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The fatigue strength of ferritic, pearlitic, and solution strengthened ferritic ductile irons taken from heavy sections and characterized by long solidification times has been assessed. Starting from the idea of Murakami and co‐workers, a new model for the prediction of the fatigue strength is proposed. It allows a sound fatigue assessment of the fatigue strength of as‐cast ductile irons containing solidification defects, such as low nodule count, exploded, chunky and spiky graphite, or microshrinkage porosities. The newly developed equation validated by means of an extensive benchmarking with data taken from the literature has shown a very high potential for applications to thick‐walled components. This is the pre-peer reviewed version of an article, which has been published in final form at [https://doi.org/10.1111/ffe.12815]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.

Thermomechanical fatigue (TMF) behaviors of ductile cast iron (DCI) were investigated under out-of-phase (OP), in-phase (IP), and constrained strain-control conditions with temperature hold in various temperature ranges: 573 K to 1073 K, 723 K to 1073 K, and 433 K to 873 K (300 °C to 800 °C, 450 °C to 800 °C, and 160 °C to 600 °C). The integrated creep-fatigue theory (ICFT) model was incorporated into the finite element method to simulate the hysteresis behavior and predict the TMF life of DCI under those test conditions. With the consideration of four deformation/damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement, (iii) creep, and (iv) oxidation, as revealed from the previous study on low cycle fatigue of the material, the model delineates the contributions of these physical mechanisms in the asymmetrical hysteresis behavior and the damage accumulation process leading to final TMF failure. This study shows that the ICFT model can simulate the stress–strain response and life of DCI under complex TMF loading profiles (OP and IP, and constrained with temperature hold).

The proceedings contain the contributions wich are delivered as presentations during the Seventh International Conference on Very High Cycle Fatigue taking place from 3rd through 5th of July 2017 in Dresden, Germany

Hot-forging is a process commonly used in the manufacturing of automobile parts such as connecting rods. Most hot-forged components are shot-blasted after forging in order to clean off the forging scale. The shotblasting process is akin to shot-peening and greatly affects the surface integrity of the components by introducing hardening and residual stresses. This study focuses on the influence of the surface integrity on the fatigue behaviour of a hot-forged C70 steel connecting rod. Specimens were machined out of the connecting rods in order to perform fatigue testing on the forged surface. Several surfaces states, including shot-peened surfaces, were studied in order to quantify the influence of the surface integrity. A thorough characterisation of the surface integrity of the specimens was first performed. The hardness, residual stresses and microstructure gradients were analysed, and the surface of each specimen was scanned using a profilometer. The specimens show complex networks of surface defects introduced during forging, and the shot-blasting process introduces important surface residual stress and microstructure gradients. High cycle fatigue tests in plane bending were then performed on the specimens, with the surface scans helping to identify the critical defect on which crack initiation occurred. The fatigue results, presented in the form of a Kitagawa diagram, are analysed in order to determine which surface integrity parameters are the most influential on fatigue behaviour. The forging defects have an important negative effect on fatigue strength. After shot-blasting, the fatigue strength increases considerably because of the large compressive residual stresses introduced by the shot-blasting process. This work has been performed within the ANR (National Research Agency) DEFISURF project, in a partnership including several industrial (Ascometal, CETIM, Renault, Transvalor, Atelier des Janves, Gévelot Extrusion) and academic (INSA Lyon MATEIS, ENSMPCEMEF, Arts et Métiers ParisTech LAMPA) institutions.

In this work a numerical procedure, based on a finite element approach, is proposed to simulate multiple three-dimensional crack propagation in a welded structure. Cracks are introduced in a friction stir welded AA2024-T3 butt joint, affected by a process-induced residual stress scenario. The residual stress field was inferred by a thermo-mechanical FEM simulation of the process, considering temperature dependent elastic-plastic material properties, material softening and isotropic hardening. Afterwards, cracks introduced in the selected location of FEM computational domain allow stress redistribution and fatigue crack growth. The proposed approach has been validated by comparison with numerical outcomes provided by a consolidated FEM-DBEM procedure, available in literature. The discussed procedures are substantially equivalent in terms of SIFs evaluation along the crack front at the cracks insertion, as well as with respect to crack sizes measured in three different points for each propagation step. This FEM-based approach simulates the fatigue crack propagation by considering accurately the residual stress field generated by plastic deformations imposed on a structural component and has general validity.

cited By 2; International audience; Among the prevalent tribological failures affecting rolling element bearings, an unconventional rolling contact fatigue mode has been identified as white etching cracks. Those correspond to three-dimensional branching crack networks partially bordered by white etching microstructure, eventually leading to premature and unpredictable failure. Recent work supports that this failure mode may be associated with various combinations of operating conditions depending on the application or test rig, but that all seem to converge towards similar tribological drivers related to surface-affected hydrogen evolution at asperity scales, which is known to embrittle the bearing steel. Nevertheless, as white etching cracks remain delicate to reproduce without artificial hydrogen charging, the underlying formation mechanisms remain unsettled. The present work aims to better understand how some of the main tribomechanical and tribochemical drivers may trigger white etching cracks and premature failures. In this study drivers such as sliding kinematics, water contamination, and electrical potential and lubricant additives are progressively transposed on a twin-disc machine that provides an enhanced control of contact parameters. Various attempts advocate that the tested drivers are not self-sufficient to reproduce the failure mode in such apparatus, but confirm that specific lubricant additives may reduce the fatigue life by promoting surface-initiated embrittled cracking similar to white etching cracks. A local criterion accounting for the local sliding frictional power dissipation and the lubrication regime is further proposed to assess the risk of white etching cracks based on the analysis of various reproduction and occurrences. © IMechE 2016.

In this study, the microstructural length of magnesium welded joints was determined by using experimental data acquired from three different weld geometries and Neuber's stress averaging method. The aim was to determine microstructural length, which is assumed to be a material constant that is identical for all Mg-materials, so that it can be employed for effective stress and fictitious notch radius rf calculations. By considering the worst case scenario, rreal = 0, this fictitious notch radius can be used as a new reference radius rref for magnesium welded joints. Using the reference radii from two different hypotheses rref = 1 mm and rref = 0.05 mm, calculations were performed for notches and data were employed in the calculations. Also FE-analyses were utilised in order to identify the stress gradients for weld geometries. Effective stresses were calculated using experimental data along with the stress gradients in Neuber's stress averaging method. Finally, S-N lines were derived by correlating effective stresses with fatigue life for the worst case with R = 0.5 to account for possible high tensile residual stresses. The scatters of these S-N lines were calculated and compared for every ?* iteration. The length value that resulted in the minimum scatter corresponded to the microstructural length. The identified microstructural length was ?* = 0.12 mm. Until now, there were no published results for microstructural length of magnesium welded joints and the findings in this paper can be used to replace the current recommendations regarding magnesium welded joints. © 2016 Elsevier Ltd

Titanium–tantalum based alloys can demonstrate a martensitic transformation well above 100 °C, which makes them attractive for shape memory applications at elevated temperatures. In addition, they provide for good workability and contain only reasonably priced constituents. The current study presents results from functional fatigue experiments on a binary Ti–25Ta high-temperature shape memory alloy. This material shows a martensitic transformation at about 350 °C along with a transformation strain of 2 pct at a bias stress of 100 MPa. The success of most of the envisaged applications will, however, hinge on the microstructural stability under thermomechanical loading. Thus, light and electron optical microscopy as well X-ray diffraction were used to uncover the mechanisms that dominate functional degradation in different temperature regimes. It is demonstrated the maximum test temperature is the key parameter that governs functional degradation in the thermomechanical fatigue tests. Specifically, ω-phase formation and local decomposition in Ti-rich and Ta-rich areas dominate when T max does not exceed ≈430 °C. As T max is increased, the detrimental phases start to dissolve and functional fatigue can be suppressed. However, when T max reaches ≈620 °C, structural fatigue sets in, and fatigue life is again deteriorated by oxygen-induced crack formation. Copyright © Materials Research Society 2017

cited By 0; International audience; In this paper, the tension-tension fatigue behavior of unidirectional SiC/Si3N4 ceramic-matrix composite with strong and weak interface bonding at room temperature has been investigated using a micromechanical approach. The hysteresis loops models considering different interface slip cases have been developed to establish the relationships between fatigue hysteresis loops, hysteresis dissipated energy, hysteresis modulus, and the interface shear stress. The damage evolution process under tension-tension fatigue loading has been analyzed using hysteresis loops. By comparing experimental fatigue hysteresis dissipated energy with theoretical computational values, the interface shear stresses of SiC/Si3N4 composite with weak and strong interface bonding were obtained for different cycle numbers. The fatigue life S‒N curves and broken fibers fraction versus cycle number curves corresponding to different fatigue peak stresses have been predicted. For SiC/Si3N4 with strong interface bonding, the fatigue limit stress approaches to 75% tensile strength, which is much higher than that of composite with weak interface bonding, i.e., 58% tensile strength, due to the higher interface shear stress degradation rate for weak bonding interface. © 2017 Elsevier Ltd and Techna Group S.r.l.

In the present study, monotonic tension tests and low cycle fatigue tests were performed on aluminum alloy EN AW-2024-T3 under various operating temperatures. The results were assessed in order to determine the Bauschinger effect in the aluminum alloy under elevated temperatures. Findings of monotonic tests served as a basis to compare the influence of temperature on mechanical properties of the material. The results of the cyclic tests were used to determine the Bauschinger effect. Finally, the changes in the presence of the effect at various testing temperatures were presented. © 2017 Carl Hanser Verlag, München.

U doktorskoj disertaciji obrađen je problem procjene cikličkih Ramberg–Osgoodovih i zamornih Basquin–Coffin–Mansonovih parametara čelika na osnovi monotonih značajki primjenom umjetnih neuronskih mreža. Za potrebe istraživanja iz relevantne je literature i putem on-line baze podataka o materijalima MATDAT prikupljen velik broj eksperimentalnih podataka za čelike. Pregledom postojećih istraživanja utvrđeno je da se podjelom čelika u skupine prema kriteriju udjela legirajućih elemenata može poboljšati točnost procjene cikličkih i zamornih parametara na osnovi monotonih značajki. U skladu s tim, čelici su grupirani u nelegirane, niskolegirane i visokolegirane čelike. Različitost vrijednosti cikličkih i zamornih parametara spomenutih grupa čelika i formalno je potvrđena provođenjem jednofaktorske analize varijance i Welchovog testa. Dodatno provedenim post-hoc analizama utvrđena je različitost na razini parova nelegiranih, niskolegiranih i visokolegiranih čelika. Provođenjem unaprijedne selekcije određene su monotone značajke relevantne za procjenu svakog od cikličkih i zamornih parametara različitih skupina čelika. Na osnovi rezultata statističkih analiza, predložena je procjena cikličkih i zamornih parametara primjenom neuronskih mreža, zasebno za svaku skupinu čelika i uz korištenje samo onih monotonih značajki koje su se pokazale statistički relevantnim za procjenu pojedinog parametra. Za učinkovitije korištenje prikupljenih podataka u razvoju neuronskih mreža primijenjena je metoda k-struke unakrsne validacije. Rezultati dobiveni razvijenim umjetnim neuronskim mrežama vrednovani su usporedbom s eksperimentalnim vrijednostima cikličkih i zamornih parametara, ali i onima dobivenim postojećim empirijskim metodama procjene. Za odabrani skup podataka umjetne neuronske mreže pokazale su se uspješnijim od empirijskih metoda procjene većine cikličkih i zamornih parametara i ponašanja različitih skupina čelika. Razvijeni pristup procjeni cikličkih i zamornih parametara na osnovi lako dostupnih monotonih značajki primjenom neuronskih mreža može poslužiti jednostavnijem, točnijem i bržem određivanju opteretivosti i trajnosti čeličnih dijelova i konstrukcija u raznim industrijskim djelatnostima (automobilskoj, zrakoplovnoj i dr.). Razvojem pouzdanog sustava za procjenu cikličkih i zamornih parametara smanjuje se potreba za eksperimentalnom karakterizacijom cikličkog i zamornog ponašanja materijala u ranim fazama razvoja proizvoda u kojima se vrednuju različiti materijali i konstrukcijska rješenja, što za posljedicu ima i smanjenje troškova i vremena potrebnih za razvoj proizvoda., Research presented in this doctoral thesis deals with estimation of cyclic Ramberg–Osgood and fatigue Basquin–Coffin–Manson parameters i.e. stress–strain and strain–life behaviour of steels on the basis of their monotonic properties using artificial neural networks. For the purpose of this study, a large number of experimental data for steels were collected from relevant literature and online Materials Properties Database MATDAT. The overview of existing methods showed that separate consideration of steels divided according to the content of alloying elements can improve the accuracy of estimations of cyclic and fatigue parameters on the basis of their monotonic properties. Thus, steels were divided into unalloyed, low-alloy and high-alloy steels. Differences among cyclic and fatigue parameters of steels divided in such a way were formally confirmed by performing one-way analysis of variance and Welch’s test. Additionaly, pairwise differences between groups were found to exist by performing post-hoc analyses. Further detailed statistical analysis was performed by means of forward selection, and monotonic properties relevant for estimation of each cyclic and fatigue parameter of each group of steels were determined. Based on results of performed statistical analyses, estimation of cyclic and fatigue parameters using artificial neural networks was proposed, separately for each parameter and each steel subgroup, using only monotonic properties that proved to be relevant for estimation of particular parameter. Data collected were efficiently used in artificial neural network development by implementing k-fold cross-validation technique. Results obtained by artificial neural networks have been evaluated by comparison with experimental values and values obtained using existing empirical estimation methods. For used test data, artificial neural networks proved to be more successful than empirical methods for estimation of most of the cyclic and fatigue properties and behaviour of different steel subgroups. Proposed and developed estimation of cyclic and fatigue parameters from readily available monotonic properties using artificial neural networks can facilitate faster and more accurate load capacity and durability analyses of steel components and structures during early stages of product design in various industrial applications (automotive, aeronautical etc.). Furthermore, it can contribute to the reduction of the need for experimental characterisation of material behavior and help decrease time and costs of product development.

This research uses a non-destructive method of neutron diffraction to measure the tri-axial residual stresses in a friction stir welded aerospace fuselage component: a stringer-to-skin lap joint. Two different specimens were examined. Fatigue testing was performed on both specimens to determine their fatigue lives. Effects of the different components of residual stresses were examines and related to fatigue performance. A combination of fractography, hardness testing, and residual stress measurement was used to predict areas of high probability of structural failure in the friction stir welded lap joints., 9th European Conference on Residual Stresses, ECRS 2014, 7 July 2014 through 10 July 2014, Troyes

An experimental investigation aimed at identifying the presence and onset of an asymptotic stable fracture region in the mode II fatigue delamination growth behaviour of composites is presented. The study is motivated by the possibility that experimental data sets, particularly those obtained at high R-ratios, may unknowingly contain data points within the asymptotic stable fracture region that influence its perceived log-linear behaviour and the fit of various log-linear delamination growth models. Results from the experimental investigation indicate that the asymptotic stable fracture region can extend to GIImax values as low as 0.7 GIIc. The implications of this result on characterizing and fitting of various delamination growth models (including models assuming log-linear behaviour) to delamination growth behaviour are discussed.

SAE 9260 spring steel specimens after enduring 50% of their mean fatigue life were subjected to laser shock peening using an in-house developed 2.5. J/7. ns pulsed Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser for studying their fatigue life enhancement. In the investigated range of process parameters, laser shock peening resulted in the extension of fatigue life of these partly fatigue damaged specimens by more than 15. times. Contributing factors for the enhanced fatigue life of laser peened specimens are: about 400. ?m thick compressed surface layer with magnitude of surface stress in the range of -600 to -700. MPa, about 20% increase in surface hardness and unaltered surface finish. For laser peening of ground steel surface, an adhesive-backed black polyvinyl chloride (PVC) tape has been found to be a superior sacrificial coating than conventionally used black paint. The effect of repeated laser peening treatment was studied to repair locally surface melted regions and the treatment has been found to be effective in re-establishing desired compressive stress pattern on the erstwhile tensile-stressed surface. � 2013 Elsevier Ltd.

This methodological paper presents a novel approach to predict operator's mechanical exposure and fatigue accumulation in discrete event simulations. A biomechanical model of work-cycle loading is combined with a discrete event simulation model which provides work cycle patterns over the shift resulting in a load-time trace for the entire shift. This trace was tested with four different muscle endurance-recovery model pairs yielding a fatigue-time history for the entire shift. An electronics assembly case with shift-long perceived fatigue data was compared to the simulation model results. Sensitivity testing of the input work-rest ratios found the best correlation (r2=0.84) at 17% of the modeled rest level. The need for this adjustment is discussed in terms of limitations of available muscle endurance and recovery models. Muscle model limitations notwithstanding, this approach allows system designers to understand the mechanical exposure and fatigue-related effects of proposed alternatives in system design stages and can contribute to 'Virtual Human Factors' approaches for pro-active ergonomics capability. Relevance to Industry: This paper demonstrates an approach to quantifying operator exposure patterns and fatigue levels using dynamic simulations of the proposed operations. This allows system designers to understand the ergonomic impacts of proposed alternatives in system design. Design level tools allow early stage application of ergonomics where costs are lower and solution options are greatest. © 2013 Elsevier B.V.

Laser Engineered Net Shaping (LENS), a Direct Energy Deposition (DED) additive manufacturing process is a 3D manufacturing process generally used to produce fully dense parts or to repair/add additional material to an existing component. The main aim of this work is to evaluate the fatigue behavior of LENS specimens in the presence of geometrical discontinuities and to compare its performance to the one obtained from wrought specimens. For this aim, axial fatigue tests are carried out on three sets of specimens namely, smooth, semi‐circular and V‐notched specimens to determine the fatigue strength and notch sensitivity of the LENS and wrought Ti‐6Al‐4V materials. The LENS material shows higher fatigue strength and notch sensitivity compared to wrought material which is attributed to the unique microstructural features leading to different fatigue failure mechanisms. Further, the fatigue data is assessed by use of strain energy density as a failure criterion. © 2019 The Authors. Published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

Axle housing tubes are used in automobiles and are subjected predominantly to bending fatigue during its service life. The fatigue life of the tubes is largely dependent on the residual stresses induced in them at the manufacturing stage. The manufacturing processes and their sequence of execution have profound influence on the nature of residual stress distribution. Induction hardening and tempering, extrusion, and turning are the manufacturing processes involved. Residual stresses induced by each of the manufacturing processes involved are studied. The influence of process sequence on residual stresses is studied by conducting experimental fatigue tests and measuring residual stresses by X-ray diffraction. Based on the studies, it is found that the manufacturing process sequence with turning as the final process step is detrimental to fatigue life, whereas the sequence with induction hardening and induction tempering as the final process step produces least tensile surface residual stress and hence improves the fatigue life. � 2013 Elsevier Ltd.

In this study, digital image correlation was used for two widely different cases to assess the potential and the limitations of the technique for applications at high temperatures. Specifically, digital image correlation was employed in high-temperature low-cycle fatigue experiments in a nickel-based superalloy and in phase transformation experiments conducted on bainitic steel in order to shed light on the microstructural processes. Depending on the type of experiments, the microstructure was characterized prior to the experiments (fatigue) or after the experiments (phase transformation). In the fatigue experiments, it was found that the features dominating damage evolution were the dendrites resulting from the solidification of the cast material. In the phase transformation experiments, variant selection is active when stresses are superimposed during the phase transformation process, which resulted in the evolution of transformation plasticity strains. Thereby, mainly the bainite variants oriented along the [101], [201] and [121] directions were observed to grow parallel to the loading axis, which in turn led to transformation plasticity strains. For validation of the digital image correlation data, average strains were calculated for the surface area probed and compared to strain values obtained by conventional extensometry. In all cases studied, the correlation was satisfactory, indicating that digital image correlation can provide for additional insight into processes active at the micro level.

An experimental investigation of resistance welding of thermoplastic composite double lap shear (DLS) joints is presented. DLS specimens consisting of unidirectional carbon fibre/polyetheretherketone (CF/PEEK), carbon fibre/polyetherketoneketone (CF/PEKK), carbon fibre/polyetherimide (CF/PEI) and 8-harness satin weave fabric glass fibre/polyetherimide (GF/PEI) composites were resistance welded using a stainless steel mesh heating element. The welded specimens were tested under static and fatigue loadings, and the quality of the welds was examined using optical and scanning electron microscopy. Weld strengths of 53, 49, 45 and 34 MPa were obtained for CF/PEEK, CF/PEKK, CF/PEI and GF/PEI DLS joints, respectively. Indefinite fatigue lives were obtained between 20 and 30% of the ultimate static failure loads of the joints. Performances of the resistance-welded DLS and single lap shear (SLS) joints were compared. It was shown that the effect of joint geometry, that is, DLS versus SLS, on the mechanical performance of the resistance-welded joints is minimal, indicating a good resistance of welded joints to peel stresses.

Three types of welded joints have been assessed with regard to their fatigue strength based on the mean-stress damage parameter model according to Smith, Watson, and Topper (PSWT) and on the reference notch radius concept. These analyses were performed with three different stress ratios, R = -1, R = 0 and R = 0.5, under axial loading. For each stress level, the corresponding Neuber-Hyperbolas, Masing-loops and their maximum stress and maximum strain values were determined in order to calculate damage parameter (PSWT) values. For a given weld geometry, this damage parameter is able to unify the fatigue results for different R-values within at a tight scatter band and therefore to consider the mean-stress effect. The unification of the results for different weld geometries is performed by applying the reference radii rref = 0.05 and rref = 1.00 mm as suggested by the IIW-Recommendations. © 2012 Elsevier Ltd. All rights reserved.

Lightweighting is currently considered as an effective way in improving fuel efficiency and reducing anthropogenic greenhouse gas emissions. The structural applications of lightweight magnesium and aluminum alloys in the aerospace and automotive sectors unavoidably involve welding and joining while guaranteeing the safety and durability of motor vehicles. The objective of this study was to evaluate the lap shear strength and fatigue properties of friction stir spot welded (FSSWed) dissimilar AZ31B-H24 Mg alloy and Al alloy (AA) 5754-O in three combinations, i.e., (top) Al/Mg (bottom), Al/Mg with an adhesive interlayer, and Mg/Al with an adhesive interlayer. For all the dissimilar Mg-to-Al weld combinations, FSSW induced an interfacial layer in the stir zone (SZ) that was composed of intermetallic compounds of Al3Mg2 and Al12Mg17, which led to an increase in hardness. Both Mg/Al and Al/Mg dissimilar adhesive welds had significantly higher lap shear strength, failure energy and fatigue life than the Al/Mg dissimilar weld without adhesive. Two different types of fatigue failure modes were observed. In the Al/Mg adhesive weld, at high cyclic loads nugget pull-out failure occurred due to fatigue crack propagation circumferentially around the nugget. At low cyclic loads, fatigue failure occurred in the bottom Mg sheet due to the stress concentration of the keyhole leading to crack initiation followed by propagation perpendicular to the loading direction. In the Mg/Al adhesive weld, nugget pull-out failure mode was primarily observed at both high and low cyclic loads. © 2012 Elsevier B.V.

Temperature changes are exhibited by a material when subjected to mechanical loads in the elastic as well as the plastic regimes. In this paper, we analyze the observed thermo-mechanical phenomenon from elastic cyclic loading tests (stress below yield point) conducted on stainless steel (SS304) using two well-known rheological models viz., Kelvin-Voigt model and Maxwell's models. The Kelvin-Voigt model is shown to be well-suited in characterizing the mechanical as well as the associated thermal response. In seeking a deeper basis for the success of the Kelvin-Voigt model, correlations are sought between the model's key parameter - viscosity and the material's microscopic property viz. the grain boundary sliding coefficient. A plausible description is offered for the ability of Kelvin-Voigt model to explain the thermo-mechanical response under elastic cyclic loading. The effect of grain size on thermomechanical response and the variation of grain boundary diffusion coefficient with applied load is demonstrated, theoretically. The new description is used to predict the thermo-mechanical behavior of various other polycrystalline materials such as aluminum. Based on the models developed, experiments are proposed for further research. � 2012 Elsevier B.V.

Manoeuvre Load Alleviation (MLA) is the concept of redistribution of forces and moments on airframe through optimal actuation of control surfaces. The effect is to minimise the stresses near wing root and improve fatigue life of airframe components, such as, the frequently studied wing root fitting connecting wing to the fuselage. The configuration is a typical tailless delta wing aircraft having inboard and outboard Elevons (a combination of Elevator and Aileron) placed symmetrically on starboard and port side. The problem is formulated as minimisation of independent conflicting multiple objectives of wing root bending and twisting moments, with stability equations as equality constraints and actuator hinge moments as inequality constraints. Hybrid method is used as optimisation technique, which is evolved from the combination of heuristic based Elitist non-dominated Sorting Genetic Algorithm (NSGA-II) and calculus based Goal Programming methods. The primary objective of this paper is to bring out the structural benefits attainable for some of the combined critical manoeuvre load cases at subsonic and supersonic flight points. The combined critical manoeuvre load cases demarcate the limit to which airframe is loaded. The minimisation achieved is better for flight points at supersonic as compared to subsonic Mach numbers. � 2011 Elsevier Masson SAS.

The fatigue characteristic of a lightly stabilized granular material under traffic loading is an important consideration for the design of a pavement containing such material. This paper presents the evaluation of fatigue behavior of lightly stabilised granular materials using flexural and indirect diametral tensile (IDT) testing. The experimental program included cyclic load flexural and IDT testing to determine the fatigue life of a typical granular material stabilized lightly with 1-3% cement-flyash. Fatigue life was estimated using the approach of approximate energy ratio method and empirical relationships were proposed to relate the fatigue life with tensile strain similar to that proposed in the literature. Details of the experimental investigation, the analysis carried out to determine the fatigue life of the lightly stabilized granular material and comparisons of fatigue characteristics determined from two test methods are discussed in the paper. ASCE. Scopus

In the framework of elastocaloric (eC) refrigeration, the fatigue effect on the eC effect of natural rubber (NR) is investigated. Repetitive deformation cycles at engineering strain regime from 1 to 6 results in a rapid rupture (approx. 800 cycles). Degradation of properties and fatigue life are then investigated at three different strain regimes with the same strain amplitude: before onset strain of strain-induced crystallization (SIC) (strain regime of 0–3), onset strain of melting (strain regime of 2–5) and high strain of SIC (strain regime of 4–7). Strain of 0–3 leads to a low eC effect and cracking after 2000 cycles. Strain of 2–5 and 4–7 results in an excellent crack growth resistance and much higher eC effect with adiabatic temperature changes of 3.5 K and 4.2 K, respectively, thanks to the effect of SIC. The eC stress coefficient index γ (ratio between eC temperature change and applied stress) for strains of 2–5 and 4–7 are γ 2–5 =4.4 K MPa −1 and γ 4–7 =1.6 K MPa −1 , respectively, demonstrating the advantage of the strain regime 2–5. Finally, a high-cycle test up to 1.7×10 5 cycles is successfully applied to the NR sample with very little degradation of eC properties, constituting an important step towards cooling applications. This article is part of the themed issue ‘Taking the temperature of phase transitions in cool materials’.

MITICA is the prototype of the Heating Neutral Beam Injectors (HNB) for ITER and is constituted by a negativeion source, a multi-grid electrostatic accelerator, a neutralizer and a residual ion dump. The injector is designed to produce a 17 MW beam of neutral particles (deuterium or hydrogen) up to 1 MeV. Two HNBs are planned to be installed in ITER at Cadarache, France. MITICA is under construction in the PRIMA facility in Padova, Italy. The design of MITICA/HNB [1] has required extensive optimizations in order to guarantee that the thermomechanical stresses in the materials do not exceed the tolerable limits for the required fatigue life. This result has been achieved by: (a) reducing and uniforming the heat loads on the accelerator grid and beam line components, and (b) improving the heat removal capability of the active cooling system of the grids. This involved an extensive optimization of the electric and magnetic field configuration and of the geometry of the accelerator grids, suppressing the electrons before they are accelerated at higher energy, and improving the optics of the ion beamlets. However, deviation from the expected magnetic and electrostatic configuration can be caused by "off-normal" or "failure" operating conditions of the accelerator, such as undesired mechanical displacement of the grids, nonuniform extracted ion current, demagnetization of magnets, partial failure of the accelerator grid power-supplies and also operation with different ion species. Purpose of the present work is to analyse and identify the "off-normal" operating conditions which could possibly become critical in terms of thermomechanical stresses or of degradation of the optical performances of the beam, and to give indications on protective actions to be taken.

A tailored-for-purpose environmental fatigue testing facility was previously developed to perform direct strain-controlled tests on stainless steel in simulated PWR water. Strain in specimen mid-section is generated by the use of pneumatic bellows, and eddy current measurement is used as a feedback signal. The procedure conforms with the ASTM E 606 practice for low cycle fatigue, giving results which are directly compatible with the major NPP design codes. Past studies were compiled in the NUREG/CR-6909 report and environmental reduction factors Fen were proposed to account for fatigue life reduction in hot water as compared to a reference value in air. This database exclusively contained non-stabilized stainless steels, mainly tested under stroke control. The applicability of the stainless steel Fen factor for stabilized alloys was already challenged in past papers (PVP2013-97500, PVP2014-28465). The results presented in this paper follow the same overall trend of lower experimental values (4.12–11.46) compared to those expected according to the NUREG report (9.49–10.37). In this paper results of a dual strain rate test programme on niobium stabilized AISI 347 type stainless steel are presented and discussed in the context of the NUREG/CR-6909 Fen methodology. Special attention is paid to the effect of strain signal on fatigue life, which according to current prediction methods does not affect the value of Fen.

Cold extrusion is a process commonly used to manufacture drive train components in the automotive industry. Large plastic strains can be applied during this operation (up to 1.5) and greatly changes the mechanical properties of the resulting material. This study focuses on the impact of cold extrusion process parameters on the multiaxial fatigue behaviour of steel components. A specific set of forward rod extrusion tools was developed to get original fatigue specimen able to characterise the effect of the manufacturing process on the fatigue behaviour. The specimens were extruded from two different initial diameters, giving two different reductions in cross-section of 18% and 75% respectively. To understand the influence of cold extrusion, the following analyses have been undertaken for each condition and on the initial material: monotonic tensile properties, microstructure, EBSD, residual stresses and hardness. Simulation of the forming process and microstructural observations show that the plastic strain is homogeneous in the specimen section. For both reduction factors, the forming process has a positive effect on the components properties: induced residual stresses in compression and improved hardness and roughness (Ra decreasing). Tension, plane bending and torsion fatigue tests show that the fatigue strength is about 30% higher for the batch with 75% reduced cross-section. All investigations show that strain hardening is the principal material parameter responsible for the increase in fatigue strength. A multiaxial fatigue criterion taking into account the effects of the forward rod extrusion process was also developed. This work has been performed within the ANR (National Research Agency) DEFISURF project, in a partnership including several industrial (Ascometal, Cetim, PSA, Transvalor, Atelier des Janves, Gévelot) and academic (INSA Lyon MATEIS, ENSMP-CEMEF, Arts et Métiers ParisTech LAMPA) institutions.

In this cross-sectional study associations were examined between eight shift schedule characteristics with shift-specific sleep complaints and need for recovery and generic health and performance measures. It was hypothesized that shift schedule characteristics meeting ergonomic recommendations are associated with better sleep, need for recovery, health and performance. Questionnaire data were collected from 491 shift workers of 18 companies with 9 regular (semi)-continuous shift schedules. The shift schedule characteristics were analyzed separately and combined using multilevel linear regression models. The hypothesis was largely not confirmed. Relatively few associations were found, of which the majority was in the direction as expected. In particular early starts of morning shifts and many consecutive shifts seem to be avoided. The healthy worker effect, limited variation between included schedules and the cross-sectional design might explain the paucity of significant results. © 2016 Elsevier Ltd and The Ergonomics Society.

Rolling contact fatigue (RCF) damage is becoming more frequent with increased traffic, accelerations, and loading conditions in the railway industry. Defects which are characterized by a two-lobe darkened surface and a V-shaped surface-breaking crack are defined as squats. The origination and propagation of squats in railway rails is the topic of many recent studies; the associated crack networks develop with complicated geometry near the surface of rails, but can be difficult to detect and distinguish from normally existing head checks in their early stages, using in-field non-destructive detection techniques. After cutting out damaged sections of rail, there are a number of options to characterize the damage. The aim of this study was to evaluate different methods to geometrically describe squat crack networks; through X-ray radiography complemented with geometrical reconstruction, metallography, X-ray tomography, and topography measurements. The experiments were performed on squats from rail sections taken from the field. In the first method, high-resolution and high-energy X-ray images exposed through the entire rail head from a range of angles were combined using a semi-automated image analysis method for geometrical reconstruction, and a 3D representation of the complex crack network was achieved. This was compared with measurements on cross-sections after repeated metallographic sectioning to determine the accuracy of prediction of the geometrical reconstruction. A second squat was investigated by X-ray tomography after extraction of a section of the rail head. A third squat was opened by careful cutting, which gave full access to the crack faces, and the topography was measured by stylus profilometry. The high-energy X-ray, 3D reconstruction method showed accurate main crack geometry at medium depths; the advantage of the method being that it potentially could be developed for non-destructive testing in field. However significant drawbacks exist due to limitations in radiography in terms of detecting tightly closed cracks in very thick components. This includes the inability to detect the crack tips which is an important factor in determining the risks associated to a specific crack. Metallographic investigation of the cracks gave good interpretation of crack geometry along the sections examined, and gave the possibility to study microstructure and plastic deformation adjacent to the crack face. However this time-consuming method requires destruction of the specimen investigated. The X-ray tomography revealed the 3D crack network including side branches in a 10×10×30mm3 sample, and provided topographic information without completely opening the squat. Topography measurements acquired by stylus profilometry provided an accurate description of the entire main crack surface texture, including features such as surface ridges and beach marks.

This study investigated the mechanical properties of aluminum matrix functionally graded material (FGM) reinforced by integration of aluminum 2014 alloy (AlCu4SiMg) and 15 vol% SiC. The specimens were obtained by centrifugal casting technique, followed by aging treatment. The variations that occurred in microstructure, hardness, Young's modulus, tensile strength, yield strength, elongation, fatigue, and fretting fatigue behaviors were analyzed. In both cast and aged conditions, it was observed that hardness values and mechanical properties changed between SiC-rich and aluminum-rich regions. Fatigue and fretting fatigue data were similar. It was determined that greater wear was occurring on the pad surfaces compared to that occurring on the sample surfaces. © 2015 Institution of Mechanical Engineers.

Retardation is a load sequence effect, which causes a reduced fatigue crack growth rate after an overload is encountered. Retardation can be cancelled when the overload is followed by an underload. The net effect is beneficial to the fatigue lifetime of Offshore Wind Turbines (OWTs). To be able to take this into account, computationally demanding cycle-by-cycle approaches are required. This paper presents a methodology which aims at reducing a very long variable amplitude stress signal, such that it can be used to estimate the cycle-by-cycle fatigue damage, without jeopardizing accuracy. Filtering and reduction techniques are combined, based on typical events seen in the loading pattern of an OWT, e.g. during a storm. The effectiveness of the method is shown by comparing the number of cycles and the fatigue damage estimation, before and after reducing.

In the present study, the results of the monotonic tension tests and low cycle fatigue tests performed on aluminium alloy EN AW-2024-T3 under various operating temperatures are presented in order to assess the fatigue behaviour of the aluminium alloy under evaluated temperatures. Monotonic tests were performed to determine the influence of temperature on mechanical properties of the material. The aim of cyclic tests was to acquire the parameters required for Manson-Coffin equation in order to plot strain-fatigue life curves. Moreover, stress-strain behaviour of the alloy and the cyclic hardening behaviour were evaluated using Ramberg-Osgood equation. Finally, PSWT-damage parameters for each temperature have been calculated for further investigation of the effects of the temperature on fatigue life using acquired data while taking the account of mean stress effect into calculations. Variations in the experimental data due to various test temperatures are presented for both monotonic and cyclic tests. © 2015 Wiley Publishing Ltd.

Fabric reinforced cementitious matrix (FRCM) is a relatively new material system recently developed for the repair, retrofit, and rehabilitation of reinforced concrete (RC) and masonry structures. Concrete structures such as bridges experience high traffic volumes and varying vehicle axle weights causing repeated cyclic loading throughout their lifetime. Cyclic loading may cause damage to the structure, a phenomenon known as fatigue. Due to the novelty of FRCM technology, there is a lack of research regarding the long-term performance of FRCM systems for RC strengthening. This study aims to investigate experimentally the parameters that most influence the flexural fatigue performance of Polyparaphenylene benzobisoxazole (PBO) FRCM strengthened RC beams. For members subject to cyclic loading, a stress ratio vs. the number of cycles (S-N) curve is developed with the objective of defining the endurance limit of the strengthened beams. Failure mode and fatigue life of the beams during cyclic loading are investigated and discussed. 2016 International Committee of the SCMT conferences. All rights reserved. The project was made possible with the financial support received from the University Transportation Center RE-CAST and the Qatar National Research Fund (a member of Qatar Foundation) under NPRP grant # 7-1720-2-641. The statements made herein are solely the responsibility of the authors. Scopus

Polymer nanocomposite has received great research interest in design of engineering components owing to its remarkable improvement in tribological characteristics. Rolling contact fatigue is a predominant failure mode of the many functional components like gears, bearings, cams, ball screw rods and rail wheels. Nanosize clay fillers were dispersed into the polymer using melt intercalation method to produce polymer nanocomposite material. Injection-molded disc-type specimens were made to run against each other on twin-disc test rig designed in-house. To understand the behaviour of the materials, rolling contact fatigue behaviour against different contact loads under constant speed were studied. Rolling contact fatigue testing of polymer nanocomposite has revealed significant difference from the pristine PA6 behaviour in failure modality and temperature rise. Addition of nanoclay to polymer although improved the modulus and strength of the nanocomposite, deteriorated the rolling contact behaviour. Rolling contact fatigue performance of PA6 was better than that of the clay-reinforced polymer nanocomposite under all tested conditions. Polymer nanocomposite materials have shown poor wear resistance as the specific wear rate was calculated to be higher for PNC materials under rolling contact fatigue conditions. Difference in surface temperature rise in PA6 and polymer nanocomposite has led to the different failure mechanism and reduction in rolling contact fatigue life of polymer nanocomposite materials.

Commonly used fatigue crack growth prediction models estimate life in a deterministic manner. Realizing that several variables influence fatigue crack growth, it is pertinent to assess crack growth using probabilistic models. In the present work, a probabilistic model is studied using continuous and segmented crack growth rate data models. It is observed that the prediction of life using Paris constants from continuous data model is accurate only in a finite region of the crack growth. The model based on segmented data provides more accurate life predictions with lesser variance with experimental data than the continuous data model. � 2011 Elsevier Ltd. All rights reserved.

Stress peening forming is widely used in the aeronautics industry to induce curvatures in wing skins. Most of the investigations of stress peen forming are empirical and experimental. In this paper, a three step numerical model that can simulate this process was developed. First, an implicit Finite Element Analysis (FEA) with ANSYS where a prebending moment along the spanwise direction of the component was performed. Then, an explicit FEA with LS-DYNA simulating shot impacts on the pre-stressed component was executed in order to obtain the resulting stresses inside the component. Finally, an implicit FEA with ANSYS was performed for calculating the arc heights and the curvature radii of the component in chordwise and spanwise directions. Numerical analysis of the process shows that the prebending moments have an influence not only on the residual stress profiles but also on the curvatures of the deformed component in chordwise and spanwise directions. This model was used to establish a relationship between the prebending moment and the resulting arc heights and residual stress profiles. The numerical strategies developed in this paper supply a useful tool for studying and optimizing the stress peening process. © 2011 Elsevier Ltd. All rights reserved.