DMMCTE - DEL - Artículos de revistas

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Lifetime optimization of solar central receivers via linear actuators
(Elsevier, 2022-07-15) Moreno Moreno, Javier Antonio; Montoya Sancha, Andrés; López Puente, Jorge; Santana Santana, Domingo José; Ministerio de Economía y Competitividad (España)
The receiver is a key component of concentrated solar power plants, whose operation can be interrupted by its early failure. In this research, a novel approach to the enhancement of solar receiver lifetime is presented, studying the use of linear actuators in the longitudinal supports of the tubes to induce forced displacements, reducing thermal stresses. Existing analytical models have been improved and joined together, in order to be implemented in a genetic algorithm to optimize the solar receiver lifetime. In a first approach, the maximum equivalent elastic stress, produced by the thermal gradients over the receiver, has been minimized. This approach reduces the maximum thermoelastic stress up to a 9.5%, and increases the lifetime of the receiver to an 8% when a forced displacement of 100 mm (1% of the tube length) is considered. When the rupture time due to creep is optimized, with the same forced displacement of 100 mm, the tube lifetime is enhanced up to a 25%. Small forced displacements (0.1% of the tube length) may lead to a lifetime improvement up to 6%. The small amount of force necessary to carry out the forced displacement of the supports makes feasible the implementation of linear actuators in future solar power plants.
Longitudinal supports shape influence on deflection and stresses in solar receiver tubes
(European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ), 2022-09) Montoya Sancha, Andrés; López Puente, Jorge; Santana Santana, Domingo José; Ministerio de Ciencia e Innovación (España)
Longitudinal supports have a key role in solar central receivers, preventing tubes from excessive deflection. In this work, its influence on tube deflection and thermo-mechanical stresses has been studied. In exiting literature, the longitudinal supports are not modelled when the behaviour of solar receiver tubes is studied. In this research, they have been considered developing numerical models using a finite element analysis software. To carry out the analysis, a new geometry of the metal sheet attached to the receiver tubes has been proposed. With this new shape, different cases have been studied, varying the separation between supports and their size to study its impact on stress and deflection in the tubes. Results have shown that extremely rigid supports may induce additional stress in the receiver tube. With the geometry considered in this research, supports do not cause additional mechanical stress in tubes. Small supports are preferred to bigger ones due to the stresses arisen in the own support.
Experimental Investigation on the Low Velocity Impact Response of Fibre Foam Metal Laminates
(MDPI, 2021-10-01) Jakubczak, Patryk; Drozdziel, Magda; Podolak, Piotr; Pernas Sánchez, Jesús
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 materials
High-velocity ice impact damage quantification in composite laminates using a frequency domain-based correlation approach
(Elsevier, 2021-01-15) Pérez, Marco A.; Pernas Sánchez, Jesús; Artero Guerrero, José Alfonso; Serra López, Roger; Ministerio de Economía y Competitividad (España)
This paper investigates the feasibility of using a novel domain-based correlation approach derived from the complex frequency domain assurance criterion (CFDAC) for the detection and quantification of impact damage in composite laminates. The CFDAC is essentially a complex-valued two-dimensional indicator of the covariance between two sets of frequency response functions for each pair of spectral lines corresponding to vibration-response of pristine and damage states. The study focuses on damage induced by high-velocity ice impacts on carbon fiber laminated plates. The experimental results demonstrate that the proposed methodology correctly identifies the level of induced damage via a user-independent scalar damage indicator. Therefore, this approach has potential use as a damage indicator, which could be adapted as a structural assessment non-destructive method. This research aims to contribute to the further development of functional, autonomous, and reliable structural health monitoring systems for composite structures based on spectral-domain indices.
Morphological study of damage evolution in woven-laminates subjected to high-velocity impact
(Taylor & Francis, 2019-11-20) Gil Alba, Raúl; Alonso, Luis; Navarro Ugena, Carlos; García Castillo, Shirley Kalamis
The aim of this experimental work was to study the evolution of damage in woven E-glass fiber/polyester laminates of four different thicknesses. After being impacted, these plates were inspected by nondestructive inspection techniques: ultrasound by C-Scan and B-Scan and visual inspection in order to confirm the qualitative and quantitative results. The damage presented an opening cone shape towards the rear face of thin laminates. On the other hand, two different opening cones of delamination grew towards the front and rear faces after a certain thickness in thick laminates.
Numerical model of solar external receiver tubes: Influence of mechanical boundary conditions and temperature variation in thermoelastic stresses
(Elsevier, 2018-11-01) Montoya Sancha, Andrés; Rodríguez Sánchez, María de los Reyes; López Puente, Jorge; Santana Santana, Domingo José; Ministerio de Economía y Competitividad (España)
Failure in solar external receivers is mainly originated from the thermal stress, caused by the high non-uniform transient solar flux. The heat-up and cooldown of tube receivers in daily cycles produce low-cycle fatigue that limits the lifetime of tubes. The corrosion of tube materials produced by incompatibility between the decomposed heat transfer fluid and tube material may increase this issue. The temperature spatial distribution in these tubes has strong variations in radial, circumferential, and axial directions. The stress field, produced by the temperature gradients, has been commonly analyzed using bidimensional models in isolated tube cross sections, without taking into account the axial temperature variation, the mechanical boundary conditions, and the temperature-dependent thermomechanical properties. In this work, a three-dimensional finite element model has been developed in order to calculate the stress field distribution, without performing any geometrical simplification. In addition, appropriate mechanical boundary conditions have been imposed in order to adequately simulate the tube behavior. Besides, radial, circumferential and axial temperature variations have been studied separately to analyze how each of them influences the maximum stress distribution. This 3D modelhas been compared with analytical solutions for the two-dimensional thermal stress problem incircular hollow cylinders. The results show that the boundary conditions have a significant effect on the tube stresses, increasing the axial stress component and therefore the equivalent stress. The analysis of each of the temperature variations showed that the circumferential variationtemperature is the one that produces most of the stress, since it tries to strongly bend the tube, which is impeded by the boundary conditions. The results also present that 2D models are not capable of obtaining the correct stress distribution along the tube, since they are not taking into account the lo
Experimental characterization framework for SLA additive manufacturing materials
(MDPI, 2021-04-01) Martin Montal, Jordi; Pernas Sánchez, Jesús; Varas Doval, David; Ministerio de Ciencia e Innovación (España)
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.
Model updating of uncertain parameters of carbon/epoxy composite plates using digital image correlation for full-field vibration measurement
(Elsevier, 2020-07-15) Cuadrado Sanguino, Manuel; Pernas Sánchez, Jesús; Artero Guerrero, José Alfonso; Varas Doval, David; Ministerio de Economía y Competitividad (España); Universidad Carlos III de Madrid
Model updating is usually based on the contrast between the modal characteristics predicted by the models and those experimentally identified. Traditional experimental methods are based on the use of contacting sensors, but more recently other techniques as 3D Digital Image Correlation (DIC) have also been used successfully. In this paper the results obtained by applying these alternative techniques are compared, to obtain physically-sound models of carbon/epoxy composite plates. Primarily a roving hammer exciting the plates at evenly distributed degrees of freedom (DoF), and a mono-axial accelerometer attached to a single DoF reference point, have been used for modal identification. Alternatively, high speed cameras were applied to measure full-field vibrations of the plates. 3D DIC allowed obtaining a lower number of natural frequencies but much smoother mode shapes and similar results for model updating. The experimental setup has been benchmarked using two different sets of plates varying thickness and ply stacking.
Cork Core Sandwich Plates for Blast Protection
(MDPI, 2020-08-01) Pernas Sánchez, Jesús; Artero Guerrero, José Alfonso; Varas Doval, David; Teixeira-Dias, Filipe; Ministerio de Economía y Competitividad (España); Universidad Carlos III de Madrid
A 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.
Experimental and numerical analysis of step drill bit performance when drilling woven CFRPs
(Elsevier, 2018-01-15) Feito Sánchez, Norberto; Díaz Álvarez, José; López Puente, Jorge; Miguélez Garrido, María Henar; Ministerio de Economía y Competitividad (España)
This paper focuses on the influence of the step drill bit geometry on the damage induced during drilling Carbon Fiber Reinforced Polymer materials (CFRPs). Step geometry designed with the aim of avoiding composite damage in CFRPs drilling, is compared to conventional twist configuration. Despite the reduction of thrust force and torque observed when using the step drill, the delamination was only reduced at low feed rates. A numerical model developed for the step geometry was validated with experimental data demonstrating its ability to predict thrust force and delamination for different values of feed rate and cutting speed. Numerical model allowed the development of a parametrical study. Finally, using a response surface methodology a mechanistic model and surface diagrams have been presented in order to help in the selection of optimum variables minimizing drilling induced damage.
Numerical analysis of the influence of tool wear and special cutting geometry when drilling woven CFRPs
(Elsevier, 2016-03-15) Feito Sánchez, Norberto; Díaz Álvarez, José; López Puente, Jorge; Miguélez Garrido, María Henar; Ministerio de Economía y Competitividad (España); Ministerio de Ciencia e Innovación (España)
CFRPs drilling is a common process in the aerospace industry carried out prior to components assembly. Machining induced damage leads to significant percentage of component rejection. Damage extension strongly depends on drilling geometry and cutting parameters. Fresh drill geometry changes with cutting time due to the wear progression and the risk for hole quality is enhanced as cutting progresses. The influence of wear on hole quality has been analyzed in the literature using mainly an experimental approach. Simulation of drilling process is an effective method that can be used to optimize drill geometry and process parameters in order to control hole quality and analyze the drill wear evolution. In this paper a finite element model for drilling woven CFRPs, reproducing both fresh and worn tools, is presented. Two different point angles considering fresh and honned edge were modeled. A progressive intra-laminar failure model based on the Chang and Chang model is considered. Cohesive elements allowed the analysis of inter-laminar damage (delamination). The model demonstrated its ability to predict thrust force and delamination for different values of feed rate and cutting speed. Model predictions show the influence of tool geometry (including variations induced due to wear) on delamination.
Influence of longitudinal clips in thermal stresses and deflection in solar tubular receivers
(Elsevier, 2020-03-01) Montoya Sancha, Andrés; Rodríguez Sánchez, María de los Reyes; López Puente, Jorge; Santana Santana, Domingo José; Ministerio de Ciencia e Innovación (España)
Mechanical boundary conditions in tubular receivers of solar power tower plants have a main role in the thermal stress distribution and tube deflection. Longitudinal supports, particularly, has an strong influence on stress and displacements, since they prevent the tube bending. In this work, the influence of longitudinal supports, on tube deflection and stress has been studied in external-cylindrical receivers, using an analytical methodology, which it is able to take into account the tube geometry in the deflection calculation. Therefore, real tube geometry with elbows can be considered. Results for two aiming strategies, one equatorial and another that flattens the heat flux, have been compared for different clips distances, from 1 to 9 meters. The analytical methodology developed in Matlab provides lower computational cost than the numerical model developed in Abaqus. Results show that clip distribution has a significant impact on thermal stress. For clips distance of 2 meters or lower, the generalised plane strain solution provides the stress distribution along the tube accurately, with a tube deflection lower than 1 millimetrer. When clips distance increases, the longitudinal stress distribution differs from the plane strain case, and the deflection increases to non-desirable values. Deflection is greater at tube ends, and aiming strategies that flatten the heat flux increases the displacement in that regions.
The high-velocity impact behaviour of kevlar composite laminates filled with cork powder
(MDPI, 2020-09-03) Amaro, Ana Martins; Reis, Paulo; Iváñez del Pozo, Inés; Sánchez Sáez, Sonia; García Castillo, Shirley Kalamis; Barbero Pozuelo, Enrique; Ministerio de Economía y Competitividad (España)
The literature reports benefits when the cork powder obtained from industrial by-products is used as the filler of composite laminates. For example, while the fatigue life is insensitive to the presence of cork in the resin, significant improvements are achieved in terms of to low-velocity impact strength. However, in terms of ballistic domain, the literature does not yet report any study about the effect of incorporating powdered cork into resins. Therefore, this study intended to analyse the ballistic behaviour and damage tolerance of Kevlar/epoxy reinforced composites with matrix filled by cork powder. For this purpose, high-velocity impacts were studied on plates of Kevlar bi-directional woven laminates with surfaces of 100 × 100 mm2. It was possible to conclude that the minimum velocity of perforation is 1.6% higher when the cork powder is added to the resin, but considering the dispersion, this small difference can be neglected. In terms of damage areas, they are slightly lower when cork dust is added, especially for velocities below the minimum perforation velocity. Finally, the residual bending strength shows that these composites are less sensitive to impact velocity than the samples with neat resin. In addition to these benefits, cork powder reduces the amount of resin in the composite, making it more environmentally friendly.
Numerical study of damaged micro-lattice blocks subjected to uniaxial compressive loading
(Elsevier, 2020-09-01) Braun, Matías Nicolás; Iváñez del Pozo, Inés; Ministerio de Economía y Competitividad (España)
This article presents a numerical study on the mechanical behaviour of damaged micro-lattice (ML) blocks submitted to uniaxial compressible loads. The numerical model is implemented in the commercial finite-element code Abaqus/Standard. From the finite-element model, the initial stiffness and the Yield stress of ML blocks are calculated. The damage in ML blocks is modelled as manufacturing defects, that are included in the ML structures using a random algorithm implemented in MatLab. The numerical model is validated with experimental data from uniaxial compression tests carried out on ML intact blocks by other authors. The analysis of the mechanical behaviour of ML blocks is presented in terms of variations of damage percentage, cell type and cell size.
Model updating of uncertain parameters of carbon/epoxy composite plates from experimental modal data
(Elsevier, 2019-09-01) Cuadrado Sanguino, Manuel; Artero Guerrero, José Alfonso; Pernas Sánchez, Jesús; Varas Doval, David; Ministerio de Economía y Competitividad (España); Universidad Carlos III de Madrid
This work presents a methodology to obtain physically-sound models of composite structure laminates using a combination of modal analysis, numerical modelling and parameter updating, avoiding the common uncertainties on the constructions of similar numerical models. Moreover this model establishes the baseline (pristine situation) of the dynamic behaviour of the set of composite plates. Therefore it could be applied for condition assessment or quality manufacturing control of existing structures through a non-destructive Structural Health Monitoring (SHM), and hence it could help to detect degradation or defects of the composite components. The driven data of the methodology were the modal frequencies and shapes of composite plates. To obtain these values an extensive experimental campaign of modal analysis has been performed on a set of carbon/epoxy laminates. A multiple input single output technique has been applied, using a roving hammer exciting the plates at evenly distributed Degrees of Freedom (DoF), and a mono-axial accelerometer attached to a single DoF reference point. The use of a high dense grid of points has allowed to identify a number of natural frequencies greater than usual in similar works, as well as improving the smoothness of the mode shape. Modal characteristics numerically obtained from a Finite Element Method (FEM) model based on manufacturer reference data were compared with experimental results. This baseline model was updated through a gradient based optimization algorithm. Before the process of model updating, a sensitivity analysis has been performed to identify the driven uncertain parameters using a Montecarlo approach. This technique reduces the number of parameters to be optimized to a small set increasing the efficiency of the methodology. As a result of the whole process, a physically more accurate model is obtained on which discrepancies with the corresponding experimentally measured modal parameters are drastically reduced. Analy
Analysis of the impact location on damage tolerance of bonded-repaired composite laminates
(Elsevier, 2019-07-16) Iváñez del Pozo, Inés; García Castillo, Shirley Kalamis; Sánchez Sáez, Sonia; Barbero Pozuelo, Enrique; Ministerio de Economía y Competitividad (España)
In this work, the influence of impact point on the damage tolerance of repaired laminates was studied experimentally. Two configurations, thin carbon/epoxy laminates and the same laminate with a double patch repair, were impacted in two different locations, at the specimen centre and at the edge of the patch. Afterward, compression after impact (CAI) tests were performed, analysing the residual strength and failure progression. In repaired laminates, a significant influence of the point of impact on the impact resistance was observed, specifically for impact energies higher than 15 J. Both specimen configurations showed similar trends in all impact variables analysed when the impact was located at the centre. Related with damage tolerance, the CAI strength of repaired specimens impacted at the centre is significantly higher than the residual strength of those impacted at the patch edge. The latter have a similar trend that the non-repaired laminates in both impact locations.
Numerical analysis of surface cracks repaired with single and double patches of composites
(SAGE, 2018-04-01) Iváñez del Pozo, Inés; Braun, Matías Nicolás; Ministerio de Economía y Competitividad (España)
In this work, the performances of circular single-and double-sided composite patch repairs are compared by computing the maximum stress intensity factor of a repaired surface crack. The three-dimensional finite-element method is used to calculate the stress intensity factor along the crack. The effects of the crack depth, composite patch thickness and patch material on the stress intensity factor variation are highlighted. The obtained results show that the selection of single-or double-sided patches depends on both the crack depth and patch thickness.
Compressive deformation and energy-absorption capability of aluminium honeycomb core
(2017-08-15) Iváñez del Pozo, Inés; Moreno Fernández-Cañadas, Lorena María; Sánchez Sáez, Sonia
In this study, the crush behaviour and the energy absorption capability of an aluminium honeycomb core is discussed. A three-dimensional finite-element model of a honeycomb-core structure was developed using the commercial code Abaqus. Flatwise and edgewise experimental compressive tests were made to validate the numerical model and good agreement was found between the experimental data and the numerical results. Virtual compressive tests varying the cell size, cell-wall thickness, and material properties were performed. The deformation mode, compressive core behaviour and its energyabsorption capacity were examined. The crushing parameters at in-plane directions were more affected by the variations of the characteristic core parameters; although, in general, increasing the cell-wall thickness and the yield stress of the aluminium alloy give higher crush loads, and therefore the absorbed energy increases. However, if the cell size increases, the energy-absorption capacity decreases. (C) 2017 Elsevier Ltd. All rights reserved.
Manufacture of compression moulded PLA based biocomposites: A parametric study
(Elsevier, 2015-11-01) Rubio López, Ángel; Olmedo Marcos, Álvaro; Díaz Álvarez, Antonio; Santiuste Romero, Carlos; Ministerio de Economía y Competitividad (España)
In this study, an analysis of the fabrication parameters that influence on the strength of biodegradable composites is presented. The effect of heating temperature, pressure, number of plies, fibre, and matrix on the tensile strength was studied. Biodegradable composites were manufactured using film stacking and compression moulding process. The strengths of biocomposite based on two different polylactic acid (PLA) matrix, and reinforced with four different woven fibres of jute, flax and cotton were compared. The aim of this work is the development of an optimised manufacture process to reduce costs and production time of high strength biocomposites. As a result, a tensile strength higher than 100 MPa was obtained with a preheating time of 2 min and 3 min of heating under pressure. This result means a significant reduction of production time that can lead to reduce the manufacture cost of these materials. (C) 2015 Elsevier Ltd. All rights reserved.
Numerical analysis of the dynamic frequency responses of damaged micro-lattice core sandwich plates
(Sage, 2020-01-01) Braun, Matías Nicolás; Iváñez del Pozo, Inés; Aranda Ruiz, Josué; Ministerio de Economía y Competitividad (España)
In this work, a numerical analysis of the dynamic frequency responses of sandwich plates with micro-lattice core is presented. The finite element analysis is implemented in the commercial software Abaqus/Standard, calculating the natural frequencies and eigenmodes of sandwich plates containing defects on the micro-lattice structure. In order to include the presence of defects, an aleatory algorithm is developed in MATLAB. The effect of the damage percentage, cell type, cell size and material on the frequency and modal responses of the sandwich plates is highlighted. Results show that the dynamic frequency response may be useful for analysing practical issues related to non-destructive damage identification of imperfections in the micro-lattice core of sandwich structures.

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