DMMCTE - MMA - Artículos de revista

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Prediction of critical buckling load on open cross-section columns of flax/pla green composites
(MDPI, 2022-11-23) Wang, Liujiao; Puerta Hueso, Sergio; Sánchez Pedroche, David; Santiuste Romero, Carlos; Ministerio de Economía y Competitividad (España)
The present work aims to analyze the buckling behavior of nonlinear elastic columns with different open cross-sections and slenderness ratios to verify the limits of the modified Ludwick law to predict the critical buckling load. The results of the analytical formulation based on the modified Ludwick law are compared with a FEM numerical model using the Marlow hyperelastic behavior and experimental results conducted on flax/PLA specimens with three different open cross-sections. The comparative results show that the numerical predictions agree with the experimental results in all the cases. The FEM model can exactly reproduce the buckling behavior of the C-section columns. However, the prediction errors for the C90 and C180 columns are higher than for the C60 columns. Moreover, the theoretical estimations indicate that the C90 cross-section column is the limit of application of the modified Ludwick law to predict the critical buckling load of nonlinear elastic columns with open cross-sections, and the C180 column is out of the prediction limits. Generally, the numerical and theoretical models underestimated the scattering effects of the predictions because more experimental variables were not considered by the models.
Modelling of woven CFRP plates subjected to oblique high-velocity impact and membrane loads
(Elsevier, 2023-01-01) Carrasco-Baltasar, Daniel; García Castillo, Shirley Kalamis; Iváñez del Pozo, Inés; Navarro Ugena, Carlos; Comunidad de Madrid; Universidad Carlos III de Madrid
In this work, an analytical model was employed to model the perforation of woven plates made of AS4/8552 (carbon/epoxy) laminates exposed to oblique impact and preload in plane. The model assumed six mechanisms for the absorption of the kinetic energy of projectile: the laminate acceleration, elastic deformation of fibres, fibres failure, shear plugging, delamination and matrix cracking. The model was validated with numerical and experimental data from previous works and, was used to determine the influence of an oblique and perpendicular impacts on laminates with and without the in-plane preload.
Experimental analysis of the impact behaviour of sandwich panels with sustainable cores
(Elsevier, 2023-03) Gómez Meisel, Edgar Arturo; Sánchez Sáez, Sonia; Barbero Pozuelo, Enrique; Ministerio de Economía y Competitividad (España)
This paper studies the behaviour of sandwiches subjected to impact loads that result in penetration but not complete perforation. The perforation velocity in panels with two different core materials was determined, and the panel response under complete perforation was assessed using 3D-DIC analysis. The out-of-plane displacements were greater in the sandwich with agglomerated cork due to its lower stiffness. The damage and failure mechanisms that appear in both sandwich configurations were also studied using visual inspection and X-ray computed tomography. An explanation of the physics involved in the impact event is proposed based on the qualitative and quantitative analyses of the damage. It was found that the type of core material affected the failure modes that appeared in the sandwich. Skin delamination and skin/core debonding were important failure mechanisms in sandwich panels with a PET foam core, while in sandwiches with an agglomerated cork core, these mechanisms were not observed.
Experimental analysis at different loading rates of 3D printed polymeric auxetic structure based on cylindrical elements
(Elsevier, 2023-02-01) Varas Doval, David; Pernas Sánchez, Jesús; Fjeldberg, N.; Martin Montal, Jordi; Ministerio de Asuntos Económicos y Transformación Digital (España)
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.
On the experimental validation of Ludwick law to predict critical buckling load of nonlinear elastic columns
(Elsevier, 2023-01-01) Wang, Liujiao; Larriba, Carlos; Santiuste Romero, Carlos
The main contribution of this work is validating the Ludwick law to model the nonlinear mechanical behavior in the prediction of the critical buckling load of nonlinear elastic columns. The critical buckling loads of specimens with different slenderness ratios were obtained by conducting experimental tests on flax/PLA columns with pinned–pinned boundary conditions. The modified Ludwick law parameters were calibrated to fit the stress–strain curve obtained in tensile tests of flax/PLA specimens. The flax/PLA specimens were manufactured using the compression molding method. Moreover, a numerical model considering the Marlow hyperelastic constitutive model was used to predict the critical buckling load. Theoretical predictions using Ludwick law and numerical results were in excellent agreement with experimental data. Results showed that the maximum error of the numerical predictions for critical buckling load is 14.3%, and the maximum error of the theoretical predictions is 8.0%. Additionally, a parametric study was developed to analyze the influence of material's nonlinearity on the numerical prediction accuracy of the Marlow model.
Ánalisis del comportamiento de reparaciones adhesivas sometidas a cargas estáticas
(Asociación Española de Materiales Compuestos (AEMAC), 2019-04-14) Moreno Fernández-Cañadas, Lorena María; Iváñez del Pozo, Inés; Sánchez Sáez, Sonia; Ministerio de Asuntos Económicos y Transformación Digital (España)
Los elementos estructurales de una aeronave fabricados de materiales compuestos son susceptibles de sufrir daños durante su vida en servicio. Debido al alto nivel de integración y al gran tamaño de los componentes estructurales, la sustitución completa de los componentes dañados no siempre es viable, por lo que la reparación puede suponer un gran ahorro tanto desde el punto de vista económico como temporal. Dado que las reparaciones adhesivas pueden ofrecer ciertas ventajas con respecto a las mecánicas, existe un gran interés por aumentar el conocimiento sobre su comportamiento frente a las distintas cargas estáticas a las que va a estar sometido en su vida en servicio, el cúal depende de un gran número de parámetros. En este trabajo se ha desarrollado un modelo numérico de elementos finitos implementado en Abaqus/Explicit que permite analizar la respuesta mecánica de laminados reparados frente a cargas estáticas. Se ha validado experimentalmente, usándose posteriormente para realizar ensayos virtuales de probetas reparadas con parche doble sometidas a tracción estática, analizando los resultados de fuerza máxima y rigidez al variar el tamaño y la topología (rectangulares y circulares).
Analytical solution for plane stress/strain deformation of laminates with matrix cracks
(Elsevier, 2015-11-15) Barbero, Ever José; Cabrera Barbero, Javier; Navarro Ugena, Carlos
An analytical, closed form solution for laminated composites with transverse matrix cracks is presented. The deformation is shown to consist of a homogeneous deformation plus a perturbation near the crack. A methodology is proposed to separate the perturbation from the homogeneous deformation to eliminate ill-conditioning of the eigenvalue/eigenvector problem. While the homogeneous deformation provides a macroscopic measure of damage in terms of reduced stiffness of the laminate, the perturbation solution provides the intralaminar shear near the crack, which is used to calculate the extent of shear lag and the maximum intralaminar shear stress. The equations of elasticity are reduced to one-dimension in a two-step approach, first assuming plane strain (stress) along one of the in-plane dimensions and then introducing approximations through the thickness of the laminate. The intact portion of the laminate is modeled without using a single equivalent laminate. Furthermore, plies are subdivided into multiple sub-plies to increase the accuracy of the representation of intralaminar/interlaminar shear, which is shown to have relevance on the predicted value of maximum interlaminar shear stress and is crucial for the prediction of matrix-crack induced delamination.
A finite element approach to model high-velocity impact on thin woven GFRP plates
(Elsevier Ltd., 2020-08) Alonso San José, Luis; Martínez Hergueta, Francisca; Garcia Gonzalez, Daniel; Navarro Ugena, Carlos; García Castillo, Shirley Kalamis; Teixeira-Dias, Filipe; Universidad Carlos III de Madrid; Comunidad de Madrid
A finite element model to predict the ballistic behaviour of woven GFRP laminates is presented. This finite element model incorporates a new constitutive model based on a continuum damage mechanics approach able to predict the performance of these laminates under high-velocity impacts. The material parameters of the model are identified from the literature and original experiments conducted in this work. The predictive capability of the model is verified against experimental impact tests. Finally, the model is used to analyse the influence of laminate thickness on different energy absorption mechanisms at velocities near the ballistic limit. This analysis allows for the determination of the principal deformation and failure mechanisms governing the perforation process.
Seismic analysis of the zaouiat ait mellal twin tunnels of Agadir motorway (Morocco)
(EDP Sciences, 2020) El Omari, Abdelhay; Chourak, Mimoun; Navarro Ugena, Carlos; Cherif, Seif Eddine; Rougui, Mohamed; Bakali, Hassan; Sánchez Merino, Ángel Luis
Underground structures, such as tunnels, are vital for ensuring all kinds of transportation; and being buried under the surface makes them exposed to soil dynamics. Added to the moderate seismic activity in Morocco, the stability of tunnels is put to the test. This paper examines the interaction between the ZAM (Zaouit Ait Mellal ) twin tunnels between the cities of Marrakesh and Agadir, using the Difference Element Method provided by FLAC 2D software. The acceleration is introduced as the one related to the historic event of El centro 1940 with free-field boundary conditions in the numerical model, with three configurations: tunnel 1 without tunnel 2, tunnel 2 without tunnel 1 and tunnel 1 with tunnel 2. The results of the simulations indicate that the differences values of the maximum displacement, axial force and bending moment on structural elements are very noteworthy from the configuration of the tunnel (single) to the twin tunnels in order to prove the interaction between these latter under seismic loading.
Analysis of damage localization in composite laminates using a discrete damage model
(Elsevier, 2014-11-01) Moure Cuadrado, Marta María; Sánchez Sáez, Sonia; Barbero Pozuelo, Enrique; Barbero, Ever José
Damage localization around stress raisers and material defects in laminated composites is studied using a discrete damage mechanics model augmented by a fiber damage model. The proposed formulation captures the damaging behavior of plates with initial defects and stress raisers such as holes, including damage initiation, evolution, and ultimate fracture of the specimen. It also helps explain the reduction of stress concentration factor when matrix and fiber damage develop. The state variables are the crack density and the fiber failure damage. The formulation is implemented as a material model in Abaqus applicable to laminated composite plates and shells. Material defects are simulated by inserting an initial crack density in a small region of the specimen. Stress raisers are simulated by an open hole. The predictions are shown to be insensitive to mesh density. Further, damage localizes near stress raiser and material defects, thus numerically demonstrating the objectivity of the proposed model. Qualitative and quantitative comparisons with experimental data are presented.
Damage in preloaded glass/vinylester composite panels subjected to high-velocity impacts
(Elsevier, 2014-01-01) García Castillo, Shirley Kalamis; Navarro Ugena, Carlos; Barbero Pozuelo, Enrique
This paper examines the influence of in-plane preloading on the damage of thin composite panels under high-velocity impact loading. The composite was a tape laminate made with a glass-fibre and vinylester matrix. Impact on a preloaded laminate was analysed experimentally, comparing their behaviour with the condition in which the laminate was load-free. Two preload cases representative of actual structures were selected, uniaxial and biaxial load cases. An experimental device was developed to apply the load in two perpendicular directions. This device was combined with a gas gun to carry out impact tests in a broad range of impact velocities. The static preload altered the perforation-threshold velocity and the damage area in the laminate. Decrements of the both variables were detected in the preloaded specimens, both with uniaxial and biaxial loads. The reduction of the damage area was greater for impact velocities close to the perforation-threshold velocity in all the cases analysed.
Numerical analysis of the ballistic behaviour of Kevlar® composite under impact of double-nosed stepped cylindrical projectiles
(SAGE, 2016-01) Rodríguez Millán, Marcos; Moreno Sánchez, Carlos Edgar; Marco Esteban, Miguel; Santiuste Romero, Carlos; Miguélez Garrido, María Henar; Ministerio de Economía y Competitividad (España)
This paper focuses on the numerical analysis of the ballistic performance of Kevlar ®-29 under impact of different doublenosed stepped cylindrical projectiles. Numerical modelling based on finite element method was carried out in order to predict the failure mode of the target as well as the ballistic limit. A detailed analysis of the ballistic limit, failure mode and deformation of the targets due to impact of double-nosed projectiles was developed, discussed and compared with those involved in penetration of single-nosed flat and conical projectiles. Significant influence of the projectile geometry was demonstrated: the lowest ballistic limit was obtained with the conical–conical nose shape projectiles.
Effect of temperature on the low-velocity impact response of environmentally friendly cork sandwich structures
(SAGE, 2022-02-01) Sergi, Claudia; Sarasini, Fabrizio; Russo, Pietro; Vitiello, Libera; Barbero Pozuelo, Enrique; Sánchez Sáez, Sonia; Tirillò, Jacopo
Impact events are common in every-day life and can severely compromise the integrity and reliability of high-performing structures such as sandwich composites that are widespread in different industrial fields. Considering their susceptibility to impact damage and the environmental issues connected with their exploitation of synthetic materials, the present work aims to propose a bio-based sandwich structure with an agglomerated cork core and a flax/basalt intraply fabric as skin reinforcement and to address its main weakness, i.e. its impact response. In-service properties are influenced by temperature, therefore the effect of high (60 °C) and low (−40°C) temperatures on the impact behavior of the proposed structures was investigated and a suitable comparison with traditional (polyvinyl chloride) (PVC) foams was provided. The results highlighted the embrittlement effect of decreasing temperature on the impact resistance of the sole cores and skins and of the overall structures with a reduction in the perforation energy that shifted, in the last case, from 50–60 J at – 40 °C up to more than 180 J at 60 °C. A maleic anhydride coupling agent in the skins hindered fundamental energy dissipation mechanisms such as matrix plasticization, determining a reduction in the perforation threshold of all composites. In particular, neat polypropylene (PP) skins displayed a perforation energy of 20 J higher than compatibilized (PPC) ones at 60 °C, while agglomerated cork sandwich structures at 60 °C were characterized by a perforation threshold higher of at least 50 J.
The effects of water absorption and salt fog exposure on agglomerated cork compressive response
(Springer, 2022-02-01) Sergi, Claudia; Sarasini, Fabrizio; Fiori, Vincenzo; Barbero Pozuelo, Enrique; Sánchez Sáez, Sonia; Tirillò, Jacopo; European Commission
The replacement of synthetic foams with agglomerated cork in sandwich composites can meet the increasing environmental concerns. Its peculiar morphology and chemical composition lead to outstanding dimensional recovery that endorsed a broad investigation of its compressive behavior. The knowledge of neat material response is fundamental to obtain a reliable design dataset, but it is necessary to consider all the environmental factors (water, moisture and sunlight) that significantly modify material mechanical properties. In view of this, the present work investigates the effect of distilled and seawater absorption and salt fog exposure on the compressive behavior of two agglomerated corks with different densities to simulate their potential employment in marine environment. The results were suitably compared with the ones of a traditional PVC foam used as benchmark. A dependence of water uptake and diffusivity on cork density and water type was detected. The less dense cork displayed a water uptake between 36.7 and 46.5% higher than the denser cork, and seawater uptake was between 21.8 and 44.4% lower than distilled water one. Concerning the compressive response, water and fog moisture plasticizing effect in wet conditions and a partial healing after drying due to salt crystal deposits were identified. Water plasticizing effect determined a reduction in the compressive modulus between 35.1 and 37.9% for the lighter cork and between 17.7 and 21% for the denser cork whereas fog moisture induced a reduction between 52 and 74% for the lighter cork and between 24 and 76.1% for the denser one.
Failure maps of biocomposites mechanical joints reinforced with natural fibres
(Elsevier, 2021-07) Estrada Moyano, Rafael Guillermo; Santiuste Romero, Carlos; Barbero Pozuelo, Enrique
Failure maps of mechanical joints have been developed for traditional composites as CFRPs and GFRPs to predict failure modes as a function of joint geometry. Nevertheless, the results of these failure maps cannot be applied to biocomposites reinforced with natural fibres. This paper presents a novel study of the failure modes of biodegradable composite mechanical joints. The influence of joint geometrical parameters, as sample width and the distance of the hole to the free edge, on peak loads and failure modes is analysed for different natural fibres reinforcements. Biodegradable composites were manufactured with PLA matrix reinforced with flax, jute and cotton fibres. A failure map for each material is obtained identifying the regions of typical failure modes of mechanically fastened joints. The comparison of different natural fibres indicates that the fibre strength has a clear influence on the prevention of shear out failure mode but the influence on the net-tension failure is not so clear.
Analytical models for the perforation of thick and thin thickness woven laminates subjected to high-velocity impact
(Elsevier, 2018-06-15) Alonso San José, Luis; Navarro Ugena, Carlos; García Castillo, Shirley Kalamis; Universidad Carlos III de Madrid
This paper deals with the problem of high-velocity impact of a low-mass projectile on woven composite plates. A nondimensional formulation of two analytical models has been developed (one for thin laminates and the other for thick ones). Both analytical models are based on energy conservation and have been applied for the ballistic impact on E-glass woven fibres/polyester composite plates. The results of the models (mainly the ballistic limits) have been compared with experimental results. The value of the ratio target thickness/projectile diameter determining whether the laminate behaves as thick or thin has been established.
Impact response of repaired sandwich structures
(Wiley, 2020-08) Iváñez del Pozo, Inés; Sánchez Sáez, Sonia; García Castillo, Shirley Kalamis; Barbero Pozuelo, Enrique; Amaro, Ana M.; Reis, Paulo N. B.; Ministerio de Economía y Competitividad (España)
The low-velocity impact behavior of repaired sandwich structures with woven carbon/epoxy face-sheets and Nomex honeycomb core is studied experimentally. First, sandwich plates were subjected to ballistic impacts; the damaged area was removed, filled by nano-enhanced resin and covered by a double-external patch. Afterwards, the repaired sandwich plates were impacted at low-velocity. Peak load and absorbed energy were determined for several impact energies and compared with results for non-repaired (intact) sandwich plates. For all impact energies tested, repaired specimens show higher peak load and lower absorbed energy than the intact ones. Additionally, tested sandwich plates were cut transversally in order to observe the resulting damage, concluding that is different in both configurations, and confirming that it is initiated at higher impact energies in repaired structures.
Modelling of carbon/epoxy sandwich panels with agglomerated cork core subjected to impact loads
(Elsevier, 2022-01) Gómez Meisel, Edgar Arturo; Barbero Pozuelo, Enrique; Sánchez Sáez, Sonia; Ministerio de Economía y Competitividad (España)
This work studies the behaviour of sandwich panels made of woven carbon/epoxy face-sheets and agglomerated cork as core material subjected to impacts at intermediate velocities, below the perforation velocity of the panel. Agglomerated cork was selected as an eco-friendly alternative to traditional synthetic polymeric foams. A nonlinear/explicit finite element model was implemented to study the problem. Continuous damage models were used to predict the intra-laminar and inter-laminar damage evolution in the face-sheets. The core behaviour was modelled through a hyperelastic elastomeric foam model with multiaxial failure criteria. The numerical model was validated in two phases. First, the numerical models of face-sheet and core were validated with experimental data from the open literature. Second, the precision of the model of the complete sandwich is assessed with experimental tests carried out in this work. Two cases were studied one when the projectile does not perforate the front face-sheet and another when the projectile does not perforate the back face-sheet. Results show that the numerical model accurately predicts transverse displacements when compared to DIC measurements. Additionally, the model can predict the panel's penetration when comparing with real specimens. Finally, the model provides the damage evolution and the evolution of the different energy absorption mechanisms during the perforation process, something that is not possible to obtain experimentally and provides a valuable tool to understand the phenomenon.
Experimental and numerical analysis of the ballistic response of agglomerated cork and its bio-based sandwich structures
(Elsevier, 2022-01) Sergi, Claudia; Sarasini, Fabrizio; Russo, Pietro; Vitiello, Libera; Barbero Pozuelo, Enrique; Sánchez Sáez, Sonia; Tirillò, Jacopo
Considering the susceptibility of sandwich structures to impact events and the increasing environmental awareness due to pollution, the present work provides a thorough understanding of the ballistic impact behavior of agglomerated cork and of the resulting green sandwich structures produced with polypropylene (PP) skins reinforced with a flax/basalt intraply hybrid fabric. The effect of density on the agglomerated cork response was evaluated (NL10 ρ = 0.14 g/cm3, NL20 ρ = 0.20 g/cm3 and NL25 ρ = 0.25 g/cm3) and a comparison with commercial polyvinyl(chloride) foams was provided (HP130 ρ = 0.13 g/cm3, HP200 ρ = 0.20 g/cm3 and HP250 ρ = 0.25 g/cm3). The effect of a maleic anhydride coupling agent on the mechanical properties of the skins and of the overall sandwich structures was also investigated. The results highlighted a compromising effect of the weak interface between cork granules and polymeric binder on the impact resistance of the agglomerated cork, but a clear improvement of its performance was observed when embedded as core material between the two skins. Indeed, the two classes of sandwich structures produced with neat PP skins and with the two cores with the same density, i.e. agglomerated cork NL10 and PVC foam HP130, displayed the same ballistic limit of 171 m/s confirming that cork integration in the overall structures allows to approach PVC foam performance. The high-velocity impact response of one agglomerated cork (NL25) and one PVC foam (HP130) was also subjected to finite element analysis employing the CRUSHABLE FOAM model available in ABAQUS obtaining a good fitting with the experimental data.
Analysis of the influence of ply-orientation in delamination progression in composites laminates using the Serial/Parallel Mixing Theory
(Elsevier, 2021-07-28) Solís Fajardo, Alberto; Barbero Pozuelo, Enrique; Sánchez Sáez, Sonia; Ministerio de Economía y Competitividad (España)
In this work, an analysis on the influence of fibre-orientation in the progression of delamination was carried out. The study was focused on a cracked beam according to an End Notch Flexure test configuration. The Serial/Parallel Mixing Theory was used as the composite constitutive law along with a continuum damage model to simulate delamination. This mathematical approach was implemented in a custom-made FEM code and applied to model the delamination progression. The model was validated with two sets of experimental results from the literature involving 0 degrees fibre-oriented laminates. After validation, a beam made of plies oriented between 0 degrees and 90 degrees was analysed. The model predicts the loss of stiffness and strength due to the increment of fibre angle. In addition, the stress concentration phenomenon at the crack tip and delamination onset was properly represented. The difference observed in the progression of delamination along the width of the beam highlights the need for a three-dimensional representation to model fibre-oriented beams.

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