Tesi sul tema "High fatigue cycles"
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Kim, Tae Hyun. "Fatigue of surface engineered steel in rolling-sliding contact". Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325019.
Testo completoSimon, Julien. "Influence de micro-entailles sur le comportement en fatigue à grand nombre de cycles d'un alliage de TA6V : Comparaison avec le fretting-fatigue". Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0034/document.
Testo completoThis study is about the influence of micro-notches on the high cycle fatigue behavior of a Ti64 alloy and the comparison with similar fretting fatigue tests. Preliminary studies showed that fretting-fatigue stress fields can be reproduced by micro-notched. The COGNAC project leaded by Safran Aircraft Engines was built to verify if a unique model can reproduce both fretting-fatigue and notched samples fatigue tests. The scope of this experimental study is limited to the notched samples. In this PHD thesis, the notches are grinded and the results are compared with fretting-fatigue tests on grinded surfaces. V-notched with notch root radius from 50 to 500 μm were chosen to reproduce the stress gradient of fretting-fatigue tests. A geometry with two inclined notches facing each other allows to reproduce shear stress and stress triaxiality from fretting-fatigue tests. Three different experimental studies were performed. First on un-notched specimens with a grinded surface state to produce a reference fatigue limit for grinded surface state without stress concentration. The second study the notch root radius effect on the fatigue limit with samples with one non-inclined notch of 500 μm of depth. The last one is a series of fatigue tests on samples with two inclined notches that reproduce the stress distribution of fretting-fatigue tests. Pseudo-cleavage facets, multi cracks initiations in the notch root and the presence of two propagation stages is similar to the fretting-fatigue tests mechanisms. However, non propagating cracks were not observe at the notch root while many of them were present during the fretting-fatigue test. The initiation sites and the early stages of propagation seem to be controlled by grinded affected areas. Finally, three fatigue criteria were used to try to reproduce the experimental results. The criteria based on the critical distance theory and gradient theory –with a local gradient and an affine effect of the gradient term- can reproduce the fatigue limits of notched samples but fail to predict both notched and un-notched specimen fatigue limits with a unique data set. The third one is a probabilistic criterion which success to predict the experimental fatigue limits not only of notched samples but also smooth ones. The comparisons between the experimental results of the fatigue on the specimens with two inclined notches and the fretting-fatigue shows a difference of 20%. The distribution of the Crossland stress is quite similar. In the future, it would be useful to make a new comparison between fretting-fatigue and fatigue on notches using the probabilistic criterion to design the tests. This new comparison could lead to the proposal of a unique methodology to take into account the fretting-fatigue and the fatigue on stress concentrators
Torabiandehkordi, Noushin. "High and very high cycle fatigue behavior of DP600 dual-phase steel : correlation between temperature, strain rate, and deformation mechanisms". Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0020/document.
Testo completoThis work is an attempt towards a better understanding of the high cycle and very high cycle fatigue behaviors of a ferritic-martensitic dual-phase steel, with a regard to temperature and strain rate effects, resulting from accelerated fatigue loading frequencies. The influence of frequency on fatigue response of DP600 steel was investigated by conducting ultrasonic and conventional low frequency fatigue tests. Fractography studies and microscopic observations on the surface of specimens were carried out to study the deformation and fracture mechanisms under low and ultrasonic frequencies. Moreover, in situ infrared thermography was carried out to investigate the thermal response and dissipative mechanisms of the material under fatigue tests. The S-N curves were determined from ultrasonic 20-kHz fatigue loadings and conventional tests at 30 Hz. Fatigue life for a given stress amplitude was found to be higher in the case of ultrasonic fatigue whereas the fatigue limit was the same for both cases. Moreover, crack initiation was always inclusion-induced under ultrasonic loading while under conventional tests it occurred at slip bands or defects on the surface. The inevitable temperature increase under ultrasonic fatigue at high stress amplitudes along with the rate dependent deformation behavior of ferrite, as a body centered cubic (BCC) structure, were found as the key parameters explaining the observed fatigue behavior and thermal response under low and ultrasonic frequencies. The discrepancies observed between conventional and ultrasonic fatigue tests were assessed through the mechanisms of screw dislocation mobility in the ferrite phase as a BCC structure. The higher fatigue life and inclusion-induced crack initiations in the case of ultrasonic loading were attributed to the dynamic strain aging, which resulted from the high temperature increases at high stress amplitudes. The existence of a transition in deformation regime from thermally-activated to athermal regime under ultrasonic fatigue loading by increasing the stress amplitude was confirmed. Below the fatigue limit, deformation occurred in thermally-activated regime while it was in athermal regime above the fatigue limit. Under conventional loading deformation occurred in athermal regime for all stress amplitudes. From the analysis of the experimental data gathered in this work, guidelines were given regarding the comparison and interpretation of S-N curves obtained from conventional and ultrasonic fatigue testing. A transition map was produced using the experimental results for DP600 steel as well as data available in the literature for other ferrite based steels, showing the correlation between thermally-activated screw dislocation movement and the absence of failure in very high cycle fatigue
Tarar, Wasim Akram. "A New Finite Element Procedure for Fatigue Life Prediction and High Strain Rate Assessment of Cold Worked Advanced High Strength Steel". The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204575243.
Testo completoZhao, Mengxiong. "Ultrasonic fatigue study of Inconel 718". Thesis, Paris 10, 2018. http://www.theses.fr/2018PA100063/document.
Testo completoInconel 718 is widely used in turbine disk of aeronautic engines, due to its high resistance to corrosion, oxidation, thermal creep deformation and high mechanical strength at elevated temperature. The total cycle of these mechanical components is up to 109~1010 during its whole lifetime. It endures high-amplitude low-frequency loading including centrifugal force or thermal stress, and also low-amplitude high-frequency loading came from vibration of blade.In this work, the very high cycle fatigue (VHCF) behaviour of Inconel 718 with self-heating phenomenon without any cooling is studied using ultrasonic fatigue system at 20KHz. Acquisition system is improved using NI capture card with LabView for monitoring the frequency, temperature, displacement and so on during all the tests. Keyence laser sensor with two probes at the top and bottom surfaces of the specimens is used to reveal the frequency and vibration mode. The difference of mean values between these two probes is the elongation of the specimen caused by self-heating phenomenon.Three sets of materials with different heat treatment, As-Received (AR), Directly Aged (DA) and Directly Aged High Quality (DAHQ) from ONERA and SAFRAN are compared. The difference of grain size, phase, precipitate particle, etc. is investigated by metallographic micrograph using optical microscope (OM) and scanning electron microscope (SEM). Quasi-static uniaxial tensile property and cyclic stress-strain response is also proposed. The transition from cyclic hardening to cyclic softening appears after aged heat treatment. Finally, fracture surfaces are observed using optical camera and scanning electron microscope in order to identify the mechanism of fracture of Inconel 718 in the VHCF domain
Marti, Nicolas. "Effets de la fréquence et de la température sur les mécanismes de microplasticité en fatigue à grand et très grand nombre de cycles". Thesis, Paris, ENSAM, 2014. http://www.theses.fr/2014ENAM0041/document.
Testo completoNowadays there is a growing demand for the development of fast and robust fatigue life prediction methods in the very high cycle fatigue domain. In this way, ultrasonic fatigue technique which appeared in 1950 is very interesting for manufacturers. Because the typical frequency of these tests is 20 kHz, this technique is efficient to perform tests up to a very high number of cycles in a reasonable time (109 cycles are reached in 14 h). However, the frequency domain of these fatigue tests facilities raises the issue of the effect of frequency and more generally the validity of the obtained results for estimating fatigue life of structures loaded at frequencies three or four order of magnitude below ultrasonic frequencies. The objective of this work is to evaluate the effect of the loading frequency on the precursors of fatigue damage, namely the microplasticity at the grain scale. This thesis work deals with the case of polycrystalline pure copper loaded in fully reversed tensioncompression. To show the effect of frequency, the Wöhler or S-N curves were constructed at different frequencies. Then, the study focused on the mechanisms of microplasticity preceding crack initiation and several criteria were investigated: the morphologies of the slip bands and their locations in the microstructure, the thresholds of appearance of the slip bands, the evolution of the slip bands amount with the number of cycles, the distribution of the microplasticity in the grains, the dissipated energy during a fatigue cycle. Cross slip and vacancies production and diffusion are two mechanisms which play a part in the formation of slip bands and extrusions in surface. Their respective roles on the effects of frequency observed are discussed
Ma, Zepeng. "Fatigue models for life prediction of structures under multiaxial loading with variation in time and space". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX117/document.
Testo completoThe aim of this work is to propose a multi-scale approach to energy-based fatigue, which can estimate lifetimes associated with variable multidimensional loading. The foundation of the approach is to assume that the energy dissipated on a small scale governs the fatigue behavior. Each material point is associated to a stochastic distribution of weak points that are likely to plasticize and contribute to the dissipation of energy without affecting global macroscopic stresses. This amounts to adopting Dang Van's paradigm of high cycle fatigue. The structure is supposed to be elastic (or adapted) on a macroscopic scale. In addition, we adopt on the mesoscopic scale an elastoplastic behavior with a dependence of the plastic load function not only of the deviatoric part of the stresses, but also of the hydrostatic part. Linear kinematic hardening is also considered under the assumption of an associated plasticity. Instead of using the number of cycles as an incremental variable, the concept of temporal evolution of the load is adopted for a precise follow-up of the history of the actual loading. The effect of mean stress is taken into account in the mesoscopic yield function; a law of nonlinear accumulation of damage is also considered in the model. Fatigue life is then determined using a phenomenological law based on mesoscopic energy dissipation from the plastic accommodative cycle. The first part of the work focused on a proposal for a fatigue model with a simpler implementation gradient than the previous models
Guerchais, Raphaël. "Influence d'accidents géométriques et du mode de chargement sur le comportement en fatigue à grand nombre de cycles d'un acier inoxydable austénitique 316L". Thesis, Paris, ENSAM, 2014. http://www.theses.fr/2014ENAM0020/document.
Testo completoThe aim of this study is to analyze the influence of both the microstructure and defects on the high cycle fatigue (HCF) behaviour of a 316L austenitic stainless steel thanks to finite element (FE) simulations of polycrystalline aggregates.%The scatter encountered in the HCF behavior of metallic materials is often explained by the anisotropic elasto-plastic behavior of individual grains leading to a highly heterogeneous distribution of plastic slip.Since fatigue crack initiation is a local phenomenon, intimately related to the plastic activity at the crystal scale, it seems relevant to rely on this kind of modeling to evaluate the mechanical quantities.A preliminary numerical study, based on experimental data drawn from the litterature, was conducted on an electrolytic copper using simulations of 2D polycrystalline aggregates. The effect of the loading path and small artificial defects on the mesoscopic mechanical responses have been analyzed separately. Moreover, the predictive capabilities of some fatigue criteria, relying on the mesoscopic mechanical responses, has been evaluated. It was shown that the macroscopic fatigue limits predicted by a probabilistic fatigue criterion are in accordance with the experimental trends observed in multiaxial fatigue or in the presence of small defects.An experimental campaign is undertaken on an austenitic steel 316L. Low cycle fatigue tests are conducted in order to characterize the elasto-plastic behavior of the material. Load-controled HCF tests, using both smooth specimens and specimens containing an artificial hemispherical surface defect, are carried out to estimate the fatigue limits under various loading conditions (tension, torsion, combined tension and torsion, biaxial tension) and several defect radii. To complete the characterization of the material, the microstructure is studied thanks to EBSD analyzes and the cristallographic texture is measured by X-ray diffraction. These experimental data are used to reproduce, with FE simulations, the HCF tests on 2D and 3D microstructures representative of the austenitic steel. The heterogeneity of the mesoscopic mechanical quantities relevant in fatigue are discussed in relation to the modeling. The results from the FE models are then used along with the probabilistic mesomechanics approach to quantify the defect size effect for several loading paths. The relevance, with respect to the experimental observations, of the predicted fatigue strength distributions is assessed
Bracquart, Benoît. "Etude des interactions défaut géométrique / microstructure dans les mécanismes d’endommagement en fatigue à grand nombre de cycles d’alliages métalliques". Thesis, Angers, 2018. http://www.theses.fr/2018ANGE0009.
Testo completoThe aim of this study is to analyze the influence of microstructure and geometrical surface defects on the high cycle fatigue (HCF) behavior of acommercial purity polycrystalline aluminium. This work relies on an experimental test programme and numerical Finite Element (FE) simulations, in order to better understand microstructural parameters governing crack initiation at defects. To this end, both caracteristic dimensions (grains and defect) are varied. Thermomechanical treatments are set up to control the grain size, and obtained microstructures are caracterized monotonically and cyclically. Then, uniaxial fully reversed tension-compression HCF tests are carried out on specimens with defects, either with an in-situ surface crack monitoring, or a study of the crack initiation at the defect root after cycling. Results are then analyzed in order to determine the influence of different characteristic lengths, as well as crystalline orientation, via EBSD maps. Numerical FE simulations are then carried out to detetermine precisely local mechanical fields. To this end, polycrystalline aggregates 3D meshes representative of experimental configurations are set up. A crystal plasticity constitutive model with gradient is used in order to reproduce the plastic slip at the glide system scale, and the grain size effect. The distribution of afatigue indicator parameter in the different configurations is studied, in order to complement experimental results
Alarcon, Tarquino Eduardo Augusto. "Structural fatigue of superelastic NiTi wires". Thesis, Brest, 2018. http://www.theses.fr/2018BRES0019/document.
Testo completoThis Ph.D. dissertation thesis addresses the conditions and mechanisms that lead superelastic NiTi wires to fail under cyclic mechanical loads. NiTi shape memory alloys exhibit functional thermomechanical properties (superelasticity, shape memory effect, thermal actuation) due to martensitic phase transformations caused by a change of the applied stress and temperature. These phase transformations are though as fully reversible damage-free processes, however, when NiTi is subjected to repetitive stress-induced phase transformations its fatigue performance drops drastically in comparison to non-transforming NiTi. Most of fatigue S-N curves reporting this drop were measured on straight NiTi wires in which martensitic transformations proceed heterogeneously through nucleation and propagation of shear bands. Moreover, from our experience fatigue testing straight wire samples results in undesired failure inside the testing machine clamps. Hence, the reported stress-strain values in S-N curves are not necessarily representative of the critical mechanical conditions that lead the material to failure. With the aim of better characterize the fatigue performance of NiTi wires, we started by carrying out a series of pull-pull fatigue tests using hourglass-shaped samples. This sample geometry allowed us to confine all martensitic transformation and related material fatigue processes into a well-defined gauge volume. The samples’ characterization was performed by combining several experimental and analysis techniques such as Digital Image Correlation, Infrared Thermography, Synchrotron-source X-ray diffraction, Optical Microscopy, Scanning Electron Microscopy and Finite Element Analysis. A special attention was paid to the High Cycle Fatigue (HCF) performance of NiTi in which the material shows elastic behavior and/or an intermediate phase transformation (so-called R-phase). The results from HCF tests allowed us to distinguish crack nucleation and crack propagation stages during the total life of our NiTi samples. In order to get a better understanding of the mechanisms that lead to crack nucleation, we applied the nonconventional Self-Heating fatigue assessment method, which has shown efficiency in the case of aluminum and steel alloys. This method correlates the temperature elevation of a sample subjected to different cyclic load amplitudes with energy dissipating mechanisms that contribute to accumulating local damage in the material. The Self-Heating method was performed using full-field thermal measurements of cyclically loaded NiTi hourglass-shaped samples
Landron, Thomas. "effets des gradients de porosité et de contrainte sur le comportement en fatigue à grand nombre de cycles de l’alliage d’aluminium AlSi9Cu3 coulé sous pression". Electronic Thesis or Diss., Paris, HESAM, 2023. http://www.theses.fr/2023HESAE091.
Testo completoThis research deals with the effect of porosity and stress gradients on the high-cycle fatigue behavior (HCF) of the high-pressure die-cast (HPDC) aluminum alloy AlSi9Cu3 used by the automotive industry. The components produced by HPDC are characterized by a high level of porosity compared to other casting processes. In addition, the porosity or defect distribution within a component is highly heterogeneous and the existence of a porosity gradient between the surface and the in-bulk material is notable. Defects of different nature and size are present, including defects formed by complex three-dimensional pore networks.To study the effects of the porosity and stress gradients on the HCF behavior, a test methodology based on reducing the thickness of as-cast specimens by machining was developed. Four geometries machined from the same as-cast specimens were tested in HCF under different loading modes: plane bending and tension-compression with a load ratio R=-1. The analysis of the fatigue failure surfaces, combined with fatigue results in the form of Wöhler curves shows that fatigue behavior is controlled by the interaction between the porosity gradient and the stress gradient. The position of the crack initiation site (surface or in-bulk), the nature of the critical defects, as well as the fatigue strength are entirely determined by these two gradients.The effect of defects on the fatigue behavior was analyzed using an approach based on the Kitagawa-Takahashi diagram and the stress intensity factor threshold (Kth). This analysis shows that the fatigue strength of the material is controlled by the size of the defects in terms of the Murakami parameter (√area). The wide range of defect size and the variety of defect types makes it possible to characterize the behavior of the material in both the short crack and long crack regimes. It is observed that the position of the crack initiation site (surface or in-bulk) has only a small effect on the fatigue behavior. Thanks to a comparison between the studied alloy and other gravity-cast aluminum alloys, it is shown that both the fatigue strength and the crack propagation behavior, is partly controlled by (a) the microstructural characteristics of alloys (grain size and secondary dendrite arm spacing (SDAS)) and by (b) the monotonic and cyclic mechanical behavior of the materials.The complexity of the defect distribution (type, size and spatial distribution) complicates the characterization and modeling of the kinetics of crack propagation and their interactions with defects. To investigate this, in-situ image correlation was used to monitor crack growth during fatigue tests, with the aim of observing the crack interaction with natural defects, in bending at R=-1. The analysis of the crack growth kinetics and the fatigue failure surfaces reveals a strong interaction between fatigue cracks and defects. These interactions cause rapid crack accelerations, which drastically reduce the fatigue life. A HCF crack propagation model is proposed using an averaging approach with the Paris law. The coefficients are adjusted using the crack monitoring tests. The comparison between the simulated Wöhler curves at initial iso-defect-size and the experimental Wöhler curves shows that the propagation approach is not sufficient to account for all the stages leading to fatigue failure. It is clearly highlighted that the initiation phase must be taken into account and that the fatigue damage mechanisms, associated with defects comprised of complex three-dimensional pore networks, are extremely complex.Keywords: High cycle fatigue (HCF), microstructural heterogeneity, porosity gradient, stress gradient, aluminum alloy, high-pressure die-casting, porosity networks, fatigue life, crack – defect interaction
Florin, Pierrick. "Caractérisation rapide des propriétés à la fatigue à grand nombre de cycle des assemblages métalliques soudés de type automobile : vers une nouvelle approche basée sur des mesures thermométriques". Thesis, Brest, 2015. http://www.theses.fr/2015BRES0100/document.
Testo completoFatigue design of weld assemblies still remains of prior concern in the automotive industry, despite several decades of experimental, theoretical and numerical body of work. Actually, many complex components (e.g. front and rear axles) are embedded thanks to welding process. Such welded assemblies are expected to be designed as high-safety parts, for which any fatigue failure is supposed to be prevented. Despite numerical modelling is more and more effective, experimental tests are still necessary in order to provide basic design data and at last to prove the design reliability. Standard fatigue tests procedures are sensibly time consuming, are usually destructive and need for several specimens in order to manage reliable results. Conversely, the so-called self-heating tests offer the opportunity to dramatically shorten the test duration and save specimens because it is a non-destructive method. It consists in measuring the temperature evolution of the structure surface during cyclic loading. Such an approach allows to take advantage of the macroscopic thermal signature of microscopic plasticity processes responsible for fatigue damage. The purpose of the present work is the determination of a correlation between thermal measurement and fatigue properties of welded structures, and then studying the influence of parameters on fatigue properties with the developed method. An experimental protocol is first proposed to measure the temperature of the tested specimen under cyclic loading. A first analysis of the thermal response of standard steel sheet specimen under low load amplitude is proposed in order to validate a deterministic heat source model for both tensile and bending tests. These tests allow us to correctly describe the thermal behavior of the base material of welded specimen away from the joint. Then, the model is extended to welded specimen in order to take into account the dissipation of the welded area. Once the dissipative heat source is identified thanks to the model, its evolution with the applied loading leads to a self-heating curve allowing an estimation of the fatigue limit of the welded specimen after only few hours of test. The method is then applied to other configurations of welded specimens in order to study the effects of shot peening and stress gradient on fatigue properties. Finally, the testing procedure is applied for the determination of an industrial component fatigue properties, a welded car wishbone. Due to the bad heat boundary condition, another analysis is proposed to estimate the heat source along the entire component. This estimation leads to the determination of the weakest area of the structure concerned by fatigue and a first good estimation of its fatigue limit
Dehmani, Helmi. "Étude de l’influence du procédé de poinçonnage sur la tenue en fatigue à grand nombre de cycles de tôles minces ferromagnétiques". Thesis, Paris, ENSAM, 2016. http://www.theses.fr/2016ENAM0014/document.
Testo completoNew electrical steel grades, with improved magnetic properties, are used to build electric motors. For these steel grades, the iron losses are reduced by adjusting the chemical composition (mostly the Si content), decreasing the thickness below 0.5 mm and increasing the grain size. The punching is used to produce electric motor components because it generates important alterations of sheet edges, this work aims at elaborating a HCf fatigue design strategy for thin punched electrical steel sheets. First, the quasi-static and cyclic behavior of this electric steel was studied through monotonic and cyclic tests. The behavior model of this material, which will be used in FE simulation, is then identified. The study of the high cycle fatigue (HCF) resistance of this material is performed using smooth and notched specimen’s geometries. The effect of stress ratio, temperature (180°C) and the punching process are considered. Due to its influence on the fatigue resistance, the effect of the punching process is finely investigated. Different experimental techniques such as microscopic observations, 3D surface topography, micro‒hardness and X‒ray diffraction are combined to characterize the specimen’s edges. To dissociate the respective influences of strain hardening, residual stresses and geometrical defects induced by the punching process, and to quantify the contribution of each parameter to the HCF resistance, different specimen’s configurations were tested. A strategy allowing the identification of the critical defects, on which fatigue crack initiation occurs, was adopted. The stress distribution around defects is determined from finite element analyses (FEA) on real defect geometries. A non‒local high cycle fatigue criterion is finally used as post‒processing of FEA to consider the effect of defects and the associated stress-strain gradients in the HCF strength assessment
Gerin, Benjamin. "Modélisation des effets de défauts et d’intégrité de surface sur la tenue en fatigue dans les composants forgés". Thesis, Paris, ENSAM, 2016. http://www.theses.fr/2016ENAM0040/document.
Testo completoThis study is part of the DEFISURF project, with the goal of analysing and modelling the various effects of the surface on the fatigue strength of forged components. Two components are studied: a cold-extruded specimen and a connecting rod which is hot-forged and then cleaned by shot-blasting. For each component, different batches are studied in order to quantify the effects of the process on the mechanical characteristics and the fatigue behaviour. Two different reduction of sections are used for the cold-extruded specimens and shot-peening is used to obtain various surface states for the connecting rods.The various batches are thoroughly characterised and fatigue tests are performed. Traction, torsion and plane-bending tests are conducted on the cold-extruded specimens. Fatigue specimens are machined from the central part of the connecting rods and loaded in plane-bending.For cold-extrusion, the parameters with the most influence in fatigue are the prestrain induced during forging and the residual stresses. In hot-forging, the surface defects produced during forging and the residual stresses induced by the shot-blasting have the most influence.For each component, a fatigue model is suggested. For the cold-extruded specimens, a multiaxial fatigue criterion is used to take into account the various fatigue loadings and the effect of the residual stresses. Two approaches are used for the connecting rods. The first is a geometrical analysis of the defect which approximates them with an ellipsoid. The second approach uses finite element simulations of the critical defects. The shot-peening residual stresses are integrated in the simulations with a multiaxial criterion. These simulations predict the fatigue limit of the specimens with an error of around 15%
Guellec, Corentin. "Caractérisation en fatigue à grand nombre de cycles par mesures d’auto-échauffement des aciers d’arbres de transmission pour application navale sous chargements cycliques complexes". Electronic Thesis or Diss., Brest, École nationale supérieure de techniques avancées Bretagne, 2023. http://www.theses.fr/2023ENTA0001.
Testo completoMarine shaft lines undergo complex cyclic loadings. In order to characterize these structures in fatigue, two complementary objectives are achieved. Firstly, the marine shaft’s loads are characterized in order to identify relevant fatigue cycles. During this step, an original parametric fatigue design method is implemented. This method is based on the definition of an equivalent load considering multiaxiality, variability, non-proportionality and mean stress. This method allows to distinguish two damage modes with a mode associated with the established cyclic regime of rotary bending and a mode associated with the ship’s maneuvers. Secondly, a rapid characterization method is implemented to characterize in fatigue the marine shafts’ steels for a large number of loading configurations. The method is based on a model which enables fatigue identification behaviors from self-heating measurements. The steels of the study are characterized in tension-torsion for various configurations of mean stress and nonproportionality of the loading. In this context, the notion of iso-self-heating surfaces is introduced. It allows, for a specimen, to model the elastoplastic and dissipative behavior of the material in the dedicated stress space. Their use makes it possible to define a multiscale fatigue criterion based on the invariants of the stress tensor. In the study, a modeling of the behavior of the material is proposed for very low amplitude loads (VHCF) exhibiting a strong difference in dissipation compared to the regime of higher amplitudes (i.e. HCF domain)
Graux, Nicolas. "Caractérisation et modélisation des propriétés à la fatigue à grand nombre de cycles des aciers cémentés à partir d'essais d'auto-échauffement sous sollicitations cycliques". Thesis, Brest, 2017. http://www.theses.fr/2017BRES0104.
Testo completoThe rolling contact fatigue prediction between two carburizing part quickly becomes complex.On one hand, the carburizing treatment give heterogeneous properties in surface layer depending on the treatment protocol. On the other hand, the rolling contact load is a complex load with a fatigue initiation in the sub-layer. To limit the duration of the field fatigue properties characterization, self-heating measurements under cycle load are used and their interpretation by a probabilistic two scales model is proposed. Nevertheless applying this fatigue evaluation method on heterogeneous material and for rolling contact load can be difficult. ln first approach those difficulties are split.To take into account the material heterogeneity, an analysis based on a variation of one probabilistic two scales model and on carbon rate measurement is proposed. Model parameters are identified on one steel class with self-heating measurement made on specimens representative of carburizing material heterogeneity. Finally the model is validated by comparison with experimental fatigue point.Making self-heating measurement for rolling contact load is complex. Consequently a first self-heating measurement campaign is made on the intermediary case of repeated contact. With a simple analytic model, the temperature field evolution can be linked to a mean heat source whose link with fatigue mechanism must be proven. Finally, rolling contact machine prototypes are proposed. Self-heating measurement made on those prototypes and their interpretation suggest that it will be possible to identify fatigue properties with self-heating measurement
Godet, François. "Influence de la microstructure sur le comportement mécanique d’une couche nitrurée de l’acier de nuance 33CrMoV12-9 en vue de l’optimisation des propriétés en fatigue". Thesis, Paris, ENSAM, 2018. http://www.theses.fr/2018ENAM0046/document.
Testo completoDesign of high-performance and lighter mechanical systems needs a perpetual work on materials used. In the power transmission field, gaseous nitriding thermochemical treatment enhances significantly the life-cycle of the parts which are higher stressed on the surface. While the contribution of the mechanical property gradients due to the treatment on the fatigue life is well-known, the microstructure effects on the (micro-)plasticity mechanisms remains undetermined. This work concerns exclusively the nitrided 33CrMoV12-9 graded steel, used for gears and bearings in the naval and aeronautical industry. It aims particularly at defining mechanical properties linked to crack initiation mechanisms during high-cycle fatigue. Properties such as Young modulus, hardness, yield stress and fatigue limits are looked at several scales, from microstructural ones to hardened case one. In-situ and post-mortem investigation on loaded and damaged nitrided layers leads to estimating the microstructural influence on local deformations, microplasticity and damage but no particular mechanisms were found. Special fully-nitrided parts were designed to perform the experiments. This tool helps to carry out simple loadings and measure the strain-hardening curve and fatigue limits. Finally, it as been attested that measured properties depend on scales, means and methodology
Pu, Xiaoxue. "Thermomechanical study of the gigacycle fatigue behavior of pure iron and carbon-manganese steels : influence of chemical composition and microstructure on damage and crack initiation mechanism". Thesis, Paris 10, 2019. http://www.theses.fr/2019PA100051.
Testo completoThis work attempts to a better understanding of the fatigue damage in ferrite-pearlite steels in the Very High Cycle Fatigue (VHCF) domain. The influences of two parameters, pearlite phase percentage and free interstitial atoms percentage in solid solution, are investigated to understand dissipative mechanisms under 20 kHz high frequency fatigue loading. In-situ infrared thermography is carried out to record the temperature changes, while fractography studies and microscope observations are conducted to investigate the dissipative mechanism on the surface of specimens.For body centered cubic (BCC) materials, under high stress amplitudes, a sudden increase of the temperature occurs without a crack initiation and fracture. The inevitable temperature increase up to hundreds of degrees at high stress amplitudes, is caused mainly by the screw dislocations mobility, which is the key to explaining the observed fatigue behavior and thermal response of BCC structure under high frequency loading. Therefore, PSBs on surface and micro-voids in matrix emerge massively, accompanying with this abrupt temperature increase. These phenomena are considered as transition of deformation mechanism from thermal regime to athermal regime. At low amplitudes, few PSBs or surface roughness are still observed on the specimen surface. Through the cycles of PSB appearance on armco-iron, it’s found that PSBs are inclined to appear before 1x10(7)cycles, and PSB threshold lies below the conventional fatigue limit. The increase of pearlite phase content weakens the temperature elevation, and strengthens the fatigue properties. The presence of free interstitial atoms in steels results in appearence of a secondary temperature increase in the stabilized temperature part (100-200 degree). This behavior seems to be related to the interaction of edge dislocations with free interstitial atoms. Moreover, the remarkable hardening-softening-hardening phenomenon after the sudden temperature elevation to above 300 degree is thought as the interaction of multiplicated screw dislocations and free interstitial atoms
Vincent, Matthieu. "Interaction entre défaut de surface et taille de grain en fatigue à grand nombre de cycles : approche expérimentale et numérique sur un fer pur Armco". Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2018. http://www.theses.fr/2018ESMA0018/document.
Testo completoThe objective of this thesis is to study the influence of the ratio between the defect size and themicrostructure characteristic length on the fatigue limit (for a fixed fatigue life) of a metallic material, under highcycle fatigue (HCF). Pure Armco iron is chosen because its simple microstructure has a single characteristic lengthat the mesoscopic scale (grain scale) : the grain size. The aim of the study is thus to study the competition betweena structural effect (surface defect) and a material effect (grain size) in the context of mechanical stresses in HCF.In order to obtain a comparable different grain size, a thermomechanical protocol has been developed. HCF tests,using specimens from both microstructure sizes (initial material and processed hardened material) in which hemisphericaldefects of different sizes were introduced, were performed to estimate the fatigue limits for different defectsize / grain size ratios. When Kitagawa diagrams are presented in relative values (fatigue limit / fatigue limit ofdefect free material versus defect size / grain size), there is a single curve that combines the two microstructures.This dimensionless Kitagawa diagram thus makes it possible to analyze the reduction of the fatigue limit inducedby a defect. The use of the relative size of the defect with respect to the characteristic microstructural dimensionappears to be more relevant than the use of the physical size of the defect.These experimental results are used to reproduce the HCF tests with Finite Element simulations on 3D microstructuresrepresentative of Armco iron. The competition existing between the stress concentration induced by thegeometrical defect and the highly stressed regions of the microstructure generated by the anisotropy of the mechanicalbehavior of the grains is studied. A mesoscopic criterion (involving mechanical quantities averaged by grain)based on a statistical approach allows to find the evolution of the dimensionless Kitagawa diagram, ie the relativesize of the critical defect from which it predominates over the response heterogeneity of the microstructure and thusgoverns the fatigue behavior of the polycrystal. The modification of the mesoscopic criterion by taking into accountintragranular heterogeneities (with the standard deviation per grain of mechanical quantities) is discussed
Refai, Khalil. "Effet de la méso-architecture sur le comportement en fatigue des structures lattices optimisées obtenues par fabrication additive". Thesis, Paris, HESAM, 2020. http://www.theses.fr/2020HESAE028.
Testo completoA numerical approach is proposed to assess the high cycle fatigue strength of periodic cellular structures produced by SLM under multiaxial loads. The model is based on a general numerical homogenisation scheme and an explicit description of the Elementary Cell combined to an extreme values analysis making use of a fatigue indicator parameter based on Crossland’s criterion. Also, geometric discrepancy and surface roughness are experimentally characterised and considered in the numerical model using three methods which are compared to the experimental fatigue strength. Topology optimisation (TO) pushes the boundaries of design freedom even further. In our study, Topology Optimisation was developed to prevent fatigue failure using SIMP method revisited and reformulated within the mathematical framework of Non-Uniform Rational BSpline functions
Knipling, Keith Edward. "High-cycle fatigue / low-cycle fatigue interactions in Ti-6Al-4V". Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/41290.
Testo completoMaster of Science
Kazymyrovych, Vitaliy. "Very high cycle fatigue of high performance steels". Licentiate thesis, Karlstad University, Faculty of Technology and Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-3066.
Testo completoMany engineering components reach a finite fatigue life well above 109 load cycles. Some examples of such components are found in airplanes, automobiles or high speed trains. For some materials the fatigue failures have lately been found to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicted the established concept of fatigue limit for these materials, which postulates that having sustained 107 load cycles the material is capable of enduring an infinite number of cycles provided that the service conditions are unchanged. With the development of modern ultrasonic fatigue testing equipment it became possible to experimentally establish VHCF behaviour of various materials. For most of them the existence of the fatigue limit at 107 load cycles has been proved wrong and their fatigue strength continues to decrease with increasing number of load cycles.
One important group of materials used for the production of high performance components subjected to the VHCF is tool steels. This study explores the VHCF phenomenon using experimental data of ultrasonic fatigue testing of some tool steel grades. The causes and mechanisms of VHCF failures are investigated by means of high resolution scanning electron microscopy, and in relation to the existing theories of fatigue crack initiation and growth. The main type of VHCF origins in steels are slag inclusions.
However, other microstructural defects may also initiate fatigue failure. A particular attention is paid to the fatigue crack initiation, as it has been shown that in the VHCF range crack formation consumes the majority of the total fatigue life. Understanding the driving forces for the fatigue crack initiation is a key to improve properties of components used for very long service lives. Finite element modelling of VHCF testing was added as an additional perspective to the study by enabling calculation of local stresses at the fatigue initiating defects.
Louge, Julien. "Apports des mesures d’auto-échauffement pour l’étude de la fatigue des aciers : effets d’histoire et cisaillement pur". Thesis, Brest, École nationale supérieure de techniques avancées Bretagne, 2019. http://www.theses.fr/2019ENTA0001.
Testo completoIn the automotive industry, rolled steels are widely used to produce constituent parts of a car. The high cycles fatigue properties of these flat steel are usually determined in a virgin state of the material (i.e., without preliminary loading) under uniaxial cyclic loading with a constant stress amplitude. However, production of structural parts mostly involves some forming processes that have for consequence to modify the material state and thus to impact the fatigue properties. Furthermore, operational loads condition actually incurred by such a part is often multiaxial and with variable amplitude. The aim of this study is to take into account multiaxial and load history aspects in the fatigue characterization by means of self-heating measurements under cyclic loading. Multiaxial fatigue characterization usually involves a fatigue criterion that required the endurance limit of the material under a shear loading. But this limit is difficult to obtain for flat steel. That why a new shear test and two new disk-shaped specimens were proposed, permitting the use of self-heating measurements. Thus, the endurance limit of the material under a shear loading was determined. In order to study the impact of load history effects on fatigue properties, various self-heating tests were performed considering several initial pre-straining levels, several cyclic pre-loading and several load ratios. From these results, a new probabilistic two-scale model was proposed capable of describes selfheating curves with any load history considered and provides a reliable estimation of these load history effects on S-N-P curves
Kazymyrovych, Vitaliy. "Very high cycle fatigue of tool steels". Doctoral thesis, Karlstads universitet, Avdelningen för maskin- och materialteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-5877.
Testo completoDureau, Clément. "Fatigue d'aciers inoxydables austénitiques traités par grenaillage ultrasonore sévère : contributions expérimentales et numériques à l'étude de l'amorçage et la propagation des fissures". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0143.
Testo completoIn the high cycle fatigue, cracks initiate most of the time at the surface of workpieces. Therefore, in addition to the overall mechanical properties, surface and sub-surface characteristics such as roughness and residual stresses affect the fatigue life. Roughness essentially influences the cracks initiation phase. Indeed, the presence of surface irregularities induces stress concentrations producing high local strains potentially leading to the formation of crack-like defects. Besides, the presence of residual stresses affects both the crack initiation and propagation phase. They affect the plasticity close to the surface and influence the crack initiation. Moreover, superposed with the macroscopic loading, they locally modify the stress field and therefore may affect the crack propagation behavior as well.The ultrasonic shot peening (SMAT) is a surface mechanical treatment which consists in impacting a sample with shots put in motion by a vibrating device operating at frequencies up to 20 kHz. The repeated impacts lead to a surface plastic strain allowing the formation of compressive residual stresses as well as a microstructure gradient characterized by highly deformed zones in the sub-surface and submicronic grain size just below the surface. Such treatment was carried out to austenitic stainless steels in order to study the fatigue crack initiation and propagation in the complex microstructure and residual stress field induced by the SMAT.Uniaxial high cycle fatigue tests have been conducted for two different load ratios (under tension-compression at RTC=-1 and under tension-tension at RTT=0.1). They allowed to highlight the variable effectiveness of the SMAT with regard of the cyclic loading conditions. Indeed, at RTC, an increase of the fatigue limit was measured whereas for RTT a reduction of the fatigue limit was observed. In order to explain this difference, an in-depth study of the initial state and SMAT treated broken and run-out samples was carried out. It turns out that under the studied loading conditions the modifications of residual stress state can be considered as the primary factor governing the varying fatigue performances and the observed triggering at different initiation sites. Considering the stabilized surface residual stress after fatigue loading, the use of a Crossland criterion allowed to explain both the effects of load ratio and SMAT on the high cycle fatigue behavior of the stainless steel.A modelling method of the mechanical properties and residual stresses gradients was then developed using the finite elements method (via ABAQUS) in order to understand and predict the residual stresses redistributions. The results of the simulations were compared to the experimental measurements, and a good agreement was observed. The capacity of the model to simulate both the strain- and stress-controlled fatigue behavior was evaluated and a good consistency between the numerical and experimental results were obtained.Specimens with an artificial surface defect were then prepared in order to evaluate the surface anomalies sensitivity, and also to study the fatigue crack propagation behavior using the surface replication method. It was shown that the SMAT samples do not exhibit an increased sensitivity to the presence of defects compared to the initial state when loaded at RTT, whereas for RTC a slightly increased sensitivity was identified. Studying the crack propagation at the surface of the specimens highlighted different behaviors for different load ratios. Also, despite the presence of a defect, the crack initiation phase remained important. Finally, crack fronts were marked by different methods which permitted plotting the fatigue crack growth curves. It was then shown that at RTC, fatigue crack growth behavior in the SMAT layer is drastically different from the initial material, whereas at RTT no difference was revealed
Utada, Satoshi. "Effect of a Prior Plastic Deformation during Heat Treatments on the Mechanical Properties of Ni-Based Superalloys for Turbine Blade Application Evolution of superalloy for turbine airfoil and development of recycling technology Platinum containing new generation nickel-based superalloy for single crystalline application Tensile, low cycle fatigue and very high cycle fatigue characterizations of advanced single crystal nickel-based superalloys Creep Property and Phase Stability of Sulfur-Doped Ni-Base Single-Crystal Superalloys and Effectiveness of CaO Desulfurization Evaluation and comparison of damage accumulation mechanisms during non-isothermal creep of cast Ni-based superalloys". Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0019.
Testo completoNi-based single crystal (SX) superalloys are used for turbine blade applications because of their high-temperature durability. During the production of a turbine blade, unexpected plastic deformation (PD) can be introduced to the material. In this study, SX materials were pre-deformed in between solution and aging heat treatments to mimic PD during production. Mechanical tests on the pre-deformed materials have been performed to understand the effect of the prior PD.During aging treatments of pre-deformed AM1 SX superalloy, faster coarsening of γ′ precipitates and enhanced void nucleation were observed in the vicinity of slip bands which were introduced by PD at room-temperature. During creep deformation of pre-deformed AM1 at high temperature/low stress conditions (≥ 950 °C), the microstructure coarsened bands act as diffusion induced creep damage accumulating paths, further triggering recrystallization and resulting in drastic reduction of creep properties. At low temperature/high stress conditions (≤ 850 °C), microstructure shearing was facilitated in the microstructure coarsened band and it decreased creep properties. Recrystallization was not observed at lower temperature creep because the diffusion damage was suppressed. These relationships have been explained by creep tests on pre-deformed materials prepared by different pre-deformation temperatures and heat treatment procedures.CMSX-4 Plus SX superalloy was tested similarly to AM1 to understand the effect of the chemical composition. Effect of pre-deformation on alloy’s microstructure was mild in CMSX-4 Plus compared to that in AM1. Therefore, the predeformation did no exhibit large creep life debit in CMSX-4 Plus at temperatures lower than 1050 °C. However, during creep of CMSX-4 Plus at 1150 °C, pre-deformation presented huge impact on creep life and ductility by the same mechanisms as the ones observed for AM1 at 1050 °C.In order to restore properties of pre-deformed SX superalloys, rejuvenation heat treatment was added after PD.Rejuvenation treatment successfully restored microstructure after PD at room-temperature, and creep properties of rejuvenated specimens were shown to be equivalent to that of original AM1 and CMSX-4 Plus without PD
Berchem, Klaus Herbert Hans. "High cycle fatigue and corrosion fatigue performance of two car body steels". Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414711.
Testo completoBarry, Nathan. "Lead-free solders for high-reliability applications : high-cycle fatigue studies". Thesis, University of Birmingham, 2008. http://etheses.bham.ac.uk//id/eprint/198/.
Testo completoLiang, Xiaoyu. "Comportement en fatigue à grand nombre de cycle d’un acier inoxydable 316L obtenu par fabrication additive : effets de la microstructure, de la rugosité et des défauts". Thesis, Paris, HESAM, 2020. http://www.theses.fr/2020HESAE017.
Testo completoThis study aims to investigate the influence of both the microstructure and surface defects on the high cycle fatigue (HCF) behavior of a 316L stainless steel obtained by additive manufacturing (AM). Surface defects and microstructure are dominant factors of fatigue behavior, while the AM materials often exhibit distinguished surface state and microstructure compared to conventional materials. The current study begins with an investigation of the material properties that are related to fatigue behavior. Microstructure observations of the powder and fabricated specimens are undertaken. Profilometry and tomography analyses make the inherent defects visible. The hardness, elastic behavior and elastic-plastic behavior are studied via mechanical tests. Then, load-controlled fatigue tests concerning different surface-treated specimens under different loading types are conducted. To reveal the mechanism of fatigue failure in the studied specimens, a comprehensive fractography analysis is carried out. Experimental research reveals the weakening of fatigue strength due to lack-of-fusion defects. Yet, the effect of the microstructural attributes is difficult to evaluate without numerical tools. A preliminary numerical study about the application of the non-local method in an explicit microstructure sensitive model is undertaken to complement the microstructure-sensitive modeling framework. Based on the data collected in the experimental campaign, a finite element model that can take into consideration of the defects and the microstructure of the SLM SS 316L is built up. Finite element analyses are performed with both cubic elasticity and polycrystal plasticity constitutive laws. With the help of the statistical method, the results from the FE model are used to quantitatively assess the influence of surface roughness and microstructural attributes on the fatigue performance of SLM SS 316L
Hall, Rodney H. F. "Crack growth under combined high and low cycle fatigue". Thesis, University of Portsmouth, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290404.
Testo completoSuresh, Shyam. "Topology Optimization for Additive Manufacturing Involving High-Cycle Fatigue". Licentiate thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-165503.
Testo completoLester, Charles Gilbert IV. "Analysis of fatigue behavior, fatigue damage and fatigue fracture surfaces of two high strength steels". Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42795.
Testo completoMorrissey, Ryan J. "Frequency and mean stress effects in high cycle fatigue of Ti-6A1-4V". Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17095.
Testo completoPirouznia, Pouyan. "High cycle fatigue properties of stainless martensitic chromium steel springs". Thesis, KTH, Materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103201.
Testo completoBantounas, Ioannis. "Microtexture and high cycle fatigue cracking in Ti-6A1-4V". Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501436.
Testo completoTEIXEIRA, MARIA CLARA CARVALHO. "ULTRA HIGH CYCLE FATIGUE BEHAVIOR OF THE DIN 34CRNIMO6 STEEL". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=35973@1.
Testo completoCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
Estudos recentes têm mostrado que para muitos materiais de Engenharia não existe um limite de fadiga. Numa análise convencional, se admite uma vida infinita em fadiga de alto ciclo quando o material atinge 10(6) - 10(7) ciclos sem a incidência de falhas. Entretanto, em função do desenvolvimento tecnológico atual, a vida-fadiga de inúmeros componentes mecânicos e estruturais pode ultrapassar a fronteira da fadiga de alto ciclo, fazendo com que a avaliação do comportamento em fadiga de altíssimo ciclo (10(7) – 10(12)), tenha se tornado extremamente importante para projetos, por ter estabelecido que uma tensão limite de fadiga não existe em muitos casos. Pesquisas recentes demonstram que a maioria dos materiais, incluindo ligas ferrosas, apresentam falhas em até 10(10) ciclos, com um decréscimo contínuo do limite de fadiga após 10(6) ciclos, o que torna a resistência à fadiga associada com um número de ciclos mais importante do que o próprio limite de fadiga. No regime de altíssimo ciclo de fadiga as trincas se iniciam a partir de defeitos internos do material, como inclusões, gerando mecanismos de iniciação de trincas caraterísticos das superfícies de fratura, tais como olho de peixe (fish-eye), ODA (Optically Dark Area) e FGA (Fine Granular Area). Neste estudo foram usinados corpos de prova do aço DIN 34CrNiMo6, que foram ensaiados entre 10(6) e 10(9) ciclos, sob fadiga ultrassônica do tipo tração-compressão, com frequência de 20 kHz e razão de carregamento -1. Os resultados mostraram que o material tem uma tendência maior a vida-fadiga sob valores baixos de tensão e na superfície de fratura de alguns corpos de prova formação de fish-eye.
Recent studies have shown that for many engineering materials there is no fatigue limit. In a conventional analysis, infinite life in high cycle fatigue is allowed when the material reaches 10(6) - 10(7) cycles without the occurrence of failures. However, due to the current technological development, the fatigue life of several mechanical and structural components can exceed the boundary of high cycle fatigue, making the evaluation of ultra high cyle fatigue behavior (10(7)-10(12)), or fatigue of very high cycle, has become extremely important for projects, because it has established that a stress of fatigue limit does not exist in many cases. Current research has shown that most materials, including ferrous alloys, exhibit failures in up to 10(9) cycles, with a continuous decrease in the fatigue limit after 10(6) cycles, which makes strength fatigue associated with a number of cycles most important than own fatigue limit. In the very high fatigue cycles regime, cracks start from internal defects of the material, such as inclusions, generating a feature mechanisms of crack initiation on the fracture surfaces, such as fish-eye, ODA (Optically Dark Area) and Fine Granular Area (FGA). This study, specimens of DIN 34CrNiMo6 steel were machined and were tested between 10(6) and 10(9) cycles, under ultrasonic fatigue, with a frequency of 20 kHz and a loading ratio of -1. The results showed that the material has a tendency to fatigue life under low stress values and in some fracture sufaces of the specimens the fish-eye formation.
Berchem, Klaus [Verfasser]. "The High-Cycle Fatigue and Corrosion Fatigue Performance of two Car Body Steels / Klaus Berchem". Aachen : Shaker, 2005. http://d-nb.info/1181607590/34.
Testo completoKarlsson, Daniel. "Life and fracture in very high cycle fatigue of a high strength steel". Thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik (from 2013), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-86135.
Testo completoKlassiska utmattningsmodeller lär ut att det finns en utmattningsgräns för stål, vilket representerar en spänningsnivå som är för låg för regelbunden sprickväxt där varje cyklisk belastning sprider en utmattningsspricka genom materialet. Moderna applikation med extrema livstider har visat att utmattning fortfarande äger rum i stål med spänningsnivåer långt under den förväntade utmattningsgränsen. Detta relativt nya studieområde har fått namnet Very High Cycle Fatigue, eller VHCF, och beskriver utmattningsfall med ett antal belastningscykler som överstiger 107. Fraktografi av stål som har drabbats av VHCF tenderar att ha en särskilt gropig sprickyta som ligger intill där utmattningssprickan har sitt ursprung, vilket typiskt är någon form av defekt i stålets bulk. Detta område tros vara kritiskt för VHCF och har hänvisats till på ett antal sätt av olika studier, men kommer här att kallas Fine Granular Area eller FGA. Syftet med denna studie är att försöka få en bättre förståelse för VHCF. Detta gjordes genom fraktografianalys av testprover av verktygsstål med hög hållfasthet som drabbades av utmattningsbrott vid livstider från cirka 106 cykler till 1,9x109 cykler. De lägre livslängderna uppnåddes med hjälp av hydraulisk testutrustning, medan proverna i VHCF-området drabbades av utmattningsbrott i ultraljudstestutrustning som klarar att applicera en cyklisk stress med en frekvens på 20 kHz. De resulterande sprickytorna undersöktes sedan med hjälp av ett svepelektronmikroskop, eller SEM, med särskild fokus på utmattningsinitierande defekter och, i fallet med VHCF, det grova området som hittades intill det, FGA. I kombination med SEM utfördes en elementanalys av utmattningsinitierande defekter liksom huvuddelen av materialet med energidispersiv röntgenspektroskopi, eller EDS. Detta gjordes för att ta reda på vad inneslutningarna bestod av för att bekräfta att de var slagg samt kontrollera att sammansättningen av materialet i huvuddelen av provet matchar det som förväntades. Med användning av optisk ljusmikroskopi i kombination med syraetsning av ytan på prover som skars ut ur testproverna undersöktes stålets struktur. Beräkning av de lokala spänningarna på platsen för den utmattningsinitierande defekten gjordes med hjälp av FEM i kombination med förskjutningsamplituden som samlats från ultraljudsutrustningen. De insamlade uppgifterna mättes sedan och jämfördes med tidigare studier genom att använda diverse modeller och se hur de matchar de experimentella resultaten. Resultaten antyder att stressintensitetsfaktorn vid inneslutningarna är kritisk för VHCF och att man med lägre stressintensitetsfaktorer kan förvänta sig längre livstid. En annan observation är en relativt konsekvent stressintensitetsfaktor vid kanten av FGA, vilket sannolikt markerar övergången från skapandet eller utbredning av FGA till traditionell sprickutbredning. Det verkar också finnas en koppling mellan storleken på FGA och antalet cykler till fel, med större FGA med ökande livslängd. Den mest uppenbara bristen i denna studie är mängden tillfredsställande tester som genomförts. Därmed är mängden datapunkter mycket låg, detta på grund av att majoriteten av proverna misslyckades vid gängningen som användes för att ansluta dem till ultraljudstestutrustningen vid livstider alltför låga för att vara relevanta.
Radonovich, David Charles. "Methods of Extrapolating Low Cycle Fatigue Data to High Stress Amplitudes". Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3460.
Testo completoM.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering MSME
Courty, Diana [Verfasser]. "Ultra high cycle fatigue of thin Al-based films / Diana Courty". Aachen : Shaker, 2010. http://d-nb.info/1104047705/34.
Testo completoSeidt, Jeremy Daniel. "Development of a novel vibration based high cycle fatigue test method". Connect to resource, 2001. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1209585565.
Testo completoMONTAGNOLI, FRANCESCO. "Very-High Cycle Fatigue: Size Effects and Applications in Civil Engineering". Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2945177.
Testo completoHilgendorff, Philipp-M., Andrei C. Grigorescu, Martina Zimmermann, Claus-Peter Fritzen e Hans-Jürgen Christ. "Cyclic deformation behavior of austenitic stainless steels in the very high cycle fatigue regime: Experimental results and mechanismbased simulations". Cambridge University Press, 2017. https://tud.qucosa.de/id/qucosa%3A70666.
Testo completoGe, Yindong. "HIGH CYCLE FATIGUE STUDIES OF CARBURIZED NICKEL-BASE SUPERALLOYS AND STAINLESS STEELS". Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1244230393.
Testo completoRoy, Alexander M. "Prediction of low and high cycle multiaxial fatigue of superelastic nitinol stents via uniaxial fatigue based equations". Thesis, California State University, Long Beach, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1527412.
Testo completoBobyliov, Konstantin. "Casting voids influence on spheroid graphite cast iron high-cycle fatigue strength". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2008. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2008~D_20081128_120950-42235.
Testo completoNagrinėjamas liejimo tuštumų poveikis stipriojo ketaus pleišėjimo slenksčiui. Pateikiami eksperimentiniai rezultatai ir jų analitinė bei skaitinė analizė, remiantis tiesine irimo mechanika.
Исследуется влияние литейных пустот на порог трещиностойкости чугуна с шаровидным графитом. Представлены результаты экспериментального исследования и их аналитический и численный анализ, опираясь на линейную механику разрушения.
Hastings, Abel Z. 1973. "An investigation of the high cycle fatigue behavior of bovine trabecular bone". Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/30123.
Testo completoIncludes bibliographical references (p. 64-70).
Fractures can be caused by fatigue loading due to prolonged exercise and age-related fragility. Fatigue loading causes microdamage in bone that leads to both a loss of stiffness and strength. Some engineering materials, such as steels, have a fatigue limit, which is represented by a stress plateau in the stress-life (S-N) curve. When loaded to levels below the stress plateau, these materials have an infinite fatigue life. Other materials, such as aluminum, do not exhibit a fatigue limit. For these materials, the endurance limit is defined as the stress amplitude corresponding to a somewhat arbitrary large number of cycles of fatigue (e.g. various texts suggest 10⁶ to 10⁸ cycles ). In previous work on compressive fatigue of bovine trabecular bone, it was hypothesized that there was a fatigue limit at a normalized stress, [Delta] [rho]/E₀, of approximately 0.0035. This study tested this hypothesis by fatigue testing bovine trabecular bone loaded to one of four normalized stresses ranging from 0.0015 to 0.0035. Failure was defined as a 10% loss in the secant modulus of the specimen. The data show that the rate of decrease of modulus reduction per cycle increased with increasing normalized stress. A fatigue limit in bovine trabecular bone was not found. While a threshold below which the fatigue life is infinite was not found, an endurance limit corresponding to 10⁶ cycles to failure was found at a normalized stress of about 0.00137. The study also showed that normalized secant modulus decreased with normalized number of cycles in the same manner for all normalized stresses.
by Abel Z. Hastings.
S.M.
Cheng, Deborah Wen-hsin. "Compressive high cycle at low strain fatigue behavior of bovine trabecular bone". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38042.
Testo completoTofique, Muhammad Waqas. "Very high cycle fatigue of duplex stainless steels and stress intensity calculations". Licentiate thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-34591.
Testo completoArticle III was still in manuscript form at the time of the defense.
Very high cycle fatigue of stainless steels
Gundmi, Satish Sajjan. "Continuous Time Fatigue Modelling for Non-proportional Loading". Thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-164950.
Testo completo