Papers by Author: François Ducobu

Abstract: This study presents a static finite element analysis of the milling of a flexible unidirectional glass fiber–reinforced polymer (UD-GFRP) plate. The workpiece is modeled as a clamped–free cantilever, with cutting forces evaluated independently of structural deflections and applied along the machined edge. SC8R continuum shell elements are employed to accurately represent through-thickness loading and bending behavior. A mesh sensitivity analysis is conducted to determine a suitable discretization, leading to a 64 × 56 × 8 element mesh. For the investigated configuration (, mm/tooth), the out-of-plane displacement reaches approximately 120 µm near the free end of the plate, whereas in-plane displacements reach up to-75 µm. These in-plane displacements are greater than or equal to the nominal feed per tooth, indicating a highly significant influence on chip formation. This work provides a basis for understanding the structural response of flexible composite plates during trimming and emphasizes the need for coupled force–deformation formulations.

Abstract: This paper examines the use of adaptive mesh refinement in Coupled Eulerian-Lagrangian (CEL) finite element modeling of the Taylor impact test. Traditional Lagrangian models suffer from severe mesh distortion under large strains, while CEL avoids this issue but requires much longer computation times. Using Abaqus/Explicit 2025, a mesh convergence study was performed to identify an accurate reference mesh. Adaptive mesh refinement was then applied to refine the mesh dynamically based on equivalent plastic strain. Results show that CEL models achieve convergence, unlike Lagrangian models, and that adaptive mesh refinement reduces computation time by up to 67%, with minimal impact on accuracy. This approach provides an efficient and reliable solution for high-strain simulations.

Abstract: Continuous monitoring of additively manufactured structures is essential for understanding their mechanical behavior and durability. This study investigates the electromechanical behavior of additively manufactured PETG specimens reinforced with continuous carbon fiber, with a particular focus on the influence of reinforcement geometry on strain-sensing performance. Specimens were fabricated using Fused Filament Fabrication and designed with four different reinforcement configurations: a reference single-layer layout, an extended-length reinforced region, a wider reinforced region, and a double-layer reinforcement. A total of twelve specimens were experimentally characterized. Electrical resistivity measurements were conducted under unloaded conditions and during bending induced by a low applied load of approximately 1.6 N. The initial electrical resistivity was found to depend on reinforcement geometry, with average values of approximately 523 Ω for the reference configuration, 888 Ω for the extended-length reinforcement, 1066 Ω for the wider reinforcement, and 285 Ω for the double-layer configuration. Under mechanical loading, the relative resistance variation remained below 0.6% for all specimens, indicating that the induced strain was very small. To further quantify strain sensitivity, the gauge factor was calculated for each configuration. Low average gauge factor values were obtained for the reference (K ≈ 0.1), extended-length (K ≈ 0.38), and wider (K ≈ 0.5) configurations. In contrast, the double-layer reinforcement exhibited a higher average gauge factor of approximately 2.24. These results indicate that reinforcement architecture affects the electromechanical sensitivity under low applied loads and offer insights for the design of multifunctional additively manufactured composite structures.

Abstract: The important portion of machining costs associated with cutting inserts and scraps induces the search for better effectiveness in turning. This paper presents the results of an exploratory study on the influence of tool flank wear on roughness indicators (arithmetic average roughness, root mean square roughness and maximum height of the roughness profile). The objective is to determine which of these indicators is best correlated with the cutting tool flank wear. In order to do this, specimens of AISI 1045 are machined until the end of life of a cutting insert. Significant, strong and positive correlations are found between all three roughness indicators and the tool flank wear. The most significant correlation is found with the arithmetic average roughness and the root mean square roughness of the profile. The choice of the end-of-life criteria for cutting inserts in industrial contexts is also discussed.

Abstract: The final aim of finite elements modelling is to help in the choice of the cutting parameters and in the comprehension of the involved phenomena. Representing correctly the behaviour of the machined material is hard due to the extreme conditions encountered, although this is a key parameter to develop a realistic model. Four laws are used in this paper to represent the Ti6Al4V. They are all based on the Johnson-Cook law. This study shows that the influence of the behaviour law is high on the chip morphology and on the forces and that the strain softening phenomenon should be taken into account. For the cutting conditions adopted, it is however necessary to add damage properties in the chip to obtain a morphology and a cutting force evolution close to the experimental reference.

Abstract: Virtual manufacturing is a field of research which numerically simulate all the manufacturing processes seen by a mechanical part during its production (for example casting, forging, machining, heat treatment,…). Its use is rising on various industries to reduce production costs and improve quality of manufactured parts. One of the most challenging component of the whole simulation chain is the simulation of machining operations due to some of its specificities (need of material law at high strain, strain rates and temperature, heterogeneities of machined material, influence of residual stresses,…).In order to circumvent these difficulties, macroscopic models of machining process have been developed in order to compute more global information (cutting forces, stability of the process, tolerance or roughness for example). For this approach, the cutting forces computation is done by using simple analytical law based on mechanistic approach. The parameters of the models have no clear physical meaning (or at least cannot be linked to intrinsic properties of the material to be machined) and are therefore considered constants for a given set of simulations.The aim of this paper is to take into account the uncertainty on the variability of the cutting force signal during machining operation used as input for mechanistic model identification. The variability of the response during a test on fixed conditions (cutting tool, machined material and cutting parameters) is taken into account to develop a model where parameters of the model can evolve during a given operation.The proposed model is then used as an input of a milling operation simulation in order to study its influence on machining stability as compared to a classical approach.

Abstract: Micro-milling with a cutting tool is a manufacturing technique that allows production of parts ranging from several millimeters to several micrometers. The technique is based on a downscaling of macroscopic milling process. Micro-milling is one of the most effective process to produce complex three-dimensional micro-parts, including sharp edges and with a good surface quality. Reducing the dimensions of the cutter and the cutting conditions requires taking into account physical phenomena that can be neglected in macro-milling. These phenomena include a size effect (nonlinear rising of specific cutting force when chip thickness decreases), the minimum chip thickness (under a given dimension, no chip can be machined) and the heterogeneity of the material (the size of the grains composing the material is significant as compared to the dimension of the chip). The aim of this paper is to introduce some phenomena, appearing in micromilling, in the mechanistic dynamic simulation software ‘dystamill’ developed for macro-milling. The software is able to simulate the cutting forces, the dynamic behavior of the tool and the workpiece and the kinematic surface finish in 2D1/2 milling operation (slotting, face milling, shoulder milling,…). It can be used to predict chatter-free cutting condition for example. The mechanistic model of the cutting forces is deduced from the local FEM simulation of orthogonal cutting. This FEM model uses the commercial software ABAQUS and is able to simulate chip formation and cutting forces in an orthogonal cutting test. This model is able to reproduce physical phenomena in macro cutting conditions (including segmented chip) as well as specific phenomena in micro cutting conditions (minimum chip thickness and size effect). The minimum chip thickness is also taken into account by the global model. The results of simulation for the machining of titanium alloy Ti6Al4V under macro and micro milling condition with the mechanistic model are presented discussed. This approach connects together local machining simulation and global models.

Abstract: The foundations of micro-milling are similar to macro-milling but the phenomena it involves are not a simple scaling-down of macro-cutting. The importance of the minimum chip thickness is one of the significant differences between the two processes. The lagrangian FEM model presented in this paper aims to study the depth of cut influence on chip formation of Ti6Al4V in orthogonal cutting. It is firstly used to compare the modelled saw-toothed macro-chip morphology and cutting forces to experimental cutting results from literature. Then a minimum chip thickness prediction is performed by decreasing the depth of cut. Finally this study is the opportunity to highlight the specific features of micro-cutting reported in literature, such as the effective negative rake angle of the tool or the size effect. The model presented brings therefore a numerical contribution to the comprehension of these phenomena.