Open Access
Greenstick fracture in composite pultruded rods
(Elsevier, 2017) Vargas Silva, Gustavo Adolfo; Mujika, Faustino; Ingeniería; Ingeniaritza
The paper analyses the greenstick fracture mode on anisotropic beams subjected to flexural loading. This fracture mode can be seen in plant branches, young mammal bones or reinforced plastic rods. Two analytical models have been studied: a straight beam model and a uniform curved beam model. Circumferential normal stress distribution has been determined considering the classical beam theory, and radial and shear stresses have been predicted by using the Airy's stress function. Experimental work has been implemented on initially straight pultruded rods with longitudinally oriented fibres. Three and four-point bending tests adopting several span-to-diameter ratios have been performed. Experimental conditions that promote a greenstick fracture mode in composite pultruded rods have been considered.
Open Access
Analysis of the validity of the three-point off-axis bending method
(Elsevier, 2015-09-01) Cabrero, José Manuel; Vargas Silva, Gustavo Adolfo; Ingeniería; Ingeniaritza
Several methods for determining in-plane shear properties of anisotropic materials (i.e. fibre reinforced composite materials and natural wood) based on flexural loading have been proposed. One of those methods is the off-axis flexural test that considers unidirectional composite materials subject to three-point bending loading. As a result of the anisotropic behaviour, unidirectional off-axis laminates subjected to flexure present a bending¿twisting coupling that may cause, in the case of 3-point bending loading, a lift-off of the specimen on the fixture supports. Such specimen lift-off has been considered one of the critical features to be considered on the mentioned experimental method. Besides geometrical parameters, material elastic constants, as longitudinal, transversal and shear elastic moduli, influence the validity to use this method for characterising in-plane shear properties. On that sense, an analytical approach for studying the material conditions for which the application of the off-axis 3P-B test is adequate is presente
Open Access
In-plane shear behaviour of multiscale hybrid composites based on multiwall carbon nanotubes and long carbon fibres
(SAGE, 2015) Vargas Silva, Gustavo Adolfo; Ramos, José Ángel; Gracia, Juan de; Ibarretxe, Julen; Mujika, Faustino; Ingeniería; Ingeniaritza
Both in-plane shear modulus and in-plane shear strength of multiscale hybrid composites have been studied. Carbon fibre-based laminates have been fabricated including functionalized multiwall carbon nanotubes by means of solvent spraying method and hot compression process. Mechanical in-plane shear characterization has been carried out using off-axis three-point flexure test. Fibre volume fraction of multiscale hybrid composites has been determined through thermogravimetric analysis and fracture surfaces after testing have been imaged by scanning electron microscopy. Results reveal that the inclusion of functionalized multiwall carbon nanotubes on laminates has a small influence on in-plane shear modulus, although it increases up to 15% of the in-plane shear strength. Multiwall carbon nanotube functionalization improves shear stress transmission between matrix and carbon nanotubes, which represents a reinforcement effect responsible for the increase in in-plane shear strength. Scanning electron micrographs have confirmed in-plane shear tests results.
Open Access
Biomimetic economy: human ecological-economic systems emulating natural ecological systems
(Emerald, 2019) Tamayo, U.; Vargas Silva, Gustavo Adolfo; Ingeniería; Ingeniaritza
Open Access
Estrategias mecánicas de las plantas arborescentes: enseñanzas estructurales de los árboles
(Universidad de Tarapacá, 2017-09-01) Vargas Silva, Gustavo Adolfo; Ingeniería; Ingeniaritza
Los árboles son los seres vivos más grandes que jamás han poblado la Tierra, pudiendo tener más de cien metros de altura, masas de varios miles de toneladas y alcanzar edades de varios miles de años. Para conseguirlo, entre otros condicionantes funcionales, los árboles deben hacer frente a todo tipo de cargas mecánicas. Así, para cumplir con estos requisitos estructurales, los árboles cuentan con la madera, un material excepcional desde un punto de vista mecánico, y ofrecen un sinnúmero de estrategias de diseño que van desde garantizar la estabilidad estructural hasta ofrecer un adecuado factor de seguridad empleando una cantidad mínima de material, con la consecuente eficiencia metabólica. De esta forma, este trabajo presenta las estrategias más importantes de crecimiento, anatomía y morfología que emplean las principales familias de plantas arborescentes, las gimnospermas y las angiospermas, destacando especialmente las características de los materiales naturales vegetales, que poseen una organización jerárquica y que, en la mayoría de los casos, son materiales compuestos reforzados con fibras, materiales con estructura celular, o ambos, como la madera.
Open Access
Fiber optic and KNX sensors network for remote monitoring a new building cladding system
(Elsevier, 2013) Unzu Ripoll, Ruth; Nazábal Urriza, Juan Antonio; Vargas Silva, Gustavo Adolfo; Hernández, Rufino; Fernández Valdivielso, Carlos; Urriza Ezcurra, Nuria; Galarza Galarza, Marko; López-Amo Sáinz, Manuel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC
Open Access
Mode-displacement method for structural dynamic analysis of bio-inspired structures: a palm-tree stem subject to wind effects
(Taylor & Francis, 2022) Plaza Puértolas, Aitor; Vargas Silva, Gustavo Adolfo; Iriarte Goñi, Xabier; Ros Ganuza, Javier; Ingeniería; Ingeniaritza
Biological materials (orthotropic materials), like wood, can offer good mechanical properties with a minimum amount of material, making their internal structure the suitable one to be applied on bio-inspired structures. The knowledge of the exceptional structural performance of palm trees, and specially its response to different loading conditions, provides useful information when lightweight structures with high slenderness ratio are desired. Recent researches focused on the analysis of palm trees subject to static loading conditions, ignoring the fluctuating nature of the wind speed. The purpose of this study is to simulate in a computational efficient way the effect of dynamic loading conditions applied on palm trees. Using the mode displacement method, the number of degrees of freedom of a dynamic finite element analysis can be drastically reduced with a minimal loss of accuracy. It was applied to simulate the behavior of structures comprised of an orthotropic material subject to a stochastic dynamic load. The influence of the number of selected degrees of freedom has also been studied. In addition, an exponential integration method is proposed to perform the time integration procedure. The results obtained show that a properly reduced model suitably represents the full finite element model without any appreciable loss of accuracy; it is also shown that computational cost can be drastically reduced. This method could give an appropriate computational representation of the behavior of orthotropic structures, and it could be used for studying more complex bio-inspired structures.
Open Access
Giant stress-impedance (GSI) sensor for diameter evaluation incylindrical elements
(Elsevier, 2018-01-01) Beato López, Juan Jesús; Vargas Silva, Gustavo Adolfo; Pérez de Landazábal Berganzo, José Ignacio; Gómez Polo, Cristina; Ingeniería; Ingeniaritza; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Gobierno de Navarra / Nafarroako Gobernua
In this work, a magnetoelastic sensor to detect the micrometer diameter variations of cylindrical elements is analyzed. A nearly zero magnetostrictive amorphous ribbon with nominal composition (Co₀.₉₃Fe₀․₀₇)₇₅Si₁₂․₅B₁₂․₅ was selected as sensor nucleus. The sensor, based on Giant Stress-Impedance (GSI), is attached (glued) along the external perimeter of the cylindrical element. Changes in the cylindrical diameter, DM, induce effective tensile stresses, S, on the ribbon, giving rise to sensitive changes in the high frequency impedance, Z. The sensor response is analyzed in terms of the relationship between the induced strains and the diameter variations, where the effect of geometrical factors (cylinder diameter and sample length) is taken into account. The results indicate that although the maximum GSI ratio depends on the pre-induced bending stresses associated to the cylindrical configuration, the sample length plays the dominant role in the sensor sensitivity. The proposed device enables to monitor the micrometric diameter variation in cylindrical elements, with a maximum strain gauge factor (GF≈-80) for low induced strains.
Open Access
Determination of in-plane shear properties by three-point flexure test of ±45° anti-symmetric laminates
(Elsevier, 2011) Vargas Silva, Gustavo Adolfo; Mujika, Faustino; Ingeniería; Ingeniaritza
The aim of this work is to propose a new method for determining both the in-plane shear modulus and the in-plane shear strength of composite materials by using three-point flexure tests on [±45] angle-ply laminates. Symmetric and anti-symmetric configurations have been analysed by Classical Laminated Plate Theory. The anti-symmetric configuration has been considered more suitable than the symmetric one, due to the absence of bending/twisting coupling effects. Three-point bending tests have been performed on [±45] anti-symmetric laminates of AS4/8552 carbon/epoxy material. Experimental results obtained by flexure tests in anti-symmetric laminates agree with the values attained by tensile tests on symmetric laminates, and with values reported in literature. Experimental conditions for determining in-plane shear properties by using the anti-symmetric three-point bending method are recommended.
Open Access
Analysis of in-plane and out-of-plane thermo-mechanical stresses in un-symmetric cross-ply curved laminated strips
(SAGE, 2009) Vargas Silva, Gustavo Adolfo; Arrese, A.; Carbajal, N.; Mujika, Faustino; Ingeniería; Ingeniaritza
A new approach for determining in-plane and out-of-plane stresses due to thermal and mechanical loading, in un-symmetric [0n/90 m] cross-ply curved laminated strips is presented in this work. This approach can also be applicable to bi-modulus curved laminated strips. Predictions of curvatures, displacements, and stresses based on the superposition principle are carried out. In-plane stresses are calculated considering classical beam theory. In addition, out-of-plane stresses are predicted by using the Airy¿s stress function in polar coordinates. The new approach satisfies the continuity conditions at the interface between 0° and 90° layers. Results show that in-plane and out-of-plane stresses are particularly sensitive to the thickness ratio and to geometric conditions. Finally, thermo-mechanical predictions have revealed that out-of-plane stresses are much lesser than in-plane stresses for initially flat laminates. For laminates with high imposed curvatures out-of-plane stresses are high, leading to delamination failure.

Vargas Silva, Gustavo Adolfo

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