DIMM-Artículos
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Ítem Machining characteristics based life cycle assessment in eco-benign turning of pure titanium alloy(2019-12) Gupta, Munish; Song, Qinghua; Liu, Zhanqiang; Pruncu, Catalin; Mia, Mozammel; Singh, Gurraj; Lozano, José Adolfo; Carou, Diego; Mashood Khan, Aqib Mashood; Jamil, Muhammad; Pimenov, Danil YuMinimum quantity lubrication (MQL) is considered as an eco-benign, greener, and socio-economic alternative to dry cutting. Nevertheless, its effectiveness is limited to mild cutting materials owing to less generation of heat during machining. In order to address this challenge regarding hard-to-cut materials, energy requirement, and material flow, Ranque-Hilsch Vortex Tube assisted Minimum Quantity Cutting Fluids (RHVT-MQCF) has been practiced in the turning of pure titanium and compared its effectiveness with conventional MQL cooling techniques. The turning experiments were performed on pure titanium alloy by varying the cutting speed (250–300 m/min), feed rate (0.05–0.13 mm/rev), and depth of cut (0.3–0.5 mm), respectively. In addition, a statistical modeling technique and desirability function approach was used to analyze and optimize the sustainable indicators for the machining process associated with the cutting force, power consumption, specific cutting energy, chips morphology, material removal rate, and surface quality (i.e. surface roughness). Regarding sustainability performance, Life Cycle Assessment (LCA) model was applied using Simapro 8.3 software connected to EPS 2000 and ReCiPe Endpoint v1.12 databases. Findings have depicted the high performance of RHVT-MQCF conditions regarding machining characteristics compared to MQL under same conditions. In-depth analysis has shown that RHVT-MQCF is a sustainable and useful alternative to the manufacturing sector.Ítem Numerical analysis of compliance and fatigue life of the CCC specimen(Elservier, 2023-01-23) Neto, Diogo Mariano; Antunes, Fernando Ventura; Sérgio, Edmundo; Branco, Ricardo; Camacho-Reyes, Alonso; Díaz-Garrido, Francisco Alberto; Gómez-Gonzales, Giancarlo Luis; Vasco, José ManuelThis study presents the numerical evaluation of the compliance in the CCC specimen aiming to assess the crack length inside the specimen. The numerical model considered the elastoplastic behaviour of the specimen, which is modelled using axisymmetric finite elements. The results shown that the propagation of the crack yields a nonlinear increase of the compliance. Nevertheless, variation of the compliance is very small for small values of crack radius. Considering a loading sequence composed by four load blocks of constant amplitude, the fatigue crack growth was predicted both using the Paris law and the numerical model. Both predictions agree but only the numerical simulation is able to capture the crack retardation between load blocksÍtem Investigation of Plasticity Effects on Growing Fatigue Cracks Using the CJP Model of Crack Tip Fields(MDPI, 2023-08-22) Vasco, José Manuel; Camacho-Reyes, Alonso; Gómez-Gonzales, Giancarlo Luis; Diaz-Garrido, Francisco AlbertoA growing fatigue crack gives rise to a plastic enclave that envelops the crack and can exert a shielding effect on the crack from the global elastic stress field driving fatigue propagation. This work presents the potential of the CJP model of crack tip fields to investigate the plasticity-induced shielding effects on growing fatigue cracks as well as its ability to characterise the size and shape of the plastic zone generated at the tip of a growing fatigue crack. The model was specifically developed to consider the influence of the plastic enclave generated around a fatigue crack on the surrounding elastic material. Different aspects related to fracture mechanics and its implications for fatigue crack growth have been investigated, namely plasticity-induced crack shielding, the retardation effect induced on fatigue crack growth due to the application of an overload and the estimate of the size and shape of the crack tip plastic zone. The model has been successfully applied by analysing displacement fields experimentally measured by DIC in different CT specimens made of 2024-T3 aluminium alloy and commercially pure titanium. Results presented in this work intend to contribute to a better understanding of the shielding effects during fatigue crack growth.Ítem Effect of crack flank holes on fatigue crack growth(Elsevier, 2023-01-07) Neto, Diogo Mariano; Cavaleiro, Nuno; Sérgio, Edmundo; Jesus, Joel de; Camacho-Reyes, Alonso; Antunes, Fernando VenturaThe effect of drilling two symmetric holes along the crack flanks on the fatigue crack growth (FCG) rate was evaluated numerically. The FCG increases (decreases) when the crack tip is behind (ahead) the holes. This behaviour is enlarged both by increasing the diameter of the holes and by reducing the distance between them. This is consequence of the geometrical effect, which modifies the plastic zone size. Experimental work validated the numerical model, indicating that that cumulative plastic strain at the crack tip is an adequate crack driving force and that cyclic plastic deformation is the main damage mechanism of FCG.Ítem A meshfree approach for analyzing strain fields near crack tips from Digital Image Correlation displacement data(Wiley, 2024-03-24) Gómez-Gonzales, Giancarlo Luis; Camacho-Reyes, Alonso; Ortiz-González, Julián Andrés; Diaz-Garrido, Francisco AlbertoThe element-free Galerkin (EFG) meshfree method is employed in this research to compute strain fields based on discrete displacement data obtained from digital image correlation (DIC). To validate the method's accuracy, both simulated images with highly heterogeneous deformations and real tests conducted on notched specimens with known solutions are initially employed. The study then investigates the strain field near the crack tip in an AISI 1020 steel specimen through a multiscale experiment. From the macroscale experiment, the strain data are used to determine the crack-tip plastic zone size, and the solution is compared with predictions from linear-elastic fracture mechanics. The stress intensity factor is also determined. Furthermore, the high strain gradient ahead of the crack tip is determined from the microscale experiment and compared against commercial DIC software. Experimental results confirm the effectiveness of the proposed formulation in crack tip analysis.Ítem Study of Effective Stress Intensity Factor through the CJP Model Using Full-Field Experimental Data(MDPI, 2023-08-20) Camacho-Reyes, Alonso; Vasco, José Manuel; Gómez-Gonzales, Giancarlo Luis; Diaz-Garrido, Francisco AlbertoIn this work, the Christopher–James–Patterson crack tip field model is used to infer and assess the effective stress intensity factor ranges measured from thermoelastic and digital image correlation data. The effective stress intensity factor range obtained via the Christopher– James–Patterson model, which provides an effective rationalization of fatigue crack growth rates, is separated into two components representing the elastic and retardation components to assess shielding phenomena on growing fatigue cracks. For this analysis, fatigue crack growth tests were performed on Compact-Tension specimens manufactured in pure grade 2 titanium for different stress ratio levels, and digital image correlation and thermoelastic measurements were made for different crack lengths. A good agreement (~2% average deviation) was found between the resultsobtained via thermoelastic stress analysis and digital image correlation indicating the validity of theChristopher–James–Patterson model to investigate phenomena in fracture mechanics where plasticityplays an important role. The results show the importance of considering crack-shielding effects usingthe Christopher–James–Patterson model beyond considering an exclusive crack closure influence.Ítem The Evolution of Internal Damage Identified by Means of X-ray Computed Tomography in Two Steels and the Ensuing Relation with Gurson’s Numerical Modelling(MDPI, 2019-03) Suárez-Guerra, Fernando; Sket, Federico; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José Miguel; Molina-Aldareguia, JonThis paper analyzes the evolution of the internal damage in two types of steel that show different fracture behaviors, with one of them being the initial material used for manufacturing prestressing steel wires, and the other one being a standard steel used in reinforced concrete structures. The first of them shows a flat fracture surface perpendicular to the loading direction while the second one shows the typical cup-cone surface. 3 mm-diameter cylindrical specimens are tested with a tensile test carried out in several loading steps and, after each of them, unloaded and analyzed with X-ray tomography, which allows detection of internal damage throughout the tensile test. In the steel used for reinforcement, damage is developed progressively in the whole specimen, as predicted by Gurson-type models, while in the steel used for manufacturing prestressing steel-wire, damage is developed only in the very last part of the test. In addition to the experimental study, a numerical analysis is carried out by means of the finite element method by using a Gurson model to reproduce the material behavior.Ítem A material model to reproduce mixed-mode fracture in concrete(Wiley, 2018-08) Suárez Guerra, Fernando; Gálvez, Jaime C.; Cendón , David A.This paper presents a material model to reproduce crack propagation in cement-based material specimens under mixed-mode loading. Its numerical formulation is based on the cohesive crack model, proposed by Hillerborg, and extended for the mixed-mode case. This model is inspired by former works by Gálvez et al but implemented for its use in a finite element code at a material level, that is to say, at an integration point level. Among its main features, the model is able to predict the crack orientation and can reproduce the fracture behaviour under mixed-mode fracture loading. In addition, several experimental results found in the literature are properly reproduced by the model.Ítem On the localisation of damage under pure bending using a nonlocal approach(Elsevier, 2018-06) Suárez Guerra, FernandoTo reproduce the behaviour of quasibrittle materials mathematically, constitutive laws with softening are needed, which often leads to development of damage localisation bands. If a standard local formulation is used, this approach leads to a pathological mesh dependence, which can be eliminated by making use of alternative nonlocal formulations. The aim of this paper is to assess the localisation properties of damage models under pure bending using different nonlocal formulations; to permit a partially analytical treatment, the idealised case of pure bending is studied. Under these conditions, the localisation process starts at the tensile face of the beam, which belongs to the boundary of the domain on which the problem is solved. Consequently, localisation patterns are affected by the boundary treatment as well as other parameters, such as the characteristic length that defines the area contributing to the nonlocal averaging. This paper presents an analytical study of the onset of localisation of different nonlocal formulations for a beam under pure bending. In addition to it, the subsequent evolution of the localised solution is explored by numerical simulations, analysing the localisation bands spacing, the dissipated energy profile along the fracture plane and the Moment-curvature diagrams, with curvature being a parameter that represents the rotation that drives the loading process (ϕ stands for the relative rotation angle of the cross section and L for the beam length). An analysis of damage localisation on longer beams where damage localises in several areas is also carried out and, finally, the damage localisation due to shrinkage is studied as a more realistic example of the problem addressed here.Ítem Distinct Fracture Patterns in Construction Steels for Reinforced Concrete under Quasistatic Loading— A Review(MDPI, 2018-03) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José MiguelSteel is one of the most widely used materials in construction. Nucleation growth and coalescence theory is usually employed to explain the fracture process in ductile materials, such as many metals. The typical cup–cone fracture pattern has been extensively studied in the past, giving rise to numerical models able to reproduce this pattern. Nevertheless, some steels, such as the eutectoid steel used for manufacturing prestressing wires, does not show this specific shape but a flat surface with a dark region in the centre of the fracture area. Recent studies have deepened the knowledge on these distinct fracture patterns, shedding light on some aspects that help to understand how damage begins and propagates in each case. The numerical modelling of both fracture patterns have also been discussed and reproduced with different approaches. This work reviews the main recent advances in the knowledge on this subject, particularly focusing on the experimental work carried out by the authors.Ítem Macro Photography as an Alternative to the Stereoscopic Microscope in the Standard Test Method for Microscopical Characterisation of the Air-Void System in Hardened Concrete: Equipment and Methodology(MDPI, 2018-08) Suárez Guerra, Fernando; Conchillo, José J.; Gálvez, Jaime C.; Casati, María J.The determination of the parameters that characterize the air-void system in hardened concrete elements becomes crucial for structures under freezing and thawing cycles. The ASTM C457 standard describes some procedures to accomplish this task, but they are not easy to apply, require specialised equipment, such as a stereoscopic microscope, and result in highly tedious tasks to be performed. This paper describes an alternative procedure to the modified point-count method that is described in the Standard that makes use of macro photography. This alternative procedure uses macro-photographic images that can be obtained with a quite standard photo camera and it is successfully applied to a large set of samples and presents some advantages over the traditional method, since the required equipment is less expensive and provides a more comfortable and less tedious procedure for the operator.Ítem Estudio de la influencia de la adición de fibras en la rotura en modo II de materiales cuasifrágiles(UK Zhende Publishing Limited, 2021-08) Suárez Guerra, Fernando; Felipe-Sesé, Luis; Castilla-Gonzalo, Francisco-José; Díaz-Garrido, FranciscoLa rotura de materiales cuasifrágiles, tales como el hormigón o el yeso, ha sido objeto de estudio desde hace décadas. Estos estudios han ampliado el conocimiento de los mecanismos de rotura así como de los parámetros que gobiernan este fenómeno y han permitido proponer modelos numéricos que lo reproducen mediante herramientas tales como el método de los elementos finitos. Por otro lado, de los tres posibles Modos de rotura que se diferencian a la hora de analizar problemas de Mecánica de la Fractura, el Modo I es sin duda el mejor conocido, reproducido experimentalmente y empleado como base para los modelos numéricos. No obstante, existen situaciones en las que la rotura es el resultado de un estado de tensiones que moviliza un mecanismo en el que participan los Modos I y II simultáneamente. A este respecto, la rotura en Modo II ha sido estudiada con menos profundidad, en parte porque las roturas en Modo I son más habituales, pero también porque su reproducción experimental y, por tanto, su estudio, resulta más complejo. En este estudio se presentan resultados experimentales de ensayos que movilizan la rotura en Modo II en probetas de yeso adicionadas con fibras de refuerzo. En concreto se emplean el ensayo de cortante definido por la norma japonesa JSCE y el ensayo de push-off. El campo de desplazamientos se obtiene empleando la técnica de correlación digital de imágenes (DIC), lo cual ayuda a entender cómo las fibras modifican los mecanismos de rotura de la matriz cuando ésta se produce en condiciones de Modo II.Ítem Fracture and Size Effect of PFRC Specimens Simulated by Using a Trilinear Softening Diagram: A Predictive Approach(MDPI, 2021-07) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; García-Alberti, Marcos; Enfedaque, AlejandroThe size effect on plain concrete specimens is well known and can be correctly captured when performing numerical simulations by using a well characterised softening function. Nevertheless, in the case of polyolefin-fibre-reinforced concrete (PFRC), this is not directly applicable, since using only diagram cannot capture the material behaviour on elements with different sizes due to dependence of the orientation factor of the fibres with the size of the specimen. In previous works, the use of a trilinear softening diagram proved to be very convenient for reproducing fracture of polyolefin-fibre-reinforced concrete elements, but only if it is previously adapted for each specimen size. In this work, a predictive methodology is used to reproduce fracture of polyolefin-fibre-reinforced concrete specimens of different sizes under three-point bending. Fracture is reproduced by means of a well-known embedded cohesive model, with a trilinear softening function that is defined specifically for each specimen size. The fundamental points of these softening functions are defined a priori by using empirical expressions proposed in past works, based on an extensive experimental background. Therefore, the numerical results are obtained in a predictive manner and then compared with a previous experimental campaign in which PFRC notched specimens of different sizes were tested with a three-point bending test setup, showing that this approach properly captures the size effect, although some values of the fundamental points in the trilinear diagram could be defined more accurately.Ítem Cumulative effects of cracking in monoblock multipurpose precast concrete sleepers on railway tracks(Elsevier, 2025-03) Donaire-Ávila, Jesús; Fernández-Aceituno, Javier; Suárez-Guerra, FernandoThis work addresses the phenomenon of cracking in multipurpose precast monoblock concrete sleepers by examining the entire process from fabrication to final installation on railway tracks. This includes stages such as manufacturing, stockpiling, track installation for rail neutralization, and eventually fastening the rails to the sleepers. A nonlinear numerical model, which is experimentally validated, is used to analyze this effect. Also, thermal and mechanical actions are considered at each stage of the process. Accordingly, different types of polymeric dowels and concrete aggregates—siliceous and carbonate—are evaluated to assess their impact on cracking. The results indicate that the thermal expansion capacity and elastic stiffness of the dowels, as well as the outdoor temperatures during fabrication, stockpiling, and installation, play critical roles in the cracking process. Sleepers made with carbonate aggregate, stiff-expansive dowels, fabricated in cold environments, and installed in hot conditions are particularly prone to severe cracking. Consequently, these conditions should be avoided to minimize cracking in multipurpose sleepers.Ítem Analysis of two experimental setups to study mode II fracture on fibre-reinforced gypsum notched specimens(CSIC, 2023-09) Suárez-Guerra, Fernando; Fernández-Aceituno, Javier; Donaire-Ávila, JesúsThe main aim of this work is to study two relevant experimental setups designed for studying shear fracture and see if any of them allows studying the evolution of fracture under Mode II conditions, not only inducing a shear stress state at the onset of fracture. Two tests have been selected, a standardised test described by a Japanese standard, here referred to as the JSCE test, and the push-off test. These tests have been carried out on fibre-reinforced gypsum specimens with increasing proportions of polypropylene fibres and monitored by means of digital image correlation (DIC). The results show that fracture under Mode II conditions is relatively easy to induce with both tests, but once fracture begins, it is extremely difficult to induce a fracture process under Mode II. In general, Mode II has an important role at the onset on fracture, but Mode I predominates afterwards.Ítem A smeared crack formulation for simulating fracture of fibre-reinforced concrete by means of a trilinear softening diagram(Elsevier, 2023-08) Suárez Guerra, FernandoThis study presents a smeared crack model for reproducing the fracture behaviour of FRC that is based on an embedded crack formulation used lately with this material. In both cases, a trilinear softening diagram allows reproducing the post-peak behaviour correctly. The model proposed here differs from the one on which it is inspired, since it is a smeared crack model based on the crack band concept where the material damage is isotropic and controlled by a damage factor ranging from 0 to 1, while the original model is an embedded crack model that allows fracture in three directions per element. This new formulation overcomes some limitations of the embedded crack model, that could only be used with triangular elements with an only integration point, since it can be used with triangular and quadrilateral elements with any number of integration points. Unlike previous models, developed for commercial codes, this model is developed in OOFEM, a free finite element code developed at the Czech Technical University in Prague (Czech Republic) and Chalmers University of Technology (Sweden), thus providing the general public with an advanced tool that allows reproducing fracture in structural elements made with fibre-reinforced concrete elements. This work shows that the proposed formulation provides similar results to those obtained with the model on which it is inspired under different situations: mode I fracture, size effect analysis and, finally, modes I and II mixed fracture.Ítem Suitability of Constitutive Models of the Structural Concrete Codes When Applied to Polyolefin Fibre Reinforced Concrete(MDPI, 2022-03) Enfedaque, Alejandro; Suárez-Guerra, Fernando; García-Alberti, Marcos; Gálvez-Ruíz, Jaime CarlosThe use of fibres as structural reinforcement in concrete is included in standards, providing guidelines to reproduce their behaviour, which have been proven adequate when steel fibres are used. Nevertheless, in recent years new materials, such as polyolefin fibres, have undergone significant development as concrete reinforcement. This work gives insight on how suitable the constitutive models proposed by the Model Code 2010 (MC2010) are in the case of such polymer fibres. A set of numerical models has been carried out to reproduce the material behaviour proposed by the MC2010 and the approach based on the softening function proposed by the authors. The results show remarkable differences between the experimental results and the numerical simulations when the constitutive models described in the MC2010 are employed for different polyolefin fibre reinforced concrete mixes, while the material behaviour can be reproduced with greater accuracy if the softening function proposed by the authors is employed when this type of macro-polymer fibres is used. Moreover, the relatively complex behaviour of polyolefin fibre reinforced concrete may be reproduced by using such constitutive model.Ítem Damage tolerance in engineering components: Implementation to anchor heads(Elsevier, 2022-06) Olivares, Miguel A.; Gálvez, Jaime C.; Suárez Guerra, FernandoDamage tolerance is commonly used as a design criterion in some engineering fields, such as aerospace engineering, but is not usual in civil engineering, where structural safety often relies on safety coefficients. This work presents a study on how using damage tolerance for designing post-tensioning anchor heads, usual mechanisms in many civil engineering works, can be useful for building safer structures. Damage is simulated using 2D and 3D finite element models, considering axisymmetric damage and single damage, respectively. The influence of several aspects, such as the crack depth, the crack orientation angle or the shape of the anchorage, is studied. Lastly, a specific anchorage geometry is analysed using the damage tolerance concept to show that this approach may help in the design of this type of elements.Ítem Modelling fracture on polyolefin fibre reinforced concrete specimens subjected to mixed-mode loading(Elsevier, 2019-02) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Enfedaque, Alejandro; García-Alberti, MarcosIn recent years, polyolefin fibres have proved a remarkable performance as reinforcement of concrete, which has inspired a number of studies involving, among others, the simulation of fracture on polyolefin fibre reinforced concrete (PFRC) specimens. Fracture has been successfully reproduced on PFRC specimens in the past by means of an embedded crack model with a trilinear softening function, but always using for comparison the classical three-point bending test, which employs a symmetrical setup and induces fracture under pure mode I conditions. In the present study, six sets of specimens tested under an alternative setup of the three-point bending test, which induces fracture under mixed-mode conditions (I and II), are simulated using the same numerical approach. The results not only prove that the use of a trilinear softening function together with an embedded cohesive crack approach can reproduce fracture under mixed-mode conditions, but also provide interesting insights on how the trilinear softening function may be designed for suiting the usage of different fibre lengths or varying the proportions of polyolefin fibres.Ítem Fracture of eutectoid steel bars under tensile loading: Experimental results and numerical simulation Author links open overlay panel(Elsevier, 2016-06) Suárez-Guerra, Fernando; Gálvez-Ruíz, Jaime Carlos; Cendón, David Ángel; Atienza, José MiguelConstruction steel bars tested under tension usually show a cup-cone fracture pattern. Nevertheless, some steels, such as the eutectoid one used for manufacturing prestressing steel wires, show a different pattern: a flat fracture surface with a dark region inside. This paper presents experimental work performed to identify the fracture mechanisms that trigger this particular flat fracture pattern and numerical simulations where it is reproduced numerically. The experimental tests are carried out on cylindrical specimens of three diameters, 3, 6 and 9 mm, subjected to tension. In order to analyse the fracture mechanism, numerical simulations are performed by using the finite element method and the cohesive zone approach. To that end, a cohesive interface element with mechanical properties that depend on the stress triaxiality is presented and assessed. This approach provides reasonably good agreement with the experimental results. In addition, when compared with other popular models such as the GTN model, it presents certain advantages since it requires a smaller number of parameters to be defined.