Simulación numérica del impacto de un sólido contra el agua

El objetivo principal de este proyecto de n de carrera es el estudio, mediante el método de elementos nitos (MEF), del impacto de un solido contra el agua, para su posterior uso en el estudio del ditching. Por lo que los datos que se obtendrán serán comparados con los estudios experimentales existentes, de tal manera que clarifiquen cual es la mejor manera de simular el impacto, variando diferentes parámetros, como son el método de integración y la densidad de nodos, del diseño de la malla del agua. Una vez obtenidos los parámetros que definen el mejor diseño del mallado del agua, se aplicarán a la simulación del impacto de un modelo de avión, simulación que introduce como nueva variable de estudio la velocidad tangencial al agua, con el fin estudiar el comportamiento del mallado resultante del estudio del impacto vertical, ante esta nueva variable, para su aplicación al estudio del ditching. El uso del método de elementos finitos para el estudio del ditching es viable, dado que los resultados que se han obtenido en el estudio del impacto de la cuña contra el agua son verdaderamente fidedignos tanto en deceleración como en presiones. Las condiciones mas influyentes para el correcto diseño de una malla que simule el agua en estas condiciones son: - Los métodos de integración - Las condiciones de contorno que se aplican al mallado de agua - La densidad de nodos en la zona de impacto Es posible obtener resultados correctos utilizando los métodos de integración: Lagrangiano y ALEIngeniería Industria

Experimental Investigation on the Low Velocity Impact Response of Fibre Foam Metal Laminates

The combination of fibre metal laminates (FML) and sandwich structures can significantly increase the performance under impact of FMLs. The goal of this work was to create a material that will combine the superior properties of FMLs and foam sandwich structures in terms of the impact resistance and simultaneously have lower density and fewer disadvantages related to the manufacturing. An extensive impact testing campaign has been done using conventional fibre metal laminates (carbon- and glass-based) and in the proposed fibre foam metal laminates to assess and compare their behaviour. The main difference was observed in the energy absorption mechanisms. The dominant failure mechanism for fibre foam laminates is the formation of delaminations and matrix cracks while in the conventional fibre metal laminate the main failure mode is fibre cracking due to high local stress concentrations. The reduction in the fibre cracking leads to a better after-impact resistance of this type of structure improving the safety of the structures manufactured with these materialsThis research was financed in the framework of the project Lublin University of Technology–Regional Excellence Initiative, funded by the Polish Ministry of Science and Higher Education, grant number 030/RID/2018/19

Experimental characterization framework for SLA additive manufacturing materials

This article belongs to the Special Issue Mechanical Performance of Polymeric Parts Obtained by Additive Manufacturing.Additive manufacturing (AM) is driving a change in the industry not only regarding prototyping but due to the ease of including printed parts in final designs. Engineers and designers can go deeper into optimization and improvements of their designs without drawbacks of long manufacturing times. However, some drawbacks such as the limited available materials or uncertainty about mechanical properties and anisotropic behavior of 3D printed parts prevent use in large-scale production. To gain knowledge and confidence about printed materials it is necessary to know how they behave under different stress states and strain-rate regimes, and how some of the printing parameters may affect them. The present work proposes an experimental methodology framework to study and characterize materials printed by stereolithography (SLA) to clarify certain aspects that must be taken into account to broaden the use of this kind of material. To this end, tensile and compression tests at different strain rates were carried out. To study the influence of certain printing parameters on the printed material behavior, samples with different printing angles (θ = [0–90]) and different printing resolution (layer height of 50 and 100 µm) were tested. In addition, the effects of curing time and temperature were also studied. The testing specimens were manufactured in the non-professional SLA machine Form 2 from Formlabs® using resin called Durable. Nevertheless, the proposed experimental methodology could be extended to any other resin.Ministerio de Asuntos Económicos y Transformación Digital, Gobierno de España grant number DPI2017-85073-R, and Vicerrectorado de Política Científica UC3M (Projects 2013/00413/003 and 2014/00006/003)

Experimental analysis at different loading rates of 3D printed polymeric auxetic structure based on cylindrical elements

This work proposes the experimental study of an auxetic polymeric structure manufactured by 3D printing (SLA). The structure is composed by a re-entrant unit cell based on cylindrical elements not previously studied. The effect of the number and size/scale of the unit cells used in the specimens, subjected to both static and dynamic loads, has been analysed. The results show how the studied variables affect the behaviour of the structure in terms of stress and strain and that the dimensions of the cylindrical elements, as well as the contact between them, could help to modify the stiffness structure as required. The tests performed have allowed to understand the sequence of physical phenomena that appears at different strain rates and how they affect the response of the structure. The results obtained may contribute to the knowledge of both polymeric auxetic structures and the use of additive manufacturing methods for such structures.This research was funded by Ministerio de Asuntos Económicos y Transformación Digital, Gobierno de España grant number DPI2017-85073-R, and Vicerrectorado de Política Científica UC3M (Projects 2013/00413/003 and 2014/00006/003)

Cork Core Sandwich Plates for Blast Protection

This article belongs to the Special Issue Armour and Protection SystemsA numerical model is developed and validated to analyse the performance of aluminium skin and agglomerated cork core sandwich plates subjected to blast loads. Two numerical approaches are used and thoroughly compared to generate the blast loading: an Arbitrary-Lagrangian–Eulerian approach and the Load Blast Enhanced method. Both of the models are validated by comparing the numerical results with experimental observations. A detailed analysis of the sandwich behaviour is done for both approaches showing small differences regarding the mechanical response of the sandwich structure. The results obtained from the numerical models uncover the specific energy absorption mechanisms happening within the sandwich plate components. A new core topology is proposed, based on these results, which maximises the energy absorption capacity of the plate, keeping the areal density unchanged. A wavy agglomerated cork core is proposed and the effects of different geometrical parameters on the energy absorption are thoroughly analysed and discussed. The proposed optimised plate configuration shows an increase in the total absorbed energy of close to 40% relative to a reference case with the same areal density. The adopted optimisation methodology can be applied to alternative configurations to increase the performance of sandwich structures under blast events.This research was funded by Ministerio de Economía y Competitividad, Gobierno de España grant number DPI2017-85073-R, and Universidad Carlos III of Madrid grant numbers 2013/00413/003 and 2014/00006/002. And the travel expenses were funded by Universidad Carlos III de Madrid grant number Programa propio de investigación-Convocatoria 2014 movilidad

Experimental analysis of normal and oblique high velocity impacts on carbon/epoxy tape laminates

In this work, the effect of high velocity impacts on carbon/epoxy tape quasi-isotropic laminates is studied. Experimental test were carried out at two different impact angles and in a wide range of velocities (from 80 to 490 m/s). Both parameters, the residual velocity and the damaged area, are used to evaluate the effect of the kinetic energy of the projectile on the laminate response. In addition it has been proposed a simplified analytical model which allows to identify the different energy absorbtion mechanisms and predict the residual velocity of the projectile. Finally the energy absorbed by the laminate during the impact is studied.This research was done with the financial support of the Spanish Ministry of Ed- ucation under Project reference DPI2010-15123 and of the Region of Madrid and University Carlos III of Madrid under Project reference CCG10-UC3M/DPI-4694

Analysis of high velocity impacts of steel cylinders on thin carbon/epoxy woven laminates

In this work a numerical model was developed to predict the behavior of thin woven laminates under high velocity impacts. The material model, implemented in a user subroutine to be used with a commercial FE code, takes into account different failure mechanisms. The inter-lamina failure prediction is achieved by means of the use of cohesive elements. Finally, in order to validate the model, experimental tests were accomplished in a wide range of velocities from 100 to 400 m/s. Residual velocity of the projectile and damaged area of the laminates are compared with the numerical results. Once the model is validated, a further investigation has been made in order to analyze the influence of projectile slenderness on the laminate response.This research was done with the ¯nancial support of the Spanish Ministry of Education under Project reference DPI2010-15123 and of the Region of Madrid and University Carlos III of Madrid under Project reference CCG10-UC3M/DPI-4694

On the influence of filling level in CFRP aircraft fuel tank subjected to high velocity impacts

In this work, the process of impact that takes place in a partially filled tank is analyzed, performing a numerical simulation, in order to understand the response of the composite laminated structure. The commercial finite-element code LS-DYNA v.R7 has been used to simulate an Hydrodynamic RAM event created by a steel spherical projectile impacting a partially water-filled woven CFRP square tube using two different approaches (MM-ALE and SPH). The intralaminar and interlaminar damage have been taken into account implementing an user subroutine and by means of a cohesive interaction, respectively. Once the numerical model is validated using available experimental data, the effect of the filling level in the failure of the tank is analyzed in detail taking advantage of the information provided by the numerical model. (C) 2013 Elsevier Ltd. All rights reserved.This research was done with the financial support of the Spanish Ministry of Education under Project reference DPI2010-15123 and of the Region of Madrid and University Carlos III of Madrid under Project reference CCG10-UC3M/DPI-4694

Analysis of Ice Impact Process at High Velocity

In this work the high velocity impact of ice spheres is analysed. An experimental methodology has been developed in order to launch, at high velocity, ice spheres of different diameters against a load cell to measure the force induced during the impact. An analysis of the influence of the ice mass on the impact force is accomplished using the contact force which was calculated by means of an inverse problem technique. Finally a study of the impact phenomenon has been performed using the videos obtained with a high speed camera.This research was done with the financial support of the Spanish Ministry of Education under Project reference DPI2013-41094-R

Numerical analysis of CFRP fluid-filled tubes subjected to high-velocity impact

In recent years, vulnerability against high-velocity impact loads has become an increasingly critical issue in the design of composite aerospace structures. The effects of Hydrodynamic Ram (HRAM), a phenomenon that occurs when a high-energy object penetrates a fluid-filled container, are of particular concern in the design of wing fuel tanks for aircraft because it has been identified as one of the important factors in aircraft vulnerability. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure. In the present paper, the commercial finite-element code ABAQUS/Explicit has been used to simulate an HRAM event due to the impact of a steel spherical projectile into a water-filled woven CFRP square tube. In order to simulate the fluid-structure interaction, the Coupled Eulerian Lagrangian (CEL) approach is used. Experimental tests which indicate the pressure at different points of the fluid, strains of the walls and cavity evolution for different impact velocities are compared with the numerical results in order to assess the validity and accuracy of CEL technique in reproducing such a complex phenomenon. Also, several numerical impacts at different initial projectile velocities are performed to study its influence in the HRAM phenomenon.This research was done with the fianancial support of the Spanish Ministry of Education under Project reference DPI2010-15123 and of the Region of Madrid and University Carlos III of Madrid under Project reference CCG10-UC3M/DPI-4694. The authors would like also to acknowledge the Center for the Development of Industrial Technology (CDTI) of Spain and to the company AERNNOVA Aerospace for the financial support for this research. We wish to express sincere gratitude to Mr. S. Puerta for his valuable help during the experimental testing