Gilbert Hénaff

Ecole Nationale Supérieure de Mécanique et d'Aérotechnique | ENSMA · Department of Physics and Mechanics of Materials

A test device has been developed at P′ Institute in order to investigate the mechanical behaviour of structural materials under high pressure of gaseous hydrogen. In this paper, preliminary results on fatigue crack propagation in a martensitic stainless steel are presented. A tremendous fatigue crack growth enhancement is observed at high pressure...

Uniaxial strain‐controlled fatigue tests were carried out on a 304L austenitic stainless‐steel specimens in air at 300°C and in pressurized water reactor (PWR), without or with the application of a mean stress, at different total strain amplitudes. For strain amplitude no less than 0.2%, a deleterious effect of PWR water on fatigue life is observed...

Oxide Dispersion-Strengthened (ODS) ferrito-martensitic alloys are candidate materials for the fabrication of 4 th generation nuclear reactor fuel cladding, as they present optimal response to the loading conditions foreseen for these reactors (high temperature and irradiation doses). The main objective of this study is to understand the effect of...

Oxide Dispersion-Strengthened (ODS) ferrito-martensitic alloys are candidate materials for the fabrication of 4 th generation nuclear reactor fuel cladding. These materials have optimal response to the loading conditions foreseen for these reactors (high temperature and irradiation doses), due to the homogenous dispersion of nano-oxides. The main o...

An approach coupling experimental tests and numerical simulation of the pressure resistance welding (PRW) process is proposed for optimizing fuel cladding welds for the new generation of nuclear reactors. Several experimental welds were prepared by varying the dissipated energy, which accounts for the effect of electric current and welding time app...

Les alliages ferrito-martensitiques ODS (renforcés par une distribution nanométrique d'oxydes) font partie des matériaux candidats à la fabrication de pièces pour le gainage des combustibles de réacteurs nucléaires de 4 ème génération. L'assemblage type « bouchon-gaine » se fait par le procédé de soudage par résistance (SPR) en bout. La maitrise du...

This article presents on overview on environmentally-assisted fatigue in a gaseous atmosphere, with a focus placed on ambient air that alters the fatigue resistance of most metals. The role of various parameters including intrinsic parameters or extrinsic factors in the fatigue crack growth process is discussed. The mechanisms proposed to account f...

The effects of hydrogen on the fatigue crack growth behavior of 42CrMo4 welds, present in hydrogen buffer tanks, were studied in this paper. Two different testing methodologies were compared: hydrogen pre-charge testing and in-situ testing. A comprehensive analysis of the fracture surfaces was performed using scanning electron microscopy. In genera...

The present work concerns the influence of surface (machined, as-built) on the fatigue resistance of AlSi10Mg produced by a powder-bed laser process. The competition between defects and surface roughness is assessed by using Kitagawa-type diagrams. Samples are printed along three directions: 0°, 45° and 90°. After axial fatigue tests with a load ra...

In a context of reduction of greenhouse gas emission, the development of hydrogen as an energy carrier implies the transport of large quantity of hydrogen gas over long distances. The option of using the existing Natural Gas (NG) network raises the question of the amount of hydrogen gas that can be blended with natural gas while ensuring safe opera...

this paper proposes an extended discussion of experimental results previously published by the authors and from literature about fatigue crack growth influenced by high pressure of gaseous hydrogen in a commercially pure iron. Firstly a summary of these results obtained for different exposure conditions in terms of gas pressure and loading frequenc...

The Ti 17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) alloy is used in the first stages of engine compressors, at temperatures up to 450°C. However, its use in structural parts such as engine pylons is more prospective and raises the question of damage tolerance. As the engine pylon environment involves prolonged exposures to high temperatures, the impact of aging on...

Aiming to investigate the dependency of hydrogen-affected fatigue crack growth (HAFCG) on the loading frequency f, this study experimentally characterized the HAFCG in a commercially pure iron as a function of f ranging from 0.02 to 20 Hz as well as a stress intensity factor range ΔK and hydrogen gas pressure \( P_{{{\text{H}}_{2} }} \). The crack...

The impact of a controlled surface imperfection on the low-cycle fatigue life in two different steels is investigated. After introduction of a single imperfection with a depth varying from 50 to 350 µm in cylindrical samples, fatigue tests were conducted under fully-reversed total axial strain control in air at ambient temperature. It is shown that...

The microstructural stability during aging at 750 °C of the γ/γ′ nickel-based superalloy AD730TM is investigated in this work. Strain-free aging and aging during fatigue tests are conducted, with a focus on the influence of the strain ratio, the maximum applied strain, and the cycle waveform (with or without dwell). Two classical mechanisms of γ′ p...

In a context of optimization of the crack propagation resistance properties in αβ titanium alloys, this work aim to explore interactions between microstructure and deformation at crack tip in lamellar titanium alloy, especially regarding to the differences between the two propagation regimes observed in these alloys. Analysis of crack path in these...

The Direct Current Potential Drop method is commonly used to monitor the crack growth during fatigue test when optical access to the crack is not possible. The reliability of this method depends on the calibration curve, which correlates the potential drop measurement with the crack length and shape. Using Finite Element Analysis and experimental a...

This study deals with the influence of microstructure on the fatigue crack growth resistance of αβ titanium alloys: Ti-6Al-4V ELI (Extra Low Interstitial) that may compete with the conventional Ti-6Al-4V alloy in the manufacture of high performance aircraft. Six different microstructures have been considered: the as-received bimodal microstructures...

The Fatigue Crack Growth (FCG) behavior of welded UNS N08028 (Alloy28) superaustenitic stainless steel was investigated in this paper. Alloy28 superaustenitic stainless steel was welded using Shielded Metal Arc Welding process. The FCG behavior was studied under two load ratios (0.1 and 0.5) and for different specimen configuration: Base Metal (BM)...

In this paper, the low cycle fatigue resistance of a 304L austenitic stainless steel in a simulated pressurized water reactor (PWR) primary water environment has been investigated by paying a special attention to the interplay between environmentally-assisted cracking mechanisms, strain rate, and loading waveshape. More precisely, one of the prime...

Given the stringent requirements of high levels of safety in nuclear components, stakeholders of French nuclear industry must anticipate the presence of residual surface imperfections in these components. Such imperfections could be introduced during manufacturing or maintenance operations. The incidence of surface irregularities on the fatigue str...

Hydrogen-Affected Fatigue Crack Growth (HAFCG) in commercially pure iron has been characterized in terms of hydrogen gas pressure, loading frequency and stress intensity factor range ΔK. A higher hydrogen gas pressure decreases the critical value of ΔK triggering the HAFCG enhancement, and a lower loading frequency increases the HAFCG enhancement....

This work shows the impact of microstructure and defect on the fatigue life of an AlSi10Mg manufactured by Additive Layer Manufacturing (ALM). Samples were manufactured via a laser powder-bed process: two configurations (0° and 90°) are considered in order to evaluate the impact of the building direction on fatigue properties. 3D X-Ray tomography w...

This work shows the impact of microstructure and defect on the fatigue life of an AlSi10Mg manufactured by Additive Layer Manufacturing (ALM). Samples were manufactured via a laser powder-bed process: two configurations (0° and 90°) are considered in order to evaluate the impact of the building direction on fatigue properties. 3D X-Ray tomography w...

A multi-scale characterisation of the crack tip plasticity has been investigated in a fatigue crack propagation under gaseous hydrogen at gas pressure of 35 MPa in a commercially pure iron, Armco iron. The dislocation structure beneath a fracture surface was observed by a Transmission Electron Microscopy(TEM), and the cyclic and monotonic plastic z...

This work concerns the fatigue resistance of a AlSi10Mg material produced by additive manufacturing, and more precisely the competition between as built manufacturing surface and as-machined surface on the fatigue resistance. Samples were built by a powder-bed process with an EOS-M280 machine using standard in two configurations (0° and 90°) in ord...

Due to complex microstructure and defect inherited from this ALM process, it is necessary to assess the fatigue resistance of the material constitutive of manufactured parts prior to certification. This work is precisely tackling this issue with a special attention paid to the role of microstructural parameters and defects on fatigue life. Specimen...

This paper presents an investigation on the effects of ageing on the microstructure and the corresponding physical and mechanical properties of a 2024 aluminium alloy used in a civil transport aircraft wing structure in order to assess the residual resistance of the end of a service life. More precisely, heat treatments are applied in order to simu...

This work aims to evaluate the impact of a prolonged thermal aging on the fatigue crack growth properties of a commercial Ti 17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) titanium alloy. Aging was operated at 450 °C for extended times, of 1000 h and 10,000 h respectively. In terms of room-temperature tensile properties, aging is mainly responsible for a strain harde...

In this paper, the Low-Cycle Fatigue (LCF) resistance of an austenitic 304L stainless steel used in nuclear plant components is investigated. More precisely, a special attention is here paid to the respective role of surface finishing and environmental effects on the elementary damage stages, namely crack initiation and crack propagation. The objec...

A huge enhancement of fatigue crack growth rates was observed on a 15-5PH martensitic stainless steel under gaseous hydrogen. The observation of fracture surfaces showed a change in fracture mechanisms depending on hydrogen pressure and loading condition, namely the stress intensity factor amplitude and the loading frequency. The present study was...

This study evaluates the influence of residual stresses induced by the fabrication of surface anomalies on the fatigue crack growth in a nickel based superalloy. To separate the notch effect of the geometry from the residual stress field induced by fabrication of the surface flaws, two V-type anomalies are considered: scratches and dents with equiv...

In the aircraft industry, Additive Manufacturing (AM) process is receiving more and more attention to produce parts with complex geometry and also leads to important weight reduction. Due to complex microstructure and the presence of defect both inherited from this specific process, it is necessary to assess the fatigue resistance of the material c...

304L austenitic stainless steel is notably used to manufacture pipes in primary cooling circuits of nuclear power plants operating at a temperature close to 300°C in a specific aqueous environment. Customarily, pipes are roughly polished, however, after some interventions, a few zones might be ground. Start-ups, shutdowns and operating transients o...

The issue of fatigue crack propagation assisted by gaseous hydrogen is here addressed in the case of a simple microstructure, namely a commercially pure ARMCO iron under a gas pressure of 35MPa at different load frequencies. Three characteristic regimes were identified in the da/dN curves. At low ΔK value, the exposure to gaseous hydrogen immediate...

Hydrogen generally results in a degradation of fatigue crack growth resistance in metals depending on the nature of the hydrogen interaction with crystalline defects developed during a cyclic loading. In this paper we present the first results regarding the characterization of the microstructure and the mechanical properties of Armco Iron with a fe...

This paper focused on the study of Low Cycle Fatigue of welded joints of superaustenitic (Alloy28) stainless steels. Chemical composition and microstructure investigation of Base Metal (BM) and Weld Metal (WM) were identified. The results showed that both of composition is fully austenitic with a dendritic microstructure in the WM. Low cycle fatigu...

Gaseous hydrogen substantially reduces fracture properties such as threshold stress intensity factor and crack growth resistance in the precipitation-hardened martensitic stainless steel investigated in this study. Fatigue crack propagation tests were performed on CT specimens under different atmospheres (hydrogen pressures from 0.09 to 40 MPa) on...

The Direct Current Potential Drop method is one of the possibilities to measure the crack growth during fatigue tests without optical access to the sample. The accuracy of this technique applied to short cracks mainly depends on the calibration curve. In the present work experimental and numerical approaches are proposed to calibrate the potential...

Shielded Metal Arc Welding (SMAW) was performed on UNS N08028 (Alloy 28) superaustenitic stainless steel sheets. In the present work, the microstructure and the mechanical properties of base metal (BM), weld metal (WM), and welded joint (WJ) are investigated. Optical micrographs show that the base metal presents austenitic grains, and the weld meta...

In this study, the effect of gaseous hydrogen on the fatigue crack growth behavior in a precipitation-hardened martensitic stainless steel is investigated. It is known that the degradation in fatigue crack growth behavior derives from a complex interaction between the fatigue damage and the amount of hydrogen enriching the crack tip, which is depen...

Aircraft engine manufacturers have to demonstrate that handling surface anomalies in sensitive areas of discs are not critical for in-service life of a component. Currently, the models used consider anomalies as long cracks propagating from the first cycle, which introduces a certain degree of conservatism when calculating the fatigue life of surfa...

Aircraft engine manufacturers have to demonstrate that handling surface anomalies in sensible areas of discs are not critical for in-service life of a component. Currently, the models used consider anomalies as long cracks propagating from the first cycle, which introduce a certain degree of conservatism when calculating the fatigue life of surface...

Over the last 20 years or so, many studies have revealed the deleterious effect of the environment on fatigue life of austenitic stainless steels in primary water reactor (PWR) primary water. The fatigue life correlation factor, so-called Fen, which corresponds to the ratio of fatigue life in air at room temperature to that in water under reactor o...

This paper focuses on the influence of strain rate in Low Cycle Fatigue (LCF) of a 304L austenitic stainless steel at 300 °C in different environments (secondary vacuum, air and Pressurized Water Reactor (PWR) water environment). Moreover test samples are ground to obtain a surface finish rougher than all that could be found in nuclear power plants...

This paper reports on investigations on the residual fatigue resistance of a 2024 aluminium alloy of an A320 aircraft at the end of life. The fatigue data (S-N and da/dN curves) are compared with data obtained on a pristine alloy using a similar procedure. The results are analysed on the basis of fracture surfaces observations and of AFGROW fatigue...

The 15-5PH (precipitation-hardened) martensitic stainless steel is prone to embrittlement following ageing during service at temperatures between 300°C and 350°C. This results in an increase in strength and a decrease in elongation and fracture toughness. However little information is available on the consequences of long term ageing on fatigue cra...

In this study we focus on the effect of hydrogen gas on the cracking resistance of metals. The main objective is to predict the fatigue crack propagation rates in the presence of hydrogen. For this purpose, a Cohesive Zone Model (CZM) dedicated to cracking under monotonic as well as cyclic loadings has been implemented in the ABAQUS finite element...

The fatigue design of nuclear components is based on an S-N curve established in air at 20 degrees C. To this curve, different penalty factors, representative of various effects (scale effect, material variability, surface finish, environmental effect, etc), are then applied. This method considers that these effects are independent from each other....

The high-temperature Fatigue Crack Growth (FCG) behaviour of a 15-5 PH (precipitation-hardened) martensitic stainless steel was investigated in three different metallurgical conditions, i.e., as-received, aged at 300 degrees C for 1000h and 5000h. FCG tests were conducted at room temperature and 300 degrees C under constant amplitude loading with t...

In this study, the effect of gaseous hydrogen pressure in relation with the loading frequency on the fatigue crack growth behavior of a precipitation-hardened martensitic stainless steel is investigated. It is found that increasing the hydrogen pressure from 0.09 to 9 MPa induces an enhancement of the fatigue crack growth rates. This enhancement is...

The French Regulatory Commission insisted on a survey justifying the assumed mechanical behavior of components exposed to Pressurized Water Reactor (PWR) water under cyclic loading without taking into account its effect. In the US and Japan, the fatigue life correlation factors, so called Fen, are formulated and standardized on the basis of laborat...

Over the last 20 years or so, many studies have revealed the deleterious effect of the environment on fatigue life of austenitic stainless steels in pressurized water reactor (PWR) primary water. The fatigue life correlation factor, so-called Fen, has been standardized to consider the effect on fatigue life evaluation. The formulations are function...

Different approaches have been developed to address the difficult issue of crack propagation simulation under monotonic loading. However, numerical models that can also account for crack growth under cyclic loading are much less numerous. The aim of the paper is to develop a numerical model to predict the behaviour of cracked panels under monotonic...

In this paper, two fatigue lifetime prediction models are tested on TiAl intermetallic using results from uniaxial low-cycle fatigue tests. Both assessments are based on dissipated energy but one of them considers a hydrostatic pressure correction. This work allows to confirm, on this kind of material, the linear nature, already noticed on silicon...

Experimental studies indicate a deleterious influence of a hydrogenous environment on the fatigue crack propagation resistance of metallic materials. In order to provide a predictive tool to assess fatigue lifetime of structures subjected to hydrogen, an ABAQUS finite element model of a compact tension (CT) specimen has been developed. A cohesive z...

In this paper, two examples of the influence of time-dependent processes on crack path in two 2XXX aluminium alloys are presented. The first example is concerned with corrosion–fatigue crack growth resistance of a 2024 T351 alloy cracked in the S–L direction in 3.5% NaCl solution at free corrosion potential. The second example deals with the elevat...

This study was undertaken with the aim of identifying the domains where synergistic interactions between mechanical, environmental and microstructural parameters may occur during corrosion fatigue crack growth in the aluminum alloy 2024, as well as the rate controlling factors. Corrosion fatigue crack propagation tests have been carried out at diff...

Characterization of materials requires a large number of experimental tests with various loading modes in order to ensure that it meets the design requirements. The aim of his work is to develop a numerical model to predict the behaviour of cracked panels, in place of expensive and complex experiments to generate data for designers. In particular,...

This paper reports on a study on the effect of upscaling on the fatigue crack growth resistance of a FeAl alloy prepared by mechanical alloying and forging. The alloy selected is a FeAl 40 grade 3 alloy reinforced by oxide dispersion. A batch of material prepared on a large scale mechanical alloying facility and subsequently forged is considered an...

The fatigue behaviour of a powder-metallurgy (PM) + heat-treated Ti(49)Al(47)Cr(2)Nb(2) alloy is investigated using detailed SEM characterization. Based on the results of comparative static and cyclic loadings at RT, the fracture origins for the different test specimens is investigated. Conventional fractographic analyses revealed that internal str...

The relation between microstructural parameters, microscopic cyclic deformation mechanisms and macroscopic cyclic strain hardening is investigated in the case of a heat treated PM Ti-48Al-2Cr-2Nb alloy at 20 degrees C and at 500 degrees C. In particular it is shown that, for the different microstructures considered, a moderate hardening is related...

The aim of this study is to identify domains where the interactions between mechanical, environmental and microstructural parameters may occur during corrosion fatigue crack growth in the aluminum alloy 2024. The scope considered encompasses the influence of frequency and of alternate immersion in saline solution. Corrosion fatigue crack propagatio...

This paper reports on a study on creep–fatigue crack growth resistance of a precipitation hardened 2650 T6 aluminium alloy selected for fuselage panels of a future civil supersonic aircraft. The objective is to develop a methodology to predict crack growth under very low frequency loading at elevated temperatures. With this aim, creep crack growth...

This study was undertaken in order to identify the domains of possible synergistic effects between corrosion and fatigue damage during crack growth in aluminium alloys. In this aim the 2024-T351 aluminium copper alloy was selected and tested in the S–L orientation. The effects of load frequency and waveform have been investigated at a load ratio R=...

Cet article propose tout d'abord une revue des connaissances sur l'influence d'environnements gazeux, et en premier lieu de l'air ambiant, sur la propagation des fissures de fatigue dans les alliages métalliques. Des mises en évidence expérimentales des différentes formes d'interaction entre l'exposition à l'air et la propagation de fissure sont to...

This paper presents an analysis of the ability of different criteria to predict fatigue crack initiation under thermal loading. More precisely the predictions of the number of cycles to crack initiation are compared with experimental results obtained using five different fatigue criteria in three types of thermal fatigue tests (namely the FAT3D, JR...

The incident which has occurred in the Civaux power plant has shown the nocivity of thermal loading, the specificity of this type of loading and the difficulty to take it into account at design level. The objective of this study is to examine the initiation and the propagation of crack under thermal loading for the structure with or without weld. I...

This paper addresses the issue of environmentally-assisted fatigue crack propagation in metallic and intermetallic alloys, which is essential to predict the durability of aerospace components. A review of the current understanding of the mechanisms accounting for the detrimental effect of air on fatigue crack growth resistance of conventional alloy...

The near-threshold behaviour of a high-strength low-alloy steel used in helicopter rotors under variable amplitude loading is investigated in ambient air and in vacuum. Strong sequence effects occur, in particular a high decrease in crack growth rates after overloads of 40% on maximum load while keeping the amplitude constant. A detailed study of t...

The cyclic stress–strain (CSS) behaviour of a Ti–48Al–2Cr–2Nb (atomic%) cast alloy is investigated at 25 °C and 750 °C. Meanwhile post-mortem TEM observations are carried out in order to get insights into the deformation mechanisms governing this behaviour. It has been shown that, at 25 °C, the pronounced hardening observed on CSS curves at high to...

The incident which has occurred on the Civaux power plant has shown the nocivity of thermal loading and the difficulty to take it into account at design level. The objective of this paper is to study the initiation and the propagation of crack under thermal loading. In this aim the CEA developed a new experiment named FAT3D. The various experiments...

The low cycle fatigue (LCF) behaviour has been investigated in gas atomized powder compacts of a Ti–47.2Al–2.1Cr–2.1Nb alloy. The Cyclic Stress–Strain (CSS) behaviour at 20 °C and at 500 °C was found to be strongly dependent upon the microstructure. An increasing amount of lamellar colonies, a finer lamellar spacing and a smaller γ grain size were...

TiAl-based intermetallic compounds have received considerable interest during the last years since they now appear as potential high temperature structural materials for advanced aerospace and automotive applications in the temperature range of 650-850 °C. However their fatigue crack growth resistance and the underlying mechanisms at different temp...