Alexis Oudin - Academia.edu (original) (raw)

Papers by Alexis Oudin

Strain‐controlled out‐of‐phase thermo‐mechanical fatigue (OP TR;IF) tests were performed in air o... more Strain‐controlled out‐of‐phase thermo‐mechanical fatigue (OP TR;IF) tests were performed in air on a tempered martensitic 5 % chromium hot work tool steel (X38CrMoV5). Thin‐walled tubular specimens were used. The effect of the minimal and maximal temperatures of the thermal cycle on the stress‐strain behaviour was assessed. The mechanical strain range was unchanged. Under the test conditions examined, the influence of the minimal temperature was very slight while a strong effect of the maximal temperature on the cyclic softening was observed. Increasing maximal temperature increases dramatically cyclic softening. It was observed that when the maximal temperature is near or above the second tempering temperature, steel softening process increases.

Tubular specimen of 5 % and 9 % chromium steels have been tested under out‐of‐phase thermomechani... more Tubular specimen of 5 % and 9 % chromium steels have been tested under out‐of‐phase thermomechanical low cycle fatigue (OP TMF) in air. The temperature range was 200 ‐ 600 degrees C and the strain range 0.4 % through 1.0 % (F82H‐mod, 9 % Cr) and 0.5 % through 1.5 % (AISI H11, 5 % Cr) (R‐epsilon = ‐infinity). Both steels presented a continuous cyclic softening until total fracture of specimens. Specimen surfaces were oxidized and two oxide layers were found. A combined thermo‐mechanical fatigue (TMF) and oxidation was found as the main crack initiation mechanism. TMF life have been examinated on the basis of mechanical strain, inelastic strain and stress amplitudes.

European Structural Integrity Society, 2002

The surface of the hot work tools is damaged under coupled non-isothermal fatigue, wear or erosio... more The surface of the hot work tools is damaged under coupled non-isothermal fatigue, wear or erosion and reactive environment (oxidation or corrosion). A thermomechanical fatigue (TMF) experiment using tubular specimens is developed. Tests are carried out under out-of-phase TMF cycle with strain ratio R = -∞. The behaviour, the damage and life of two tempered martensitic steels X38CrMoV5 and 55NiCrMoV7

International Journal of Fatigue, 2015

A new thermal fatigue rig using High Frequency induction heating is developed to test automotive ... more A new thermal fatigue rig using High Frequency induction heating is developed to test automotive Diesel engine pistons. An adapted test piston is internally cooled by permanent water flow while its bowl sensitive to thermo-mechanical fatigue is subjected to cyclic induction heating. The temperature is measured in depth by thermocouples and in surface by a thermal infrared camera or a pyrometer. The crack initiation and propagation and the local deformations are provided by optical means. Thermo-mechanical loadings are calibrated by thermal measurements on the piston during engine operation and the entire test is modelled by finite elements. A constitutive model and a fatigue criterion for aluminium alloys are proposed to estimate the piston lifetime under severe cyclic loading. The proposed fatigue bench allows loading the piston in thermal fatigue scheme very similar to that encountered in engine operation conditions. Crack detection is facilitated by numerical modelling that helps to detect the most critical areas and also to reliably estimate the number of cycles for initiate cracks.

Materials Science Forum, 2004

The present work examines the effect of strain and Zener Hollomon parameter, Z, on deformation an... more The present work examines the effect of strain and Zener Hollomon parameter, Z, on deformation and recrystallization of Ti-IF steel deformed in the warm temperature region. Torsion tests were performed at temperatures of 765oC and 850oC and strain rates of 0.003s-1 and 1s-1. For some conditions, an annealing treatment at the temperature of deformation was carried out using a fluidized bed furnace. Electron Back Scatter Diffraction (EBSD) maps were implemented to study the microstructure evolution. At a low value of Z abnormally large grains formed during annealing. At the higher values of Z, a more classical recrystallization reaction occurred during annealing. The latter is more desirable in most commercial applications.

Procedia Engineering, 2010

The purpose of this paper is to define a thermomechanical fatigue criterion in order to predict t... more The purpose of this paper is to define a thermomechanical fatigue criterion in order to predict the failure of the cylinder heads issued with the lost foam casting process. The microstructure of the materials (A356-A319) is affected by the lost foam casting process which can directly affect the mechanical properties, the damage mechanisms and thefatigue failure of the materials. The major problem in defining a predictive fatigue criterion in this case is the fact that it should be on one side applicable for the structure which is submitted to complex multiaxial thermomechanical loadings and on the other side should take into account the microstructural effects of casting process.

MATERIALS TRANSACTIONS, 2004

Of considerable importance to the generation of ultrafine microstructures is the development of h... more Of considerable importance to the generation of ultrafine microstructures is the development of high misorientations. The present work examines the effect of the crystallographic rotation field in simple shear upon the evolution of misorientation during plastic working. A series of Taylor simulations are presented and it is shown that the rotation field is such that small differences in orientation in the region of the main torsion texture components are considerably increased with the application of shear strain. This did not occur in simulations of rolling. The torsion simulations compare favourably with the nature of the misorientations evident in hot worked 1050 Al and Ti-IF steel. It is concluded that shear deformation, by its nature, facilitates the generation of higher misorientations.

Materials Science and Engineering: A, 2004

The effect of grain size on the warm deformation behaviour of a titanium stabilized interstitial ... more The effect of grain size on the warm deformation behaviour of a titanium stabilized interstitial free (IF) steel was investigated using hot torsion. The initial work hardening regime is followed by the development of a broad stress peak after which work softening occurs. The hypothetical saturation stress (Estrin-Mecking model) and the stress at final strain were relatively insensitive to grain size. However, the strain to the peak stress was strongly dependent on the grain size at low values of the Zener-Hollomon parameter. A simple phenomenological approach, using a combined Estrin-Mecking model and an Avrami type equation, was used to model the flow curves. The hypothetical saturation stress, the stress at final strain and the strain to peak stress were modelled using three different hyperbolic sine laws. A comparison with independent data from the literature shows that the apparent activation energy of deformation determined in this work (Q = 372 kJ/mol) can be used to rationalize the steady-state stress in compression data found in the literature.

International Journal of Fatigue, 2013

The paper discusses the lifetime prediction of structures in high-cycle fatigue based on the two-... more The paper discusses the lifetime prediction of structures in high-cycle fatigue based on the two-scale fatigue criteria of Dang Van type and several of its extensions in finite lifetime regime. The main assumptions for this criteria are (i) the material is polycrystalline and undergoes localised plasticity in one of the misoriented grains and (ii) crack initiation arises as a consequence of cumulated plasticity in this grain. The novelty of the presented approach is twofold. On the one hand a generalisation of mesoscopic plasticity model is presented, on the other a fast time scale average is introduced for tracking the cyclic material behaviour and the subsequent evolution of damage. The tracking method is based on the split between a quick quasi-periodic response of the system to the cyclic load and a slow evolution of the internal hardening and damage parameters of the material at the mesoscopic scale. The proposed method can be extended to a large class of local material behaviours involving not only plasticity, but also crack and damage evolution. The paper proposes a simplified plasticity-based model for the mesoscopic material behaviour and presents a comparison between predicted and experimental lifetimes. The results are discussed in terms of prediction capabilities and also in terms of the identification procedure of parameters of the mesoscopic model.

Materials Science and Engineering: A, 2008

ABSTRACT The effect of grain size on the warm deformation behaviour of a titanium stabilized inte... more ABSTRACT The effect of grain size on the warm deformation behaviour of a titanium stabilized interstitial free steel was investigated using hot torsion. Tests were performed at temperatures between 765°C and 850°C at strain rates between 0.003s−1 and 1s−1 for samples with grain sizes of 25μm, 75μm and 150μm. The structures were observed using EBSD analysis and are consistent with those expected for materials dominated by dynamic recovery. Some evidence was found for small amounts of thermally induced migration of pre-existing boundary (bulging) and for the generation of new segments of high angle boundaries by continuous dynamic recrystallization. The early onset of a steady-state flow stress in the finer grained samples is attributed to one or a combination of thermally induced boundary migration and enhanced rates of recovery near subgrain (and grain) boundaries.

The purpose of this paper is to define a thermo-mechanical fatigue criterion in order to predict ... more The purpose of this paper is to define a thermo-mechanical fatigue criterion in order to predict the failure of aluminum alloys components issued with the lost foam casting process and used in particular in the automotive industry. The microstructure of the studied materials (A356-A319 aluminum alloys) is clearly affected by the lost foam casting process which can directly affect the mechanical properties, the damage mechanisms and the fatigue failure of specimens and components. The major problem in defining a predictive fatigue criterion in this case is the fact that it should be applicable for the component which is submitted to complex multiaxial thermo-mechanical loadings. Since many years, energy-based criteria have been used to predict fatigue failure of this class of materials. Then, different energy-based criteria are tested in order to take into account different types of triaxiality and mean stress effects corrections. The fatigue lifetime results predicted by both of them show a good agreement with experimental results.

L'endommagement par fatigue thermique limite la duree de vie des outils de mise en forme a ch... more L'endommagement par fatigue thermique limite la duree de vie des outils de mise en forme a chaud. Un essai de Fatigue Thermo-Mecanique (TMF) est developpe pour etudier cet endommagement sur les aciers pour travail a chaud 55NiCrMoV7 et X38CrMoV5. Des cycles TMF hors-phase compression- compression avec differentes temperatures minimales et maximales sont etudies. Le comportement cyclique des deux aciers est caracterise par deux regimes successifs d'accommodation (adaptation progressive de la microstructure a la sollicitation TMF) et d'adoucissement (diminution cyclique de la resistance de l'acier). La temperature maximale controle le comportement. Pour l'acier X38CrMoV5, au dessus de la temperature critique 550°C, des processus thermiquement actives controlent le comportement cyclique. L'acier 55NiCrMoV7 presente une accommodation plus rapide et globalement un plus fort adoucissement que l'acier X38CrMoV5. L'oxydation preferentielle suivie de la fissur...

Fatigue & Fracture of Engineering Materials & Structures, 2013

Bulletin du Cercle d' …, 2000

The effect of grain size on the deformation behaviour in the fenite region of a Titanium stabiliz... more The effect of grain size on the deformation behaviour in the fenite region of a Titanium stabilized Interstitial Free steel was investigated by hot torsion. The initial work hardening regime is followed by a softening regime where a broad peak stress develops. The peak stress and the stress at final strain were relatively insensitive to grain size. However, at low values of the Zener-Hollomon parameter, the strain to the peak stress was strongly dependent on the grain size. A series of microstructural parameters were examined to explain these observations.

The design of structures against thermomechanical fatigue (TMF) is a relatively new concern and r... more The design of structures against thermomechanical fatigue (TMF) is a relatively new concern and research has generally concentrated on deterministic methods to ensure the resistance of structures undergoing thermal–mechanical loadings. Many studies have thus been conducted to better represent the nonlinear behaviour of materials or to develop thermomechanical fatigue criteria. However, fatigue is a phenomenon which is random in nature: manufacturing processes, geometric tolerances and usage conditions can affect the lifetime of a structure. Typically, the use of a car by a customer is unique (type of roads, weather conditions, drivers behaviour, etc.) and thus thermomechanical loads for instance on a cylinder head become probabilistic. Similarly, the intrinsic strength of a structure is variable (casting and machining process, specific microstructures, etc.). It is therefore necessary to be able to guarantee the TMF resistance of a particular structure itself undergoing a particular...

Scripta Materialia

The influence of the grain size on the deformation of Mg–3Al–1Zn was examined in compression at 3... more The influence of the grain size on the deformation of Mg–3Al–1Zn was examined in compression at 300 °C. At low strains the flow stress increases with increasing grain size. This is interpreted in terms of dynamic recrystallization. Empirical models of dynamic recrystallization are developed and employed to generate a microstructure map.