arXiv subjects

Guillaume Kermouche

Publications and source records attributed to Guillaume Kermouche.

6 recordsLinked to original sources

arXiv2026

Advancing in situ hydrogen embrittlement studies through an integrated charging cell for SEM micromechanical testing

A comprehensive understanding of hydrogen-deformation interactions at the microscale is essential for revealing hydrogen embrittlement mechanisms. In situ micromechanics with simultaneous hydrogen (H-) charging has therefore gained traction in recent times. In the present study, we aim to address the drawbacks of current in situ H-charging setups by developing a more robust 3-electrode-based back-side charging system for a scanning electron microscope to perform various micromechanical tests. The development of the novel setup is discussed and demonstrated through micropillar compression of an Fe-25Cr single crystal (110) during H-charging. H has increased the yield strength and the apparent strain-hardening rate. H activates multiple slip systems and enhances dislocation density and entanglement, leading to pronounced forest hardening as revealed by electron microscopy. Estimation of activation volume from strain-rate jump tests indicates that the deformation is controlled by the solute drag effect on kink mobility and dislocation forest hardening.

cond-mat.mtrl-sci↗

arXiv2026

A Combined Microbeam and Phase-Field Approach to Identify the Toughness and Ultimate Strength of Amorphous Silica

This work presents a new approach to evaluating the toughness, described by the critical energy release rate ($G_c$), and ultimate tensile strength ($σ_c$) of amorphous silica (SiO$_2$ glass), combining microbeam tests and phase-field calculations. The latter provides a numerical route to brittle fracture without prescribing explicit fracture surfaces \textit{a priori}, enabling crack initiation and propagation to be tracked. Single-notched microbeams and newly designed bone-shaped microbeams with a notch-free gauge section were fabricated by Focused Ion Beam (FIB) milling nd tested under bending in air, probing the brittle-fracture and strength-controlled regimes, respectively. Both geometries were modeled by Finite Element Analysis (FEA) coupled with a phase-field formulation. We found $G_c = 5.1$~J/m$^2$ (critical stress intensity factor $K_{IC} = 0.61$~MPa$\cdot$m$^{1/2}$), an intrinsic material length scale $\ell_c = 9.1$~nm, and $σ_c = 6.8$~GPa, consistent with previously reported brittle properties of silica glass. Through a parametric study, we show the effect of notch geometry on the fracture response of the microbeams and the impact of dimensional measurement error on the determined toughness. Unlike conventional micromechanical methods that yield only $K_{IC}$, our combined microbeam geometries and phase-field approach simultaneously deliver $G_c$ and $σ_c$, bridging brittle-fracture characterization and the strength-controlled regime inaccessible to toughness-only techniques.

cond-mat.mtrl-sci↗

arXiv2026

Amorphous Silicates -- Time-Current Superposition and the Dynamics of Plastic Flow in the Glassy State

Electron irradiation enables quantitative control over the plastic flow dynamics of silicate glasses, even far below the glass transition temperature. Through stress-relaxation experiments spanning ambient to near-glass-transition temperatures, we uncover a time-current equivalence that grants direct access to steady-state plastic flow over five decades in strain rate. This equivalence allows reconstruction of the intrinsic plastic-flow curve and quantitative assessment of the roles of network connectivity and temperature. Notably, the observed temperature dependence reveals a striking discrepancy with existing theoretical frameworks, highlighting the need for a comprehensive model of plastic flow dynamics in the glassy state.

cond-mat.soft↗

arXiv2025

Strain rate sensitivity of a Cu/Al$_2$O$_3$ multi-layered thin film

To study the size and strain rate dependency of copper polycrystalline microstructures, a multi-layered copper/Al$_2$O$_3$ thin film was deposited on a Si substrate using a hybrid deposition system (combining physical vapour and atomic layer deposition). High temperature treatment was applied on the ``As Deposited" material with ultrafine-grained structure to increase the average grain size, resulting in a ``Heat Treated" state with microcrystalline structure. Focused ion beam milling was employed to create square shaped micropillars with two different sizes, that were subjected to compressive loading at various (0.001/s -- 1000/s) strain rates. Differences in the strain rate sensitivity behavior manifesting at low and high strain rates are discussed in the context of the pillar diameters and the grain size of the deformed samples. The Al$_2$O$_3$ interlayer studied by transmission electron microscopy showed excellent thermal stability and grain boundary pinning by precipitation, also resulting in the homogeneous deformation of the pillars and preventing shear localization. Geometrically necessary dislocation densities estimated by high (angular) resolution electron backscatter diffraction presented inhomogeneous dislocation distribution within the deformed pillar volumes, that is attributed to the proximity of the sample edges. Finally, the Al$_2$O$_3$ interlayers successfully suppressed any possible recrystallization processes, contributing to the excellent film stability, that makes the proposed coating ideal to be operating under extreme conditions.

cond-mat.mtrl-sci↗

arXiv2024

Micromechanics reveal strain rate dependent transition between dislocation mechanisms in a dual phase high entropy alloy

An equimolar NiCoFeCrGa high entropy alloy having dual-phase homogeneous components was studied, where the constituent phases exhibit distinct mechanical properties. Micropillars with various diameters were created from two differently heat treated samples, then they were compressed at slow strain rates, that revealed the material's limited sensitivity to size. On the other hand, increased strain rate sensitivity at high deformation speeds was observed, that differs substantially depending on the phase composition of the specimen. Dislocations within the two phases were studied by high resolution transmission electron microscopy and high angular resolution electron backscatter diffraction. The performed chemical analysis confirmed that slow cooling during casting create Cr-rich precipitates, that have significant impact on the global strength of the material.

cond-mat.mtrl-sci↗

arXiv2022

Finite element modelling and investigation of the interaction between an ultrasonic wave and a discontinuous interface

When two surfaces are brought into contact and slide against each other, junctions are formed at the interface. The dynamics of formation, rupture and evolution of these junctions governs the tribological response of the macro-contact. Getting insight on the real behavior of these junctions is a challenging task. Theory states that contacts and asperities are continuously altered in two bodies due to applied pressure, which increases the number of active contacts. To addresses such altering interface conditions, wave propagation through tribological interface by means of the development of a numerical model is proposed. The proposed method is used to study and relate crucial parameters like stiffness, contact width, number of asperities that form a basis for an interface.

cond-mat.soft↗