Title Participants Abstract "Material Variability across the Scales in Unidirectional Composites - Virtual Material Characterisation under Longitudinal Tension" "Fabio Malgioglio" "Their high stiffness, strength and low density make composite materials an excellent choice for lightweight structural components. However, the high performance of these materials comes at the cost of complex mechanical characterisation, certification and design. For this reason, composite components are often designed applying large safety factors, limiting their lightweight potential. Virtual testing is a cheaper and faster alternative to physical testing, and therefore it can be used to predict material properties and their variability inexpensively. Nevertheless, virtual testing presents several challenges. The complex mechanisms at the microscale, such as the fibre break development occurring during failure, need to be simulated (e.g. by means of fibre break models) to reproduce failure correctly. Moreover, computational time becomes critical when modelling large volumes of material while considering the variability of the microstructure. Fibre break development and material variability can be considered at the same time by incorporating fibre break models into a multiscale framework. In this thesis, a virtual testing methodology (based on multiscale modelling) is developed to predict longitudinal tensile strength in unidirectional carbon fibre composites considering material variability. Three sources of variability are considered: fibre strength variability, local fibre volume fraction variability and local fibre misalignment. In the first part of the work, a finite element model of a tensile coupon (representative of a unidirectional ply) is developed to predict longitudinal tensile strength considering material variability. To accelerate the simulation process, a computationally efficient strategy is developed. A linear regression model, inspired by machine learning, is used to predict the stress field in the coupon, based on the experience built with a small number of FE simulations. This strategy proves very effective in reaching the same results of the full FE model, while reducing the computational time by a factor of 60. The virtual testing method is extended to a multidirectional composite ring loaded with internal pressure, representative of the cylindrical section of a composite pressure vessel. Material variability parameters used in the simulations were measured from a real composite pressure vessel, produced by filament winding. Including material variability in the model lowered the burst strength predictions, showing the importance of variability on the performance of the component." "Characterisation of the fracture properties in the ductile to brittle transition region of the weld material of a reactor pressure vessel" "Eric van Walle" "This work presents the results of the fracture characterisation of the weld material of a nuclear vessel, currently in service, in the ductile to brittle transition region. The tests consisted of Charpy impact and tensile tests, performed in the framework of the surveillance programme of the plant. Moreover, in the context of this research, KJc fracture toughness tests on pre-cracked Charpy V notch specimens (evaluated according to the Master Curve methodology) together with some mini-tensile tests, were performed; non-irradiated and several irradiated material conditions were characterised. The analysis of the experimental results revealed some inconsistencies concerning the material embrittlement as measured through Charpy and K Jc fracture tests: in order to obtain an adequate understanding of the results, an extended experimental scope well beyond the regulatory framework was developed, including Charpy tests and KJc fracture tests, both performed on reconstituted specimens. Moreover, Charpy specimens irradiated in the high flux BR2 material test reactor were tested with the same purpose. With this extensive experimental programme, a coherent and comprehensive description of the irradiation behaviour of the weld material in the transition region was achieved. Furthermore it revealed better material properties in comparison with the initial expectations based on the information obtained in the framework of the surveillance programme. © 2011 Elsevier B.V. All rights reserved." "Geochemical and mineralogical characterisation of vitrified waste material discovered in large quantities on Roman salt production sites along the southern North Sea coast" "Michiel Dekoninck, Eric Goemaere, Stijn Dewaele, Johan De Grave, Thierry Leduc, Dimitri Vandenberghe, Wim De Clercq" "Along the southern North Sea coast, Roman salt production sites are characterised by extensive refuse zones containing large quantities of what has been described as 'salt slags'. These 'salt slags' are in fact amorphous, heavily vitrified waste materials. This is rather surprising since large-scale vitrification has never been associated with the salt production process. In this paper, these materials are for the first time systematically studied macroscopically, mineralogically and geochemically to determine their composition, formation and relation to the salt production process. To achieve these objectives, 30 samples from 7 Roman salt production sites were analysed by combining several analytical methods (thin-section petrography using Polarised Light Microscopy, Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectroscopy and X-Ray diffraction). This approach enabled a detailed characterisation of the vitrification process in the waste materials, as well as the identification of high temperature mineral transformations formed in specific (archaeological) conditions. Based on these results, the amorphous waste materials should be interpreted as vitrified hearth base fragments. This study shows that the current interpretations regarding the firing conditions on Roman salt production sites needs major adjustments. In addition, this paper demonstrates the value of geochemical and mineralogical research on discarded waste materials to study poorly understood aspects of not only the salt production process, but arti-sanal activities in general." "Characterisation of capacitive field-effect sensors with a nanocrystalline-diamond film as transducer material for multi-parameter sensing" "Maryam H. Abouzar, A. Poghossian, A. Razavi, Oliver WILLIAMS, Nathalie BIJNENS, Patrick WAGNER, M. J. Schoening" "The feasibility of a capacitive field-effect EDIS (electrolyte-diamond-insulator-semiconductor) platform for multi-parameter sensing is demonstrated by realising EDIS sensors with an O-terminated nanocrystalline-diamond (NCD) film as transducer material for the detection of pH and penicillin concentration as well as for the label-free electrical monitoring of adsorption and binding of charged macromolecules, like polyelectrolytes. The NCD films were grown on P-Si-SiO2 substrates by microwave plasma-enhanced chemical vapour deposition. To obtain O-terminated surfaces, the NCD films were treated in an oxidising medium. The NCD-based field-effect sensors have been characterised by means of constant-capacitance method. The average pH sensitivity of the O-terminated NCD film was 40 mV/pH. A low detection limit of 5 mu M and a high penicillin G sensitivity of 65-70 mV/decade has been obtained for an EDIS penicillin biosensor with the adsorptively immobilised enzyme penicillinase. Alternating potential changes, having tendency to decrease with increasing the number of adsorbed polyelectrolyte layers, have been observed after the layer-by-layer deposition of polyelectrolyte multilayers, using positively charged PAH (poly (allylamine hydrochloride)) and a negatively charged PSS (poly (sodium 4-styrene sulfonate)) as a model system. The response mechanism of the developed EDIS sensors is discussed. (C) 2008 Elsevier B.V. All rights reserved." "Visco-elastic material characterisation by means of the Ultrasonic Polar Scan" "Arvid Martens" "Advances in material science and engineering have always been a key factor in any kind of progress made at the industrial scene. The drive towards novel, lighter and stronger materials, for instance, empowered companies to construct the highly efficient airplanes and automobiles as we know them today. One of the main protagonist in this development is the initiation and subsequent investigation of composite (and multilayered) materials, such as carbon fiber reinforced plastics (CFRP), which is nowadays one of the most heavily used materials in load-bearing components due to their excellent strength to density ratio. Indeed, after its initial introduction in the 60's and 70's, the use of CFRP experienced an exponential growth in many application fields. The downside of the medal is, however, that composite materials generally have a vastly complex nature, represented by material properties that are directional dependent (anisotropic) and potentially also frequency dependent (dynamic). This makes it especially difficult to either extract the material properties or, when in operation, to identify potential flaws inside the material. As a sequel, several non-destructive testing (NDT) procedures based on ultrasound have been proposed, through the years, in view of resolving the characterization and damage detection problem. However, as will be demonstrated during this thesis, many of these conventional characterization techniques are hampered by quite a few limitations. Therefore, manufacturing and engineering businesses are looking for new state-of-the-art characterization procedures that are capable of inferring the full set of material parameters by which the mechanics and dynamics of these materials can be properly described and evaluated. In the doctoral research work presented here, we develop and enhance modular tools that facilitate a novel ultrasound based NDT methodology for material characterisation. We first identify the limitations experienced by the current (traditional) ultrasonic characterization techniques. Proper knowledge of these limitations and their origin provides the opportunity to introduce and advance to a new inversion procedure based on the Ultrasonic Polar Scan (UPS). While the concept of the UPS technique had been proposed for quite some time, it was only resurfaced in the last decade as a viable means for characterizing complex viscoelastic materials. As a first contribution to this thesis, a UPS based two-stage inversion scheme using pulsed input signals is introduced and discussed, having the favorable characteristics to resolve most of the limitations of the traditional techniques. Inversion results obtained on both artificial (numerical) and experimental UPS data sets validate that this approach produces more accurate and robust inverted values for the material parameters over the conventional techniques. Recognizing the fact that the use of pulsed signals requires a priori knowledge on the frequency dependence of the material parameters (which is not readily available), a second approach of the two-stage UPS inversion scheme employing single-frequency input signals is proposed and applied on both numerical and experimental data. The use of harmonic signals however requires a careful account of the transducer characteristics used during UPS measurements, as their finite size renders the assumption of impinging plane waves invalid. Having solved this problem by means of an angular decomposition of the wavefield, we are convinced that, in the future, a phased array UPS setup should be considered, as preliminary studies demonstrate its capability of measuring these plane wave characteristics in a similar way, albeit much faster. The third and last part of the thesis deals with the numerical investigation of multilayered composite materials consisting of layers with the either different base material or different orientation (cross-ply). The first part of this study is dedicated to the homogenization of a multilayer material into a single material layer. Within the frequency limt of the homogenization concept, which can be estimated by the theory of Floquet waves, it is demonstrated that the proposed UPS homogenization procedure possesses similar frequency-dependent material properties and enables to include viscoelasticity into the homogenized material. Hence, the previously introduced inversion procedure for harmonic signals can be safely applied below the cutoff frequency. Further, as an closing application, a method for the extraction of the single-layer characteristics within a plane multilayered structure is investigated and successfully tested on a numerically simulated UPS data set of a cross-ply material, giving rise to the anisotropic layer parameters as well as the mutual orientation and thicknesses of the layers." "Simulation of wave propagation problems for automated characterisation of material parameters" "Steven Vandekerckhove" "In many application fields, non-destructive testing and evaluation (NDT&E) is useful to determine material properties and detect faults of objects before or during operation. In the past decades, a wide range of experimental NDT&E techniques has been developed and successfully tested for many problem classes. In the past few years, the collection of experimental NDT&E techniques has been extended with hybrid methods, i.e., methods that combine experiments and numerical simulation. The main drawback of all existing NDT&E methods, is that they need a-priori knowledge and expertise of the operator. In this work, we aim to develop automated procedures for the characterisation of material parameters based on the simulation of wave propagation problems, thereby extending the application range of NDT&E, especially to problems with little a-priori knowledge. We propose the use of gradient based optimisation methods to develop automated procedures for the characterisation of material parameters. To achieve this, we first select efficient numerical procedures for the solution of wave propagation problems. For the spatial discretisation, we consider the finite integration technique and the finite element method with both continuous and discontinuous elements. We study the performance of several time integration methods in combination with these spatial discretisation methods, from which we learn that third order discontinuous elements in combination with second order time stepping methods are performing best. We compute gradient information of the time-dependent wave propagation problem and use this in combination with the forward solver to efficiently solve the inverse problems that occur in NDT&E. For the efficient computation of gradients, adjoint methods are used. The proposed gradient based optimisation method is compared to gradient free methods for determining the wave speeds in a homogeneous isotropic medium, from which we conclude that gradient based methods are the only feasible option to tackle more complicated inverse problems. The challenges involved in solving optimisation problems with spatially dependent control parameters are described and successfully demonstrated for determining a spatially dependent wave speed distribution. We show that the use of proper function spaces and associated Riesz maps is a key ingredient to obtain correct results. We also use gradient information to automatically calibrate absorbing layers to mimic open boundaries. The automatic calibration is performed for perfectly matched layers and for the simpler and computationally faster approach of using consecutive absorbing layers. We show that after calibration, both approaches have a comparable performance. Throughout this work, we use a high level of genericity to describe and simulate wave propagation problems so that all presented methods are applicable to acoustic, electromagnetic and elastic wave propagation problems in one two and three dimensions. This work demonstrates that numerically solving inverse NDT&E problems with many, e.g. spatially dependent, parameters is possible." "Global optimisation methods for poroelastic material characterisation using a clamped sample in a Kundt tube setup" "Johan Vanhuyse, Elke Deckers, Stijn Jonckheere, Bert Pluymers, Wim Desmet" "© 2015 Elsevier Ltd. All rights reserved. The Biot theory is commonly used for the simulation of the vibro-acoustic behaviour of poroelastic materials. However, it relies on a number of material parameters. These can be hard to characterize and require dedicated measurement setups, yielding a time-consuming and costly characterisation. This paper presents a characterisation method which is able to identify all material parameters using only an impedance tube. The method relies on the assumption that the sample is clamped within the tube, that the shear wave is excited and that the acoustic field is no longer one-dimensional. This paper numerically shows the potential of the developed method. It therefore performs a sensitivity analysis of the quantification parameters, i.e. reflection coefficients and relative pressures, and a parameter estimation using global optimisation methods. A 3-step procedure is developed and validated. It is shown that even in the presence of numerically simulated noise this procedure leads to a robust parameter estimation." "Production and characterisation of filament-based Material Extrusion (MEX) additively manufactured copper parts" "Fankai Meng, Jef Vleugels, Eleonora Ferraris" "Material Extrusion (MEX) Additive Manufacturing of metal components is increasingly applied in recent years due to its low cost and potential for multi-material printing, with filament-based MEX being widely developed among all subdivisions of MEX. This technology utilises a compounded filament of polymeric binders and metal powder. The printing process involves hot extrusion of the compounded filament, which acts as a carrier of the metal powder and is deposited along a programmed print path to construct a 3D part. The as-printed parts are debound in several steps to ensure complete binder removal and pressureless sintered, targeting high densification levels. In this work, a copper-based filament was utilised as feedstock material and a full factorial design of experiments was performed to study the effect of layer height, volumetric speed and flowrate multiplier on the density of the as-printed part. Selected specimens from the DoE were debound and sintered and characterised. Various tests including density measurements, SEM, optical microscopy, micro-CT, etc., were applied at different stages to evaluate the porosity in the filament and printed parts. As a result, a relative density of 94% and an electrical conductivity of 63 %IACS (international annealed copper standard) were achieved for the sintered copper, which could be directly linked to the purity of the feedstock material." "A neutral form for experiential material characterisation" "Lore Veelaert, Ingrid Moons, Els Du Bois" "Materials experience in design involves the meanings that materials convey to users through its expressive characteristics. Such meaning evoking patterns are influenced by parameters such as context, product (e.g.shape) and user. Consequently, there is a need to standardise experiential material characterisation and large-scale data collection, by means of a meaning-less or ‘neutral’ demonstrator to objectively compare materials. This paper explores the conception of this neutrality and proposes two opposing strategies: neutrality through complexity or through simplicity. In a pre-study with 20 designers, six associative pairs are selected as neutrality criteria, and shaped in 240 forms by 20 (non) designers in a main workshop. Following the simplicity strategy, these forms are averaged out in three steps by a team of five designers, based on a consensus on of delicate-rugged, aggressive-calm, futuristic-calm, masculine-feminine, traditional-modern, and toylike-professional, resulting in a selection of four averaged neutral forms. Finally, future research will focus on complexity to increase interactivity, so that consumers might be triggered in extensive material exploration." "Optimised Experimental Characterisation of Polymeric Foam Material Using DIC and the Virtual Fields Method" "Pascal Lava" "This article presents a methodology to optimise the design of a realistic mechanical test to characterise the material elastic stiffness parameters of an orthotropic PVC foam material in one single test. Two main experimental techniques were used in this study: Digital Image Correlation (DIC) and the Virtual Fields Method (VFM). The actual image recording process was mimicked by numerically generating a series of deformed synthetic images. Subsequent to this, the entire measurement and data processing procedure was simulated by processing the synthetic images using DIC and VFM algorithms. This procedure was used to estimate the uncertainty of the measurements (systematic and random errors) by including the most significant parameters of actual experiments, e.g. the geometric test configuration, the parameters of the DIC process and the noise. By using these parameters as design variables and by defining different error functions as object functions, an optimisation study was performed to minimise the uncertainty of the material parameter identification and to select the optimal test parameters. The confidence intervals of the identified parameters were predicted based on systematic and random errors obtained from the simulations. The simulated experimental results have shown that averaging multiple images can lead to a significant reduction of the random error. An experimental determination of the elastic coefficient of a PVC foam material was conducted using the optimised test parameters obtained from the numerical study. The identified stiffness values matched well with data from previous tests, but even more interesting was the fact that the experimental uncertainty intervals matched reasonably well with the predictions of the simulations, which is a highly original result and probably the main outcome of the present paper."