Cedric Vuye

Development of an Equivalent Composite Honeycomb Model: A Finite Element Study

Finite element analysis of complex geometries such as honeycomb composites, brings forth several difficulties. These problems are expressed primarily as high calculation times but also memory issues when solving these models. In order to bypass these issues, the main goal of this research paper is to define an appropriate equivalent model in order to minimize the complexity of the finite element model and thus minimize computation times. A finite element study is conducted on the design and analysis of equivalent layered models, substituting the honeycomb core in sandwich structures. A comparison is made between available equivalent models. An equivalent model with the right set of material property values is defined and benchmarked, consisting of one continuous layer with orthotropic elastic properties based on different available approximate formulas. This way the complex geometry does not need to be created while the model yields sufficiently accurate results.

Determining the Power Flow in a Rectangular Plate Using a Generalized Two-Step Regressive Discrete Fourier Series

The evaluation of structural power flow (or structural intensity (SI)) in engineering structures is a field of increasing interest in connection with vibration analysis and noise control. In contrast to classical techniques such as modal analysis, the SI indicates the magnitude and direction of the vibratory energy traveling in the structures, which yields information about the positions of the sources/sinks, along with the energy transmission path. In this paper, a new algorithm is proposed to model operational deflection shapes (ODS). The model is a two-dimensional Fourier domain model that is estimated by using a weighted nonlinear least-squares method. From the wave number-frequency domain data thus obtained, the spatial derivatives that are necessary to determine the structural power flow are easily computed. The proposed method is less sensitive to measurement noise than traditional power flow estimation techniques. A numerical model of a simply supported plate excited by two shakers, phased to act as an energy source and sink, is used as a simulation case. Measurements are executed on a clamped plate excited by an electromagnetic shaker in combination with a damper.

Characterization of acoustic materials using the scanning laser Doppler vibrometer

In this article we will present a method to estimate sound absorption coefficients from measurements of the incident and reflected sound fields near the material under test. The sound fields are visualized using a scanning laser Doppler vibrometer (SLDV). By aiming the SLDV at a rigid (non-vibrating) object and letting the beam pass through a sound field the spatial pressure distribution can be made visible. By visualizing both incident and reflected sound field with respect to a material sample in this manner, the acoustic absorption coefficients can be determined (this is the ratio of the absorbed energy and incident energy). Two alternative set-ups are proposed in this article: a one-dimensional set-up where the sound field (i.e. the standing waves) inside a thin glass tube is measured, and a two-dimensional set-up where the propagating and reflecting sound field between two parallel glass plates is visualized. While the former can only be used to obtain normal incidence absorption coefficients the latter can also be used to estimate oblique incidence absorption values. It is shown that the method is accurate at high frequencies where traditional standardized acoustic material characterization techniques mostly fail.

Digital Image Correlation to Investigate Crack Propagation and Healing of Asphalt Concrete

Accurate determination of the mechanical properties of asphalt concrete is very important in Road Engineering. The traditional method to calculate these properties is to run experiments using a hydraulic/pneumatic actuator and strain gauges to apply stress and measure the strain. However, in the last decade optical measurement techniques have become popular for strain calculation on the surface of the specimen and detecting the cracks on the surface. In this study, digital image correlation is used to estimate the strain map on the surface of an asphalt specimen, predict the location of crack initiation, and investigate the healing phenomenon in asphalt concrete.

The use of a non-nuclear density gauge for monitoring the compaction process of asphalt pavement

The mechanical performance of an asphalt pavement affects its durability – thus carbon footprint. Many parameters contribute to the success of a durable asphalt mix, e.g. material selection, an accurate mix and even the road design in which the asphalt mix quality is quantified. The quality of the asphalt mix, by its mechanical properties, is also related to the compaction degree. However, and specifically for high volume rates, the laying process at the construction site needs an effective method to monitor and adjust immediately the compaction quality before cooling and without damaging the layer, which is now absent. In this paper the use of a non-nuclear density gauge (PQI – Pavement Quality Indicator) is evaluated, based on a site at Brussels Airport. Considering the outcome of the present research, this PQI is advised as a unique tool for continuous density measurements and allow immediate adjustments during compaction, and decreases the number of core drilling for quality control, and as a posteriori asphalt pavement density test where cores are prohibited. The use of PQI could be recommended to be a part of the standard quality control process in the Flemish region.

The influence of mixture composition, adhesion promotor and compaction degree on the groove stability of grooved Marshall asphalt

After the first rehabilitation of runway 07R/25L in 2015, runway 01/19 was reconstructed in the summer of 2016, as part of a cycle where all runway pavements at Brussels airport are completely renovated each thirty years. The top layer is a Marshall asphalt with a polymer modified bitumen. To optimize the water drainage the central part of the runway (47 m wide) is grooved instead of applying an anti-skid layer. In this paper the focus is on the durability of the grooved top layer. Two different Marshall asphalt mixtures with a different maximum granulate size (10 mm or 14 mm) are compared, both in the laboratory and in a full-scale trial. In the laboratory the resistance against rutting and raveling are investigated for both mixtures with and without adhesion promotor, which did not show a positive effect. In the full-scale trial the compactability and impact of both a longer curing period and a variation in the degree of compaction on the groove stability is investigated for both mixtures using a heavy truck. No visual differences could be found except in areas which were undercompacted and showed more damage to the grooves.

Identification of pavement material properties using a scanning laser Doppler vibrometer

This paper presents an inverse modeling approach to estimate mechanical properties of asphalt concrete (i.e. Young’s modulus E, Poisson ratio ν and damping coefficients). Modal analysis was performed on an asphalt slab using a shaker to excite the specimen and an optical measurement system (a Scanning Laser Doppler Vibrometer or SLDV) to measure the velocity of a measurement grid on the surface of the slab. The SLDV has the ability to measure the vibration pattern of an object with high accuracy, short testing time and without making any contact. The measured data were used as inputs for a frequency domain model parameter estimation method (the Polymax estimator). Meanwhile, natural frequencies and damping ratios of the system were calculated using a Finite Element Modeling (FEM) method. Then, the Modal Assurance Criterion (MAC) was used to pair the mode shapes of the structure determined by measurements and estimated by FEM. By changing the inputs of the FEM analysis (E, ν and damping coefficients of the...

Recycling reclaimed asphalt in Flanders: state of the art 2014

This contribution illustrates the state of the art of the use of reclaimed asphalt pavement (RAP) in bituminous mixtures for roads in Flanders. A first part will give a summary of the supply of reclaimed asphalt and its use for the last decade in Flanders. Different mixtures with the use of RAP are compared by means of stiffness and fatigue properties. In Flanders, the regulation and the composition of asphalt is different for non-public and public works. For the latter, the Flemish Regulation must be followed and till 2011 recycling was allowed both for mixtures for base and surface layers, up to 50% binder substitution. However, after 2011 recycling became prohibited for top layers. Since 2013, the Flemish Agency for Road and Traffic and the University of Antwerp started an experimental program to evaluate the limited use of reclaimed asphalt in mixtures for surface layers, e.g. AC-10 and SMA. A LCA study showed that the use of RAP is beneficial compared to the use of warm mix asphalt. Further, in this paper, the results of this experimental program for AC-10 and SMA with RAP are discussed. The study recommended allowing the use of RAP up to 50% for AC-10. In a second project, the performance characteristics of SMA mixtures (SMA-C1 with 70/100 and SMA-C2 with 45/80-50) with reuse of reclaimed asphalt pavement are explored. The experimental study of the performance characteristics consist of % Voids, resistance to water sensitivity, rutting, stiffness modulus and ravelling (Darmstadt scuffing device prTS12697-50). The study showed that the addition of RAP has no negative effect on the performance of the mixtures. The contribution concludes with a recommendation to re-evaluate the prohibition of RAP in surface layer mixtures.

Analysis of a heat exchanging asphalt layer using a finite element approach

Current aims regarding environmental protection, like reduction of fossil fuel consumption and greenhouse gas emissions, require the development of new technologies. These new technologies should enable the production of renewable energy which is both cleaner and cheaper. This necessity encourages engineers to develop new ways to capture energy for later use. In this paper, the use of a heat exchanging asphalt layer (HEAL), as a means to extract low temperature heat, is studied in detail. Such a system, which harvests heat energy by flowing water through a heat exchanger embedded in the pavement structure, could definitely have a significant thermal energy output since pavement materials absorb large amounts of solar insolation. The focus in this paper is on asphalt concrete pavements since these absorb the largest amount of solar insolation and will benefit the most from the removal of heat in the form of an increase in lifetime. The main objective is to study the energy output and efficiency of the HEAL. In order to achieve this, a parametric study on different thermal properties of the asphalt pavement has been performed using a validated Finite Element (FE) model of the collector. It is shown that both the absorptivity and thermal conductivity have a large influence on the outlet temperature and solar efficiency. Using this FE model it will be possible to predict the long-term energy output of the HEAL taking into account all geometrical, material and weather parameters.

Implementation of the Scanning Laser Doppler Vibrometer Combined with a Light-Weight Pneumatic Artificial Muscle Actuator for the Modal Analysis of a Civil Structure

The identification of the modal parameters of bridges and other large civil constructions has become an important research issue. Different approaches have been proposed depending on the excitation used: ambient excitations (due to wind, traffic, ... )o r artificial excitations (e.g. impact test with heavy drop weights). In practice it turns out that not all modes are well excited by the ambient forces. Hence the application of an artificial actuator is advisable. The problem is that larger constructions often require large and heavy excitation devices, which are hard to manipulate. Another difficulty encountered in performing a modal analysis on large civil constructions is the necessity for a large number of high sensitivity sensors. Consequently a large number of cables has to be installed resulting in a large setup time. Thispaperisaproof-of-conceptwhichdemonstratesthepossibilityofusinglightweightPneumaticArtificialMusclescombined with the scanning laser Doppler vibrometer to perform a modal analysis on a civil structure. This combination allows for an important reduction in setup time and allows for sine testing as well as the application of broadband signals such as periodic chirps, true noise or multisines.