Laurent Barrallier

Ecole Nationale Supérieure d'Arts et Métiers | ENSAM · Laboratoire Mécanique, Surfaces, Matériaux et Procédés (MSMP)

Digital image correlation (DIC) is expanding in many fields. In particular, it requires that the acquisition conditions and speckle be adapted to each application. A new methodology allowing to define the quality of the images in a fast and precise way is proposed. An analytical model based on mean intensity gradient of speckle pattern criterion an...

The influence of oxidizing and nitriding parameters on the nitrogen concentration of grain-oriented electrical steels preliminary to the development of the final Goss texture was explored. Results show that the nitrogen enrichment is driven by a ferrite to austenite transformation during thermochemical treatments. Such a transformation is promoted...

In this study, the residual stresses in the laminated polymer-matrix composite sample with a configuration of [04/904]s were measured and investigated using the incremental hole-drilling and slitting methods combined with the digital image correlation (DIC) technique. By averaging the values of strain obtained by the DIC technique in the location o...

Directional solidification of a cast mono silicon seed and of a float-zone (FZ) silicon seed was performed and the grain and defect structures of the seeds as well as of the regrown parts are analyzed. In situ X-ray diffraction imaging enabled the observation of the dislocation arrangements. During the heating process, in the FZ seed, mobile disloc...

Background The slitting method is a widely used destructive technique for the determination of residual stresses. Because of the rich data content of the full-field methods, optical techniques such as digital image correlation (DIC) are replacing strain gages for surface measurements.Objective The objective of the current paper is to overcome the d...

To control the final grain structure and the density of structural crystalline defects in silicon (Si) ingots is still a main issue for Si used in photovoltaic solar cells. It concerns both innovative and conventional fabrication processes. Due to the dynamic essence of the phenomena and to the coupling of mechanisms at different scales, the post-m...

This work is dedicated to the grain structure formation in silicon ingots with a particular focus on the crystal structure strain building and its implication in new grain nucleation process. The implied mechanisms are investigated by advanced in situ X-ray imaging techniques during silicon directional solidification. It is shown that the grain str...

Nitriding of low-alloy steels is widely used for gears and bearings in aerospace industry. Some highly stressed surfaces require high nitrided depth, which involves long time/high temperature nitriding treatment. This study focused on identifying process parameter effects on hardness and residual stress profiles in a large range of nitriding time a...

Gaseous nitriding of steels is a well-established thermochemical surface treatments that increases the fatigue resistance of treated parts. The present work proposes a modelling of the fatigue life as a function of the applied stress. It takes into account the hardness and compressive residual stresses that developed during nitriding. The model is...

The gaseous nitriding behaviour of 33CrMoV12-9 steel was investigated. The co-diffusion of nitrogen and carbon, precipitation at grain boundaries and mechanical properties evolutions (microhardness, residual stresses) are compared for several nitriding potentials, nitriding time and temperatures. While hardening unequivocally depends on the precipi...

Binary alloys were gas-nitrided at a temperature of 520 °C for 70 h and with a N2/NH3 ratio of 15 to 20%. The thickness of the nitrided layers was evaluated by Vickers hardness testing. The morphology and composition of the nitrided layers were investigated by light and scanning electron microscopy (SEM). Phase depth distributions were calculated b...

Anomalous small angle scattering (ASAXS) is a powerful non-destructive technique that can provide characteristic features of nanoscale precipitates such as the volume fraction, and chemical composition. In this paper, the technique is used for the first time to explore nanoscale MN nitrides (M = Cr,Fe) after nitriding of a model iron alloy (Fe-0.35...

The aim of this study is to adapt and use a procedure to investigate the influence of the microstructure on the local mechanical behavior of a tempered and nitrided low-alloyed steel. A well-known technique is employed, consisting in Digital Images Correlation (DIC) of SEM field images acquired during In-situ loads. To avoid heterogeneous macroscop...

Uniaxial cyclic loadings of homogeneously nitrided steel plates were carried out to charac-terize the crack initiation mechanisms with respect to the microstructure. S-N (Stress - Num-ber of cycles to failure) curves corresponding to the nitrided layer of a 33CrMoV12-9 steel grade were created in order to estimate the number of cycles for interrupt...

Le traitement thermochimique de nitruration est un traitement de surfaces permettant d'améliorer la durée de vie en fatigue des pièces traitées. Les dernières avancées dans ce domaine permettent de relier les paramètres technologiques du procédé (temps, température, potentiel azote, composition de l'acier) aux caractéristiques mécaniques des couche...

The present work focuses on the industrial inhibition of gaseous nitrided parts and on the industrial in-situ pre-treatment that can be used to avoid these inhibitions. The first objective is to obtain a repeatable defective nitriding process on carbon iron-based alloys, while the second is to determine the ability of determined in-situ pre-treatme...

This work is dedicated to the advanced in situ X-ray imaging and complementary ex situ investigations of the growth mechanisms when silicon solidifies on a monocrystalline seed oriented 〈110〉 in the solidification direction. It aims at deepening the fundamental understanding of the phenomena that occur throughout silicon crystal growth with a parti...

The objective of this work is to propose a model abled to optimize the mechanical properties from gaseous nitriding of steels (hardness, residual stresses) for a given loading and fatigue lifetime. Multiaxial fatigue criteria are used and the present study focuses on the influence of residual stresses. Starting from a surface loading profile, the t...

Shot-peening is a common mechanical surface treatment used in automotive and aeronautical industries to enhance life duration of mechanical parts by introducing compressive residual stresses. TRIP 780 steel fatigue type specimens are shot-peened and loaded under cyclic bending. The martensite phase transformation and the evolution of residual stres...

Manufacturing industries perform mechanical surface treatments like shot peening at the end of the manufacturing chain to protect important working parts. This treatment modifies the near surface of the treated part with the introduction of compressive residual stresses due to the repeated impacts of the shot. Then, the treated part exhibits, not o...

The behaviour of gases produced by fission is of great importance for nuclear fuel in operation. Within this context, a decade ago, a general method for the characterisation of the fission gas including gas bubbles in an irradiated UO2 nuclear fuel was developed and applied to determine the bubbles internal pressure. The method consists in the dete...

The objective of this study was to evaluate the residual stresses of FSW welding magnesium alloys (AZ31). The results show that the FSW processes lead to the formation of several distinct zones with differing mechanical properties. The residual stresses evolution have been explained by the heterogeneous modifications of the microstructure particula...

The present study aims to develop an algorithm able to predict the fatigue lifetime of nitrided steels. Linear multi-axial fatigue criteria are used to take into account the gradients of mechanical properties provided by the nitriding process. Simulations on rotating bending fatigue specimens are made in order to test the nitrided surfaces. The fat...

This chapter discusses the benefits of nitriding on the mechanical properties of steels. The generation of a compressive residual stress using nitriding can have beneficial impacts on such characteristics as hardness and fatigue life. These effects are explained in terms of the effect of nitrogen diffusion on the microstructure of the steels and a...

Le grenaillage de précontrainte a pour but d’augmenter la durée de vie des matériaux traités en introduisant des contraintes résiduelles de compression. Cette étude porte sur la modélisation de la tenue en fatigue d’aciers grenaillés et plus particulièrement d’aciers à transformation austénite-martensite sous sollicitation. L’approche utilise la de...

Le but de cette étude est de mettre en place un modèle de calcul en fatigue prenant en compte les caractéristiques mécaniques d’un matériau nitruré. Le travail est réalisé sur acier de nuance 32CrMoV13 utilisé dans la conception de pignon de transmission de puissance par Hispano-Suiza.

The effect of the composition of two steels (B and 6MnCr5) on precipitation of undesirable phases (carbides, nitrides and carbonitrides) under thermochemical treatment (low-pressure or vacuum carbonitriding) is investigated. Metallographic and x-ray diffraction studies and thermodynamic computations are performed.

A model reproducing strain softening behavior in ceramic materials is proposed. This model is base on a critical treatment of previous mechanical experimental results, mainly on uranium dioxide. The main hypothesis is that the strain softening phenomenon is related to an ageing process, where some point defects move towards the dislocations and mod...

The objective of the study was to characterize the properties of a magnesium alloy welded by friction stir welding. The results led to a better understanding of the relationship between this process and the microstructure and anisotropic properties of alloy materials. Welding principally leads to a large reduction in grain size in welded zones due...

Low velocity perforation of aeronautical aluminium alloy sheets 2024 T3 is studied in this paper. After a literature review on recent experiments and models of plate’s perforation, experimental results for 2 thicknesses (2 mm and 4 mm) of plates are presented. Perforation tests are performed with an instrumented drop test. The striker has a large d...

Thermochemical surface engineering significantly improves the properties of steels. Edited by two of the world’s leading authorities, this important book summarises the range of techniques and their applications. It covers nitriding, nitrocarburizing and carburizing. There are also chapters on low temperature techniques as well as boriding, sheradi...

U-Mo/Al based nuclear fuels have been worldwide considered as a promising high density fuel for the conversion of high flux research reactors from highly enriched uranium to lower enrichment. In this paper, we present the annealing test up to 1800°C of in-pile irradiated U-Mo/Al-Si fuel plate samples. More than 70% of the fission gases (FGs) are re...

The evolution of residual stresses during short time gas nitriding of 33CrMoV12-9 steel grade is studied. It aims understanding the influence of nitriding parameters (temperature T and nitriding potential Kn) on the generation and evolution of residual stresses in the very first stage of nitriding. The samples are gas nitrided using a thermobalance...

Recent programs of aircraft design are characterized in terms of materials, by introducing weldable alloys as alternatives to the traditional technique of riveting, open the way to reduce weight and allow cost reductions in production and maintenance. Understanding the influence of various parameters of TIG welding process applied to the alloy 2024...

Micropitting is a form of surface fatigue damage that occurs in the gear teeth. It is due to the effect of variation in the mechanical loading in the contact zone between the two teeth, induced especially by flank roughness. In this study, generic roughness profiles were built with geometrical parameters to simulate the contact between two rough su...

Low velocity perforation of an aeronautical aluminum alloy sheet 2024 T3 subjected to impact is studied in this paper. The main objective is to compare experimental results and simulations by analysis of the failure. The perforation test is made with an instrumented 3 meter drop test. The striker has a large diameter (45 mm) and a conical shape. Sh...

Friction stir welding induces a microstructural evolution and residual stresses that will influence the resulting mechanical properties. Friction stir welds produced from magnesium alloy hot rolled plates were studied. Electron back scattered diffraction was used to determine the texture evolution, residual stresses were analysed using X ray diffra...

In a previous study, the capability of X-ray diffraction technique to qualify damage occurring during friction had been proven [1]. The purpose of this study is to complete this research in order to develop a method to quantify the damage induced by the friction loading.

The present study deals with a microstructural characterisation of a biphasic titanium alloy Ti‐10V‐2Fe‐3Al. The near β titanium alloy is primarily used for high strength applications, such as components for aeronautical industry. The forging process and the heat treatments of Ti‐10V‐2Fe‐3Al induce a complex microstructure, which consists of an equ...

The objective of this investigation was to study the mechanical properties of a magnesium alloy welded by a CO2 laser. Residual stresses were measured by X-ray diffraction. They were calculated by the classic sin2 ψ method in the isotropic zones by using the orientation distribution function (ODF) in the textured zones. The results demonstrated tha...

Effective prediction methods are needed by engineers to design parts used in fatigue conditions. In gears, surface fatigue damage is observed at two scales: pitting and micropitting. These two phenomena occur in response to the variation of the local loading on the contact zone between teeth. The loading is influenced by the shape of the teeth and...

Development and evolution of compressive residual stress during nitriding treatment are studied. A model carbon iron-based alloy Fe-3wt.%Cr-0.35wt.%C was nitrided in gas at 550 °C for different times. Microstructural investigation indicated an influence of the transformation and the associated carbon diffusion on the in-situ relaxation of residual...

Nitriding is a well-established thermochemical surface treatment of carbon micro-alloyed steels aiming enhancing surface properties such as fatigue, wear and corrosion resistances. The idea is taking benefits from the high hardening level due to a fine nitride precipitation and also the compressive residual stress state. Due to some complex interac...

Residual stresses are to be determined to predict mechanical behaviour of vital parts in aircraft. This part constituted by Ti-10V-2Fe-3Al is analysed using x-ray diffraction (XRD). However, the broadening and sometime the disappearance of peaks involve a major difficulty to quantify the strains and the stresses which are close to the surface. In t...

This experimental study focuses on the influence of shot peening on parts initially treated by carburizing or carbonitriding. Experimental investigations have been carried out: optical observations of the microstructures, in-depth hardness measurement, X-ray diffraction analysis of residual stresses. A comparison is made between the carburizing ana...