Departamento de Ingeniería Mecánica y Minera

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En esta Comunidad se recogen los documentos generados por el Departamento de Ingeniería Mecánica y Minera y que cumplen los requisitos de Copyright para su difusión en acceso abierto.

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A comparative study of performance and regulated emissions in a medium-duty diesel engine fueled with sugarcane diesel-farnesane and sugarcane biodiesel-LS9
(ELSEVIER, 2019-06-01) Soto, Felipe; Marques, Gian; Torres-Jiménez, Eloísa; Vieira, Bráulio; Lacerda, André; Armas, Octavio; Guerrero-Villar, Francisca
Two sugarcane biofuels and mineral diesel fuel are tested under full load conditions, under the same values of performance and under the European Transient Cycle on an engine test bench, without any modifications to the ECU. The target is to compare engine performance and emissions. At full load, engine performance varies due to the variation in LHV. Under the same values of performance, the sugarcane biodiesel-LS9 provides the lowest THC emissions. The higher CN and exhaust gas recirculation of the sugarcane biodiesel-LS9 and the higher H/C ratio of the sugarcane diesel-farnesane compared to the diesel S50 provide a NOx reduction. Neither the increment in bsfc nor the increment of %EGR for the sugarcane biodiesel-LS9 deteriorate the combustion, so its CO emissions are lower. The sugarcane biodiesel-LS9 leads to the lowest NOx and PM specific emissions under transient operation, followed by the sugarcane diesel-farnesane. The THC and CO specific emissions are higher for the biofuels in comparison to the diesel S50. The main reason for these results is the impact of the properties of the biofuels on the ECU response However, both biofuels produce less harmful emissions at idle conditions, which supports their usage to reduce exhaust emissions in urban areas.
A fracture model for pearlitic steel bars using a cohesive model
(2012-09) Suárez Guerra, Fernando; Gálvez, Jaime C.; Cendón, David A.; Atienza, José Miguel; Elices, Manuel
The fracture of ductile materials, such as metals, is usually explained with the theory of nucleation, growth and coalescence of microvoids. Based on this theory, many numerical models have been developed, with a special mention to Gurson-type models. These models simulate mathematically the physical growth of microvoids, leading to a progressive development of the internal damage that takes place during a tensile test. In these models, the damage starts to develop in very early stages of the test.
A higher order thermoelastic analysis of fatigue crack growth can assess crack tip shielding
(Wiley, 2023-06-30) Camacho-Reyes, Alonso; Vasco-Olmo, José M.; James, M. Neil; Díaz, Francisco A.
The present work uses a more accurate thermoelastic formulation than the classical equation, based on the inclusion of a higher order term, to analyze crack tip thermoelastic data. It is shown that this thermoelastic analysis (TSA) model can be fitted to the Christopher–James–Patterson crack tip field model and hence provides information on crack tip shielding. To validate the results of this analysis, stress intensity factors (SIFs) were compared with results obtained from digital image correlation (also fitted to the CJP model). A comparison was also made between these CJP-derived SIF values and those obtained using a purely elastic Irwin–Westergaard approach. A high level of agreement was observed between DIC and TSA results in assessing ΔKCJP that is the net result of the driving and the shielding forces on the crack tip. The ability to assess shielding using TSA is a significant step forward in its potential use in a more accurate characterization of crack tip fields.
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.
A single-stage megaflood at the termination of the Messinian Salinity Crisis: Geophysical and modelling evidence from the eastern Mediterranean Basin
(Elsevier, 2020-09-10) Spatola, Daniele; del Moral-Erencia, José D.; Micallef, Aaron; Camerlenghi, Angelo; García-Castellanos, Daniel; Gupta, Sanjeev; Bohórquez, Patricio; Gutscher, Marc-André; Bertoni, Claudia
The Messinian salinity crisis was an extraordinary event that resulted in the deposition of kilometre-thick evaporite sequences in the Mediterranean Sea after the latter became disconnected from the world's oceans. The return to fully and stable marine conditions at the end of the crisis is still subject to debate. Three main hypotheses, based on geophysical and borehole data, onshore outcrops and climate simulations, have been put forward. These include a single-stage catastrophic flood, a two-step reflooding scenario, and an overspill of Paratethyan water followed by Atlantic inflow. In this study, two research questions are addressed: (i) Which event marked the termination of the Messinian salinity crisis? (ii) What was the sea level in the eastern Mediterranean Sea during this event? Geophysical data from the western Ionian Basin are integrated with numerical simulations to infer that the termination of the crisis consisted of a single-stage megaflood following a sea level drawdown of 1900 m. This megaflood deposited an extensive sedimentary body with a chaotic to transparent seismic signature at the base of the Malta Escarpment. Fine, well-sorted sediments are predicted to have been deposited within the thicker sections of the flood deposit, whereas a more variable distribution of coarser sediments is expected elsewhere. The north-western Ionian Basin hosts evidence of episodic post-Messinian salinity crisis slope instability events in the last ~1.8 Ma. The largest of these emplaced a >200 km3 deposit and is associated with failure of the head of Noto Canyon (offshore SE Sicily). Apart from unravelling the final phase of the Messinian salinity crisis and the ensuing stratigraphic evolution of the western Ionian Basin, our results are also relevant to better understand megafloods, which are some of the most catastrophic geological processes on Earth and Mars.
A smeared crack formulation for simulating fracture of fibre-reinforced concrete by means of a trilinear softening diagram
(Elsevier, 2023-08) Suárez Guerra, Fernando
This 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.
A technical overview of metallic parts in hybrid additive manufacturing industry
(Elsevier, 2022-05) Erdi Korkmaz, Mehmet; Waqar, Saad; García-Collado, A.; Kumar Gupta, Munish; Krolczyk, Grzegorz
Additive manufacturing technologies have emerged as the promising alternatives of conventional manufacturing techniques. Conventional manufacturing techniques involves cutting and removal of material by mechanical procedures to achieve final product. Whereas, discrete chunks of material in any form are combined point by point and layer by layer for the fabrication of final product in additive manufacturing processes. Numerous advantages and inefficiencies of these manufacturing techniques are reflected in factors such as the design, fabrication, material properties and working condition etc. Therefore, development of a production technology by combining the benefits of both conventional and additive techniques is significantly important. “Hybrid Manufacturing” jointly apply additive and conventional production methods to attain final products. Hence, this short overview covers the operation aspects of both additive and subtractive manufacturing of metallic materials.
Advances in polymers based Multi-Material Additive-Manufacturing Techniques: State-of-art review on properties and applications
(Elsevier, 2022-02) Garcia Collado, Alberto José; Blanco, J.M.; Kumar Gupta, Munish; Dorado-Vicente, R.
Recently, the demand and studies related with Multi-Material Additive Manufacturing (MMAM) is continuously increasing. To uncover the essential knowledge hidden in the current mess of research works, this study, based on a simple review methodology, helps to identify and discuss the current knowledge about: limitations of software and hardware, the interface bonding strength of dissimilar materials, polymer reinforcement with continuous fiber, polymer-based multi-materials, and future and challenges. The review method starts with a list of topics to check: MMAM of polymers, the bonding strength between materials, knowledge gaps, and new development lines in polymer applications. Then, it continues with the search procedure on electronic databases and the inclusion and exclusion criteria definition. Finally, to help the discussion and assessment, the information is collected in tables.
Alternative Calibration of Cup Anemometers: A Way to Reduce the Uncertainty of Wind Power Density Estimation
(MDPI, 2019-04-30) Guerrero-Villar, Francisca; Dorado-Vicente, Rubén; Medina-Sánchez, Gustavo; Torres-Jiménez, Eloísa
This study presents a procedure to reduce the uncertainty of wind power density estimations, which is useful to improve the energy production predictions of wind farms. Power density is usually determined from the wind speed measured by a cup anemometer and the air density value (conventional procedure). An alternative procedure based on wind speed and dynamic pressure estimations provided by a cup anemometer is proposed. The dynamic pressure is obtained by means of a calibration curve that relates the anemometer rotation frequency and the dynamic pressure measured by a Pitot tube. The quadratic regression, used to define the calibration curve, and its uncertainty are both detailed. A comparison between the alternative procedure and the conventional one points out the advantage of the proposed alternative since results show a high reduction of the indirect measurement uncertainty of wind power density.
An alternative approach for improving DIC by using out-of-plane displacement information
(Elsevier, 2020-05-01) Siegmann, Philip; Felipe-Sesé, Luis; Díaz, Francisco
A new approach to perform 2D Digital Image Correlation (DIC) on objects that are subjected to large out-of-plane displacements is presented. It employs out-of-plane information to distort the speckle images of the reference and the deformed surface, increasing their similarity and therefore their sub-set cross-correlation peaks. The new approach is implemented using the combined Fringe Projection and 2D-DIC technique on two experiments: The buckling of an initial flat plate, and the rotation of the reference surface towards the camera from 0° to 60°. In both cases large speckle distortions are produced due to two issues, the lens magnification and the surface tilting. The first speckle distortion is applied to the deformed image to perform the lens magnification correction, and the second speckle distortion is applied to the reference image. The obtained distorted speckle images become very similar, allowing to successfully compute corresponding pixels between both images in a simple way (i.e. without nonlinear minimization processes). For this propose, an analytical iterative equation is derived to determine pixel displacements due to out-of-plane surface tilting. The resulting displacements are compared with those obtained by the conventional procedure, applying 2D-DIC (using open source Ncorr software) on the non-distorted speckle images and then making the lens magnification correction. The novel procedure proposed makes it possible to successfully find the corresponding pixels at the reference surface for out-of-plane rotations of 55° and 60° for which Ncorr failed. 3D-DIC (using commercial VIC software) is also employed to validate the results.
An alternative procedure to measure railroad track irregularities. Application to a scaled track
(ELSEVIER, 2019) Aceituno, Javier F.; Chamorro, Rosario; Muñoz, Sergio; Escalona, José L.
In this paper an alternative procedure to accurately measure static railroad track irregularities is proposed and applied to a scaled railroad track. The purpose of this work is the determination of highlyprecise measured data in short track segments that needs to be used as input in the validation of railroad computational models that are used for on-board railroad track measurement systems. The procedure consists of the use of a topographic total station combined with a postprocessing of the measured data that reduces misalignment errors and provide the analytical ideal geometry of the track together with its irregular geometry characterized in terms of the magnitudes of track gauge, vertical profile, alignment and cross level. Experimental results are compared to standard magnitudes of full scale tracks showing that real track geometry can differ from PSD-based predicted one. This supports the application of the proposed procedure for an accurate geometric determination of short track segments.
An automatic procedure for calibrating the fracture parameters of fibre-reinforced concrete
(Elsevier, 2025-02-21) Suárez Guerra, Fernando; Donaire Ávila, Jesús; Aceituno, Javier F.
In this work a calibration procedure to obtain the material parameters that characterize the fracture behaviour of fibre-reinforced concrete (FRC) is presented. This procedure uses a recently proposed trilinear softening diagram implemented in a smeared crack model of the free finite element code OOFEM that allows reproducing the fracture behaviour of FRC and takes advantage of the optimization package of SciPy, with both pieces of software being open-source and of free access for anyone interested in this field. This work presents the calibration procedure, which uses the Nelder-Mead algorithm to adjust the numerical result with the experimental diagram and discusses some key aspects, such as the number of reference points used in the calibration process or the weighting factors used with them, including the possibility of making some reference points more relevant than others in the calibration process. The influence of the mesh size and the element type used in the FEM model is also analysed. To evaluate the quality of the numerical approximation, a deviation factor is defined, which provides an scalar value that becomes lower as the numerical adjustment is closer to the experimental diagram in the reference points. The proposed procedure allows calibrating six parameters automatically with a meaningful time reduction and good accuracy. Using a higher number of reference points may lead to a better adjustment, although this study suggests that a good selection of the reference points is more effective than using a high number of reference points or using weighting factors to make some points more relevant than others. This procedure is finally validated by applying it with experimental results obtained with other types of FRC materials (different fibres and different fibre proportions) and specimen geometries.
Análisis comparativo en docencia no presencial síncrona y asíncrona empleada en asignaturas de Resistencia de Materiales y Cálculo de Estructuras motivadas por la Covid-19 en la Universidad de Jaén
(2021-06) Suárez Guerra, Fernando; Aceituno, Javier F.
Durante los últimos meses del segundo cuatrimestre del curso 2019-2020, debido a la situación sobrevenida con motivo de la pandemia mundial de Covid-19, la mayor parte de las universidades españolas se han visto forzadas a modificar su metodología docente y sustituir la habitual docencia presencial por una docencia no presencial en su totalidad. Este nuevo escenario ha obligado a todos los docentes a buscar estrategias que les permitieran impartir sus asignaturas empleando metodologías no presenciales que, en la mayoría de los casos, eran la primera vez que utilizaban. Entre ellas, cabe diferenciar entre las metodologías síncronas, aquellas que se imparten en horas de clase, y las metodologías asíncronas, aquellas a las que el estudiante puede acceder en cualquier momento, no necesariamente en las horas establecidas oficialmente para la impartición de la asignatura. En esta contribución se presentan unas primeras experiencias llevadas a cabo en la Universidad de Jaén en asignaturas de Elasticidad, Resistencia de Materiales y Cálculo de Estructuras. Se presentan las metodologías docentes empleadas, siendo en unos casos síncronas y en otros asíncronas y se analiza el resultado de cada una de ellas. Se determinan las fortalezas y las debilidades de cada una de las estrategias adoptadas, se analizan las valoraciones anónimas extraídas de los alumnos y se identifican las posibles mejoras de la aplicación de cada una de ellas. El objetivo de este trabajo es contribuir a la puesta en común de experiencias docentes realizadas de una manera particularmente intensa en los últimos meses del curso 2019-2020, extrayendo conclusiones que faciliten a docentes de las mismas áreas de conocimiento el diseño de sus metodologías docentes en escenarios no presenciales. Somos conscientes de que esta situación ha supuesto numerosas dificultades para el desarrollo de la docencia, pero creemos que también ha permitido experimentar nuevas metodologías docentes que, una vez haya vuelto la normalidad de la docencia presencial, puedan aprovecharse en ciertos contenidos. El objetivo de este trabajo, por tanto, es contribuir a este debate que, probablemente, va a ser de mucha actualidad en los próximos años.
Análisis de la deformación de rotura en el ensayo de tracción en probetas cilíndricas de acero perlítico
(2011-04) Suárez Guerra, Fernando; Cendón, David A.; Atienza, José Miguel; Gálvez, Jaime C.; Elices, Manuel
El ensayo de tracción permite obtener la curva tensión-deformación hasta el instante de carga máxima, sin embargo, a partir de ese momento el análisis de las tensiones y de las deformaciones resulta complicado. Conocer el comportamiento del material a partir del instante de carga máxima resulta fundamental para diseñar estrategias que mejoren la seguridad estructural. Este trabajo presenta los resultados de una campaña experimental de ensayos de tracción sobre acero perlítico en la que se han estudiado sus deformaciones de rotura así como sus superficies de fractura, todo ello en probetas cilíndricas con diferentes diámetros. Esta campaña ha sido acompañada de simulaciones numéricas con el fin de analizar el comportamiento del material en el interior de la sección. Adicionalmente, se han analizado las superficies de fractura de las probetas y se ha observado una relación no proporcional entre el tamaño de las probetas y el tamaño de la zona interna atribuida al crecimiento de poros. Esta relación no proporcional sugiere que dicha zona actuaría como un concentrador de tensiones, de forma similar a una fisura, y estaría afectado por el efecto de la triaxialidad de las tensiones en la zona de rotura.
Análisis del método de Borino para formulaciones no locales en modelos de elementos finitos
(2016-04) Suárez Guerra, Fernando
A diferencia de lo que ocurre con los modelos usuales de elementos finitos, en los modelos no locales el comportamiento del material en un punto de integración no depende únicamente del estado del material en ese punto sino de un valor promediado utilizando otros puntos de integración que lo rodean. Esto disminuye notablemente la dependencia del tamaño de malla de los modelos. Cuando el punto de integración en cuestión se encuentra cerca de un borde del cuerpo han de adoptarse estrategias que permitan corregir el valor no local obtenido por la fórmula estándar. Además de algunas que dependen de la cercanía al borde y otras que lo hacen del estado de tensiones de dicho punto, existe un método propuesto por Borino que añade al valor obtenido por la fórmula estándar un cierto valor que depende del local. En algunos estudios realizados con modelos no locales se han observado resultados que presentan ciertas irregularidades cuando se emplea el método propuesto por Borino. En esta contribución se estudian los motivos que provocan estas irregularidades y por qué otras formulaciones proporcionan modelos más estables sin irregularidades en los resultados.
Analysis of mode II fracture of fibre-reinforced gypsum specimens using an anchor bolt test
(2020-09) Suárez Guerra, Fernando; Aceituno, Javier F.
Fibre reinforcement is not a new idea, but it has experienced a very important development in the last years. Many recent studies have analysed the effect of fibre reinforcement on fracture [1], which is of special interest in the case of concrete, given the high production of this material and its impact on the global economy and the world environment, due to the carbon footprint its production generates. Nevertheless, the use of gypsum is also widespread in the construction field and is the most used material for interior lining. Although this is not a structural material, the use of fibre reinforcement may be of interest in some cases, increasing the fracture energy of the elements and reducing tearing [2]. In the analysis of fracture of quasi-brittle materials, studies have traditionally focused on mode I. Mode I is indeed the most usual fracture mode, but in some cases Mode II has a strong influence at the onset of fracture. There is not much information about Mode II fracture in the literature and almost none about fracture of fibre-reinforced quasi-brittle materials. In this contribution mode II fracture of fibre reinforced gypsum (FRG) is studied by means of anchor bolt tests. This test was analysed in depth by RILEM [3] and consists of pulling an embedded T-shaped steel element out of a block of concrete. In the case of this study, the test is used with fibre-reinforced gypsum specimens.
Analysis of the damage evolution in steel specimens under tension by means of XRTC
(2017-03) Suárez Guerra, Fernando; Gálvez, Jaime C.; Cendón, David A.; Atienza, José Miguel; Sket, Federico; Molina-Aldareguia, Jon
When a steel specimen is tested under tension, damage usually develops evenly all along the specimen, finally necking and leading to the typical cup-cone fracture surface. Nevertheless, some steels present an unusual fracture pattern consisting on a plane fracture surface with a dark region in the centre of the fracture zone. In this contribution, the authors analyse the evolution of the internal damage by using X-ray computed tomography (XRCT) on 3mm-diametre specimens of two steels. The specimens are tested in subsequent loading steps, after each of which it is unloaded and analysed with XRCT. This procedure helps to identify the evolution of damage developed inside each specimen at predefined strain levels. XRCT reveals a very high initial porosity in the material with the cup-cone fracture pattern and a very low initial porosity in the other. In the latter, fracture is triggered by a concentrated internal damage that can be seen as an internal notch which produces a stress concentration that leads to the eventual failure.
Analysis of the two-point wheel-rail contact scenario using the knife-edge-equivalent contact constraint method
(ELSEVIER, 2020) Aceituno, Javier F.; Urda, Pedro; Briales, Eduardo; Escalona, José L.
This paper presents a rigid contact approach to analyse the two-point wheel-rail contact scenario using the simplified constraint-based contact method called Knife-edge Equivalent Contact method (KEC-method). The proposed approach makes use of the computationally efficient online solution of the KEC constraints, where a single-point rail is in contact with an equivalent wheel profile, and provides an exact relation between the location of the contact points in the equivalent and real profiles. In this context, the two-point contact scenario can be easily dealt by linearly softening the KEC-constraints in the vicinity of the two-point contact, that gives a continuous and unique contact point solution between each wheel-rail pair and avoids finite contact point jumps between tread and flange. This allows an efficient kinematic solution of the two-point contact scenario. However, to properly ac- count for a dynamic equivalence of the two-point contact scenario in the computation of the tangential contact forces, the reaction force acting on the wheel when the contact point lies on the tread-flange transition, is transformed into two contact forces acting on the tread and flange respectively maintaining the resultant equilibrium of forces at the wheel.
Analysis of two experimental setups to study mode II fracture on fibre-reinforced gypsum notched specimens
(CSIC, 2023-09) Suárez Guerra, Fernando; Aceituno, Javier F.; Donaire-Ávila, Jesús
The 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.
Application of the Finite Element Method to the Incremental Forming of Polymer Sheets: The Thermomechanical Coupled Model and Experimental Validations
(MDPI, 2020-07) GARCIA-COLLADO, ALBERTO; Medina-Sanchez, Gustavo; Kumar Gupta, Munish; Dorado-Vicente, R.
Single Point Incremental Forming (SPIF) is an innovative die-less low-cost forming method. Until now, there have not been viable numerical solutions regarding computational time and accuracy for the incremental forming of polymers. Unlike other numerical approaches, this novel work describes a coupled thermomechanical finite element model that simulates the SPIF of polymer sheets, where a simple elastoplastic constitutive equation rules the mechanical behavior. The resulting simulation attains a commitment between time and accuracy in the prediction of forming forces, generated and transmitted heat, as well as final part dimensions. An experimental test with default process parameters was used to determine an adequate numerical configuration (element type, mesh resolution, and material model). Finally, compared to a set of experimental tests with different thermoplastics, the proposed model, which does not consider complex rheological material models, shows a good agreement with an approximation error of less than 11% in the vertical forming force prediction.

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