SEMTA. Sociedad Española de Mecánica Teórica y Aplicada

Sociedad Española de
Mecánica Teórica y Aplicada

The analysis of concrete microstructure by X-ray CT scans allow to obtain three-dimensional information on the morphology of the pores and fiber distribution. In this work, it was assessed the effect of the addition of polypropylene (PP) fibers in a heated ultra-high performance fiber reinforced concrete (UHPFRC). To this end, three sets of specimens with identical cementitious materials were manufactured at room temperature (RT) and 300oC: plain concrete (RC), exclusively with steel fibers (DSL), and with steel and PP fibers (DSLPP). It was observed as the addition of PP fibers leads to an increase of the total porosity with respect to the DSL mix, and an increase in the amount of large pores in comparison with RC mix at RT. These effects are beneficial at high temperatures since it was observed as the heating specially affects the small pores and the deleterious effect of melting of the PP fibers is compensated by a lower thermal damage. No significant damage was observed in the matrix of DSLPP mix. Indeed, the mechanical and fracture properties recorded at 300oC for DSLPP mix were higher than RC and DSL mixes due to lower inside pressure at 300oC.  

Soft materials have experienced an increasing interest from both scientific and industrial communities during the last years. This interest has become even stronger with the potential of such materials to mechanically respond to external stimuli. Among these materials, magneto-active hydrogels (MAHs) offer great opportunities for novel applications, especially within the biomedical field. However, the design of these stimuli-responsive materials is rather complex as they combine nonlinear mechanical behaviour, rate dependences, magneto-active responses and solvent diffusion processes. To help the understanding of the magneto-mechanical behaviour of these materials, their design and optimization, this work proposes a general continuum framework to couple magnetics, solvent diffusion and nonlinear mechanics. This framework is specialised to and implemented within the finite element method for 3D problems. Different rate-dependent responses of a free-standing MAH are analysed: (i) the strain rate dependency of the instantaneous response to magnetic fields applied at different rates; (ii) the viscous relaxation mechanisms occurring after the complete application of the magnetic field; and (iii) the long-time responses due to solvent diffusion. In addition, an evaluation of the interplay between magnetic fringing effects and solvent diffusion processes is performed. This work provides a flexible computational framework to model the coupled effects of different physical processes occurring within MAHs and highlights the importance of considering rate dependences. The computational framework has the potential to guide the future design of bioactive scaffolds and drug delivery systems based on MAHs.

Twinning is a mechanism of deformation in which crystals adapt to certain stresses. There are numerous works on twinning in 3D materials, which shows that the presence of twins strongly modifies the mechanical and electronic properties of materials. However, this kind of structure has been barely studied in graphene. In this work, we show that twins may arise spontaneously in graphene layers containing arrays of dislocations and that twinning results in a significant reduction in energy. To achieve this, we first define the harmonic dipoles configurations in graphene by the discrete dislocation theory (DDT). These initial configurations are subsequently relaxed using the software LAMMPS. We verify that the obtained twin configurations satisfy the theoretical twinning relations. Additionally, we show that twin configurations present some characteristic out of plane displacements depending on their geometry, and that they are thermally stable up to high temperatures.

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