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Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Charge variable, Variable load, Carga variable, Ungleichmaessige Beanspruchung, Contrainte seuil, Threshold stress, Tension umbral, Fatigue, Fatiga, Ermuedung, Fissure courte, Short crack, Fisura corta, Propriété mécanique, Mechanical properties, Propiedad mecánica, Non-propagating small cracks, Threshold stress intensities, Ultrasonic fatigue, Variable amplitude loading, and Very high cycle fatigue (VHCF)

Ever since high-strength steels were found to fail below the traditional fatigue limit when loaded with more than 108 cycles, the investigation of metals' and alloys' very high cycle fatigue properties has received increased attention. A lot of research was invested in developing methods and machinery to reduce testing times. This overview outlines the principles and testing procedures of very high cycle fatigue tests and reports findings in the areas of crack formation, non-propagating small cracks, long crack propagation and thresholds. Furthermore, superimposed and variable amplitude loading as well as frequency effects are reported.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Alliage base aluminium, Aluminium base alloys, Charge variable, Variable load, Carga variable, Ungleichmaessige Beanspruchung, Fatigue, Fatiga, Ermuedung, Propriété mécanique, Mechanical properties, Propiedad mecánica, 2024 Aluminium alloy, Damage accumulation, Ultrasonic fatigue, Variable amplitude loading, and Very high cycle fatigue

Ultrasonic fatigue tests with variable amplitude are performed for the first time at positive load ratios. The method utilising ultrasonic equipment, a servo-hydraulic or electromechanical load frame and computer control is described. Aluminium alloy 2024-T351 is tested at approximately 20 kHz with variable amplitude in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime at load ratios R = -1, R = 0.1 and R = 0.5. Constant amplitude data are available and are used for Miner damage accumulation calculations. For load ratio R = -1, the mean damage sum decreases from 0.5 to 0.3 when lifetimes increase from the HCF regime to 109 cycles, and increases at higher numbers of cycles. For load ratio R = 0.1, the mean damage sum decreases from 1.1 to 0.2 when lifetimes increase from HCF to VHCF. At load ratio R = 0.5, the mean damage sum is approximately 0.1 in the VHCF regime. Cracks leading to VHCF failures start at broken constituent particles, probably Al7Cu2(Fe,Mn), or at agglomerations of fractured particles. Crack initiation occurs at the surface or less frequently in the interior.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Acier cémenté, Case hardened steel, Acero cementado, Amorçage fissure, Crack initiation, Iniciación grieta, Risseinleitung, Fatigue, Fatiga, Ermuedung, Microstructure, Microestructura, Mikrogefuege, Propriété mécanique, Mechanical properties, Propiedad mecánica, Case-hardened steel, Competing sites of crack initiation, Kitagawa diagram, and Very high cycle fatigue (VHCF)

In this investigation notched and fracture mechanics specimens were machined from the steel SAE 5120 (DIN EN 20MnCr5) in two cleanliness conditions. The first material is used for high-performance components and is nearly free of oxides. The second material is standard steel and used for common requests in the field of drive engineering containing non-metallic inclusions in a dimension that is state of the art in steel making. The notched specimens were case-hardened in two different ways. Afterwards, the surfaces were ground and therefore showed compressive residual stresses. Uniaxial VHCF tests were performed up to 200 million cycles under the stress ratios R = ―1 and R = 0 using two resonant pulse systems. For this purpose the geometries of the specimens had been optimised so that the achieved test frequency was 190 Hz. Fatigue failure is possible at all applied numbers of cycles meaning that there is no real fatigue limit in this region. Fatigue crack initiation took place from different origins and at different sites. Different analyses are shown for interpretating the type of fatigue crack initiation and its site in the specimen. The fracture mechanics specimens were blank hardened in order to have the core properties of the notched specimens. Crack propagation was measured in the near-threshold region. An extended Kitagawa diagram is shown to demonstrate the influence of stress amplitude and flaw size on the failure probability.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Acier austénito ferritique, Austenitic ferritic steel, Acero ferrítico austenítico, Austenitisch ferritischer Stahl, Acier double phase, Dual phase steel, Acero doble fase, Dualphasenstahl, Acier inoxydable duplex, Duplex stainless steel, Acero inoxidable duplex, Acier inoxydable, Stainless steel, Acero inoxidable, Nichtrostender Stahl, Contrainte thermomécanique, Thermomechanical stress, Tensión termomecánica, Décomposition spinodale, Spinodal decomposition, Decomposición espinodal, Spinodale Entmischung, Fatigue, Fatiga, Ermuedung, Point Curie, Curie temperature, Punto Curie, Curie Temperatur, Propriété mécanique, Mechanical properties, Propiedad mecánica, Température, Temperature, Temperatura, Temperatur, and Thermo mechanical fatigue

The thermo mechanical fatigue behaviour of a ferritic-austenitic duplex stainless steel has been investigated in a temperature range of 350-600 °C. The Curie temperature (TCURIE) was determined by an abrupt increase of the power of the inductive heating device and a small control deviation of the temperature. Thus, according to Tavares et al. [1] the evolution of the spinodal decomposition in the DSS was characterised by the shift of the Curie temperature for each test. The results are compared with ageing and annealing experiments in combination with tensile tests at room temperature. In addition, microstructure observations were performed in a field-emission scanning electron microscope.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Corrosion, Action des agents de corrosion, Corrosion environments, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Techniques de l'ingénieur appliqués à la métallurgie. Applications. Divers, Engineering techniques in metallurgy. Applications. Other aspects, Applications, Industrie automobile, Automotive engineering, Application, Aplicación, Anwendung, Châssis véhicule, Vehicle chassis, Chasis vehículo, Fahrgestell, Conception, Design, Diseño, Gestaltung, Corrosion sel, Salt corrosion, Corrosión sal, Salzkorrosion, Durée vie, Lifetime, Tiempo vida, Lebensdauer, Fatigue, Fatiga, Ermuedung, Industrie automobile, Automobile industry, Industria automóvil, Autoindustrie, Propriété mécanique, Mechanical properties, Propiedad mecánica, Forged aluminium, Special events, Spectrum loading, and Tension strut

The structural durability design of a tension strut of forged aluminium (EN AW 6082 T6), which is a safety component of the automotive chassis, is described. The first step of the structural durability design is the knowledge of the mechanical and environmental loadings. The mechanical loadings are the spectrum loading for the designated normal driving conditions and unintended special event loadings by e.g. braking over road bumps, which are introduced into the component through the wheels. The local stresses imposed on the component are also influenced by kinematics, stiffness, axle mass, dampers, bearings, bump geometry, etc. The environmental loading is the corrosion caused, in winter-time, by salty water on the roads. For design according to the local stress concept, the knowledge of Woehler-curves without and with salt corrosion effects is necessary. On this basis, cumulative fatigue under spectrum loading, which also comprises the special events mentioned, is assessed for a standard configuration and for an optimised one. The numerical results are verified by experimental proofs on the component in the laboratory and on the proving ground as well as by field tests with vehicles.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Anisotropie, Anisotropy, Anisotropía, Fatigue, Fatiga, Ermuedung, Glissement, Slip, Deslizamiento, Gleiten, Joint grain, Grain boundary, Limite grano, Korngrenze, Microstructure, Microestructura, Mikrogefuege, Modélisation, Modeling, Modelización, Méthode élément fini, Finite element method, Método elemento finito, Finite Element Methode, Propagation fissure, Crack propagation, Propagación fisura, Rissausbreitung, Propriété mécanique, Mechanical properties, Propiedad mecánica, Prédiction, Prediction, Predicción, Système glissement, Slip system, Sistema deslizamiento, Gleitsystem, Crack path, and Extended finite element

This study develops a new method for the analysis of fatigue crack growth at micro-structural scale. Proposed model was constructed based on material anisotropic properties and crystallographic planes. In this research, it has been attempted to suggest an accurate and precise criterion for the prediction of crack growth path at micro-structural scales by the study of various criteria for crack growth. For this purpose, considering fracture energy for trans-granular and inter-granular fracture as well as dominant slip planes, a criterion was proposed to predict crack growth. In the current research, fatigue tests were performed on two different alloys and the real path of the crack growth was obtained. Next, by the simulation of tested pieces through finite element software (ABAQUS) and using extended finite element method, various criteria to predict crack growth path were studied. The microstructures of both specimens tested in considered areas were modelled with an anisotropic behaviour and their crystal orientations were gained using electron-back-scattering-diffraction-pattern (EBSP) method. The results suggest the accuracy and precision of proposed criterion with minor error in single-phase alloys and major difference in two-phase alloys.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Acier austénito ferritique, Austenitic ferritic steel, Acero ferrítico austenítico, Austenitisch ferritischer Stahl, Acier double phase, Dual phase steel, Acero doble fase, Dualphasenstahl, Acier inoxydable, Stainless steel, Acero inoxidable, Nichtrostender Stahl, Fatigue oligocyclique, Low cycle fatigue, Fatiga oligocíclica, Ermuedung bei niedrigen Lastspielzahlen, Fissure courte, Short crack, Fisura corta, Fissure fatigue, Fatigue crack, Fisura fatiga, Ermuedungsriss, Modélisation, Modeling, Modelización, Propagation fissure, Crack propagation, Propagación fisura, Rissausbreitung, Propriété mécanique, Mechanical properties, Propiedad mecánica, Duplex steel, LCF, Short fatigue cracks, and VHCF

The present paper reviews experimental results on the fatigue damage of austenitic-ferritic duplex steel under various load levels ranging from LCF to VHCF, placing the focus towards the relationship between the crystallographic orientation of individual grains and grain patches that exhibit slip band formation, fatigue crack initiation and growth. A combination between fatigue testing of electropolished specimens and analytical electron microscopy (SEM/EBSD, TEM) revealed that under LCF loading conditions almost all the ferrite and the austenite grains showed plasticity, while under HCF and VHCF loading conditions, slip band formation was limited to the softer austenite grains and a low plastic activity is observed in the ferrite. Once being formed, the bands generate high stress concentrations, where they impinge the α-γ phase boundaries, eventually, leading to the crack initiation. This is discussed by applying a numerical simulation approach based on the finite-element (FEM) and the boundary-element (BEM) method.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Transformation de matériaux métalliques, Production techniques, Métallurgie des poudres. Matériaux composites, Powder metallurgy. Composite materials, Métaux renforcés par des fibres, Fibre reinforced metals, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Amortissement, Damping, Amortiguación, Durée vie fatigue, Fatigue life, Longevidad fatiga, Ermuedungslebensdauer, Fatigue, Fatiga, Ermuedung, Fibre verre, Glass fiber, Fibra vidrio, Matériau composite, Composite material, Material compuesto, Verbundwerkstoff, Métal renforcé fibre, Fibre reinforced metal, Metal reforzado fibra, Faserverstaerktes Metall, Propriété mécanique, Mechanical properties, Propiedad mecánica, Prédiction, Prediction, Predicción, Composites, Frequency response function (FRF), and Natural frequency

The main objective of the present work is to investigate the capability of experimental modal analysis as a nondestructive tool to characterize and quantify the fatigue behavior of laminated composite beam with different lamina orientations and cantilevered boundary condition. In the present work, experimental modal analysis was conducted on the specimens previously subjected to fatigue loading to determine the modal parameters (natural frequency, damping ratio and mode shape). This was achieved through studying the response of modal testing with different specimens of different lamina orientations as a main factor affecting fatigue life. This correlates modal parameters such as: damping ratio, natural frequency and mode shape to fatigue behavior. The composite material used in experiments is glass fiber reinforced polyester (GFRP) laminate. Plane bending fatigue tests were performed on standard fatigue specimens. The fatigue test was interrupted at different fatigue life ratios (n/Nf) and modal testing was conducted to determine the change in modal parameters. The results showed that the changes of modal parameters provide a proper means for predicting the fatigue behavior of composite structures. From the experimental results of both dynamic and fatigue tests, curve fitting technique was used to correlate modal parameters to fatigue life. An exponential and quadratic equations have been obtained which correlate fatigue life ratio to damping ratio and resonant frequency respectively. It was noticed from the curves representing exponential and quadratic equations that the value of damping ratio ς is more noticeable than the value of frequency, which means that the extent of fatigue damage determines the damping ratio, hence damping ratio could be said to be a good indicator of the fatigue life ratio.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Durée vie fatigue, Fatigue life, Longevidad fatiga, Ermuedungslebensdauer, Fatigue, Fatiga, Ermuedung, Méthode contrôle, Control method, Método control, Propriété mécanique, Mechanical properties, Propiedad mecánica, Fatigue life evaluation, Maximum amplitude principle, Rainflow method, and Shadow method

It is shown in present study that Rainflow method is unable to accurately estimate fatigue life of components under random loading, almost always. The inconsistencies between results of Rainflow method and hysteresis curve are also discussed. Alike the Peak counting method, it is shown that Shadow method doesn't consider the possibility of deformation within individual cycles. Hence, Moshrefifar and Azamfar method is proposed as a novel technique having accurate results in different analytical conditions which are in good consistence with results obtained from hysteresis curves. Authors finally propose an algorithm as well as a C language program for this method.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Alliage forgé, Wrought alloy, Aleación forjada, Schmiedelegierung, Amorçage fissure, Crack initiation, Iniciación grieta, Risseinleitung, Fatigue, Fatiga, Ermuedung, Microstructure, Microestructura, Mikrogefuege, Propriété mécanique, Mechanical properties, Propiedad mecánica, Résistance fatigue, Fatigue strength, Resistencia fatiga, Dauerfestigkeit, Résistance mécanique, Strength, Resistencia mecánica, Festigkeit, Aluminum alloys, Microstructures, and Very high cycle fatigue

Fatigue studies were conducted under load control with a servo-hydraulic testing machine with smooth specimens of the aluminum wrought alloys EN AW-6056-T6 (Rm = 399 MPa) and EN AW-6082-T5 (Rm = 356 MPa) up to a maximum number of N = 2 x 108 and 109 cycles, respectively. The results show for both aluminum alloys that the fatigue strength decreases with increasing number of cycles after the kneepoint of the S-N-curve and that approximately at this point a transition of the crack initiation site from the surface to the subsurface occurs. All fractured specimens were investigated with a scanning electron microscope (SEM). Large defects like primary intermetallic particles could not be found at the crack initiation sites. The difference between the subsurface non-defect crack initiation sites of both alloys is to be found in the fractographic structure. The internal crack initiation site of EN AW-6056-T6 shows a multiplicity of cleavage-like planes contrary to the flat area found at the alloy EN AW-6082-T5. These results were already presented in [1]. The scope of this present paper is new microstructural investigations and the formulation of a failure model which respects the results of different scales of microscopy. Electron back scatter diffraction analysis (EBSD analysis) and transmission electron microscopy (TEM) were done for both alloys to characterize the microstructure and to compare unstressed and tested materials. These differences are discussed with regard to the differences in failure mechanisms.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Alliage base titane, Titanium base alloys, Aluminium alliage, Aluminium alloy, Aluminio aleación, Aluminiumlegierung, Dislocation, Dislocación, Versetzung, Fatigue oligocyclique, Low cycle fatigue, Fatiga oligocíclica, Ermuedung bei niedrigen Lastspielzahlen, Haute température, High temperature, Alta temperatura, Hochtemperatur, Microstructure, Microestructura, Mikrogefuege, Propriété mécanique, Mechanical properties, Propiedad mecánica, Température, Temperature, Temperatura, Temperatur, Dislocations, High temperature fatigue, and Lamellar TiAl alloy

Low cycle fatigue properties of lamellar TiAl with 8 at.% Nb were studied at four temperatures: room temperature, 700, 750 and 800 °C. Up to 750 °C, stable cyclic behaviour is observed while cyclic softening is characteristic for 800 °C. The strength of the alloy is still high even at 800 °C. The TEM observation did not reveal any substantial changes in the microstructure due to the cycling at RT. At 750 °C, the lamellar structure was in some places destroyed by cyclic plastic straining and pure γ-phase islands with high density of dislocation debris were formed. At 800 °C, the domains without lamellar structure cover about 10% of volume and are almost dislocation free. The destruction of lamellar microstructure and possible annealing of dislocation debris is the reason for marked cyclic softening at 800 °C.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Acier austénitique, Austenitic steel, Acero austenítico, Austenitischer Stahl, Basse température, Low temperature, Baja temperatura, Tieftemperatur, Déformation, Deformation, Deformación, Verformung, Fatigue, Fatiga, Ermuedung, Martensite, Martensita, Martensit, Microscopie électronique transmission, Transmission electron microscopy, Microscopía electrónica transmisión, Transmissionselektronenmikroskopie, Microstructure, Microestructura, Mikrogefuege, Propriété mécanique, Mechanical properties, Propiedad mecánica, Température ambiante, Room temperature, Temperatura ambiente, Raumtemperatur, Transformation martensitique, Martensitic transformation, Transformación martensítica, Martensitische Umwandlung, Transformation phase, Phase transformation, Transformación fase, Phasenumwandlung, Deformation induced martensite formation, Fatigue behavior, and TEM

Microstructural investigations of the fatigue behavior and phase transformation in the metastable austenitic steels AISI 304 and 348 were performed. The specimens were cyclically loaded with a constant total-strain-amplitude in the temperature range -60 °C to 25 °C. By means of stress-strain hysteresis and magnetic measurements, the fatigue behavior and phase transformation were characterized. Microstructural changes were evaluated by transmission electron microscopy and by scanning electron microscopy by means of electron backscatter diffraction technique at defined fatigue states. The steels show differences in austenite stability, which lead to significant changes in the deformation induced martensite formation and the fatigue behavior. Dependent on the type of steel and the testing temperature similar α'-martensite fractions but different strengths developed.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Alliage base nickel, Nickel base alloys, Contrainte thermomécanique, Thermomechanical stress, Tensión termomecánica, Dislocation, Dislocación, Versetzung, Déformation, Deformation, Deformación, Verformung, Fatigue, Fatiga, Ermuedung, Monocristal, Single crystal, Einkristall, Propagation fissure, Crack propagation, Propagación fisura, Rissausbreitung, Propriété mécanique, Mechanical properties, Propiedad mecánica, Superalliage, Superalloy, Superaléación, Superlegierung, Crack paths, Deformation twin, Dislocations, Superalloys, and Thermomechanical fatigue

The deformation and damage mechanisms of a single crystal nickel-based superalloy CMSX-4 have been investigated under out-of-phase thermomechanical fatigue (OP TMF) condition. The deformation was highly localized to the area near the crack tip, where multiple groups of parallel twin plates on {111} planes formed during the high temperature-compressive half cycle. The atomistic a/6 〈112〉 twinning shear-based approach is presented which explains the origin of twinning. The localized twins provided a preferential path for crack propagation. OP TMF deformation was dominated by partial dislocation movement with {111}〈112〉 slip system, resulting in the formation and propagation of deformation twins.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Acier ressort, Spring steel, Acero resorte, Federstahl, Défaut surface, Surface defect, Defecto superficie, Oberflaechenfehler, Fatigue, Fatiga, Ermuedung, Microstructure, Microestructura, Mikrogefuege, Propriété mécanique, Mechanical properties, Propiedad mecánica, Rectification plane, Surface grinding, Rectificación plana, Flachschleifen, Rectification surface, Grinding, Rectificación superficie, Ressort, Spring, Resorte, Feder, Usinage, Machining, Mecanizado, Zerspanen, Clean spring steel, Inhomogeneous microstructure, Loading condition, Surface grinding defect, and Very high cycle fatigue

Very high cycle fatigue (VHCF) properties of a newly developed clean spring steel were experimentally examined under rotating bending and axial loading. As a result, this steel represents the duplex S-N property only for surface-induced failure under rotating bending, whereas it represents the single S-N property for surface-induced failure and interior inhomogeneous microstructure-induced failure under axial loading. Surface small grinding defect-induced failure is the predominant failure mode of this steel in VHCF regime. The surface morphology of the interior inhomogeneous microstructure with distinct plastic deformation is much rougher than that of the ambient matrix, which means the stress concentration resulted from the strain inconsistency between the microstructural inhomogeneity as soft phase and the ambient matrix as hard phase plays a key role in causing interior crack initiation. Considering the effect of surface compressive residual stress, the threshold stress intensity factor for surface small defect-induced crack propagation of this steel is evaluated to be 2.04 MPam1/2, which means that the short crack effect plays a key role in causing the surface small defect-induced failure of this steel in the VHCF regime. From the viewpoint of defect distribution, surface and interior failure probabilities are equivalent under a fixed characteristic value of defect density. If the interior defect size is less than or even equal to the surface defect size, surface defect-induced failure will become the predominant failure mode in VHCF regime, especially under rotating bending.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Effet concentration, Concentration effect, Efecto concentración, Fatigue, Fatiga, Ermuedung, Hydrogène, Hydrogen, Hidrógeno, Wasserstoff, Microstructure, Microestructura, Mikrogefuege, Propriété mécanique, Mechanical properties, Propiedad mecánica, Fine grain area (FGA), Optically bright zone (OBZ), SAE 52100, and Very high cycle fatigue (VHCF)

The fatigue life of the bearing steel 52100 (100Cr6) in bainite and martensite conditions was investigated up to 2 × 109 cycles. The tests were performed under cycling tension (R = 0.1) and tension-compression (R = -1) on a piezo-electric ultrasonic testing equipment. The specimens are designed with a cylindrical part in the highly stressed centre. Due to grinding, compressive residual stresses are found at the surface, hence crack initiation solely occurs subsurface. Prior testing half of the specimens was charged with hydrogen. The hydrogen content varies from 0.6 as initial condition to 3 ppm after charging. The increased hydrogen content decreased the endurance limit to nearly half of the value of uncharged conditions and crack initiation changed: Conditions with low hydrogen content failed from chromium carbides, titanium nitrides or slag agglomerations. Conditions with 3 ppm hydrogen failed from slag agglomerations, often in combination with aluminium magnesium oxides, and manganese sulphides. Next to the inclusions a fine granular area (FGA) could be observed in some cases, and nearly all fractured surfaces showed a fisheye surrounded by an Optically Bright Zone (OBZ) with the crack initiating inclusion in its centre. Furthermore, selected specimens where analysed using secondary ion mass spectroscopy in a time of flight setup (ToF-SIMS) to ascertain the local hydrogen content. From the results it is assumed that hydrogen accumulates in the cavity at inclusions or bonds to the inclusion if it contains silicon.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Assemblage et découpage thermique: aspects métallurgiques, Joining, thermal cutting: metallurgical aspects, Soudage, Welding, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Alliage mémoire forme, Shape memory alloy, Aleación memoria forma, Formgedaechtnislegierung, Fatigue, Fatiga, Ermuedung, Fil métallique, Wire, Hilo metálico, Draht, Propriété mécanique, Mechanical properties, Propiedad mecánica, Soudage sous flux, Submerged arc welding, Soldadura por arco sumergido, UP Schweissen, Constant-strain, Constant-stress, Functional fatigue, Limited maximum strain, and SMA wires

The rational design of smart actuators based on shape memory alloys requires reliable strength data from the thermo-mechanical cycling of the material (functional fatigue). Functional tests results do not abound in the technical literature and the few data available are mostly limited to the condition of constant applied stress, which is hardly achieved in operation. The disagreement between actual working conditions and laboratory conditions leads to suboptimal designs and undermines the prediction of the life of the actuator. To bridge the gap between experiment and reality, this paper envisions four cyclic tests spanning the range of loadings which can occur in practice: constant-stress, constant-strain, constant-stress with limited maximum strain and linear stress-strain cycle. Commercial NiTi wires (0.15 mm diameter) are tested under constant-stress, constant-strain and constant stress with limited maximum strain conditions using a custom machine and the disclosed results are critically discussed.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Alliage base aluminium, Aluminium base alloys, Contrainte résiduelle, Residual stress, Tensión residual, Eigenspannung, Dépôt projection, Spray coating, Depósito proyección, Spritzbeschichten, Fatigue, Fatiga, Ermuedung, Métallurgie poudre, Powder metallurgy, Metalurgia polvo, Pulvermetallurgie, Nanocristal, Nanocrystal, Propriété mécanique, Mechanical properties, Propiedad mecánica, Résistance fatigue, Fatigue strength, Resistencia fatiga, Dauerfestigkeit, Résistance mécanique, Strength, Resistencia mecánica, Festigkeit, Cold spray, and Nanocrystalline

Nanocrystalline cryomilled and microcrystalline Al7075 powders have been deposited on Al5052 substrates using the low-pressure cold spray coating technique in order to study the effect of the powder micro/nano structure on fatigue behavior of coated samples. Microstructural characteristics and fatigue behavior of the coated structure have been surveyed through experimental tests. The powders' size and shape distribution have been studied using scanning electron microscopy. In order to obtain the S-N diagrams, grit blasted and coated samples with different treatment parameters have been tested for fatigue at load control condition. Grain size measurement has been performed by X-ray diffraction. X-ray diffraction has also been used to measure the residual stress distribution in both the deposited material and the substrate. Surface roughness measurements have been performed on all series. It has been observed that, although the coating porosity was not zero, the fatigue limit is slightly increased by using the cryomilled powders.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Acier, Steel, Acero, Essai non destructif, Non destructive test, Ensayo no destructivo, Zerstoerungsfreie Pruefung, Essai ultrason, Ultrasonic control, Ensayo ultrasonido, Ultraschallpruefung, Fatigue, Fatiga, Ermuedung, Propriété mécanique, Mechanical properties, Propiedad mecánica, Carburized alloy steel, Torsional loading, Ultrasonic fatigue testing, and Very high cycle fatigue

A very high cycle fatigue diagram and crack propagation behavior of carburized SCM420H are obtained using an ultrasonic torsional fatigue testing machine and are compared with those of non-carburized SCM420H. Fatigue crack initiation and growth are observed in the very high cycle regime for both carburized and non-carburized SCM420H. Results show that carburizing of SCM420H is effective for fatigue life enhancement in the very high cycle regime. Furthermore, crack deflection from mode II to mode I occurs under torsional fatigue. This behavior is discussed based on fracture mechanics.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Corrosion, Action des agents de corrosion, Corrosion environments, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Application, Aplicación, Anwendung, Aube turbine, Turbine blade, Paleta turbina, Turbinenschaufel, Corrosion piqûre, Pitting corrosion, Corrosión superficial, Lochkorrosion, Croissance, Growth, Crecimiento, Durée vie fatigue, Fatigue life, Longevidad fatiga, Ermuedungslebensdauer, Fatigue, Fatiga, Ermuedung, Fissure fatigue, Fatigue crack, Fisura fatiga, Ermuedungsriss, Propagation fissure, Crack propagation, Propagación fisura, Rissausbreitung, Propriété mécanique, Mechanical properties, Propiedad mecánica, Taux contrainte, Stress ratio, Porcentaje tensión, Turbine vapeur, Steam turbine, Turbina vapor, Dampfturbine, Vapeur eau, Water vapor, Vapor agua, Wasserdampf, Vitesse propagation, Propagation velocity, Velocidad propagación, 12% Cr steam turbine blade steel, Fatigue crack growth rate, Kitagawa-Takahashi diagram, and Very high cycle fatigue

The influence of corrosion pits on the endurable fatigue loading in different environments and at various stress ratios has been investigated for 12% Cr steam turbine blade steel. Very high cycle fatigue measurements were performed using ultrasonic fatigue testing technique with superimposed static load at stress ratios ranging from R = 0.05 to R = 0.9. Fatigue crack growth rate (FCGR) measurements in the near threshold regime and S-N tests were conducted at a temperature of 90 °C in air, de-aerated 300 ppb Cl- solution and aerated 6 ppm Cl- solution. The influence of corrosion pits on the fatigue limit was determined with artificially generated corrosion pits. It was found that the FCGRs in solution are lower and the threshold stress intensity factor ranges ΔKth are higher than in air. Fracture surface investigation with scanning electron microscope and roughness measurement were made which suggest oxide and roughness induced crack closure as the most appropriate explanation. Data evaluation of fatigue life tests with pre-pitted specimens supports the applicability of treating pits as effective cracks. An estimation for the stress intensity factor range of pits which allows determining the endurable fatigue loading was empirically found.

Mechanical engineering, Génie mécanique, Metallurgy, welding, Métallurgie, soudage, Polymers, paint and wood industries, Polymères, industries des peintures et bois, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Metaux. Metallurgie, Metals. Metallurgy, Propriétés mécaniques. Rhéologie. Mécanique de la rupture. Tribologie, Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology, Fatigue, Amorçage fissure, Crack initiation, Iniciación grieta, Risseinleitung, Bande glissement, Slip band, Banda deslizamiento, Gleitband, Défaut ponctuel, Point defect, Defecto puntual, Punktfehler, Fatigue, Fatiga, Ermuedung, Filage, Spinning, Hilado, Strangpressen, Fissure fatigue, Fatigue crack, Fisura fatiga, Ermuedungsriss, Formage, Forming, Conformado, Umformen, Glissement, Slip, Deslizamiento, Gleiten, Propriété mécanique, Mechanical properties, Propiedad mecánica, Extrusion, Fatigue crack initiation, Intrusion, Persistent slip band (PSB), and Point defects

The role of point defects in the formation of surface relief and in the initiation of a fatigue crack in crystalline materials is analyzed. The dislocation interactions in the bands of intensive cyclic slip (persistent slip bands - PSBs) are specified and relations describing the formation and annihilation of interstitial and vacancy type defects in the channels of the ladder-like PSB are derived. The continuous formation, annihilation and primarily the migration of point defects are proposed to be responsible for the mass redistribution within PSB and between PSB and the PSB/matrix boundary. The redistribution of the matter results in local tensile and compressive stresses that are the sources of the principal irreversibility of slip within PSB. Local tensile and compressive stresses are relaxed by dislocation movement within PSB in the direction of the active Burgers vector and lead to the formation of characteristic surface relief in the form of extrusions and intrusions. The intrusions represent crack-like defects and fatigue cracks initiate in the tip of intrusions.