Publications

A novel multiscale computational framework based on Crystal Plasticity Finite Element (CPFE) modeling is proposed to investigate the effect of grain size on the mechanical behavior and ductility limits of thin metal sheets, featuring both uniform and gradient grain structures. This approach relies on designing unitcell models that reflect the microstructural characteristics of thin metal sheets. The overall response of the unit cell is obtained from that of its single crystal constituents using the periodic homogenization scheme. At the single crystal level, the mechanical behavior is modeled within a finite strain, rate-independent plasticity framework, where the plastic flow is governed by the classical Schmid law. The effect of individual grain size is incorporated at the single crystal scale by adjusting the critical resolved shear stress (CRSS) evolution, using a combination of the microscopic Hall–Petch relationship and a dislocation density-based hardening model. To efficiently solve the single crystal constitutive equations, a return-mapping algorithm coupled with the Fischer–Burmeister complementarity function is developed and implemented into ABAQUS/Standard through a user-defined material subroutine (UMAT). At the macroscopic level, the ductility limits are predicted by the Rice bifurcation theory. The performance of the proposed strategy is validated through a series of polycrystalline aggregate simulations. The numerical results demonstrate a significant influence of grain size on both the macroscopic strength and ductility limits of polycrystalline aggregates. Additionally, the introduction of gradient grain structures is shown to substantially enhance both strength and ductility. These findings provide valuable insights for optimizing material performance in engineering applications.

Inconel 718 alloy is used for high‐temperature industrial applications in its optimized multiphase metallurgical state. Nevertheless, the machining of Inconel 718 alloy becomes problematic and challenging. One alternative consists of developing a new material design strategy based on the metallurgy of high‐entropy alloys (HEAs). These alloys have become a hotspot in the field of innovative high‐temperature metallurgy toward the improvement of the alloy's manufacturability and thermomechanical properties. This study aims at designing, elaborating, and characterizing a new class of alloys with increased entropy, referred to as: “Inco‐like.” The mechanical responses of the alloys, in terms of hardness, have been analyzed using an indentation test at a wide range of temperatures. The dry machinability of the developed alloys has been performed and compared with that characterizing the Inconel 718 in terms of several machining features. Finally, the phases of the studied alloys have been analyzed using metallurgical investigations. The experimental findings and comparisons underscore the advantages of the high‐entropy strategy in terms of tool wear reduction and cutting tool durability. The results demonstrate that the Inco‐like HEA retains a significantly higher hardness of 291 Hv at 800 °C, compared to 160 Hv for Inconel 718 at the same temperature.

Plant fibres are promising reinforcements for bio-composites in additive manufacturing, but their use as long fibres remains limited, often reduced to short particles that underuse their potential. This study presents a customised yarn design that not only maintains fibre alignment parallel to the yarn axis but also ensures core resin impregnation. Commingling and wrap spinning techniques were used to produce four flax/PLA yarns with varying compositions. The manufacturing process and printing of unidirectional composite specimens are detailed. Tomography revealed up to 3.3 times lower intra-yarn porosity thanks to commingling, and tensile tests showed a modulus increase by a factor of 2.1 compared to similar previous works using conventional twisted yarns. These results pave the way for broader use of long flax fibres in 3D printing.

This paper proposes a novel methodology of the topology optimization method considering eddy current effects. The method is applied on chip inductors modelled by the Finite Element Method (FEM). Aiming to meet a specified inductance value while minimizing eddy current losses, we employ a density-based approach to construct a continuous material distribution. The derivative of the objective function with respect to the material distribution is obtained using the adjoint variable method, then the material layout is iteratively updated via the L-BFGS-B algorithm. The proposed framework is validated on both single-turn and multi-turn inductor structures, achieving designs that satisfy the target performance within a limited number of iterations. A key innovation of this work lies in the integration of field-circuit coupling into the topology optimization framework, enabling the analysis of inductors under complex coil configurations involving both series and parallel connections. Additionally, we present an original derivation of the sensitivity formulation associated with the inductance value ensuring that the optimized inductance meets the design specification.

This research focuses on the development and experimental validation of a novel printed piezoelectric transducers network employed on a foreign object damage panel substructure of an aircraft engine fan blade. The main goal of the work is to leverage the screen printing technology to fabricate arrays of piezoelectric transducers and ultimately employ these transducers for operations, enabling the development of structural health monitoring methods for the panel. The printed transducer is made up of a piezoelectric layer sandwiched between two silver electrodes, each printed in a controlled manner. Upon printing and drying of the layers, the transducers undergo polarization. The electromechanical behaviour of the printed transducers, characterized using impedance measurements, exhibits high repeatability, thus indicating its potential for large scale industrial deployment. Following this, it is demonstrated that the transducers are capable of accurately sensing impact, which is one the most common yet critical sources of damage to an engine fan blade. It is also shown that the printed transducers are able to detect acoustic emission events. The ability of the printed transducers to actuate and sense guided wave signals over a range of ultrasonic frequencies is also demonstrated. Furthermore, apart from the noticeable advantages of the non-intrusive nature, and negligible weight as compared to their traditional ceramic counterparts, the printed piezoelectric transducers can potentially be integrated into the manufacturing process in the future, and the presence of transducer arrays ensures the availability of other transducers in case of an individual failure during service. This innovative printing technology for PZT transducer networks thus holds significant promise in bridging the gap between research advancements and the industrial implementation of SHM technology.

This research focuses on the development and experimental validation of a novel printed piezoelectric transducers network employed on a foreign object damage panel substructure of an aircraft engine fan blade. The main goal of the work is to leverage the screen printing technology to fabricate arrays of piezoelectric transducers and ultimately employ these trans- ducers for operations, enabling the development of structural health monitoring methods for the panel. The printed transducer is made up of a piezoelectric layer sandwiched between two silver electrodes, each printed in a controlled manner. Upon printing and drying of the layers, the transducers undergo polarization. The electromechanical behaviour of the printed transducers, characterized using impedance measurements, exhibits high repeatability, thus indicating its potential for large scale industrial deployment. Following this, it is demon-strated that the transducers are capable of accurately sensing impact, which is one the mostcommon yet critical sources of damage to an engine fan blade. It is also shown that the printed transducers are able to detect acoustic emission events. The ability of the printed transducers to actuate and sense guided wave signals over a range of ultrasonic frequencies is also demonstrated. Furthermore, apart from the noticeable advantages of the non-intrusive nature, and negligible weight as compared to their traditional ceramic counterparts, the printed piezoelectric transducers can potentially be integrated into the manufacturing process in the future, and the presence of transducer arrays ensures the availability of other transducers in case of an individual failure during service. This innovative printing technol-ogy for PZT transducer networks thus holds significant promise in bridging the gap between research advancements and the industrial implementation of SHM technology.

The work presented here focuses on the structural health monitoring (SHM) of a foreign object damage (FOD) composite panel equipped with an innovative printed piezoelectric transducer network. The 3D woven composite FOD panel measures approximately 800 mm x 320 mm, is curved with a cross-sectional thickness varying from approximately 2 mm to 12 mm, and a stainless-steel leading edge is bonded at one of its sides. The core idea explored here is to rely on an innovative screen-printing technology to print a full piezoelectric transducer allowing to successfully achieve SHM on such a complex composite structure. This work is being carried out within the European project MORPHO – H2020. After printing a 25 elements PZT network, a four points bending fatigue experimental campaign using the PZT network along with other sensor technologies (embedded optical fibres with FBG sensors and acoustic emission sensors) is carried out. This unique experimental campaign allows to generate data and will help to develop diagnostic and prognostic methodologies for remaining life estimation and SHM of the FOD panel. It is demonstrated here through impedance measurements that the printing process associated with the printed PZT transducers is highly repeatable thus validating its use at a larger industrial scale. Furthermore, the printed piezoelectric transducers electromechanical behaviour is characterized and they are shown to be able to detect foreign object impact and to size and localize resulting damage using Lamb waves signals collected at different locations of the network. This innovative printing technology for PZT transducers network is thus extremely promising. It is furthermore highly advantageous to use the printed transducers for SHM instead of regular ceramic ones as this technology is non-intrusive, add negligible weight, can be printed during the manufacturing process, and arrays of transducers ensure easy availability of another transducer in case of failure of one.

Rock salt, owing to its viscoplastic behavior and structural integrity under high pressure, is a promising candidate for safe and large-scale underground energy storage. This study presents a comprehensive numerical framework for modeling the viscoplastic deformation of rock salt, accounting for both intragranular and grain boundary (GB) deformation mechanisms. Intragranular deformation is modeled using a crystal plasticity approach governed by a power-law relation, capturing the activity of crystallographic slip systems. Concurrently, a cohesive zone model (CZM) is introduced to simulate grain boundary sliding (GBS) and opening via a rate-dependent traction–separation law. This modeling strategy enables a detailed analysis of the coupled interplay between crystal plasticity and intergranular decohesion phenomena.

New standards are being introduced to eliminate toxic elements in materials. For instance, copper alloys should no longer contain lead, although this makes them more challenging to machine. Additionally, for environmental reasons, it is crucial to eliminate cutting oils. To address these two challenges, cryogenic cooling during machining can be considered. However, it is first essential to understand the precise mechanical response of the material at low temperatures. This study conducts compression tests on copper across a wide temperature range, from cryogenic temperatures (liquid nitrogen, LN2) to 700°C, and at strain rates from 0.01/s to 10/s. The microstructure of deformed test samples is also characterized by electron back-scattered diffraction (EBSD) to compare the different plastic deformation characteristics under low and high temperature. The stress-strain curves are fitted with Johnson-Cook (JC) model, which is then implemented into the finite element simulation of the compression process. The results indicate that the JC model with the fitted parameters is not precise enough in terms of modelling very low temperature dynamic response of copper alloy, thus is not proper for the simulation of cryogenic cooling assisted cutting. This is because different characteristics of strain hardening behavior is discovered under LN2 atmosphere temperature and ordinary cutting temperature, which is further induced by a transition of plastic deformation mechanism with increased temperature. Therefore, a new constitutive law is proposed considering deformation mechanism at both traditional cutting temperature and cryogenic conditions. The results indicate that the new model has a better fitting of experimental curves than JC model. This study is helpful for the understanding of low temperature copper deformation behavior and new constitutive model exploitation oriented to cryogenic cooling assisted cutting.

Abstract. In machining industry, there is a growing interest in cryogenic cooling techniques, because of their environmental benefits, including reduced toxicity, safer operation, and lower environmental impact compared to conventional cutting fluids. The titanium alloy Ti6Al4V, which is commonly used in aerospace, automotive and biomedical industries, presents low machinability and often requires abundant use of cutting fluids to inhibit tool wear. This study investigates the machinability of Ti6Al4V, comparing conventional lubrication (water-oil emulsion) with two cryogenic fluids: liquid nitrogen (LN2) and liquid carbon dioxide (LCO2). Longitudinal turning tests were conducted and tool life, wear mechanisms, and cutting forces were evaluated for each lubrication condition. The tool life provided by emulsion, LN2 and Vc were 8.2 min, 17.7 min and 9.9 min, respectively. Adhesion was identified as the predominant wear mechanism across all conditions. Overall, the results suggest that the cryogenic coolants can effectively increase tool life and reduce cutting forces in comparison with conventional lubrication, however, further optimizations of the delivery system of the cryogenic coolants are still necessary.