experimentally examined and the ability of classical yield criteria to capture their deformation response assessed. A series of biaxial loading tests (pure shear, combined shear and tension/compression, pure tension/compression) using a designed Arcan testing apparatus were performed. In order to investigate a wider range of stress states, flat and cylindrical notched specimens with different curvature radii were also tested. The predictive ability of the Von Mises and the Drucker-Prager yield criteria are compared against the acquired experimental data. The Drucker-Prager yield model allowed an improved description of the available experimental results, demonstrating the need to account for pressure dependency in the yield model's formulation for semi crystalline polymers. Some differences observed may be attributed to the third invariant stress tensor effects. The evolution of stress triaxiality and Lode angle parameters with equivalent plastic strain were extracted from simulations with Drucker-Prager yield criterion. The results show sensitive stress state dependency of the plastic yielding behaviour, which can be attributed to different combinations of stress triaxiality and Lode angle parameters. Also numerical simulations show that there is variation of the stress triaxiality and equivalent plastic strain along the cross section and the location of the maximum plastic strain and maximum stress triaxiality in the specimens are located at the centre of the specimens.

In this paper, the failure probability of corroded pipelines made by X60 steel grade is evaluated. For this complex real engineering failure problem, the burst corroded performance function is developed using an M5Tree model based on calibration with real burst test database. In addition statistical analysis of ILI-report data is conducted for best modeling of corrosion defects geometries (i.e. defects length and depth) based on Anderson-Darling statistic where different PDFs (i.e. Normal, Lognormal, Frechet, Gumbel, Weibull) were tested. Moreover, the effect of defects geometries on the failure probability of the case-studies were investigated for various operating regimes. Then the influence of distributions on the reliability analysis were also illustrated. Results indicated that increases in defects depth are strongly reduced the safety levels of this problem, where miss-selection of defects distributions could lead to conservatives results.

Engineering structures, such as bridges, pressure vessels, machines, etc., are subject to variable load cycles during their lifetime that can cause fatigue damage. Fatigue design of steel structures is based on double S-N curves and the estimation of fatigue damage caused by load cycles. This estimation is calculated by cycle counting methods combined with the Palmgren-Miner rule. The presented software, Fatigue Damage Tool (FDT), is based on the design assumptions of the Eurocode 3 EN1993-1-9 standard. The cycle counting method implemented in FDT is the rainflow counting algorithm according to the ASTM E1049-85 standard, and it uses the Palmgren-Miner rule to calculate de fatigue damage for a critical detail. In this paper, the software is applied to estimate the fatigue damage accumulation for a critical detail at the mid-span of the Varzeas railway bridge. Additionally, FDT can also be applied to several other types of engineering structures.

The First International Symposium on Risk Analysis and Safety of Complex Structures and Components (IRAS 2019) was organised in-teamed with the ESIS/TC12 Technical Committee on Risk Analysis and Safety of Large Structures and Components, which took place between 1-2 July 2019 at the Faculty of Engineering of the University of Porto (FEUP), in the City of Porto, located at seaside in the northwest region of Portugal. The guest editors of the IRAS 2019 deeply acknowledges all members of the International Scientific Committee, Thematic Sessions Organizers, Keynote Speakers and authors that contributed to the success of this event, that gathered more than 126 participants presenting more than 168 papers and posters. Sponsors are also fully acknowledged for their important contributions. The ESIS/TC12 2019 winners of the Robert Moskovic Award, Award of Merit TC12, and ESIS/TC12 Young Scientist Award were announced during the conference. Additionally, the guest editors (conference chairs) sincerely thank the tireless efforts of the Organizing Committee members as well as students and other FEUP and Construction Institute staff involved in the organization. Finally, the guest editors are pleased to inform that the second edition of the IRAS event will be organised by Prof. Aleksandar Sedmak (University of Belgrade, Serbia) which will take place in Belgrade in Serbia in the year 2021.

In the context of fatigue evaluation of riveted railway bridges, cross-girder to main beam connections are frequently critical details. Secondary effects, such as out-of-plane bending and dynamic amplifications due to the proximity to loading paths which in the case of old bridges were not taken into account in the original design, may lead to severe increase of fatigue damage. The fatigue assessment of old riveted railway bridges has been addressed in the last years by developing local models of critical riveted joints that are linked to global models. This local-global modelling approach aims at evaluating local secondary stresses. Former fatigue probabilistic analyses of riveted joints have been focused on resistance variability rather than on loading/stresses (actions) variability. In this paper a probabilistic procedure to include the variability of loading in the fatigue analysis of complex riveted joints of railway bridges is proposed assuming loading as a random variable. Local finite element models were developed and later coupled with the global model in order to obtain the real stresses associated to real trains crossing the bridge. To reduce computational time, the results obtained from these local models were inputted in a Linear Fracture Mechanics model, supported by Paris fatigue crack propagation law. Monte Carlo simulation technique was applied to calculate the fatigue reliability of an old riveted railway bridge, considering traffic records from previous studies on the bridge.

Aero engine components like compressor discs normally operate under harsh conditions like complex multiaxial stress states. Notch effect is often critical for structural integrity assessment in virtue of complex structure and discontinuities. According to the notch effect under cyclic loadings, a computational framework for multiaxial fatigue analysis of compressor discs is established by coupling finite element (FE) simulation of stress gradient with Fatemi-Socie (FS) criterion. Specifically, a notch support extension method accounting for stress gradient effect is elaborated through elasto-plastic FE analysis, which can be determined for fatigue life prediction of arbitrary shaped components. Experimental fatigue data for smooth and notched specimens of TC4 and GH4169 alloys demonstrated the appropriateness of the proposed computational approach. The applicability and performance of the prediction model to a compressor blade-disc attachment subjected to field spectra is presented. Results show that testing effect can be significantly reduced by using this framework with acceptable prediction accuracy.

This paper presents the results of an experimental investigation about fatigue crack paths and fatigue crack growth on S355J0 steel subjected to I + II and I + III mixed mode conditions both under load ratios R = 0 and 0.1 and different mode mixities. In particular, compact specimens with distinct notch inclinations were exposed to mixed mode I + II (tension and shear) whereas prismatic specimens provided with an external one-sided sharp notch were subjected to mixed mode I + III under distinct bending to torsion ratios. The influences of distinct load mixities on fatigue crack growth rates and fatigue crack growth directions are analysed and discussed in relation to existing theories. Also the influence of each loading mode for the resulting mixed mode fatigue crack propagation is also discussed.

The fatigue damage assessment of large bridges is highly conditioned by the required computational high demands. Generally, in order to overcome the multi-scale problem, global and local models are needed to properly account for both global structural behaviour and the local nature of the fatigue damage. The analysis of such structural problems using direct time-integration algorithms is impracticable in most of the cases, which leads to the necessity of developing alternative methodologies in order to increase the computational efficiency and the accuracy of fatigue cracking assessments. In this respect, effective computational algorithms based on the modal superposition technique have been proposed and implemented in previous works. Overall, such workflow considers the interaction between the global and local models combined with the application of the modal stress intensity factor concept. Aiming at performing an efficient and accurate assessment of the fatigue damage, firstly, combining the Fracture Mechanics principles and crack propagation laws, the crack propagation phase in a complex bridge detail is analysed. In this regard, the present paper aims at proposing relevant improvements to the above-mentioned methodology, namely: i) the refinement of the implemented submodelling techniques in order to increase the accuracy of stress and strain fields computation and allow to account for smaller initial crack lengths; ii) the analysis and limitation of the considered number of vibration modes to the relevant ones for the local dynamic response; and iii) the implementation of a parallel computing approach for the calculation of the modal stress intensity factors related to the vibration modes defined in ii). The fatigue assessment procedures were applied to an assumed cracked welded detail of a recent railway composite bowstring bridge located in Portugal. Also, since the assumption of a pre-existing crack may lead to very conservative predictions, the modal superposition technique is further extended to evaluate the fatigue crack initiation phase, demonstrating the safety of the analysed case study in the absence of existing defects.

Steel and composite steel-concrete bridges are subjected to random traffic loads along their life cycle which generate significant dynamic impacts. The road-roughness of asphalt pavements is one of the most important aspects that contributes to the significant increase of the stress amplitudes and hence to serious load-induced fatigue concerns. In this context, welded joints are well known as the weakest points in bridges, since they are prone to stress concentrations leading to initiation of fatigue cracks being in current design codes evaluated using primarily the nominal stress method (NSM). However, a more accurate stress definition, which considers the complexity of the stress field at the welds, becomes necessary mainly in old roadway steel bridges that are often subjected to out-of-plane stresses. In this paper, the hot-spot stress method (HSM) is used to evaluate the fatigue life of a welded joint subjected to distortion induced-fatigue, considering the vehicle speeds and a progressive deterioration model for the road pavement. The welded joint was modelled by solid elements and was integrated with a 3D dynamic bridge model using the sub modelling technique. Besides the importance of considering the bridge-vehicle dynamic interactions with the pavement road-roughness, the dynamic amplification effects on local stresses and the relatively high scatter found in the fatigue lives considering global and local approaches show that a detailed local stress definition is fundamental to evaluate the fatigue performance of existing roadway bridges. The effects of the annual traffic increase rate on the fatigue life are also discussed.

This work presents global and local fatigue approaches for snug-tight (common in rack structures) and preloaded bolted joints using thin hot-dip galvanized steel plates, where the zinc coating results in a low friction coefficient. Moreover, S-N data supporting the current revision of Eurocode 3 (EN 1993-1-9) is generated by considering remote and net stresses computed directly or by numerical analysis. Additionally, a master S-N curve based on elastic peak stresses is obtained encompassing the effects of the various tested conditions. Finally, a local fatigue life prediction based on the modified Morrow model combined with elastoplastic numerical analysis returns satisfactory results.

Local fatigue approaches, such as, the stress-life, strain-life or energetic approaches defines a framework to estimate the fatigue crack initiation from notches of structural details. Various engineering structures, such as, bridges, wind towers, among others, are subjected to cyclic dynamic loadings which may substantially reduce the strength of these structures. Nowadays, the structural systems tend to be more complex being necessary to find computationally efficient solutions to perform their fatigue analysis, accounting for dynamic actions corresponding to long complex loading events (e.g. diversity of trains crossing a bridge), mainly if local approaches are envisaged. Thus, this paper aims at presenting and validating a generalization of a methodology based on modal superposition technique, for fatigue damage parameters evaluation, which can be applied in fatigue analysis using local approaches. This technique was applied recently in the context of fatigue crack propagation based on fracture mechanics, although it can be extended to compute the history of local notch stresses and strains at notches. A very important conclusion is that the technique can be explored for the case of local confined plasticity at notches whenever the global elastic behaviour of the component prevails. Local submodelling can be explored with this technique to avoid the necessity of large computational models. Local models are only needed to be run under linear elastic conditions for the selected modal shapes of the structure, being the local time history of fatigue damage variable computed by modal superposition for each loading event. That time history may be further post-processed for elastoplastic conditions using Neuber or Glinka’s analyses. Comparisons with direct integration elastoplastic dynamic analysis confirmed the feasibility of the proposed approach.

Surface damages caused by the impact of flying objects are important factors responsible for fatigue performance degradation of high-speed railway axles, both qualitative and quantitative assessment of these damages are necessary for the maintenance of these axles. In this paper, cubical projectiles were used to reproduce actual damages on S38C axle specimens by a compressed-gas gun at varying velocities. Morphologies of simulated impact damages were characterized, and fatigue strengths of specimens under different impact damages were determined by the step-loading method. Results show that fatigue strength of impacted specimens reduces with the increase of damage depth; besides, other factors, including damage orientation, damage shape, and microstructural damage also exert their contributions. Finally, evaluation on fatigue strength reduction has been performed based on the damage tolerance philosophy.

Foreign object damage (FOD) introduced in service, indentations, and nicks encountered during maintenance are typical defects leading to pre-scrap of high-speed railway axles. A comprehensive assessment of the influence of these defects on the structural integrity of axles is critical for ensuring their operation safety with low maintenance costs. Three types of defects were produced artificially on specimens extracted from EA4T axles, electronic discharge machine (EDM) crater, indentation via compressing balls, and FOD by tungsten steel balls and cubes. Rotating bending fatigue tests were performed for fatigue strength evaluation of smooth and defected specimens. Morphologies of defects and fracture surfaces were studied. EDM defect surface is rough and the secondary notches are the fatigue crack initiation sites, while fatigue crack of indented and impacted specimens initiates from the sharp point of defect rims. Fatigue strength of specimens with indentation or tungsten ball impact damage is superior to that of EDM specimens and cubical projectile impacted specimens under the same depth. A large dispersion was found in the shape of impact damages by cubic projectiles and scattered fatigue strength as a consequence. Except for the defect depth, other parameters including produce modes and shape of the defect, should be considered to give a reliable evaluation on the fatigue strength of defected specimens.

This study investigates the influence of cutting parameters on longitudinal turning of high Silicon cast aluminium alloy AlSi9Cu3 using PCD tools with and without chip breaker geometry. In order to build the 3D numerical model, the experimental and predicted cutting forces were used for inverse calibration of the Johnson–Cook material model which was implemented in DEFORM TM finite element software. A sensitivity analysis has been performed in order to obtain an acceptable prediction of the machining parameters such as chip geometry and cutting forces as well as to understand the influence of friction and mesh size effects in the predicted results. Results have shown a satisfactory correlation between experimental turning data and numerical estimates based on assumptions that have been taken for the material behaviour.

There are many old riveted bridges constructed 100–150 years ago around the world. In Portugal, it is counted that about 100 riveted bridges, which were built based on traffic intensity and vehicle weight, are no longer suitable nowadays. However, mainly due to economic reasons, those riveted bridges are still in service. Thus, the remaining performance is suggested to be accurately evaluated to determine possible repairs. However, the fatigue performance investigation of such riveted joints in old bridges is relatively limited. Then, fatigue assessment concerning the riveted joint is not contemplated in the current standard as EC3. This paper presents an experimental campaign of riveted joints. Three types of riveted connections are conducted to obtain the fatigue behaviour. Then experimental results, and its design curves obtained based on the ASTM E739 standard, are compared to S-N design curves, suggested for riveted connection. The fatigue strength predicted from class 71 in EC3 is lower than it obtained from test results.

Non-conventional machining processes, such as the Electrical Discharging Machining (EDM) offers the possibility to machine very hard materials with great potential to generate complex geometries. However, the EDM process involves significant microstructural changes in the as machined surfaces, which are known to have a significant impact on fatigue behaviour of mechanical parts. This study aims at investigating the fatigue behaviour of the AISI D2 tool steel subjected to EDM machining. Both smooth and notched specimens are tested aiming at assessing the fatigue notch sensitivity of this material and results compared with conventional grinding techniques in terms of fatigue resistance and residuals stresses. The AISI D2 steel shows a microstructure composed of large dendritic primary carbides detrimental to the fatigue resistance. Also, the EDM process is responsible for the generation of detrimental tensile residual stresses that justifies the lower fatigue resistance when compared with the ground material that exhibits beneficial compressive residual stresses. The fatigue test data of the notched specimens machined by EDM process show a high fatigue notch sensitivity of the AISI D2 tool steel. The heterogeneous structure of the material, showing large undissolved carbides, leads to a notch fatigue reduction factor that is higher to the apparent theoretical elastic stress concentration factor.

This paper presents a study aiming at characterizing the fatigue crack growth behaviour of the 6082-T6 aluminium alloy using standard CT specimens. The fatigue crack growth threshold is also characterized according to the ASTM E 647 standard. Besides the standard CT specimens with sharp notches, specimens with initial circular notches were also fatigue tested. The threshold stress intensity factor ranges, ΔK th , are compared for the distinct notches under study. The fatigue crack propagation rate in the regime II are obtained using the Paris law. A comparison is made between the CT specimens geometries with distinct notches under consideration. The ΔK th values for the geometry of standard CT specimens present lower values when compared with the geometry of the CT specimens with blunted notches.

The objective of this paper is to propose an accurate and computationally efficient method for the fatigue assessment of bridge details, using Fracture Mechanics and crack propagation laws. The proposed workflow benefits from the combination of finite element submodeling techniques and modal superposition method with the new concept of modal stress intensity factors. The new methodology was applied to the fatigue analysis of a complex bridge under real traffic conditions. The simulation of fatigue crack propagation in a critical detail of the structure was achieved with minimal computer resources and within a short time frame.

Cumulative fatigue damage is a continuous and irreversible process that refers to the degradation of the component mechanical properties under cyclic loadings. In this work, using the concept of isodamage curves, a new non-linear fatigue damage accumulation model is proposed to account for fatigue damage evolution under multiple load levels. In particular, a computational process is established in which the isodamage curves converge into one point due to the exhaustion of static toughness. Experimental data of five materials are used for model validation and comparison. Results indicate that the proposed model provides better life predictions than the other four models.

The mean stress effect plays an important role in the fatigue life predictions, its influence significantly changes high-cycle fatigue behaviour, directly decreasing the fatigue limit with the increase of the mean stress. Fatigue design of structural details and mechanical components must account for mean stress effects in order to guarantee the performance and safety criteria during their foreseen operational life. The purpose of this research work is to develop a new methodology to generate a constant life diagram (CLD) for metallic materials, based on assumptions of Haigh diagram and artificial neural networks, using the probabilistic Stussi fatigue S-N fields. This proposed methodology can estimate the safety region for high-cycle fatigue regimes as a function of the mean stress and stress amplitude in regions where tensile loading is predominance, using fatigue S-N curves only for two stress R-ratios. In this approach, the experimental fatigue data of the P355NL1 pressure vessel steel available for three stress R-ratios (−1, −0.5, 0), are used. A multilayer perceptron network has been trained with the back-propagation algorithm; its architecture consists of two input neurons ( σ m , N ) and one output neuron ( σ a ). The suggested CLD based on trained artificial neural network algorithm and probabilistic Stussi fatigue fields applied to dog-bone shaped specimens made of P355NL1 steel showed a good agreement with the high-cycle fatigue experimental data, only using the stress R-ratios equal to 0 and −0.5. Furthermore, a procedure for estimating the fatigue resistance reduction factor, K f , for the fatigue life prediction of structural details (stress R-ratios equal to 0, 0.15 and 0.3) in extrapolation regions is suggested and used to generate the K f results for stress R-ratios from −1 to 0.3, based on machine learning artificial neural network algorithm.

FBG sensors are often packaged within composites before they are pasted on the blade surface, and many studies have shown that the materials, fatigue properties, geometric parameters, etc. of intermediate layer have influences on the measuring accuracy of the FBG sensors. Thus, this paper established an reliability calculation model based on strain transfer efficiency for the measuring accuracy of FBG sensors packaged by composites, analyzed the influences of material properties and geometric parameters of the adhesive layer on the performance of FBG sensors based on finite element analysis (FEA) method, and then compared the differences of strain transfer efficiency and reliability of the FBG sensors under different load conditions. The results show that the bond length and the bond thickness of the adhesive layer have greater influences on the performance of the FBG sensors compared with other parameters, both the strain transfer efficiency and the reliability of the FBG sensors will reduce over time under suddenly applied load and increase with increasing frequency of the alternating load.

Bridge cables are subjected to small relative sliding and high contact stresses among wires under fluctuating loads and repeated bending, eventually leading to fretting-fatigue failure. This paper presents a series of fretting fatigue tests with different fretting and fatigue parameters to investigate the tribological properties, fretting fatigue characteristics and fracture failure mechanism. Results show that the fretting-fatigue failure evolved from surface micro cracks at the trailing edges generated from a mixed slip regime. Larger fretting amplitude induced larger tangential force and coefficient of friction, and decreased life. Fretting scar depth increased as fretting-fatigue proceeded while the growth rate was declining.

The mechanical responses of high‐density polyethylene (HDPE), polypropylene (PP) and polyamide 6 (PA 6) were experimentally investigated for a wide range of stress states and strain rates. This was accomplished by testing numerous specimens with different geometries. The uniaxial compression of cylindrical unnotched specimens and the uniaxial tensile behaviour of dumbbell specimens at different strain rates, was determined. A series of biaxial loading tests (combined shear and tension/compression, pure shear, pure tension/compression) using a designed Arcan testing apparatus were also performed. Flat and cylindrical notched specimens with different curvature radii were additionally tested in order to explore a wider range of stress states. The Drucker‐Prager yield criterion was calibrated with a set of experimental data, for which analytical formulae for stresses are available, and then applied to predict the deformation behaviour under different stress states, prior to strain localization. The results of the numerical simulations show that the Drucker‐Prager model can capture the initial elastic range and the post‐elastic response very satisfactorily. For triaxial and biaxial stress states there is a good agreement, however some load‐displacement responses are only satisfactorily described. Deviations observed in the predicted and experimental results are very likely attributed to the third invariant stress tensor, which was not explored in the model calibration. The evolution of stress triaxiality and Lode angle parameters with equivalent plastic strain were extracted and analysed for several specimens. The results show a plastic yielding behaviour sensitive to the stress state, which can be attributed to different combinations of stress triaxialities and Lode angle parameters.

Cumulative fatigue damage analysis and life prediction of engineering structures/components is vital for ensuring their structural integrity and operational reliability under variable amplitude loadings. In this regard, a new nonlinear fatigue damage accumulation model is proposed by introducing a damage function related to the isodamage curves and remaining life aspects. Specifically, its damage exponent is refined by considering effects of loading history. Experimental data from tests available in literature are utilized for model validation and comparison. Compared with four existing models, the proposed model shows higher precision for cumulative damage modelling and fatigue life prediction than others. Moreover, it improves the deficiencies inherent in other rules under the promise of maintaining its simplicity in practice.

This paper presents experimental and numerical results from embedment tests carried out accordingly the EN383 standard. The experimental program included series of compressive embedment tests, along the parallel and perpendicular-to-grain directions. The specimens were manufactured with maritime pine wood and were loaded using a steel dowel. The load-displacement curves resulted from experimental tests allowed to estimate the embedding strength and the foundation modulus. Concerning the numerical simulations, a plasticity model, based on Hill's criterion, was used to simulate the mechanical behaviour observed in the embedment tests. The wood was modelled as an orthotropic material following an elasto-plastic behaviour. The steel dowel was considered isotropic material and modelled with elastic behaviour. Besides, the interaction between both materials was modelled using contact finite elements. A parametric study to evaluate the influence of dowel/wood clearance and different friction coefficients was performed. The proposed 3D finite element model showed the capability to simulate the non-linear behaviour observed in the experimental embedment tests. An experimental/numerical procedure for the identification of constitutive models aiming the simulation of ductile behaviour of wood was presented. This is particularly important to simulate the mechanical behaviour of doweled joints.

Fatigue damage is a concern for riveted metallic bridges due to the long operational period they have been subjected along with increasing traffic intensity. The usual fatigue assessment approach for riveted joints consists on using the global S–N curves with nominal or net stresses. Existing practice is based on the adoption of a unique S–N curve (e.g. the Eurocode 3, Class 71 S–N curve). However, this approach may lead to excessive conservative predictions since it is applied indistinctly of the riveted detail geometries (e.g. does not recognize the need for detail categorization) and materials (e.g. not specifically developed for puddle irons). Alternatively, local approaches to fatigue may be applied to any type of joints, made of any material, providing that material fatigue properties are available as well as accurate numerical models of the joints. This paper presents a numerical study concerning the fatigue modelling of riveted and bolted joints made of puddle iron from the centenary Portuguese Fao Bridge. Fatigue is assumed a process of crack initiation and propagation, both processes modelled using respectively the local strain and the Fracture Mechanics based fatigue approaches. A finite element model of the joints is proposed using solid and contact finite elements. The effects of the clamping stresses as well as the friction are taking into account with the proposed model. Numerical S–N curves are predicted and compared with the experimental data available for the investigated joints, a good agreement being observed.

This paper presents the results of several mechanical tests aiming at characterizing the constitutive behaviour of the AlSi9Cu3 cast alloy, covering different temperatures and stress fields, including tensile and compressive tests of smooth and notched specimens as well as combined shear/tension and shear/compression with special designed specimens. The Johnson-Cook model was able to correlate the flow stress under quasi-static uniaxial compression, including thermal effects. However, under tension the yield stress does not reduces monotonically and gradually with temperature, which impedes the application of Johnson-Cook model for positive triaxialities. At room temperature, the AlSi9Cu3 alloy shows significant asymmetrical tensile and compressive behaviours requiring a plasticity model sensitive to the stress triaxiality such as the Drucker-Prager. As regards the ductility limits of the material, different data was analysed to generate fracture loci for the material where equivalent fracture strains were plotted against the stress triaxialities. The calibrated Drucker-Prager constitutive model together with a damage approach based on the fracture loci generated was successfully verified using test data from specimens loaded under combined shear/tension or shear/compression. The AlSi9Cu3 cast alloy exhibits a sharp reduction in ductility between the negative stress triaxiality cut-off and −0.1, keeping at low levels above this triaxiality value.

This paper presents an experimental investigation of the development of adhesively bonded reinforcing techniques for dowel-type wood connections. One of the proposed techniques is based on the application of carbon fiber reinforced plastic (CFRP) laminates (glued with epoxy adhesives) in the areas surrounding the holes of the wood members. The other technique is based on a novel reinforcing procedure involving the application of steel inserts that are glued to the holes of the timber members. For this latter technique, two distinct commercial epoxy adhesives were investigated. Both techniques were demonstrated for maritime pine wood. The experimental program comprised embedding tests, carried out according to the procedures of the EN 383 standard, with and without reinforcements, and included both parallel- and perpendicular-to-grain quasi-static loading. The embedding strength and foundation modulus were determined and compared between the non-reinforced and reinforced solutions. Furthermore, three series of single dowel T-connections were tested, one without reinforcement and two series reinforced with metallic inserts and CFRP laminates, respectively. The analysis of the experimental results showed the improved performance of the strengthening solutions. Additionally, it is important to emphasize that the reinforcement based on CFRP laminates was more effective in eliminating brittle failure modes in the wood members.

Traditionally, fatigue crack initiation has been modelled based on strain-life relations whereas fatigue crack propagation has been modelled using fracture mechanics concepts. Recently, new fatigue crack growth models, based on elastic–plastic stress–strain histories at the crack tip region, along with strain-life damage models have been proposed, which constitutes a class of local fatigue crack propagation models. Therefore, a unified local approach is feasible to model both crack initiation and crack propagation. An application of such a unified local approach to fatigue is presented in this paper. In particular, a notched rectangular plate, made of P355NL1 steel is modelled in order to generate S – N curves for distinct stress R -ratios. The predictions are compared with available experimental data. The required strain-life data of the P355NL1 steel is also presented in the paper, in a probabilistic form, using adequate fatigue damage parameters. Finally, the probabilistic S – N field is proposed for the notched detail and a good correlation of the available experimental data is observed.

The use of higher strength steels allows the design of lighter, slenderer and simpler structures. Nevertheless, the increase of the yield strength of the steels does not correspond to a proportional increase of fatigue resistance, which makes the application of high strength steels on structures prone to fatigue, a major concern of the design. This paper presents a comparison of the fatigue behavior between the S355 mild steel and the S690 high strength steel grades, supported by an experimental program of fatigue tests of smooth specimens, performed under strain control, and fatigue crack propagation tests. Besides the cyclic elastoplastic characterization, the fatigue tests of smooth small size specimens allow the assessment of the fatigue crack initiation behavior of the materials. Results show that the S690 steel grade presents a higher resistance to fatigue crack initiation than the S355 steel. However, the resistance to fatigue crack propagation is lower for the S690 steel grade, which justifies an inverse dependence between static strength and fatigue life, for applications where fatigue crack propagation is the governing phenomenon. Consequently, the design of structural details with the S690 steel should avoid sharp notches that significantly reduce the fatigue crack initiation process.

This paper investigates the mechanical behavior of solid wood beams reinforced with CFRP laminates. Experimental, numerical and analytical approaches are explored in order to assess the effect of the reinforcement length on the interfacial shear and peeling stresses which are critical for a failure prediction. The experimental program aimed the characterization of the base materials and the comparison of the performance of wood beams with distinct reinforcement lengths and beams without any reinforcement. Finite element models were proposed and calibrated using the experimental data. Finally, analytical models for the interfacial stresses were applied and their performance assessed and compared with the numerical results. The success of the analytical models depends on consideration of shear deformation of the adherents, in particular of the wood, which shows relative low shear modulus.

Fatigue failures are of concern for steel bridges due to the likelihood of the steel to deteriorate under variable stresses. Residual life calculations of existing bridges in operation should take into account fatigue as a progressive damaging mechanism. A consistent residual life prediction should be based on actual fatigue data from bridge members to assess. This paper presents strain-life and crack propagation fatigue data obtained using samples of original material removed from five Portuguese metallic riveted bridges. While four of the analysed bridges are centenaries, the younger bridge is little more than 50 years old which is likely one of the last metallic bridges built in Portugal using the riveting technology. Besides the fatigue properties, the monotonic and cyclic elastoplastic properties are assessed for the samples of materials. From the analysis of the results it is clear that the older materials are puddle iron, a precursor of the modern construction steels, the latter being used in the younger bridge. The generated data is essential for residual fatigue life estimations considering both crack initiation and propagation phases, respectively in the framework of Local Approaches to fatigue and Linear Elastic Fracture Mechanics.

Fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and strain-life damage models have been proposed. The UniGrow model fits this particular class of fatigue crack propagation models. The residual stresses developed at the crack tip play a central role in these models, since they are used to assess the actual crack driving force, taking into account mean stress and loading sequential effects. The performance of the UniGrow model is assessed based on available experimental constant amplitude crack propagation data, derived for several metallic materials from representative Portuguese bridges. Key issues in fatigue crack growth prediction, using the UniGrow model, are discussed, in particular the residual stress computation

A procedure for estimation of probabilistic fatigue S–N curves for notched structural components is described. Plain material strain–life data is used to identify a statistical Weibull strain–life model and, using an adequate elastoplastic analysis, material strain–life probabilistic curves are converted into probabilistic stress–life curves of the structural component. The performance of the proposed model is illustrated by a practical example of a riveted shear splice, from a Portuguese railway bridge, for which experimental resistance data is available. A simplified elastoplastic analysis based on the Neuber and the Glinka rules are used, supported by the results of an elastic finite element analysis of the riveted connection. The paper demonstrates the success of the proposed probabilistic model since it correlates satisfactorily with the available experimental data for the riveted connection. The achieved results confirm the proposed probabilistic model as well suited for notched structural components with a whole fatigue life dominated by crack initiation.

The application of the concept of glued-laminated wood (glulam) to improve the mechanical properties of the solid wood of the maritime pine ( Pinus pinaster ) is the subject of this work. Two reinforced glued-laminated wood beams are proposed and assessed. The first is based on a concept of laminated wood composite with fiber glass; the second is based on the application of pultruded lamellas glued to the most stressed tensile region of the glued-laminated beams. In order to demonstrate the potential of the proposed strengthening solutions, a comparison between their mechanical behaviors and the mechanical behaviors of the conventional glued-laminated and solid beams are performed. Static load–deflection curves, an equivalent Young’s modulus, the ultimate strain and modulus of rupture are determined using 3-point quasi-static bending tests. In general, it is demonstrated the beneficial effect of the proposed strengthening solutions both in terms of resistance and ductility.