Caracterización de las Propiedades Dinámicas de la Seda de Araña

El término Biomimética se ha hecho común en los medios científicos, se refiere al trabajo de diversos científicos (ingenieros, químicos, físicos, biólogos, etc.) que tratan de copiar los procesos biológicos y aplicarlos en distintas áreas tecnológicas y científicas. En este campo científico, uno de los productos naturales que llama más la atención es la telaraña. Numerosos científicos en todo el mundo tratan de copiar las propiedades de la seda que produce la araña, y lo más interesante es que hasta intentan reproducir el método que usan las arañas para fabricar la seda De la bibliografía consultada, se desprende la importancia de la seda en la vida de las arañas, pues toda actividad que realizan tiene que ver de alguna manera con este elemento. Uno de estos elementos es la tela de araña orbicular, que representa el objeto principal para la supervivencia de la araña y su especie. Las investigaciones realizadas en esta línea nos proporcionan información sobre sus magníficas propiedades mecánicas como de resistencia, elasticidad y tenacidad del hilo de seguridad (seda MA) segregada por una araña de la especie Argiope Argentata. El enfoque de la presente tesis se realiza desde una perspectiva analítica-experimental, tomando a la tela de araña como una clase especial de sistemas pretensados, llamados Tensegrity Structures. Se desarrolla un modelo conceptual que describe en forma aproximada el comportamiento dinámico de una estructura hecha de seda MA. Haciendo uso de las técnicas experimentales de vibraciones libres se realizan los ensayos experimentales. La evaluación de los resultados analíticos y experimentales reflejan claramente que la función principal de la tela de araña es la de convertir energía cinética en energía de deformación y primordialmente en energía de disipación, el cual se efectúa gracias a las propiedades viscoelásticas de la seda. La araña en forma instintiva recurre a la ayuda del aire (como elemento disipador) para el buen funcionamiento de la tela de araña al momento de la captura de las presas, disipándose el 99% de la energía total en los tres primeros ciclos de oscilación de la tela de araña luego del impacto de la presa. ABSTRACT The term Biomimetic has become a very common word in the scientific world to describe the reproduction of the biological processes and its application in the different technogycal and scientific areas. One of the most notably natural product of this field is the Spiderweb. In the present days, many scientists of the world are active working in the reproduction of the proprieties of the Spiderweb. Most interesting even more, is the attempt to reproduce the process of the production of the Spiderweb by the spider. Most of the bibliography references deals whit the importance of the Spiderweb silk in the life of the spiders and the orbicular Spiderweb represents the spider survival and of the species. The research conducted in this field provide information about the excellent mechanical proprieties such us strength, elasticity and tenacity of the safety fiber (silk MA Drag-line) segregated by a spider of the Argiope Argentata species. The present work is oriented to an analytical and experimental study considering the Spiderweb as a special class of pre-stressed systems called Tensegrity (tensional integrity) structures. A conceptual model maked up by a cord und a point mass has been developed. This model approximates the dynamics performance of the structure made of the silk MA. The evaluation of the analytical and experimental results clear described that the main function of the Spiderweb is the transformation of the kinetic energy in deformation energy, and mainly in dissipation energy thank to the viscoelastic proprieties of the Spiderweb. With the help of the Spiderweb, the spider instinctively resorts to the help of the surroundings air as a dissipation element. This permits to dissipative the 99% of the total energy during the three first oscillations cycles of the web after the impact of the victim.

Mechanical behavior and deformation micromechanisms of polypropylene nonwoven fabrics as a function of temperature and strain rate

The mechanical behavior and the deformation and failure micromechanisms of a thermally-bonded polypropylene nonwoven fabric were studied as a function of temperature and strain rate. Mechanical tests were carried out from 248 K (below the glass transition temperature) up to 383 K at strain rates in the range ≈10−3 s−1 to 10−1 s−1. In addition, individual fibers extracted from the nonwoven fabric were tested under the same conditions. Micromechanisms of deformation and failure at the fiber level were ascertained by means of mechanical tests within the scanning electron microscope while the strain distribution at the macroscopic level upon loading was determined by means of digital image correlation. It was found that the nonwoven behavior was mainly controlled by the properties of the fibers and of the interfiber bonds. Fiber properties determined the nonlinear behavior before the peak load while the interfiber bonds controlled the localization of damage after the peak load. The influence of these properties on the strength, ductility and energy absorbed during deformation is discussed from the experimental observations.

A gradient-enhanced large-deformation continuum damage model for fibre-reinforced materials

A non-local gradient-based damage formulation within a geometrically non-linear setting is presented. The hyperelastic constitutive response at local material point level is governed by a strain energy which is additively composed of an isotropic matrix and of an anisotropic fibre-reinforced material, respectively. The inelastic constitutive response is governed by a scalar [1–d]-type damage formulation, where only the anisotropic elastic part is assumed to be affected by the damage. Following the concept in Dimitrijević and Hackl [28], the local free energy function is enhanced by a gradient-term. This term essentially contains the gradient of the non-local damage variable which, itself, is introduced as an additional independent variable. In order to guarantee the equivalence between the local and non-local damage variable, a penalisation term is incorporated within the free energy function. Based on the principle of minimum total potential energy, a coupled system of Euler–Lagrange equations, i.e., the balance of linear momentum and the balance of the non-local damage field, is obtained and solved in weak form. The resulting coupled, highly non-linear system of equations is symmetric and can conveniently be solved by a standard incremental-iterative Newton–Raphson-type solution scheme. Several three-dimensional displacement- and force-driven boundary value problems—partially motivated by biomechanical application—highlight the mesh-objective characteristics and constitutive properties of the model and illustratively underline the capabilities of the formulation proposed