Michele Buonsanti

A Finite Element Model to Evaluate Airport Flexible Pavements Response under Impact

This paper using finite elements (FE) an approach to determine the contact stresses in a flexible pavement under landing aircraft loads is presented. The proposed 3-Dimensional model simulates the behaviour of flexible runway pavements during the landing phase. A study on the impact of a rubber solid on the free surface of a granular plate is presented, simulating an aircraft gear system landing on with a flexible surface. This study is performed considering two tires on the structural pavement, with the real loads applied directly on the two wheels of the gear system. The application takes in account the frictional phenomena developed between rubber solid and the surface of the pavement during the lockwire.

Theoretical and Computational Analysis of Airport Flexible Pavements Reinforced with Geogrids

In recent years the need to increase pavement service life and guarantee high performance has turned a greater attention on the use of pavement reinforcements. In this paper the effectiveness of geogrids as reinforcement of HMA layers in an airport flexible pavement was investigated.

Modelling Micro-Damage in Granular Solids

The prediction of the spacing and opening of cracks in asphalt or concrete pavements, and particularly in airports (runway, taxiway and apron) is important for the durability assessment. A basic problem is the spacing of parallel planar cracks from a half space surface, approached and solved by numerous authors by means of macro-scale computational models. The calculated values of crack spacing are in relatively good agreement with the values reported in observations on asphalt concrete pavements. The constituents of granular solids are, fundamentally, made of grain in contact and, these materials are highly discontinuous and non-homogeneous with two or three phases (solid, voids with air or water), and finally binding among solid parts. The aim of this paper is to suggest a micromechanical approach in granular material solids, focusing the attention on a simple RVE (representative volume element) based on two rigid particles linked through an adhesive material (bitumen). Our final aim is to propose a micro-damageability parameter (interface loss) supposing the adhesion decreasing under the action of prescribed tangential and normal relative displacement. The reduction is attributed by progressive damage and comes with energy dissipation and moreover we assume unilateral contact conditions for normal displacement and Coulomb friction for the tangential displacement.

Dynamic Behavior of Granular Mixture Solids

In this paper a theoretical and numerical study of impulsive loads over a granular medium free surface has been developed. We will model a real case, as a high deformable solid impacting a less deformable surface, and consequently subject to micro and macro medium failure. Developing a macroscopic approach we resolve the macro-stress in the homogenized two-dimensional medium and subsequently apply a representative volume element (RVE) analysis modeling to the micro-scale. The problem is developed by energetic approach on an elasto-plastic element using an energy functional containing bulk and surface contributions. Finally, a numerical application is presented.

From 3-D Nonlinear Elasticity Theory to 1-D Bars with Nonconvex Energy

This paper represents a first attempt to derive one-dimensional models with non-convex strain energy starting from “genuine” three-dimensional, nonlinear, compressible, elasticity theory. Following the usual method of obtaining beam theories, we show here for a constrained kinematics appropriate for long cylinders governed by a polyconvex, objective, stored energy function, that the bar model originally proposed by Ericksen [3] is obtainable but enriched by an additional term in the strain gradient. This term, characteristic of nonsimple grade-2 materials, penalizes interfacial energies and makes single-interface two-phase solutions preferred. The resulting model has been proposed by a number of authors to describe the phenomenon of necking and cold drawing in polymeric fibers and, here, we discuss its suitability to interpret also the elastic-plastic behavior of metallic tensile bars under monotone loading.

Eddy Current and Fuzzy Inference to Control Defects Growth in Reinforced Concrete

In reinforced concrete, when slits take places, the problem arises to control the growth of it. If the critical limit is exceeded due to further load increases, the final strength relies on the integrity of the tight rods. The ability of finding possible defects in these rods and in controlling the relevant growth is therefore of great importance in structural safety at the ultimate stage. In particular, thin reinforced concrete structures draw researchers attention to such a point that several theoretical models have been developed with the aim to reproduce with adequate reliability the real behaviour, taking into consideration the actual deformability, the rising and spreading of fissuring, together with the mechanisms and the loads leading to collapsing. In this work, an experimentation is carried out on a deflect less reinforced concrete specimen, which underwent to rising traction up to the fissuring. The employed investigation technique is an application of the well-known eddy current-based methodology. The magnetic fields maps which were got by this way constitute an electromagnetic representation of the tensional condition of the specimen at the different values of the applied traction, using the above mentioned experimental database, concerns the extraction of inferences to predict and assess the growth of defects in reinforced concrete elements similar to the employed specimen.

A Unified Model for Micromechanics Damage in the Asphalt Concrete

The particles distinct element model has the consistency to model the mechanical behavior of the microscopic structures inside an asphalt mixture. The model assumes that the schematized granular constituents are in a contact point, considering the thin asphalt films as the binding elements. In this paper, we will model (at micro-scale) the damage to a surface in asphalt concrete under an impulsive load, considering binding, interface, viscosity and friction. Our aim is to reproduce the micro-damage due to detachment among the elementary components of the concrete in airports pavements.The proposed approach is mainly from a mechanical point of view, and a general model describing adhesive contact between rigid bodies is proposed. The intensity of adhesion is supposed to decrease under prescribed shear and normal displacement fields and comes by energy reduction, where the viscosity and friction contributes are taken in account.A numerical implementation by finite element procedures has been performed, and the outcome is presented.

Runway Debris Impact on Aircraft Composite Parts

In this paper, we perform the behavior of aeronautics composite material subjected to a low energy impact. The proposed study considers the dynamic impact between a small piece of granular material and a large body of composite material. The principal aim is to simulate the impact of runway debris thrown up by the landing gear against an airplane structure. In the simulation, a CFRP composite panel impacted by granular particles at low speed is considered. The finite element analysis, initially on the macroscale and subsequently on the micro-scale, shows the delamination inside the composite according to the experimental results.

Fractal Analysis and Biophysical Investigation of Muscular Tissue Damaged due to Low Temperature: A Pilot Study

Severe damage is produced in tissues by freezing and thawing. Until now, a great majority of the studies are performed qualitatively, lacking any quantitative approach. An important step is to choose the best option among different freezing methods. To approach the complex problem of damage produced in tissues by freezing, in this paper we present the classical mechanics approach and a quantitative study making use of a fractal methodology (evaluation of fractal dimension by box-counting method). A comparative fractal analysis between two different steps of freezing the human thoracic diaphragm muscle has been performed to quantify the voids and cracks produced by freezing (samples were placed in a cryostat chamber). Moreover, a standard Euclidean morphometry was performed to determine area and shape of the muscle nuclei after the two steps of freezing. Fractal dimension of the ice-tissue interface structures increased with decreasing temperature (p<0.0001), percentage of cell muscle decreased (p<0.01), while standard morphometry of the nuclei didnt show any modifications. Our results show the ability of the fractal approach to accurately quantify the damage produced by freezing and reveals that the lowest temperature produces the most damage.

Equilibrium State of a Binary Granular Solids Mixture

We consider a possible equilibrium configuration under dead load of a vertical cylindrical specimen which is composed of a mixture of two elastic materials. An energetic approach in the mixture evolution is performed and this particular approach can be utilized to describe the bi-phase characterization of the mixture material. Our final aim is to build a theoretical simple model to determine the decrease load bearing capacity of mixture.