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See detailExperimental and Numerical Characterization of Damage and Application to Incremental Forming
Guzmán Inostroza, Carlos Felipe ULiege

Doctoral thesis (2016)

Nowadays, product manufacturing can be divided into two groups: relatively simple products produced in a large production chain and complex (specialized) components produced in reduced batches. Within the ... [more ▼]

Nowadays, product manufacturing can be divided into two groups: relatively simple products produced in a large production chain and complex (specialized) components produced in reduced batches. Within the second group, prototyping through incremental sheet forming (ISF) has been subject of several studies. ISF refers to processes where the plastic deformation occurs by repeated contact with a relatively small tool. A crucial aspect in the ISF processes is that the final shape is determined only by the tool movement. The focus of this research is the single point incremental forming (SPIF) process variant, where a clamped sheet metal is deformed by using a relatively small spherical tool. SPIF has several advantages over traditional forming, such as the high formability attainable by the material. Different hypothesis haven been proposed to explain this behavior, but there is still not a clear and definitive understanding of the relation between the particular stress and strain state induced in the material during SPIF and the material degradation leading to localization or fracture. In this thesis, a fundamental research is proposed using the finite element (FE) code LAGAMINE, developed within the University of Liège. Numerical implementation and validation of the Gurson-Tvergaard-Needleman (GTN) damage model into this FE code is performed. An experimental test campaign is developed to characterize plastic and damage behavior and to validate the damage model for the DC01 steel grade. Finally, this damage model is applied to simulate the SPIF process in order to verify if it is capable to predict failure. The thesis discusses the material parameter identification for classical plasticity models, describing the anisotropy and hardening behavior of the sheet metal. The derivation of the equations of the numerical damage model and the efficiency of the implementation is presented in great detail. A methodology for the numerical parameter identification of the damage model is proposed, including microscopic measurements by optical microscopy and strain and displacement field measurements by digital image correlation (DIC). The identified Gurson model is applied to simulate standard SPIF geometries, like the line, cone and pyramid tests. The simulations are performed using the solid-shell element formulation and validated in terms of shape and force prediction. Literature reviews of the Gurson model and the SPIF process are also included. The experimental results show that the selected material (DC01 steel sheet) exhibits a slight anisotropic behavior and work-hardening stagnation on cyclic tests. The performed microscopic measurements are not representative of the actual damage, but they give a qualitative estimation of the physical mechanism of fracture. The initial porosity of the material was determined using optical microscopy measurements in the base material. The numerical implementation of the model is developed with all variables integrated in an implicit way, based on the backward Euler scheme. Nucleation, coalescence and shear extensions implementations are validated by results obtained from the literature. The macroscopic campaign allowed to identify the parameters for nucleation, coalescence and shear. An unique set of results matching all experiments was not possible to obtain, so different sets of parameters are retrieved following an approach that includes inverse modeling and sensitivity analysis. A numerical-experimental comparison of strain values in the loading direction shows that the model is able to correctly predict the strain distribution except during localization of the strain. Globally, the obtained set of material parameters is in good agreement with the experimental results. For SPIF FE simulations, the results of the shape prediction are in good agreement with the experimental results, both for the line and pyramid test. Nevertheless, the force prediction is too high compared to reference values. On the other hand, the GTN model is capable to detect failure in a pyramid and a cone, but the prediction is too premature compared to the experimental failure angle for the same material and geometry. An accurate prediction of failure for the SPIF process was not possible to achieve. The GTN model extended to shear presents inherent flaws that prevent an accurate prediction of the failure angle for the SPIF process. Hence, an extensive research on the damage mechanisms leading to fracture for SPIF cannot rely (only) on the GTN model. The classical coalescence model of the GTN model is insufficient to correctly predict failure. Hence, it is recommended that further analysis concentrates on the description of this particular stage of damage evolution. During the development of this thesis, a robust implementation of the GTN model into the FE code LAGAMINE was done, including an extensive experimental database of microscopic and macroscopic measurements for the DC01 steel sheet. Other phenomena can be explored thanks to this model. [less ▲]

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See detailExperimental and numerical investigation of a meandering jet in shallow rectangular reservoirs under different hydraulic conditions
Camnasio, Erica; Pirotton, Michel ULiege; Erpicum, Sébastien ULiege et al

in 3rd International Symposium on Shallow Flows (2012, June)

A central meandering jet in shallow rectangular reservoirs has been investigated numerically by the model WOLF2D, on the basis of experimental evidence of this type of flow field in two different setups ... [more ▼]

A central meandering jet in shallow rectangular reservoirs has been investigated numerically by the model WOLF2D, on the basis of experimental evidence of this type of flow field in two different setups at different scales. A sensitivity analysis has been conducted with respect to the main parameters of the model. The oscillation frequency of the transversal velocity and the characteristic Strouhal number have been calculated for different Froude numbers. A logarithmic relationship has been found between the Strouhal and the Froude numbers. [less ▲]

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See detailExperimental and numerical investigation of high-strength steel circular columns subjected to fire
Tondini, Nicola; Hoang, Van Long ULiege; Demonceau, Jean-François ULiege et al

in Journal of Constructional Steel Research (2013), 80

This paper presents an experimental–numerical study on the behaviour of High Strength Steel (HSS) columns at elevated temperature, both on Circular Hollow Sections (CHS) and on a Concrete Filled Tube (CFT ... [more ▼]

This paper presents an experimental–numerical study on the behaviour of High Strength Steel (HSS) columns at elevated temperature, both on Circular Hollow Sections (CHS) and on a Concrete Filled Tube (CFT). The measured yield strength of the circular sections was in the order of 820 MPa. In detail, three HSS CHS and a HSS CFT were tested under the standard ISO fire with constant eccentric compression applied load. The evolution of temperature and deformation patterns were measured by means of a comprehensive instrumentation made of thermocouples and displacement transducers. Numerical analyses were performed and compared with experimental data by employing stress–strain relationships of carbon steel at elevated temperatures provided by the Eurocodes associated to two different sets of reduction factors: i) those provided by the Eurocodes valid up to S460 steel grades; and ii) those proposed in the literature and based on tests on HSS. [less ▲]

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See detailExperimental and Numerical Investigation of Mixed Flow in a Gallery
Erpicum, Sébastien ULiege; Kerger, François ULiege; Archambeau, Pierre ULiege et al

in Transaction: Engineering Sciences, volume 1, Computational Methods in Multiphase Flow V (2009, June)

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See detailExperimental and numerical investigation of the nonlinear dynamics of compliant mechanisms for deployable structures
Dewalque, Florence ULiege; Schwartz, Cédric ULiege; Denoël, Vincent ULiege et al

in Mechanical Systems & Signal Processing (2017), 101

This paper studies the dynamics of tape springs which are characterised by a highly geometrical nonlinear behaviour including buckling, the formation of folds and hysteresis. An experimental set-up is ... [more ▼]

This paper studies the dynamics of tape springs which are characterised by a highly geometrical nonlinear behaviour including buckling, the formation of folds and hysteresis. An experimental set-up is designed to capture these complex nonlinear phenomena. The experimental data are acquired by the means of a 3D motion analysis system combined with a synchronised force plate. Deployment tests show that the motion can be divided into three phases characterised by different types of folds, frequencies of oscillation and damping behaviours. Furthermore, the reproducibility quality of the dynamic and quasi-static results is validated by performing a large number of tests. In parallel, a nonlinear finite element model is developed. The required model parameters are identified based on simple experimental tests such as static deformed configurations and small amplitude vibration tests. In the end, the model proves to be well correlated with the experimental results in opposite sense bending, while in equal sense, both the experimental set-up and the numerical model are particularly sensitive to the initial conditions. [less ▲]

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See detailAn experimental and numerical investigation on the influence of external gas recirculation on the HCCI autoignition process in an engine: Thermal, diluting, and chemical effects
Machrafi, Hatim ULiege; Cavadias, Simeon; Guibert, Philippe

in Combustion & Flame (2008), 155(3), 476-489

In order to contribute to the solution of controlling the autoignition in a homogeneous charge compression ignition (HCCI) engine, parameters linked to external gas recirculation (EGR) seem to be of ... [more ▼]

In order to contribute to the solution of controlling the autoignition in a homogeneous charge compression ignition (HCCI) engine, parameters linked to external gas recirculation (EGR) seem to be of particular interest. Experiments performed with EGR present some difficulties in interpreting results using only the diluting and thermal aspect of EGR. Lately, the chemical aspect of EGR is taken more into consideration, because this aspect causes a complex interaction with the dilution and thermal aspects of EGR. This paper studies the influence of EGR on the autoignition process and particularly the chemical aspect of EGR. The diluents present in EGR are stimulated by N-2 and CO2, with dilution factors going from 0 to 46 vol%. For the chemically active species that could be present in EGR, the species 0 and 170 ppm, while that of CH2O alters between 0 and 1400 ppm. For the investigation of the effect of the chemical species on the autoignition, a fixed dilution factor of 23 vol% and a fixed EGR temperature of 70 degrees C are maintained. The inlet temperature is held at 70 degrees C, the equivalence ratios between 0.29 and 0.41, and the compression ratio at 10.2. The fuels used for the autoignition are n-heptane and PRF40. It appeared that CO, in the investigated domain, did not influence the ignition delays, while NO had two different effects. At concentrations up until 45 ppm, NO advanced that ignition delays for the PRF40 and at higher concentrations, the ignition delayed. The influence of NO on the autoignition of n-heptane seemed to be insignificant, probably due to the higher burn rate of n-heptane. CH2O seemed to delay the ignition. The results suggested that especially the formation of OH radicals or their consumption by the chemical additives determines how the reactivity of the autoignition changed. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved. [less ▲]

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See detailExperimental and numerical investigations for I-girders in bending and shear stiffened by closed trapezoidal stiffeners
Boissonnade, N.; Degée, Hervé ULiege; Naumes, J. et al

in Proceedings of the ICMS Conference (2006)

The paper investigates the shear resistance of I-girders longitudinally stiffened by closed trape-zoidal stiffeners. It first reports on 4 full-scale tests performed at RWTH Aachen, on stiffened panels ... [more ▼]

The paper investigates the shear resistance of I-girders longitudinally stiffened by closed trape-zoidal stiffeners. It first reports on 4 full-scale tests performed at RWTH Aachen, on stiffened panels with strong closed stiffeners. As expected, failure in the subpanels has been governing. A devoted FEA shell model is then described and validated towards these results and other experimental sources. Parametric stud-ies led with the numerical tool help pointing out several aspects where the Eurocode 3 Part 1.5 recommenda-tions on stiffened panels in bending and shear may be improved. [less ▲]

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See detailExperimental and numerical investigations for I-girders in bending and shear stiffened by closed trapezoidal stiffeners for use in steel bridges
Feldmann, M.; Naumes, J.; Oppe, M. et al

in Proceedings of the IABSE Symposium "Improving infrastructures..." (2007)

The paper summarizes the investigations on shear resistance of I-girders longitudinally stiffened by closed trapezoidal stiffeners, performed in the frame of a European RFCS project (RFS-CR-03018 ... [more ▼]

The paper summarizes the investigations on shear resistance of I-girders longitudinally stiffened by closed trapezoidal stiffeners, performed in the frame of a European RFCS project (RFS-CR-03018) designated as “ComBri” (Competitive Steel and Composite Bridges by improved Steel Plated Structures), with configurations typical of what may be expected in the design of modern steel bridges. It first reports on four full-scale tests performed at RWTH Aachen, on stiffened panels with strong closed stiffeners where the deformations have been measured with photogrammetric devices. As expected, failure in the subpanels has been governing. A devoted FEA shell model is then described and validated towards these results and other experimental sources. The numerical simulations demonstrate a very good agreement with the test-results. Parametric studies performed with a sophisticated numerical tool help pointing out several aspects where the recommendations of EN 1993-1-5 [1] on stiffened panels in bending and shear may be improved. [less ▲]

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See detailExperimental and numerical investigations for I-Girders in bending and shear stiffened by trapezoidal stiffeners
Boissonnade, N.; Degée, Hervé ULiege; Naumes, J. et al

in Advanced Steel Construction (2008), 4(1), 1-13

The paper investigates the shear resistance of I-girders longitudinally stiffened by trapezoidal stiffeners. It first reports on 4 full-scale tests performed at RWTH Aachen, on stiffened panels with ... [more ▼]

The paper investigates the shear resistance of I-girders longitudinally stiffened by trapezoidal stiffeners. It first reports on 4 full-scale tests performed at RWTH Aachen, on stiffened panels with strong closed stiffeners. As expected, failure in the subpanels has been governing. A devoted FEA shell model is then described and validated towards these results and other experimental sources. Parametric studies led with the numerical tool help pointing out several aspects where the Eurocode 3 Part 1.5 recommendations on stiffened panels in bending and shear may be improved. [less ▲]

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See detailExperimental and numerical investigations of dike-break induced flows
Roger, Sebastian; Dewals, Benjamin ULiege; Erpicum, Sébastien ULiege et al

in Journal of Hydraulic Research (2009), 47(3), 349-359

Experimental model data are compared with numerical computations of dike-break induced flows, focusing on the final steady state. An idealised scale model was designed reproducing the specific boundary ... [more ▼]

Experimental model data are compared with numerical computations of dike-break induced flows, focusing on the final steady state. An idealised scale model was designed reproducing the specific boundary conditions of dike breaks. Discharges, water levels and depth profiles of horizontal velocities were recorded and validated by numerical modeling. The latter was performed by two different models solving the two-dimensional depth-averaged shallow water equations, namely a total variation diminishing Runge-Kutta dis¬continuous Galerkin finite element method, and a finite volume scheme involving a flux vector splitting ap¬proach. The results confirmed convergence and general applicability of both methods for dike-break prob¬lems. As regards their accuracy, the basic flow pattern was satisfactorily reproduced yet with differences compared to the measurements. Hence, additional simulations by a finite volume model were performed con¬sidering various turbulence closures, wall-roughnesses as well as non-uniform Boussinesq coefficients. [less ▲]

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See detailExperimental and Numerical Investigations of the Aeroelastic Stability of Bluff Structures
Andrianne, Thomas ULiege

Doctoral thesis (2012)

The study of the dynamic interactions between the wind and civil engineering structures has become increasingly important over the last few decades. Most of these structures are aerodynamically "bluff ... [more ▼]

The study of the dynamic interactions between the wind and civil engineering structures has become increasingly important over the last few decades. Most of these structures are aerodynamically "bluff" and are becoming more flexible. Bluff-body aeroelasticity is a very challenging research area due to the unsteadiness and nonlinearity of the aerodynamic loading. This thesis presents the investigation of three aeroelastic phenomena affecting bluff-bodies: Vortex Induced Vibration (VIV), Galloping and Torsional Flutter. For each instability, extensive experimental studies are carried out in the wind tunnel. Innovative analysis, based on the Common-base Proper Orthogonal Decomposition (CPOD) method is used to study the flow visualization data. The VIV phenomenon is studied on a flexible tube with a circular cross-section, supported from its midpoint. A CPOD-based input-output model is developed to describe the system. The galloping instability is studied on a generic bridge section. A complete analysis of the aeroelastic behaviour of the structure is presented and a new polynomial empirical model is developed, which reflects accurately the nonlinear nature of the system. The torsional flutter phenomenon is extensively studied for two different structures: a generic bridge deck and a rectangular cylinder. The Motion Induced Vortex is identified as the fundamental cause of this aeroelastic phenomenon, on the basis of the analysis of the flow around the oscillating rectangle. In addition, it is demonstrated that the quasi-steady theory is not adapted to estimate the onset velocity of torsional flutter. Finally, a 2D aeroelastic simulation code, based on the Discrete Vortex Method (DVM) is developed. The non-linear aerodynamics around the body are well reproduced, allowing the simulation of all the aeroelastic instabilities investigated experimentally. [less ▲]

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See detailExperimental and numerical investigations of the torsional flutter oscillations of a 4:1 rectangular cylinder
Andrianne, Thomas ULiege; Dimitriadis, Grigorios ULiege

in Journal of Fluids & Structures (2013), 41

The torsional flutter oscillations of a 4:1 rectangular cylinder around its pitching axis are investigated through wind tunnel experiments and numerical simulations. The rectangle’s responses to different ... [more ▼]

The torsional flutter oscillations of a 4:1 rectangular cylinder around its pitching axis are investigated through wind tunnel experiments and numerical simulations. The rectangle’s responses to different initial conditions and turbulence excitations at various wind tunnel airspeeds are recorded. Timeresolved Particle Image Velocimetry measurements are taken at two different airspeeds, when the rectangle undergoes Limit Cycle Oscillations. Aeroelastic simulations are carried out using the Discrete Vortex Method and the resulting responses are compared to the experimental measurements. The Common-base Proper Orthogonal Decomposition method is used to analyse and compare the measured and simulated unsteady flow fields around the rectangle. A discussion of the participation of each mode in the different states of the flow-field is presented, at two different amplitudes of oscillation. The Motion Induced Vortex (MIV) is identified as the fundamental cause of the torsional flutter phenomenon and its role over a complete cycle is studied. MIV-induced oscillations can be started either by a suitable initial disturbance or by a second, nearly linear self-excited instability that causes negative aerodynamic damping. The combination of these two instabilities results in a complete description of the torsional flutter of the rectangle. [less ▲]

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See detailExperimental and numerical investigations on iron columns reinforced by FRP under axial compression
Ly, Dong Phuong Lam ULiege; Jaspart, Jean-Pierre ULiege; Demonceau, Jean-François ULiege et al

in Camelbeeck, Th.; Degée, Hervé; Degrande, G. (Eds.) et al Seismic risk (2008, September 11)

This paper presents experimental and numerical investigations on iron columns under axial compression, strengthened with high modulus carbon fibre reinforced polymer (FRP) sheets. It is shown that the ... [more ▼]

This paper presents experimental and numerical investigations on iron columns under axial compression, strengthened with high modulus carbon fibre reinforced polymer (FRP) sheets. It is shown that the resistance and stiffness of iron columns can be increased significantly with the use of longitudinal FRP sheets as a result of the reduction of the column slenderness, but also that transverse FRP sheets should be used to prevent any local buckling of the longitudinal FRP sheets. [less ▲]

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See detailExperimental and numerical investigations to assess and mitigate sedimentation problems: application to a large dam in India
Erpicum, Sébastien ULiege; Dewals, Benjamin ULiege; Archambeau, Pierre ULiege et al

in Proceedings of the 7th National Congress on theoretical and applied Mechanics (2006)

In the global framework of river management, sedimentation problems in dam reservoirs and adjacent structures are multiple and of major interest for designers as well as dam owners or managers. Before dam ... [more ▼]

In the global framework of river management, sedimentation problems in dam reservoirs and adjacent structures are multiple and of major interest for designers as well as dam owners or managers. Before dam construction, these problems can be assessed by several techniques. In this paper, the experimental and numerical sedimentation studies realized at the Laboratory of Applied Hydrodynamics and Hydraulic Constructions (HACH) of the University of Liège on a large hydropower plant project in India are presented. Three main issues related to sedimentation problems are analyzed in details. [less ▲]

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See detailExperimental and numerical study of an AlMgSc sheet formed by an incremental process
Bouffioux, Chantal ULiege; Lequesne, Cédric ULiege; Vanhove, H. et al

in Journal of Materials Processing Technology (2011), 211(11), 1684-1693

A recently developed AlMgSc alloy is studied since this material, which is well adapted to the aeronautic domain, is poorly known. The first objective is to reach a better knowledge of this alloy to ... [more ▼]

A recently developed AlMgSc alloy is studied since this material, which is well adapted to the aeronautic domain, is poorly known. The first objective is to reach a better knowledge of this alloy to provide the missing useful information to the aeronautic industry and to help research institutes who want to simulate sheet forming processes by Finite Element (FE) simulations. A set of experimental tests has been performed on the as-received sheets, material laws have been chosen and the corresponding material parameters have been adjusted to correctly describe the material behaviour. The second objective is to study the applicability of the Single Point Incremental Forming process (SPIF) on this material. Truncated cones with different geometries were formed and the maximum forming angle was determined. A numerical model was developed and proved to be able to predict both the force evolution during the process and the final geometrical shape. Moreover, the model helps reaching a better understanding of the process. The characterisation method described in this research and applied on the AlMgSc alloy can be extended to other alloys. In addition, the numerical simplified model, able to accurately describe the SPIF process with a reduced computation time, can be used to study more complex geometries. [less ▲]

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