'Simulation of Shakedown Behavior for Flexible Pavement's Unbound Granular Layer

Full-depth asphalt concrete pavements are generally designed to control fatigue cracking and reduce potential rutting when subjected to repeated heavy traffic loads. A particular interesting question is whether a limit load exists below which excitation shakedown in the sense that the granular layer does not accumulate further deformation. Although pavement design guides give more weight to asphalt concrete layer failures, granular failure may not be ignored; especially for thin layers and/or heavy load. The behavior of granular layers used in base and, sub-base layers of flexible pavement is complicated due to its nonlinear elastoplastic response when subjected to dynamic traffic loading. The objective of this paper is to present a new simplified simulation model for the Shakedown behavior of granular layer in flexible pavement. This method is integrated with Mohr-Coulomb criterion, which is used and applied to simulate the response of unbound granular layers to dynamic loading in a numerical analysis. The results of analysis are then compared to simplify the results of modeling without considering shakedown effects and then, the conclusions are drawn

Biocompatible polymeric microparticles produced by a simple biomimetic approach

The use of superhydrophobic surfaces to produce polymeric particles proves to be biologically friendly since it entails the pipetting and subsequent cross-linking of polymeric solutions under mild experimental conditions. Moreover, it renders encapsulation efficiencies of ∼100%. However, the obtained particles are 1 to 2 mm in size, hindering to a large extent their application in clinical trials. Improving on this technique, we propose the fabrication of polymeric microparticles by spraying a hydrogel precursor over superhydrophobic surfaces followed by photo-cross-linking. The particles were produced from methacrylamide chitosan (MA-CH) and characterized in terms of their size and morphology. As demonstrated by optical and fluorescence microscopy, spraying followed by photo-cross-linking led, for the first time, to the production of spherical particles with diameters on the order of micrometers, nominal sizes not attainable by pipetting. Particles such as these are suitable for medical applications such as drug delivery and tissue engineering.We thank Ivo Aroso and Ana Isabel Neto for their valuable support with FTIR and compression experiments, respectively. A.M.S.C. thanks FCT for financial support through grant BIM/PTDC/CTM-BPC/112774/2009_02. M.A.-M. thanks CONACyT (Mexico) for financial support through post-doc grant no. 203732. N.M.O. thanks FCT for financial support through Ph.D. scholarship no. SFRH/BD/73172/2010. This work was funded by the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. REGPOT-CT2012-316331-POLARIS, by FEDER through the Competitive Factors Operation Program-COMPETE, and by national funds through FCT - Fundacao para a Ciencia e a Tecnologia in the scope of project PTDC/CTM-BIO/1814/2012

Evaluation of Tire-Pavement Contact Stress Distribution of Pavement Response and Some Effects on the Flexible Pavements

© ASCE. Pavement distress mechanisms become more prevalent in recent years such as surface rutting and surface initiated wheel path cracking. The main objective of this study is to evaluate tire-pavement contact stress distribution of pavement response using finite element analysis. It also assesses some of the effects of tire related factors on tire contact pressures and its response on flexible pavement. Tire-pavement contact stress is simulated using 3-D finite element method in ABAQUS for five layers of flexible pavement at various loads. 40 kN wheel load to represent a set of dual tires were assumed to be uniformly distributed over the contact area between tire-pavement surface. Four different tire-inflation pressures (350, 490, 630, and 700 kPa) were used to investigate some of the effects of tire-pavement structure. The finite element (FE) model analyses were verified with experiment results. Results have shown that contact stresses vary significantly for the different types of tire-pavement contact that were investigated. The tire's finite element was validated using measured contact area and deflection