Title Promoter Affiliations Abstract "Micro-structural modelling and parameter identification of glass-fibre reinforced polymers through digital volume correlation and finite element analysis." "Martin Diehl" "Numerical Analysis and Applied Mathematics (NUMA), Structural Composites and Alloys, Integrity and Nondestructive Testing (SCALINT)" "Driven by the need for lighter materials with better performance, models for the mechanical properties of fibre-reinforced composites have reached a significant level of maturity. The key bottleneck has now become the measurement and detailed understanding of the matrix and interface properties that those models require. While some incremental progress has been achieved, those measurements remain time-consuming,expensive, lab- or operator-dependent and often prone to large scatter. InSituPro therefore develops a method for measuring in-situ matrix and interfacial properties (see Figure 1) and uses this method to develop a fundamental understanding of key properties of the matrix and interface. This will be achieved by computed tomography (CT) of particle-filled glass fibre composites at voxel sizes below 500 nm. These experiments allow digital volume correlation (DVC) to achieve 3D strain resolutions down to 8-15 µm, which will enable the proposed data reduction schemes to extract the microscale matrix properties, the interfacial normal and shear strength and toughness, the friction coefficient for interfacial sliding, and fatigue debond growth rates. Since InSituPro tests composites with hundreds of fibres, the properties are measured in situ in conditions representative for real composites. This new methodology will enable fundamental questions related to the in-situ behaviour of the constituents to be answered. The newly developed understanding will empower a breakthrough in micromechanical modelling, which would catalyse the design and implementation of novel and improved composite materials." "Understanding functioning and evolution of bird middle ear mechanics through high-realism finite element modelling and system identification." "Joris Dirckx" "Functional Morphology, Biophysics and Biomedical Physics" "When life evolved from aquatic to terrestrial animals, a biomechanical system developed which bridges the difference in acoustic impedance between air and fluid: the middle ear (ME). If this structure would not be present, the major part of sound energy in air would reflect at the interface with the fluid-filled inner ear. In mammals, this mechanical system consists of the eardrum and three ossicles, (and two muscles and some ligaments) which act as a lever system to transform sound waves in air to sound waves with higher pressure but smaller amplitude in the fluid of the inner ear (where sound energy is transformed to electric impulses going to the brain). In birds the ME is far simpler, mainly consisting of just an eardrum and one muscle and ossicle (yet partly cartilaginous), the so called columella, directly connecting the eardrum to the oval window in the inner ear. The system is enclosed in a cavity which connects to the outside world with the Eustachian tube. Under normal circumstances this tube is closed so quasi-static pressure differences exist between the ME and the outside world, e.g. due to altitude changes, meteorology circumstances etc. Acoustic information is of primary importance to birds, so it is fascinating to see that such a relatively simple middle ear developed. Moreover, birds are typically subject to sudden height changes and the single ossicle ear does not have the same flexibility to cope with large eardrum deformations as has the mammal three ossicle ear. These fundamental questions have held the attention of many researchers in the past, but up till now no in depth model based quantitative analysis is available. In this project we will measure the necessary input parameters for such a model (elasticity of eardrum and bones, vibration pattern of the eardrum and the ossicle, high resolution anatomical shape model) and use these to develop a highly realistic finite element model of the bird middle ear. We will develop new techniques to investigate how sound energy is transported from the eardrum to the inner ear, based on transfer path and power flow analysis. This will be done for two commercially available species (e.g. pigeon or duck, and chicken), representative for birds who adapted to a life upon the ground or a life facing fast pressure changes. We will measure how pressure change influences the system, and we will investigate how pressure varies in the bird ear, another question which remained unanswered up till now. Then we will use our model to reveal the functional evolution using less common species (e.g. falcons). Finally we will use the model to investigate new designs of an artificial ME ossicle which moves like in birds, and test it in our models of the mammal ear. When in humans the ossicles are blocked or missing, a prosthesis is used to connect the eardrum to the inner ear, but such prosthesis has no flexibility to deal with static pressure changes. We want to learn from nature to see which other single ossicle designs can solve this fundamental problem." "Interval methods for the identification and quantification of inhomogeneous uncertainty in Finite Element models" "David Moens, Eleonora Ferraris" "Mechanical Engineering Technology, De Nayer (Sint-Katelijne-Waver) Campus" "Numerical methods, such as the finite element method, have become an indispensable tool in the toolbox of a modern design engineer. Since these methods allow for predicting the mechanical, thermal or aerodynamic behaviour of a structural component, long before a first prototype has been produced, an immense reduction of lead-time is possible. However, it is impossible to determine all numerical model parameters deterministically, as the true parameter value is often uncertain or inherently variable. Moreover, also spatial uncertainty can exist, where the uncertainty on the model parameter is a function of the location in the structure. Therefore, it is not recommendable to base important design decisions solely on such deterministic numerical analysis, as an over-conservative design has to be constructed to prevent premature failure.During the last decades, very powerful non-deterministic numerical methods have been proposed. These techniques are usually divided in two groups: probabilistic and possibilistic methods. Probabilistic methods start from a joint probability density function to describe possible variability in the responses of the structure. Possibilistic methods on the other hand describe the uncertainty using intervals or fuzzy numbers. In case spatial uncertainty is present, respectively random fields and interval fields are used.However, in order to ensure that these advanced methods also yield a truthful estimation of the possible model responses, it is important that the non-deterministic modelling of the parameters is made accurately. In some cases (e.g., plate thickness), quantification of the variability of uncertainty is relatively straightforward. Other parameters however (e.g., contact stiffness) are not directly measurable. Therefore, inverse uncertainty quantification methods should be applied. In the specific context of interval field uncertainty, such methods do not exist in literature to date.This thesis is therefore aimed at the development and validation of a novel generic method for the identification and quantification of interval field uncertainty in the parameters of a numerical model. The method should be applicable to both dynamic and quasi-static models, and has to be able to handle both computationally demanding models and large measurement data sets. The performance of the method is tested by considering both small-scale academic case studies, as well as realistic numerical models in conjunction with experimental datasets.The proposed methods start from the description of the uncertainty in the model responses that are predicted by the numerical model and those that are experimentally obtained. These convex hulls define a convex region in which the possible model responses are deemed to be located, based on a set of linear inequalities. The identification and quantification of interval field uncertainty is then performed by minimising the discrepancy between both convex hulls. To limit the computational burden of this identification, two different methods are proposed to construct a lower-order representation of the convex hulls. A profound description of the presented methods is given in chapter 3 of the thesis. Also, specific additions are presented for the specific application of the method to dynamic and quasi-static problems. Specifically, in the latter case, it is proposed to use contactless full-field strain measurement techniques for the construction of the measurement data set, as it is expected that the high spatial resolution facilitates the interval field identification and quantification.The performed case studies show that the developed method is capable to quantify the interval field uncertain parameters of a numerical model with high accuracy within limited computational cost. However, some considerations should be made. First, the results of the quantification depend largely on the quality of the measurement data set that is used. In the method, some techniques are included to account for e.g., scarceness of the data, but also these techniques have a limit when insufficient accurate data are available. Secondly, when large scale problems are considered containing numerous uncertain parameters, the computational expense is drastically increased. This is mainly caused by the propagation routines for propagating this high-dimensional uncertainty. Finally, it is found that the applied full-field strain measurements do not have sufficient resolution to perform an accurate interval field identification. The latter two points therefore constitute the most important suggestions for future research. " "Vision based reduced order modeling approach for operational parameter identification of nonlinear dynamic finite element models" "Wim Desmet" "Mecha(tro)nic System Dynamics (LMSD)" "Accurate dynamic identification of mechanical components is key to fully exploit the potential of Digital Twins of mechanical systems. However, current state-of-the-art dynamic parameter identification methods do not allow the use of high-spatial density measurements for components under operational conditions. The focus of this project is to develop a framework for identifying these operational parameters for detailed nonlinear dynamic finite element component models from non-contact and high-spatial density optical measurements.In order to obtain this framework, a fundamentally new approach will be developed which tackles the image measurements and efficient inverse model evaluation in a strongly integrated setting. This approach will revolve around three key contributions. First a methodology will be developed for extracting a detailed deformation field over a wide frequency range from (relatively low frequency) image data. In an original contribution, this deformation field data will be exploited for setting up parameterized reduced order models in order to circumvent the high setup cost typically associated with these approaches. The image based data and reduced order models are then combined in a parameter identification process in the frequency or time domain, depending on the component of interest. These developments will be validated on a range of academic test cases and experimental setups, of industrial complexity." "Extended Finite Element Modelling of Progressive Cracking in Fibre Reinforced Composite Laminates" "Stepan Lomov" "Structural Composites and Alloys, Integrity and Nondestructive Testing (SCALINT)" "The modelling of damage in composites is critical for many applications. The main difficulty in the modelling is complex failure mechanisms intrinsic to composite materials, including their multi-scale nature and interaction of different damage modes. Fibre-reinforced plastics are the most promising of composites due to their low density combined with high mechanical performance. Predicting of crack patterns and their effect on the performance is of practical importance and has received a lot of attention from the research community.The modelling of cracking in laminates is mainly done with Continuum Damage Mechanics. These methods are adequate in predicting the effect of damage on the composite effective properties but often predict not physical distributed damage zones instead of cracks as observed in experiments. In addition, numerical and analytical models of damage in laminates also exist but they are commonly developed for a simplified geometry, which is often assuming to be two-dimensional. Among relatively new methods is the eXtended Finite Element Method (XFEM). It allows three-dimensional modelling of the onset and propagation of multiple cracks without prior assumptions on their positions. With XFEM, interactions between different damage modes such as delaminations and intralaminar cracks can also be simulated. The XFEM approach to modelling of progressive cracking in laminated composites is investigated in the current work. The model is developed using commercially available ABAQUS tools. Four addressed problems are introduced in following paragraphs.XFEM is examined for its capability to predict matrix cracking in three-dimensional cross-ply composite laminates under quasi-static tensile loading. The study focuses on the effect of numerical and physical parameters. The propagation of transverse cracks and delaminations is described by cohesive laws. The model requires multiple input parameters, such as the peak stress and critical energy release rate characteristics in the cohesive laws. These input parameters are difficult to determine experimentally, and their choice may be controversial. Hence, the influence of these parameters on the crack development history is studied, and issues are discussed.The developed model is then extended to examine the influence of voids in laminates on the intralaminar crack density. The approach to simulate the influence of intra-laminar voids on cracking in cross-ply laminates is developed. It combines finite element models of two levels: the micro-level model representing the fibres and voids explicitly and the meso-level model based on XFEM predicting crack development in the laminates. The micro-level model provides input for the meso-level model. The analysis shows that the presence of voids leads to an earlier start of the cracking, depending on the void content, size and distribution. The developed approach proposes a way to extract input parameters from the micro-level models.The model is validated and further extended to predict interactions of intra-ply cracks and delamination in the ply-by-ply unidirectional hybrid laminates. The latter exhibits different failure behaviour under tensile loading, which depends on the laminate design. The XFEM model is improved to predict ply fractures and delamination of the interface between plies. To validate the model and XFEM in particular, the model is applied to hybrid carbon/glass laminates. The latter contains a low-elongation ply of carbon/epoxy placed between two high-elongation plies of glass/epoxy. Four different configurations of thicknesses of the plies are considered. The results are found to be in good agreement with experimental observations and measurements, including predictions of the stress-strain curves and damage patterns.Finally, the model is advanced to predict matrix cracks in laminates with angled lay-ups. To do that, a possible bridge to the next level of the hierarchy of the material structure is proposed. The idea is to obtain the macro damage model parameters by running meso-level simulations. Complex and laborious experiments have to be performed to obtain the input parameters for macro-level damage model. To replace this experimental work with simulations, the XFEM model is extended to laminates with lay-ups of angles other than 0 or 90 degrees. Trial problems have been created and calculated to examine the limitations of the model. Due to more complex geometry and load cases, and limitations of ABAQUS, there are many issues which should be addressed during the modelling. Possible ways to overcome these issues are proposed.The four problems in this thesis are used to develop, to advance, and to validate the XFEM model for cracking in composite laminates. The developed model can successfully predict the number of cracks in the material in function of the applied load, and interactions between delaminations and intra-ply cracks." "Understanding functioning and evolution of bird middle ear mechanics through high-realism finite element modelling and system identification" "No name available, Steve Vanlanduit" "University of Antwerp, Applied Mechanics" "When life evolved from aquatic to terrestrial animals, a biomechanical system developed which bridges the difference in acoustic impedance between air and fluid: the middle ear (ME). If this structure would not be present, the major part of sound energy in air would reflect at the interface with the fluid-filled inner ear. In mammals, this mechanical system consists of the eardrum and three ossicles, (and two muscles and some ligaments) which act as a lever system to transform sound waves in air to sound waves with higher pressure but smaller amplitude in the fluid of the inner ear (where sound energy is transformed to electric impulses going to the brain). In birds the ME is far simpler, mainly consisting of just an eardrum and one muscle and ossicle (yet partly cartilaginous), the so called columella, directly connecting the eardrum to the oval window in the inner ear. The system is enclosed in a cavity which connects to the outside world with the Eustachian tube. Under normal circumstances this tube is closed so quasi-static pressure differences exist between the ME and the outside world, e.g. due to altitude changes, meteorology circumstances etc. Acoustic information is of primary importance to birds, so it is fascinating to see that such a relatively simple middle ear developed. Moreover, birds are typically subject to sudden height changes and the single ossicle ear does not have the same flexibility to cope with large eardrum deformations as has the mammal three ossicle ear. These fundamental questions have held the attention of many researchers in the past, but up till now no in depth model based quantitative analysis is available. In this project we will measure the necessary input parameters for such a model (elasticity of eardrum and bones, vibration pattern of the eardrum and the ossicle, high resolution anatomical shape model) and use these to develop a highly realistic finite element model of the bird middle ear. We will develop new techniques to investigate how sound energy is transported from the eardrum to the inner ear, based on transfer path and power flow analysis. This will be done for two commercially available species (e.g. pigeon or duck, and chicken), representative for birds who adapted to a life upon the ground or a life facing fast pressure changes. We will measure how pressure change influences the system, and we will investigate how pressure varies in the bird ear, another question which remained unanswered up till now. Then we will use our model to reveal the functional evolution using less common species (e.g. falcons). Finally we will use the model to investigate new designs of an artificial ME ossicle which moves like in birds, and test it in our models of the mammal ear. When in humans the ossicles are blocked or missing, a prosthesis is used to connect the eardrum to the inner ear, but such prosthesis has no flexibility to deal with static pressure changes. We want to learn from nature to see which other single ossicle designs can solve this fundamental problem." "Contribution to the Modeling of Homogenized Windings with the Finite Element Method — Eddy-Current and Capacitive Effects" "Ruth Vazquez Sabariego" "Electrical Energy Systems and Applications (ELECTA)" "This thesis focuses on the development of mathematical models to calculate electromagnetic fields in foil and stranded windings. It aims at devising finite-element formulations that consider the whole stack (bundle) of conductors as a periodic homogenizable structure. In such formulations, the eddy-current and capacitive effects are estimated without the explicit representation of each winding turn in the geometry. By doing so, affordable simulations with sufficient accuracy are intended as the research outcome; since traditional finite-element models remain too computationally expensive to be practical software tools. The proposed models are established upon the well-known Maxwell’s equations. Between the magnetic and electric fields, the strong coupling is neglected to allow a separate estimation of the eddy-current (resistive and inductive) and capacitive effects; full wave models are out of the thesis scope. While homogenized eddy-current models are formulated for both foil and stranded windings; the study of the parasitic capacitive effect is limited to the latter.To treat eddy-current effects, the foil-winding homogenization is characterized by an unidirectional current-density redistribution and an inter-turn space-dependent voltage. Conversely, when dealing with stranded windings, the model is based on the use of frequency-dependent parameters that are fitted into Foster-network forms, which allows for time-domain analysis. Furthermore, to study the parasitic capacitive effect, this work proposes two electrostatic homogenizations for the computation of a terminal capacitance and one semi-homogenized model, built upon Darwin’s formulation, that locally estimates the displacement currents. By way of validation, the results of all homogenized models are compared to those obtained by accurate but expensive reference finite-element models wherein all turns are explicitly discretized." "Analysis of the foot using finite-element modelling" "Kristiaan D'Aout" "Functional Morphology" "The technique of finite-element modeling will be applied to a complex biological structure: the human foot. After construction of the morphological model, and assigning relevant mechanical properties, the stress on internal foot structures will be evaluated, based on externally imposed loading regimes (forces and plantar pressures) known from our own previous work." "A coupled local-global structural health monitoring approach for assessing the structural performance of deteriorated concrete components with reinforcement corrosion." "Els Verstrynge" "Structural Mechanics, Materials and Constructions" "Worldwide, many civil engineering structures reach the end of their designed lifetime. Reassessing their design lifetime or performance for altered load conditions, raises questions on their remaining capacity. This doctoral research aims at developing a local-global structural health monitoring approach for assessing the performance of reinforced concrete components subjected to degradation, in particular corrosion of the reinforcing steel. The damage effect is quantified by coupling local and global monitoring techniques. Local inspection is performed through crack mapping and Acoustic Emission, the latter being a promising technique to detect internal cracks and relate the observed signals to the damage process. Local damage data, however, do not readily allow structural assessment on a larger scale. Globally, vibration-based structural health monitoring is applied, which provides an indication of the loss of stiffness, but does not provide information about the damage process. The innovative aspect of this PhD research is to couple both techniques using a meso-scale finite element model and therefore limiting the shortcomings of the individual techniques. The developed model-based coupling approach increases the efficiency and robustness of the method, which is quantified in a Bayesian framework. An experimental test program is designed to provide a validation of the approach, which is further valorised in a case study." "Reducing environmental impact of vibrations from metro trains and assessing the structural safety of railway bridges." "Guido De Roeck" "Structural Mechanics Section" "Environmental impact of vibrations from metro trains. In support of developing a sustainable urban mobility, this work package will address the environmental impact of vibrations from metro trains. To this purpose, a numerical model will be used that has been developed at K.U.Leuven in collaboration with other European partners. 1. Using the model available at K.U.Leuven, an elaborate parametric study will be set up to assess the relative importance of determining parameters. Vibrations levels in buildings will be assessed in terms of vibration norms. 2. This parametric study should result in a decision tree to support rational track and tunnel design and to identify when vibration countermeasures should be taken, what vibration countermeasures can be effective and under what conditions a detailed numerical study is certainly needed. 3. The parameteric study will particularly address the vibration isolation efficiency of different track structures as they are commonly used on the Beijing metro network. This study will also support the future extension of the test tunnels as BJTU will have a full three dimensional of the coupled track-tunnel-soil system. 4. The possibility of structural damage to buildings due to large number of vibration cycles generated by railway traffic will be evaluated. Structural safety of railway bridges. This work package will apply dynamic system identification and health monitoring to steel railway bridges as an efficient tool to assess their safety, durability and serviceability. Based on the common experience of both partneers, dynamic train-bridge interaciton analysis based on a validated finite element model will be applied to determine the stress and strain history of structural components of a railway bridge during the passage of a train. This will allow determining the fatigue load of the bridge and to assess its safety, serviceability and life time. 1. Selection of a steel railway bridge in the Beijing area, that is potentially affected (damaged) by increasing axle loads and train speeds. 2. performing vibration measurements on the instrumented bridge and its components under ambient loading (wind, micro-tremors), during the passage of trains (forced excitation involving dynamic train-bridge interaction), and during the free vibration followint the passage of a train. 3. Dynamic system identification is applied to the ambient data and/or the data extracted from the free vibration part immediately following the passage of a train. 4. Construction of a finite element model of the railway bridge. When monitoring is applied on a continuous or periodic basis, deviations of the dynamic system characteristics can be interpreted in terms of damage. Different damage indicators have been proposed. One of the most powerful methods consists of simulating damage in the finite element model of the bridge and, subsewuently, finding the damage pattern which produces dynamic system characteristics as close as possible to the measured dynamic system characteristics. 5. The forced excitation data will be used to validate three-dimensional dynamic train-bridge interaction models. Stress and strain histories in structural components are evaluated and the real fatigue load on critical details (shear studs, welds, ...) as well as the lifetime and serviceability of the railway bridge can be determined."