1,720,985 research outputs found
Effect of Micro-Particle Addition on Frictional Energy Dissipation and Strength of Concrete: Experiments and Modelling
Full text linkIn this thesis, a two-degrees-of-freedom, non-linear model is introduced aiming to describe internal friction phenomena which have been observed in some modified concrete specimens undergoing slow dynamic compression loads and having various amplitudes but never inducing large strains. The motivation for the theoretical effort presented here arose because of the experimental evidence described in some papers in which dissipation loops for concrete-type materials are shown to have peculiar characteristics. Since viscoelastic models –linear or non-linear– do not seem suitable to describe either qualitatively or quantitatively the measured dissipation loops, it is proposed to introduce a micro-mechanism of Coulomb-type internal dissipation associated to the relative motion of the faces of the micro-cracks present in the material. In addition, numerical simulations, showing that the proposed model is suitable to describe some of the available experimental evidences, is presented. These numerical simulations motivate further developments of the considered model and supply a tool for the design of subsequent experimental campaigns.
Furthermore, the effect of micro-particle additives such as calcium carbonate on internal dissipation of concrete was experimentally investigated. The damping performance of concrete can be improved by adding to the mixture different kinds of micro-particles with suitable size which fill the pores of the matrix and change the contact interaction between internal surfaces of voids. It was determined that the energy dissipation of the concrete increases with the increasing content of micro particles at least when the concrete matrix is “soft” enough to allow microscopic motions. On the other hand, the increasing percentage of micro-particles addition can affect the mechanical strength of the material. Thus, there is a reasonable compromise in incorporating these micro-particles to obtain higher damping with- out weakening the mechanical properties. Several concrete mixes were prepared by mixing cement powder with different percentages of micro-fillers. A concrete mix without addition of micro-particles was molded as a reference material for the sake of comparison. All these specimens were tested under cyclic loading in order to evaluate energy dissipation starting from the area of a dissipation loop detected in the diagram relative to a representative cycle. The experimental determination of the dissipated energy shows a significant increase in the damping capability of the cement-based materials with micro-filler compared to the standard concrete. The experimental results presented seem to indicate that the proposed model is suitable to describe the mechanical behavior of modified and unmodified concrete, provided that the introduced parameters are suitably tuned in order to best fit the available experimental data
Equilibrium of Two-Dimensional Cycloidal Pantographic Metamaterials in Three-Dimensional Deformations
No full textA particular pantographic sheet, modeled as a two-dimensional elastic continuum consisting of an orthogonal lattice of continuously distributed fibers with a cycloidal texture, is introduced and investigated. These fibers conceived as embedded beams on the surface are allowed to be deformed in a three-dimensional space and are endowed with resistance to stretching, shearing, bending, and twisting. A finite element analysis directly derived from a variational formulation was performed for some explanatory tests to illustrate the behavior of the newly introduced material. Specifically, we considered tests on: (1) bias extension; (2) compressive; (3) shear; and (4) torsion. The numerical results are discussed to some extent. Finally, attention is drawn to a comparison with other kinds of orthogonal lattices, namely straight, parabolic, and oscillatory, to show the differences in the behavior of the samples due to the diverse arrangements of the fibers
Experimental behavior of concrete with micro-particles under cyclic loading and effects due to frictional energy dissipation
No full textA model of internal frictional dissipation in concrete and mechanical effects due to micro-particles addition
No full textExperimental evaluation of frictional energy dissipation in cement-based materials with micro-particles under cyclic loading
No full textModeling and designing micro- and nano-structured metamaterials: Towards the application of exotic behaviors
No full textA continuum model of a mixture of bone tissue and bio-resorbable material for simulating mass density redistribution in a 2d sample
No full textThe bio-mechanical phenomena occurring in bones grafted with the inclusion of artificial materials demand the formulation of mathematical models which are refined enough to describe their non-trivial behavior. In this paper reference is made to earlier works, where a 3D model was proposed and numerical examples were performed in 1D space to investigate and explain some fundamental mechanisms possible during remodeling process. Herein possible effects resulting from 2D interactions are being discovered and examined which may not be present in 1D case so more realistic situations are approached and discussed. This model was used to numerically analyze the physiological balance between the processes of bone apposition and resorption and material resorption in a plate-like sample. The specimen was constituted by a portion of bone living tissue and one of bio-resorbable material and was acted by in-plane loading conditions. A range of load magnitude was identified within which a physiological state is established. A parametric analysis was carried out to evaluate the sensitivity of the model to changes of some critical quantities within physiological ranges
The influence of different geometries of matrix/scaffold on the response of a bone and resorbable material mixture with voids
No full textA 2-D dimensional sample made of natural bone tissue and artificial bioresorbable material is numerically investigated in order to study the influence of different geometries of the assemblage of matrix and scaffold. With the specific tools of the Mixture theory we consider the solid matrix with evolving apparent mass densities (rb for bone and rm for material) to describe bone tissue synthesis and resorption when a bio-resorbable material of the kind used in bone reconstruction is present (see e.g. [1, 2, 3]). To take porosity effects in account the adopted model is derived from the Nunziato-Cowin theory developed
for porous solids in which the matrix material is linearly elastic and the interstices are void of material. In detail, to describe the mechanical phenomena which influence the porosity variation we introduce,
following the aforementioned theory [4], an independent kinematic degree of freedom, namely the change in volume fraction from the reference volume fraction, namely
x = (rb+rm)/rMax-(rb R+rmR)/rMax,
with rMax the maximal density without pores. It is well established that exercise results in increased bone mass, while unloading due to immobilization, bedrest, and weightlessness results in bone atrophy.
The strains induced by external loads are sensed by mechanoreceptors, primarily on osteocytes which essentially transduce the mechanical signals into biological signals. These biological signals are able to trigger bone remodeling by directing osteoblast activity and osteoclastic resorption.
[1] T. Lekszycki and F. dell’Isola. A mixture model with evolving mass densities for describing synthesis and resorption phenomena in bones reconstructed with bio-resorbable materials. J. Applied Math and
Mech. (ZAMM), 92:426–444, 2012.
[2] A. Madeo, T. Lekszycki, and F. dell’Isola. A continuum model for the bio-mechanical interactions between living tissue and bio-resorbable graft after bone reconstructive surgery. Comptes Rendus Mécanique, 339:625–640, 2011.
[3] A. Madeo, D. George, T. Lekszycki, M. Nierenberger, and Y. Rémond. A second gradient continuum model accounting for some effects of micro-structure on reconstructed bone remodeling. Comptes
Rendus M ́ecanique, 340:575–589, 2012.
[4] S. C. Cowin and J. W. Nunziato. Linear elastic materials with voids. J. Elasticity, 13:125–147, 1983
Euromech 563 Cisterna di Latina 17-21 March 2014. Generalized continua and their applications to the design of composites and metamaterials. A review of presentations and discussions
No full textIn the present paper, a rational report on Euromech 563, Generalized continua and their applications to the design of composites and metamaterials (Cisterna di Latina 17-21 March 2014), is provided.
The frank and constructive spirit which animated the workshop by dell'Isola et al. (ZAMM 2014; 94(5): 367-372) also characterized Euromech Colloquium 563. All presentations were video-recorded and are freely available online at the address http://www.memocsevents.eu/euromech563/?page_id=1013. The topics treated were selected by the organizers in order to allow a comparison of the available experimental evidence with the predictive capability of current theoretical models. The numerical investigations selected and presented aimed to make more effective the aforementioned comparison. The interested reader will find more details about the colloquium at the dedicated webpage http://www.memocsevents.eu/euromech563. The design and use of advanced materials and structural elements requires an extensive and rigorous process of mathematical modeling. The organizers of Euromech 563, being aware of this need, have chosen as participants renowned and reputed scientists (and some promising young researchers) who all agree on recognizing to mathematical sciences their role of unifying and coordinating tool in the effort for the advance of technology. The Colloquium has indeed surely contributed to the development of more advanced technological possibilities and to the theoretical conception of completely new ones
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