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
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
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
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.
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
Determination of in-plane shear strength of unidirectional composite materials using the off-axis three-point flexure and off-axis tensile tests
(SAGE, 2010) Vargas Silva, Gustavo Adolfo; Mujika, Faustino; Ingeniería; Ingeniaritza
The aim of this work is to compare from an experimental point of view the determination of in-plane shear strength of unidirectional composite materials by means of two off-axis tests: three-point flexure and tensile. In the case of the off-axis three-point flexure test, the condition of small displacements and the condition of lift-off between the specimen and the fixture supports have been taken into account. Some considerations regarding stress and displacement fields are presented. The in-plane shear characterization has been performed on a carbon fiber reinforced unidirectional laminate with several fiber orientation angles: 10°, 20°, 30°, and 45°. Test conditions for both off-axis experimental methods, in order to ensure their applicability, are presented. Off-axis flexure test is considered more suitable than off-axis tensile test for the determination of in-plane shear strength.
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
University accreditations and publication of articles on education in Spain
(Taylor & Francis, 2021-07-01) Vargas Silva, Gustavo Adolfo; Barroso-Caro, Alberto; Ingeniería; Ingeniaritza
España lidera en los últimos años, con mucha diferencia, los registros de publicaciones sobre Educación en revistas internacionales indexadas. Los requisitos de acreditación de los cuerpos docentes universitarios incluyen desde hace unos años, las publicaciones sobre educación en revistas indexadas. En el presente trabajo se pone de manifiesto que el liderazgo de España en las publicaciones sobre educación coincide temporalmente con la inclusión de dichos requisitos en las normativas para el acceso a los cuerpos docentes universitarios. Se ha analizado igualmente el número de revistas sobre educación, con sede en España, encontrándose de igual manera incrementos significativos en el número de dichas revistas, en el periodo analizado y encontrándose España en los primeros puestos a nivel mundial, también en este indicador. La principal conclusión del presente estudio revela que los requerimientos sobre publicación en docencia en los procesos de acreditación de cuerpo docentes universitarios en los últimos años han influido de forma significativa en las cifras de publicación en revistas indexadas, así como en el número de revistas indexadas con sede editorial en España.
Open Access
Biomecánica de los árboles: crecimiento, anatomía y morfología
(Instituto de Ecología, A.C., 2019-11-13) Vargas Silva, Gustavo Adolfo; Ingeniería; Ingeniaritza
Los árboles son los seres vivos más grandes y pesados que han poblado la Tierra. Para conseguirlo, cuentan con la madera (un material estructural excepcional) y con un sinnúmero de estrategias de diseño. Este trabajo es una revisión del estado del arte relacionada con las estrategias más importantes de crecimiento, anatomía y morfología que tienen los árboles, destacando conceptos generales relacionados con atributos estructurales que tienen que ver con la biomecánica de las plantas. Asimismo, este artículo resalta las características de los materiales naturales vegetales que poseen una organización jerárquica y que, en su mayoría, son materiales compuestos reforzados con fibras, materiales con estructura celular o ambos, como la madera.