Daniel Crespo | Universitat Politecnica de Catalunya (original) (raw)

Papers by Daniel Crespo

The current prototype’s key contribution to the field of light-weight structures is that it is th... more The current prototype’s key contribution to the field of light-weight structures is that it is the first time that a pure tensegrity ring has been used in place of a compression ring. This design features a cladding structure for a sports arena, which consist of a ring-shaped outer section and a central roof structure. The ring-shaped outer section of the stadium consists of a tensegrity structure, which uses textile membranes in a place of conventional tension cables to bear the tensile forces occurring between the pressure elements. The supporting framework and spatial enclosure therefore become one an extension to the tension integrity principle. The central area of the roof is covered over by a Geiger dome, which in turn is a specific version of the tensegrity principle.

Materials, 2019

In this work, experimental and numerical analyses of repairs on carbon fiber reinforced epoxy (CF... more In this work, experimental and numerical analyses of repairs on carbon fiber reinforced epoxy (CFRE) substrates, with CFRE and aluminum alloy doublers typical of aircraft structures, are presented. The substrates have a bridge gap of 12.7 mm (simulated crack), repaired with twin doublers joined with riveted, adhesive bonded, and hybrid joints. The performance of the repairs using different doubler materials and joining techniques are compared under static loading. The experimental results show that riveted joints have the lowest strength, while adhesive bonded joints have the highest strength, irrespective of the doubler material. Finite element analysis (FEA) of the studied joints is also performed using commercial FEA tool Abaqus. In the FEA model, point-based fasteners are used for the rivets, and a cohesive zone contact model is used to simulate the adhesive bond. The FEA results indicate that the riveted joints have higher tensile stresses on the metal doublers compared to the ...

Journal of Alloys and Compounds, 2018

A model of microstructural evolution, based only on the original assumptions of the Kolmogorov, J... more A model of microstructural evolution, based only on the original assumptions of the Kolmogorov, Johnson & Mehl, and Avrami model of nucleation and growth kinetics, is presented. It is based on the computation of the average grain size of all grains born at the same time along the transformation, neglecting the dispersion of the grain size around this value. The model is computationally simple and inexpensive, and gives a good description of the grain size distribution along the transformation as well as all its distinctive features.

Metallurgical and Materials Transactions A, 2012

Advances in Materials Science and Engineering, 2017

The viscoelastic response of commercial Al–Zn–Mg and Al–Cu–Mg alloys was measured with a dynamic-... more The viscoelastic response of commercial Al–Zn–Mg and Al–Cu–Mg alloys was measured with a dynamic-mechanical analyzer (DMA) as a function of the temperature (from 30 to 425°C) and the loading frequency (from 0.01 to 150 Hz). The time-temperature superposition (TTS) principle has proven to be useful in studying mechanical relaxations and obtaining master curves for amorphous materials. In this work, the TTS principle is applied to the measured viscoelastic data (i.e., the storage and loss moduli) to obtain the corresponding master curves and to analyze the mechanical relaxations responsible for the viscoelastic behavior of the studied alloys. For the storage modulus it was possible to identify a master curve for a low-temperature region (from room temperature to 150°C) and, for the storage and loss moduli, another master curve for a high-temperature region (from 320 to 375°C). These temperature regions are coincidental with the stable intervals where no phase transformations occur. Th...

One of the main routes to obtain nanostructured materials is through the primary crystallization ... more One of the main routes to obtain nanostructured materials is through the primary crystallization of metallic glasses. In such transformations, crystallites with a different composition than the amorphous precursor grow with a diffusion-controlled regime. Particle growth is slowed and eventually halted by the impingement between the concentration gradients of surrounding particles. Primary crystallization kinetics is not well described by the KJMA equation, and this fact was generally ascribed to both the soft-impingement effect and the non-random nucleation. However, recent phase-field simulations showed that the underlying physical reason is the change in the local diffusion properties of the amorphous precursor due to the variation of the composition during the transformation. The kinetics of primary crystallization is thus well described by considering a diffusion coefficient of the slowest diffusing species dependent on the local concentration. The nanostructure developed in suc...

The structural relaxation, glass transition and crystallization processes of Mg65Cu25Y10 metallic... more The structural relaxation, glass transition and crystallization processes of Mg65Cu25Y10 metallic glass are studied by Differential Scanning Calorimetry (DSC) and Mechanical Spectroscopy. The relaxation model derived from the mechanical measurements is compared with the kinetics of these transformations obtained from the DSC curves. The structural relaxation kinetics is found to be controlled by the glassy dynamics following an Adams-GibbsVogel function. The glass transition and crystallization kinetics are controlled by the dynamics of the supercooled melt following a Vogel-Fulcher-Tammann behaviour. The results suggest that the microscopic processes responsible of structural relaxation and aging below the glass transition correspond to the same processes generating the -relaxation peak.

The influence of shear in the atomic structure of ternary Cu46Zr46Al8 metallic glass was studied ... more The influence of shear in the atomic structure of ternary Cu46Zr46Al8 metallic glass was studied at different temperatures by molecular dynamics (MD) simulation. At temperatures above and below the glass transition temperature the system was subjected to a shear deformation cycle; the shear deformation was carried in the [100] direction and then the original geometry was recovered. The system was analyzed in three states: initial state (before deformation), deformed state (sheared) and final state (recovery). The different states obtained by the atomistic simulations were examined by computing the directional pair distribution functions (dPDF) in the coordinate planes. The results showed by dPDFs of the planes perpendicular to the coordinate axis are apparently isotropic. However, the dPDF disengage when computed perpendicular to rotated axis. This reveals that the anisotropy introduced during the deformation cycles appears in directions [110] and [1 0], tilted 45 with respect to t...

Journal of Alloys and Compounds

Science China Physics, Mechanics & Astronomy

The viscoelastic response of a novel composite (A356 aluminum alloy matrix with ceramic reinforce... more The viscoelastic response of a novel composite (A356 aluminum alloy matrix with ceramic reinforcement particles developed from colliery shale waste) is measured with dynamic-mechanical analyzer, and is compared to pure aluminum, aluminum alloys A356, 7075 and 2024, and another composite (6061 aluminum alloy matrix reinforced with SiC particles). The studied materials show some common features but the novel composite is one of the most stable (a rapid decrease in stiffness starts only at very high temperature). Moreover, compared to the A356 alloy, the composite shows higher stiffness (since the reinforcement particles are stiffer than the A356 matrix and may foster precipitation hardening) and higher mechanical damping/internal friction (likely due to relaxations associated with the reinforcement particles and to the larger grain size for the A356 alloy). A typical relaxation peak in aluminum attributed to grain boundary sliding is suppressed in the composite because the reinforceme...

Materials Characterization, 2017

The microstructural evolution of an Al–Zn–Mg–Cu alloy under continuous heating over the temperatu... more The microstructural evolution of an Al–Zn–Mg–Cu alloy under continuous heating over the temperature range of 298 to 648 K (25 to 375 °C) is characterized by focused ion beam-scanning electron microscopy, transmission electron microscopy, and atom probe tomography. The chemical composition, dimensions, number density, and volume fraction of precipitates are measured comprehensively. Quantitative measurements of Guinier-Preston zones volume fraction and η′/η phase volume fraction are correlated to the viscoelastic response of the Al–Zn–Mg–Cu alloy with temperature in the studied range. This provides valuable evidence indicating that observed variations in the viscoelastic behavior of the Al–Zn–Mg–Cu alloy may be associated with phase transformations involving Guinier-Preston zones and phases η′ and η.

Journal of Non-Crystalline Solids

Metals

The mechanical relaxation behavior of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.... more The mechanical relaxation behavior of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6, and 0.8) metallic glasses was probed by dynamic mechanical analysis. The intensity of the secondary β relaxation increases along with the Co/Cu ratio, as has been reported in metallic glasses where the enthalpy of mixing for all pairs of atoms is negative. Furthermore, the intensity of the secondary β relaxation decreases after physical aging below the glass transition temperature, which is probably due to the reduction of the atomic mobility induced by physical aging.

Journal of Alloys and Compounds

Journal of Applied Crystallography, 2003

The current prototype’s key contribution to the field of light-weight structures is that it is th... more The current prototype’s key contribution to the field of light-weight structures is that it is the first time that a pure tensegrity ring has been used in place of a compression ring. This design features a cladding structure for a sports arena, which consist of a ring-shaped outer section and a central roof structure. The ring-shaped outer section of the stadium consists of a tensegrity structure, which uses textile membranes in a place of conventional tension cables to bear the tensile forces occurring between the pressure elements. The supporting framework and spatial enclosure therefore become one an extension to the tension integrity principle. The central area of the roof is covered over by a Geiger dome, which in turn is a specific version of the tensegrity principle.

Materials, 2019

In this work, experimental and numerical analyses of repairs on carbon fiber reinforced epoxy (CF... more In this work, experimental and numerical analyses of repairs on carbon fiber reinforced epoxy (CFRE) substrates, with CFRE and aluminum alloy doublers typical of aircraft structures, are presented. The substrates have a bridge gap of 12.7 mm (simulated crack), repaired with twin doublers joined with riveted, adhesive bonded, and hybrid joints. The performance of the repairs using different doubler materials and joining techniques are compared under static loading. The experimental results show that riveted joints have the lowest strength, while adhesive bonded joints have the highest strength, irrespective of the doubler material. Finite element analysis (FEA) of the studied joints is also performed using commercial FEA tool Abaqus. In the FEA model, point-based fasteners are used for the rivets, and a cohesive zone contact model is used to simulate the adhesive bond. The FEA results indicate that the riveted joints have higher tensile stresses on the metal doublers compared to the ...

Journal of Alloys and Compounds, 2018

A model of microstructural evolution, based only on the original assumptions of the Kolmogorov, J... more A model of microstructural evolution, based only on the original assumptions of the Kolmogorov, Johnson & Mehl, and Avrami model of nucleation and growth kinetics, is presented. It is based on the computation of the average grain size of all grains born at the same time along the transformation, neglecting the dispersion of the grain size around this value. The model is computationally simple and inexpensive, and gives a good description of the grain size distribution along the transformation as well as all its distinctive features.

Metallurgical and Materials Transactions A, 2012

Advances in Materials Science and Engineering, 2017

The viscoelastic response of commercial Al–Zn–Mg and Al–Cu–Mg alloys was measured with a dynamic-... more The viscoelastic response of commercial Al–Zn–Mg and Al–Cu–Mg alloys was measured with a dynamic-mechanical analyzer (DMA) as a function of the temperature (from 30 to 425°C) and the loading frequency (from 0.01 to 150 Hz). The time-temperature superposition (TTS) principle has proven to be useful in studying mechanical relaxations and obtaining master curves for amorphous materials. In this work, the TTS principle is applied to the measured viscoelastic data (i.e., the storage and loss moduli) to obtain the corresponding master curves and to analyze the mechanical relaxations responsible for the viscoelastic behavior of the studied alloys. For the storage modulus it was possible to identify a master curve for a low-temperature region (from room temperature to 150°C) and, for the storage and loss moduli, another master curve for a high-temperature region (from 320 to 375°C). These temperature regions are coincidental with the stable intervals where no phase transformations occur. Th...

One of the main routes to obtain nanostructured materials is through the primary crystallization ... more One of the main routes to obtain nanostructured materials is through the primary crystallization of metallic glasses. In such transformations, crystallites with a different composition than the amorphous precursor grow with a diffusion-controlled regime. Particle growth is slowed and eventually halted by the impingement between the concentration gradients of surrounding particles. Primary crystallization kinetics is not well described by the KJMA equation, and this fact was generally ascribed to both the soft-impingement effect and the non-random nucleation. However, recent phase-field simulations showed that the underlying physical reason is the change in the local diffusion properties of the amorphous precursor due to the variation of the composition during the transformation. The kinetics of primary crystallization is thus well described by considering a diffusion coefficient of the slowest diffusing species dependent on the local concentration. The nanostructure developed in suc...

The structural relaxation, glass transition and crystallization processes of Mg65Cu25Y10 metallic... more The structural relaxation, glass transition and crystallization processes of Mg65Cu25Y10 metallic glass are studied by Differential Scanning Calorimetry (DSC) and Mechanical Spectroscopy. The relaxation model derived from the mechanical measurements is compared with the kinetics of these transformations obtained from the DSC curves. The structural relaxation kinetics is found to be controlled by the glassy dynamics following an Adams-GibbsVogel function. The glass transition and crystallization kinetics are controlled by the dynamics of the supercooled melt following a Vogel-Fulcher-Tammann behaviour. The results suggest that the microscopic processes responsible of structural relaxation and aging below the glass transition correspond to the same processes generating the -relaxation peak.

The influence of shear in the atomic structure of ternary Cu46Zr46Al8 metallic glass was studied ... more The influence of shear in the atomic structure of ternary Cu46Zr46Al8 metallic glass was studied at different temperatures by molecular dynamics (MD) simulation. At temperatures above and below the glass transition temperature the system was subjected to a shear deformation cycle; the shear deformation was carried in the [100] direction and then the original geometry was recovered. The system was analyzed in three states: initial state (before deformation), deformed state (sheared) and final state (recovery). The different states obtained by the atomistic simulations were examined by computing the directional pair distribution functions (dPDF) in the coordinate planes. The results showed by dPDFs of the planes perpendicular to the coordinate axis are apparently isotropic. However, the dPDF disengage when computed perpendicular to rotated axis. This reveals that the anisotropy introduced during the deformation cycles appears in directions [110] and [1 0], tilted 45 with respect to t...

Journal of Alloys and Compounds

Science China Physics, Mechanics & Astronomy

The viscoelastic response of a novel composite (A356 aluminum alloy matrix with ceramic reinforce... more The viscoelastic response of a novel composite (A356 aluminum alloy matrix with ceramic reinforcement particles developed from colliery shale waste) is measured with dynamic-mechanical analyzer, and is compared to pure aluminum, aluminum alloys A356, 7075 and 2024, and another composite (6061 aluminum alloy matrix reinforced with SiC particles). The studied materials show some common features but the novel composite is one of the most stable (a rapid decrease in stiffness starts only at very high temperature). Moreover, compared to the A356 alloy, the composite shows higher stiffness (since the reinforcement particles are stiffer than the A356 matrix and may foster precipitation hardening) and higher mechanical damping/internal friction (likely due to relaxations associated with the reinforcement particles and to the larger grain size for the A356 alloy). A typical relaxation peak in aluminum attributed to grain boundary sliding is suppressed in the composite because the reinforceme...

Materials Characterization, 2017

The microstructural evolution of an Al–Zn–Mg–Cu alloy under continuous heating over the temperatu... more The microstructural evolution of an Al–Zn–Mg–Cu alloy under continuous heating over the temperature range of 298 to 648 K (25 to 375 °C) is characterized by focused ion beam-scanning electron microscopy, transmission electron microscopy, and atom probe tomography. The chemical composition, dimensions, number density, and volume fraction of precipitates are measured comprehensively. Quantitative measurements of Guinier-Preston zones volume fraction and η′/η phase volume fraction are correlated to the viscoelastic response of the Al–Zn–Mg–Cu alloy with temperature in the studied range. This provides valuable evidence indicating that observed variations in the viscoelastic behavior of the Al–Zn–Mg–Cu alloy may be associated with phase transformations involving Guinier-Preston zones and phases η′ and η.

Journal of Non-Crystalline Solids

Metals

The mechanical relaxation behavior of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.... more The mechanical relaxation behavior of the (La0.5Ce0.5)65Al10(CoxCu1−x)25 at% (x = 0, 0.2, 0.4, 0.6, and 0.8) metallic glasses was probed by dynamic mechanical analysis. The intensity of the secondary β relaxation increases along with the Co/Cu ratio, as has been reported in metallic glasses where the enthalpy of mixing for all pairs of atoms is negative. Furthermore, the intensity of the secondary β relaxation decreases after physical aging below the glass transition temperature, which is probably due to the reduction of the atomic mobility induced by physical aging.

Journal of Alloys and Compounds

Journal of Applied Crystallography, 2003