Julien Réthoré

Ecole Centrale de Nantes | EC Nantes · Research Laboratory of Civil Engineering and Mechanics

The alternate (stick-slip) cracking phenomenon in Poly(methyl methacrylate) (PMMA) was investigated using high-speed imaging and digital image correlation (DIC). PMMA is known to show a great variety of fracture behaviors by even small changes in loading conditions. With TDCB-shaped samples and under a range of constant extension rates, the phenome...

Nickel superalloys are used for harsh condition application cases as they have high chemo-thermomechanical stability. However, they can suffer from embrittlement due to stress corrosion cracking. This effect is difficult to observe as it can take place at long time scales. Here we propose a feasible experiment to study stress assisted grain boundar...

La simulation numérique de la fissuration est un enjeu industriel majeur nécessitant la prise en compte de différents facteurs ayant un impact sur le processus global de rupture des matériaux. Dans le cas des métaux, la microstructure polycristalline agit sur les étapes de fissuration et ses caractéristiques induisent des scénarios de rupture varié...

This contribution introduces a multiscale fracture model that aims to take the microstructural length scale effects into account in brittle failure. This model is formulated in the framework of Cosserat continuum theory and coupled with the phase field approach to failure to describe complex crack paths. The effectiveness of the proposed method is...

Estimating stress in statically undetermined tests remains an issue in experimental mechanics. Most estimation methods rely on the a priori choice of a behaviour equation leading to an unavoidable model bias. Recently, efforts have been made to propose methods circumventing the parametric description of constitutive behaviours. In particular, Leygu...

In this work we develop a new phase field method for modeling fracture in polycrystallinematerials. Many studies addressed this problem by combining cohesive models at thegrain boundaries and damage models for the bulk. In this paper, a unified formulationis proposed in the phase field framework. Anisotropic failure is considered within thegrain. E...

The present work proposes a metrological route for capturing spatially‐resolved ultra‐high‐speed kinematic full‐field data from high strain‐rate experiments and multi‐sensor camera technology. This paper focuses, from an application point of view, on highly resolved rotating mirror cameras, such as the Cordin‐580. This camera allows 78 frames of 8...

Magnesium oxide nanocubes are compressed along the [001] direction in situ in the transmission electron microscope. Incipient plasticity in the smaller samples is characterized by the nucleation of few 1 / 2 <110>{110} dislocations while a larger number of line defects is observed in larger nanocubes. Yield and flow stresses scattered stochasticall...

In this paper, we present a new and efficient strategy to perform 3D computational fracture modeling from computed tomography (CT) images. The image-based fracture modeling creates a new way to more accurately predict fracture in realistic structures. However, it is currently complex and expensive to perform such simulations. In this work, we propo...

Two kinds of behaviour are commonly distinguished among porous architectured materials: stretching-dominated and bending-dominated ones. One or the other is favoured depending on the mechanical appli cation. This property has been widely studied for random foams and periodic lattices, but has not yet beenconsidered for quasi-periodic ones. Generall...

X-ray tomography techniques give researchers the full access to material inner structures. With such ample information, employing numerical simulation on real material images becomes more and more common. Material behavior, especially, of heterogeneous materials, e.g. polycrystalline, composite, can be observed at the microscopic scale with the com...

Brittle and ductile dynamic fracture in solids is a complex mechanical phenomenon which attracted much attention from both engineers and scientists due to its technological interests. Modeling cracks in dynamic cases based on a discontinuous description is difficult because it needs additional criteria for branching and widening. Due to the very sh...

The design of reliable structures and the estimation of the residual fatigue life of industrial parts containing flaws or cracks rely on our ability to predict the propagation of fatigue cracks. Whereas in industrial component cracks might have a complex path due to geometry and loading, lab experiments used for identifying crack propagation law ar...

This paper presents a versatile model-free approach for linking the damage in highly heterogeneous materials at multiple scales. The proposed scheme evolves from phase-field modelling at the microscopic scale to simulate brittle failure, towards the estimation of the effective elastic, toughness and strength properties of the material at the mesosc...

Data-driven computations propose a completely new paradigm to the computational mechanics research community and to experimentalists. Classically, admissible material states can only be obtained experimentally for homogeneous stress/strain configurations or using a parametric optimization of material laws based on heterogeneous tests. Data-driven a...

The original article was published with an error in the acknowledgement section. The complete acknowledgement section is given below. Acknowledgements This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under Grant Number 107.02-2017.309. The financial support of Institut Universitaire de France...

The use of tomographic images of materials as an input for numerical simulations is becoming more and more common. The main difficulty is the computational cost, mesh generations of finite element simulations and the large discontinuities of material properties. This work proposes a strategy to use a MultiGrid method coupled with homogenization tec...

The construction of a homogeneous medium equivalent to a heterogeneous one under quasi-brittle fracture is investigated in the case of non-separated scales. At the microscale, the phase field method to fracture is employed. At the scale of the homogeneous medium, another phase field model either isotropic or anisotropic, depending on the microscale...

Interactions between multiple stress corrosion cracks (M-SCC) have a major influence on crack growth but are underestimated in models devoted to the evaluation of the lifetime of industrial components. In this study, the growth and interactions between multiple cracks on a sensitized Alloy 600 in a 0.01 M tetrathionate solution, were studied by dig...

Abstract A series of experiments has been performed to build a benchmark for the numerical modeling of mixed mode crack propagation in concrete. Two tests are selected so that the propagation is almost always stable although the material is quasi-fragile. Moreover the variation of mode mixity enables the study of the reorientation of the crack, as...

The high-cost low-resolution infrared cameras operating in middle infrared spectral ranges are widely used to detect the thermal fields. In this study, a low-cost high-resolution silicon-based sensor camera operating in near infrared spectral ranges is used to perform the observation of the thermal fields on the realistic steel specimen surface. In...

Thermal fields are usually obtained by infrared camera (operating in 3–12 μm). However, the infrared cameras are expensive, fragile and low resolution, thus the infrared camera is more used for laboratory researches. Nowadays, silicon-based sensor camera has been widely used to perform real-time observation of the kinematic fields, mainly thanks to...

A powder of transition alumina nanoparticles (including γ and a so-called δ-type) is compacted at room temperature in a diamond anvil cell (DAC) under pressures ranging from 5 GPa to 20 GPa. Characterization carried out on thin foils prepared by focused ion beam (FIB), from the compacted powder, unambiguously reveals plasticity. High resolution tra...

The phase field method is a powerful tool for studying microstructural evolution in various domains of material sciences, including phase change, initiation and propagation of fracture. In this work, a new formulation is developed based on the phase field method for modeling stress corrosion cracking (SCC) induced by anodic dissolution. This method...

There is a growing interest in the development of composites with complex structures designed to generate enhanced mechanical properties. The challenge is how to implement these structures in practical materials with the required degree of control. Here we show how freeze casting of ceramic preforms combined with metal infiltration can be used to f...

Since the pioneering works on digital image correlation, a huge effort has been devoted to the elaboration of strategies coupling measurements with numerical simulations. The main issue achieved with such coupling is the identification of constitutive law parameters from experimental configurations yielding heterogeneous strain/stress fields. The m...

This paper proposes a method to identify the strain–stress relation of non-linear elastic materials, without any underlying constitutive equation. The approach is based on the concept of Data Driven Computational Mechanics recently introduced by Kirchdoerfer and Ortiz (2016). From a collection of non-homogeneous strain fields, for example measured...

A coupled multiphysics phase field framework is proposed to model anodic dissolution induced by stress corrosion fracture growth at microstructual level. The effects of electrochemical-mechanical processes (including crystal anisotropy) are all taken into account. This new model is based upon: (i) an anisotropic phase transformation model based on...

Interactions between multiple stress corrosion cracks (M-SCC) have a major influence on crack growth but are underestimated in models devoted to the evaluation of the lifetime of industrial components. In this study, the growth and interactions between multiple cracks on a sensitized Alloy 600 in a 0.01 M tetrathionate solution, were studied by dig...

Digital Image Correlation (DIC), Acoustic Emission and Electrochemical Noise measurements were applied to study the growth of multiple intergranular cracks as a colony on an Alloy 600 in a tetrathionate solution. Cracks exceeding 55. μm in length and 0.45. μm in opening were successfully detected by DIC. Moreover, crack population was classified in...

Fretting has been the subject of numerous experimental investigations. It occurs when two surfaces rub against each other at low amplitude (some tens of microns of sliding distance). If the tangential force Q is lower than the product of the friction coefficient μ and the normal force P, two different zones can be observed within the contacting zon...

A new multi-phase-field method is developed for modeling the fracture of polycrystals at the microstructural level. Inter and transgranular cracking, as well as anisotropic effects of both elasticity and preferential cleavage directions within each randomly oriented crystal are taken into account. For this purpose, the proposed phase field formulat...

The phase field method is a powerful tool for studying microstructural evolution in various domains of material science, including initiation and propagation of fracture. In this work, a new formulation is developed within the phase field method for modeling stress corrosion cracking induced by anodic dissolution. The effects of both electrochemica...

A new multi-phase-field method is developed for modeling the fracture of polycrystals at the microstructural level. Inter and transgranular cracking, as well as anisotropic effects of both elasticity and preferential cleavage directions within each randomly oriented crystal are taken into account. For this purpose, the proposed phase field formulat...

Anisotropy is inherent to crystalline materials (among others) due to the symmetry of the atomic lattice. However, failure anisotropy is questioning the foundations of brittle failure as the equivalence between the principle of local symmetry and the maximum energy release rate criterion is no longer valid. Many experimental observations have been...

Stress Corrosion Cracking (SCC) is a very common failure mechanism characterized by a slow, environmentally influenced crack propagation in structural components. The mechanisms proposed to explain, at the microscopic scale, the cracking propagation processes are not able to elucidate all aspects of this phenomenon in different metal/environment sy...

To compensate bad quality of speckles pattern or on increase the spacial resolution by decreasing the element size, finite based DIC often requires a additional regularization. Usually the regularization introduce a cut-off length below which the wave length of the measured displacement are filtered. While this might improve the measurement for low...

Structural design with highly flowable Fibre Reinforced Concrete has to duly take into account the preferential alignment of fibers, which can be governed through the rheological properties of the fluid mixture and the casting process and by the geometry of the structure. The possibility of predicting the fiber alignment, by tailoring the casting p...

Crack propagation in carbon cathode used in the aluminium industry has been investigated through flexural tests on notched specimens. The main parameters of interest were the geometrical evolution of the crack and the stress intensity factor at the tip ends. The latter, in the case of interfacial fracture in two-dimensional geometries, can be relat...

In this study, we propose an innovative mechanical observation protocol of nanoparticles in the 100 nm size range. It consists of in situTEM nano‐compression tests of isolated nanoparticles. Load–real displacements curves, obtained by Digital Image Correlation, TEM images (BF, DF and WBDF) are analyzed and these analyses are correlated with Molecul...

This paper proposes a fracture mechanics model for the analysis of crack propagation in periodic honeycomb materials. The model is based on gradient-elasticity what enables to account for the effect of the material structure at the macroscopic scale. For simulating the propagation of cracks along an arbitrary path, the numerical implementation is e...

div class="title">Size and Environment Effect on the Room Temperature Plastic Deformation of Ceramic Nanoparticles - Volume 22 Issue S5 - I. Issa, L. Joly-Pottuz, J. Amodéo, J. Réthoré, D. J. Dunstan, T. Epicier, I. Jenei, D. Stauffer, C. Esnouf, V. Garnier, K. Masenelli-Varlot

Since the development of X-ray tomography, it has been possible to obtain 3D images of the micro-structure of materials. These data are extremely useful for analysing of the morphology of heterogeneous materials. More recently, using diffraction contrast tomography in polycrystalline materials, not only the morphology of grains but also their orien...

The fretting is a damage that occurs when two contacting surfaces rub against each other at very low amplitude. This may produce intense stress gradients resulting in crack initiation on the contact surfaces of a blade root joint. An innovative experimental test allowing superposition of a vibratory loading on a static loading made it possible to r...

The prediction of brittle fracture initiation and propagation in heterogeneous structures is one of the main challenging problems in the field of solid failure mechanics. Nowadays with the development of X-Ray tomography, it is possible to account for the real micro structure in a computational model. Recently, a new phase field method proposed by...

Stress corrosion cracking (SCC) is a very common failure mechanism characterized by a slow, environmentally influenced crack propagation in structural components. The mechanisms proposed to explain at the microscopic scale the cracking propagation processes are not able to elucidate all aspects of this phenomenon in different metal/environment syst...

Multiscale methods and homogenization techniques are usually compared to full field simulations. The accuracy of the full field simulations is well controlled in the linear elastic regime and for small strain. With non linear behaviour, large strain or multi-axial strain states the comprehension is hampered by the lack of experimental results. In t...

This chapter focuses on the nanoindentation of nanoparticles. It presents the most important works performed on thin sections of bulk materials. Most of the in situ mechanical experiments performed on nanoparticles are called "nanoindentation". Such tests can also be called "nanocompression", because they consist of a load under compression of the...

In this study, we present a method to analyse experimentally the deformation kinematics of a heterogeneous material using digital image correlation. The periodicity of the microscopic deformation patterns is assessed from the displacement measured along the edges of unit cells. The first order macroscopic transformation gradient is shown to enable...

Gradient-elasticity and more generally gradient-enhanced continuum models have been extensively developed since the beginning of the twentieth century. These models have shown the ability to account for the effect of the underlying material heterogeneity at the macroscopic scale of the continuum. Despite of a great theoretical interest, gradient-en...

With the development of full-field measurement techniques, it has been possible to analyze crack propagation experimentally with an increasing level of robustness. However, the analysis of curved cracks is made difficult and almost unexplored because the possible analysis domain size decreases with crack curvature, leading to an increasing uncertai...

In order to evaluate the relative contribution of both mechanical and electrochemical processes at the crack tip during Stress Corrosion Cracking propagation, an original combination of controlled pre-cracking followed by thermal pre-oxidation of SCC specimens was developed. It allowed localizing dissolution at the crack tip for Zircaloy-4 tested i...

The mechanical behavior of 〈1 0 0〉-oriented MgO nanocubes is investigated using in situ transmission electron microscopy (TEM) compression tests at room temperature and molecular dynamics simulations. Experiments show high strength and ductility, in addition to specific deformation mechanisms interpreted by the simulation. The nucleation and the pr...

Aluminum alloy automotive parts produced by the Lost Foam Casting (LFC) process have coarser microstructure and porosity defects than parts produced with conventional casting processes at faster cooling rates. This coarse microstructure has a major influence on the fatigue properties and crack initiation. In order to study its influence upon the me...

A unified Digital Image Correlation (DIC) / eXtended Finite Element Method (X-FEM) framework based on the Williams’ series for fatigue crack growth identification and simulation is proposed. Williams’ series are used for post-processing the displacement measured by digital image correlation. It gives access to the change of stress intensity factors...

This paper consists of an extension of simulation with direct estimation of stress intensity factors to the three-dimensional case. Here, it combines X-FEM with localized multigrids and direct estimation of quantities of interest along the crack front (SIF, T-stress, etc.) based on crack tip asymptotic series expansion. In practice, a three-dimensi...

Measuring 3D displacements usually requires at least two cameras or 3D images. However, in some especially constrained experimental circumstances, it is only possible to use a single camera. The present paper develops a methodology, based on digital image correlation that is able to measure the homogeneous 3D displacement of a plane surface using a...

This paper describes a methodology used to compute stress intensity factor values along the curved front of a fatigue crack inside a nodular cast iron. An artificial defect is introduced at the surface of a small sample. The initiation and growth of a fatigue crack from this defect during constant amplitude cycling is monitored in situ by laborator...

This paper presents a digital image correlation method able to detect and measure a contour or silhouette in a digital image, with a sub-pixel precision. A virtual image that describes a simple contour or silhouette roughly similar to the physical object to detect is created. The matching with the physical image of the object is then performed base...

Laminate composite materials are widely used for many industrial applications because of their high specific mechanical properties as well as the possibility to adapt the structure properties to its application and loading conditions by optimization of the stacking sequence. It is now well known that the mechanical properties mismatch of adjacent l...

Aluminum alloy automotive parts produced by the Lost Foam Casting (LFC) process have coarser microstructure and porosity defects than parts produced with conventional casting processes at faster cooling rates. This coarse microstructure has a major influence on the fatigue properties and crack initiation. In order to study its influence upon the me...