Francisco Gálvez - Academia.edu (original) (raw)

Uploads

Papers by Francisco Gálvez

For several decades there was a large gap between the typical masses of the meteoroids detectable... more For several decades there was a large gap between the typical masses of the meteoroids detectable by ground-based photographic camera networks that typically reach -4 magnitude (Spurný and Boroviˇ ka, 2002) and those observed visually (mag. +6). Consequently, visual observations and medium-field photographic exposures have played an important role in determining meteoric fluxes during periods of moderate or high meteoric

Proceedings of The National Academy of Sciences, 2011

Adaptive variation tends to emerge clinally along environmental gradients or discretely among hab... more Adaptive variation tends to emerge clinally along environmental gradients or discretely among habitats with limited connectivity. However, in Atlantic killifish (Fundulus heteroclitus), a population genetic discontinuity appears in the absence of obvious barriers to gene flow along parallel salinity clines and coincides with a physiologically stressful salinity. We show that populations resident on either side of this discontinuity differ in their abilities to compensate for osmotic shock and illustrate the physiological and functional genomic basis of population variation in hypoosmotic tolerance. A population native to a freshwater habitat, upstream of the genetic discontinuity, exhibits tolerance to extreme hypoosmotic challenge, whereas populations native to brackish or marine habitats downstream of the discontinuity lose osmotic homeostasis more severely and take longer to recover. Comparative transcriptomics reveals a core transcriptional response associated with acute and acclimatory responses to hypoosmotic shock and posits unique mechanisms that enable extreme osmotic tolerance. Of the genes that vary in expression among populations, those that are putatively involved in physiological acclimation are more likely to exhibit nonneutral patterns of divergence between freshwater and brackish populations. It is not the well-known effectors of osmotic acclimation, but rather the lesser-known immediate-early responses, that appear important in contributing to population differences.

Dymat 2009: 9th International Conference on the Mechanical and Physical Behaviour of Materials Under Dynamic Loading, Vol 1, 2009

This paper presents the results of an experimental programme to obtain the mechanical behaviour o... more This paper presents the results of an experimental programme to obtain the mechanical behaviour of the Inconel 713 Low Carbon alloy at different strain rates and from room up to higher temperatures. This material is used on aircraft engine turbine blades for its excellent performance at high temperatures, and is produced by cast. The experimental work has been carried out using two testing techniques covering different strain rates and using different heating devices to achieve temperatures from room up to 850xC. The testing set-up was designed to perform compression tests on prismatic specimens and tensile tests of cylindrical specimens. Low strain rate tests were performed using a servo-hydraulic Instron machine at a constant strain rate of 10 x5 s x1 and a constant temperature, using a MTS short furnace. The high strain rate tests were performed using a Hopkinson bar in conjunction with a special furnace, testing at strain rates of about 10 3 s x1 . This Hopkinson bar has been modified to test metallic materials at very high temperatures using high strength nickel super alloy bars. Stress-strain curves of the Inconel 713LC alloy have been obtained in different conditions. The materials exhibit elastic-plastic behaviour with marked strain hardening. The test results show the influence of strain rate and temperature. The material has a very good performance up to very high temperatures, even improving its yield strength when increasing the temperature. The strain rate effect is more relevant than the temperature effect; the results show that the yield strength increases about 15% at high strain rate when compared to static tests.

Available from the Minor Planet Center.

Nucleic Acids Research, 2014

Initial results from the first year of continuous CCD low-scan-rate all-sky and video monitoring ... more Initial results from the first year of continuous CCD low-scan-rate all-sky and video monitoring by the SPanish Meteor Network (SPMN) are presented. Under extraordinary weather conditions, the SPMN recorded almost 40 bright (over m=-6) fireballs, some of which were observed simultaneously from several stations. Daily observations of meteor activity have helped to increase our knowledge on cometary and asteroidal-origin meteoroid streams. The focus herein will be on the overall description of the fireballs recorded, first estimations of the measured spatial fluxes of selected streams, and information on unexpected activity from poorly-known meteoroid streams.

Journal of Composite Materials, 2010

The low-velocity impact behavior was studied in hybrid laminates manufactured by RTM with woven c... more The low-velocity impact behavior was studied in hybrid laminates manufactured by RTM with woven carbón and glass (S2) fabrics. Specimens with different thicknesses and glass fiber content (from 0 to 21 vol. %) were tested with impact energies in the range 30-245 J and the resulting deformation and fracture micromechanisms were studied using X-ray microtomography. The results of these analyses, together with those of the impact tests (máximum load and energy absorbed), were used to elucídate the role played by glass fiber hybridization on the fracture micromechanisms and on the overall lamínate performance under low-velocity impact.

Journal of Applied Mechanics, 2012

ABSTRACT An experimental and numerical study of ballistic impacts on steel plates at various temp... more ABSTRACT An experimental and numerical study of ballistic impacts on steel plates at various temperatures (700 degrees C, 400 degrees C and room temperature) has been carried out. The motivation for this work is the blade-off event that may occur inside a jet engine turbine. However, as a first attempt to understand this complex loading process, a somewhat simpler approach is carried out in the present work. The material used in this study is the FV535 martensitic stainless steel, which is one of the most commonly used materials for turbine casings. Based on material test data, a Modified Johnson-Cook (MJC) model was calibrated for numerical simulations using the LS-DYNA explicit finite element code. To check the mesh size sensitivity, 2D axisymmetric finite element models with three different mesh sizes and configurations were used for the various temperatures. Two fixed meshes with 64 and 128 elements over the 2 mm thick plate and one mesh with 32 elements over the thickness with adaptive remeshing were used in the simulations. Both the formation of adiabatic shear bands in the perforation process and the modeling of the thermal softening effects at high temperatures have been found crucial in order to achieve good results. [DOI: 10.1115/1.4004296]

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1990

The European Physical Journal Special Topics, 2012

A series of quasi-static and dynamic tensile tests at varying temperatures were carried out to de... more A series of quasi-static and dynamic tensile tests at varying temperatures were carried out to determine the mechanical behaviour of Ti-45Al-2Nb-2Mn+0.8vol.% TiB 2 XD as-HIPed alloy. The temperature for the tests ranged from room temperature to 850 • C. The effect of the temperature on the ultimate tensile strength, as expected, was almost negligible within the selected temperature range. Nevertheless, the plastic flow suffered some softening because of the temperature. This alloy presents a relatively low ductility; thus, a low tensile strain to failure. The dynamic tests were performed in a Split Hopkinson Tension Bar, showing an increase of the ultimate tensile strength due to the strain rate hardening effect. Johnson-Cook constitutive relation was used to model the plastic flow. A post-testing microstructural of the specimens revealed an inhomogeneous structure, consisting of lamellar α 2 + γ structure and γ phase equiaxed grains in the centre, and a fully lamellar structure on the rest. The assessment of the duplex-fully lamellar area ratio showed a clear relationship between the microstructure and the fracture behaviour.

Engineering Fracture Mechanics, 2012

The new generation jet engines operate at highly demanding working conditions. Such conditions ne... more The new generation jet engines operate at highly demanding working conditions. Such conditions need very precise design which implies an exhaustive study of the engine materials and behaviour in their extreme working conditions. With this purpose, this work intends to describe a numerically-based calibration of the widely-used Johnson-Cook fracture model, as well as its validation through high temperature ballistic impact tests. To do so, a widely-used turbine casing material is studied. This material is the Firth Vickers 535 martensitic stainless steel. Quasi-static tensile tests at various temperatures in a universal testing machine, as well as dynamic tests in a Split Hopkinson Pressure Bar, are carried out at different triaxialities. Using ABAQUS/Standard and LS-DYNA numerical codes, experimental data are matched. This method allows the researcher to obtain critical data of equivalent plastic strain and triaxility, which allows for more precise calibration of the Johnson-Cook fracture model. Such enhancement allows study of the fracture behaviour of the material across its usage temperature range.

For several decades there was a large gap between the typical masses of the meteoroids detectable... more For several decades there was a large gap between the typical masses of the meteoroids detectable by ground-based photographic camera networks that typically reach -4 magnitude (Spurný and Boroviˇ ka, 2002) and those observed visually (mag. +6). Consequently, visual observations and medium-field photographic exposures have played an important role in determining meteoric fluxes during periods of moderate or high meteoric

Proceedings of The National Academy of Sciences, 2011

Adaptive variation tends to emerge clinally along environmental gradients or discretely among hab... more Adaptive variation tends to emerge clinally along environmental gradients or discretely among habitats with limited connectivity. However, in Atlantic killifish (Fundulus heteroclitus), a population genetic discontinuity appears in the absence of obvious barriers to gene flow along parallel salinity clines and coincides with a physiologically stressful salinity. We show that populations resident on either side of this discontinuity differ in their abilities to compensate for osmotic shock and illustrate the physiological and functional genomic basis of population variation in hypoosmotic tolerance. A population native to a freshwater habitat, upstream of the genetic discontinuity, exhibits tolerance to extreme hypoosmotic challenge, whereas populations native to brackish or marine habitats downstream of the discontinuity lose osmotic homeostasis more severely and take longer to recover. Comparative transcriptomics reveals a core transcriptional response associated with acute and acclimatory responses to hypoosmotic shock and posits unique mechanisms that enable extreme osmotic tolerance. Of the genes that vary in expression among populations, those that are putatively involved in physiological acclimation are more likely to exhibit nonneutral patterns of divergence between freshwater and brackish populations. It is not the well-known effectors of osmotic acclimation, but rather the lesser-known immediate-early responses, that appear important in contributing to population differences.

Dymat 2009: 9th International Conference on the Mechanical and Physical Behaviour of Materials Under Dynamic Loading, Vol 1, 2009

This paper presents the results of an experimental programme to obtain the mechanical behaviour o... more This paper presents the results of an experimental programme to obtain the mechanical behaviour of the Inconel 713 Low Carbon alloy at different strain rates and from room up to higher temperatures. This material is used on aircraft engine turbine blades for its excellent performance at high temperatures, and is produced by cast. The experimental work has been carried out using two testing techniques covering different strain rates and using different heating devices to achieve temperatures from room up to 850xC. The testing set-up was designed to perform compression tests on prismatic specimens and tensile tests of cylindrical specimens. Low strain rate tests were performed using a servo-hydraulic Instron machine at a constant strain rate of 10 x5 s x1 and a constant temperature, using a MTS short furnace. The high strain rate tests were performed using a Hopkinson bar in conjunction with a special furnace, testing at strain rates of about 10 3 s x1 . This Hopkinson bar has been modified to test metallic materials at very high temperatures using high strength nickel super alloy bars. Stress-strain curves of the Inconel 713LC alloy have been obtained in different conditions. The materials exhibit elastic-plastic behaviour with marked strain hardening. The test results show the influence of strain rate and temperature. The material has a very good performance up to very high temperatures, even improving its yield strength when increasing the temperature. The strain rate effect is more relevant than the temperature effect; the results show that the yield strength increases about 15% at high strain rate when compared to static tests.

Available from the Minor Planet Center.

Nucleic Acids Research, 2014

Initial results from the first year of continuous CCD low-scan-rate all-sky and video monitoring ... more Initial results from the first year of continuous CCD low-scan-rate all-sky and video monitoring by the SPanish Meteor Network (SPMN) are presented. Under extraordinary weather conditions, the SPMN recorded almost 40 bright (over m=-6) fireballs, some of which were observed simultaneously from several stations. Daily observations of meteor activity have helped to increase our knowledge on cometary and asteroidal-origin meteoroid streams. The focus herein will be on the overall description of the fireballs recorded, first estimations of the measured spatial fluxes of selected streams, and information on unexpected activity from poorly-known meteoroid streams.

Journal of Composite Materials, 2010

The low-velocity impact behavior was studied in hybrid laminates manufactured by RTM with woven c... more The low-velocity impact behavior was studied in hybrid laminates manufactured by RTM with woven carbón and glass (S2) fabrics. Specimens with different thicknesses and glass fiber content (from 0 to 21 vol. %) were tested with impact energies in the range 30-245 J and the resulting deformation and fracture micromechanisms were studied using X-ray microtomography. The results of these analyses, together with those of the impact tests (máximum load and energy absorbed), were used to elucídate the role played by glass fiber hybridization on the fracture micromechanisms and on the overall lamínate performance under low-velocity impact.

Journal of Applied Mechanics, 2012

ABSTRACT An experimental and numerical study of ballistic impacts on steel plates at various temp... more ABSTRACT An experimental and numerical study of ballistic impacts on steel plates at various temperatures (700 degrees C, 400 degrees C and room temperature) has been carried out. The motivation for this work is the blade-off event that may occur inside a jet engine turbine. However, as a first attempt to understand this complex loading process, a somewhat simpler approach is carried out in the present work. The material used in this study is the FV535 martensitic stainless steel, which is one of the most commonly used materials for turbine casings. Based on material test data, a Modified Johnson-Cook (MJC) model was calibrated for numerical simulations using the LS-DYNA explicit finite element code. To check the mesh size sensitivity, 2D axisymmetric finite element models with three different mesh sizes and configurations were used for the various temperatures. Two fixed meshes with 64 and 128 elements over the 2 mm thick plate and one mesh with 32 elements over the thickness with adaptive remeshing were used in the simulations. Both the formation of adiabatic shear bands in the perforation process and the modeling of the thermal softening effects at high temperatures have been found crucial in order to achieve good results. [DOI: 10.1115/1.4004296]

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1990

The European Physical Journal Special Topics, 2012

A series of quasi-static and dynamic tensile tests at varying temperatures were carried out to de... more A series of quasi-static and dynamic tensile tests at varying temperatures were carried out to determine the mechanical behaviour of Ti-45Al-2Nb-2Mn+0.8vol.% TiB 2 XD as-HIPed alloy. The temperature for the tests ranged from room temperature to 850 • C. The effect of the temperature on the ultimate tensile strength, as expected, was almost negligible within the selected temperature range. Nevertheless, the plastic flow suffered some softening because of the temperature. This alloy presents a relatively low ductility; thus, a low tensile strain to failure. The dynamic tests were performed in a Split Hopkinson Tension Bar, showing an increase of the ultimate tensile strength due to the strain rate hardening effect. Johnson-Cook constitutive relation was used to model the plastic flow. A post-testing microstructural of the specimens revealed an inhomogeneous structure, consisting of lamellar α 2 + γ structure and γ phase equiaxed grains in the centre, and a fully lamellar structure on the rest. The assessment of the duplex-fully lamellar area ratio showed a clear relationship between the microstructure and the fracture behaviour.

Engineering Fracture Mechanics, 2012

The new generation jet engines operate at highly demanding working conditions. Such conditions ne... more The new generation jet engines operate at highly demanding working conditions. Such conditions need very precise design which implies an exhaustive study of the engine materials and behaviour in their extreme working conditions. With this purpose, this work intends to describe a numerically-based calibration of the widely-used Johnson-Cook fracture model, as well as its validation through high temperature ballistic impact tests. To do so, a widely-used turbine casing material is studied. This material is the Firth Vickers 535 martensitic stainless steel. Quasi-static tensile tests at various temperatures in a universal testing machine, as well as dynamic tests in a Split Hopkinson Pressure Bar, are carried out at different triaxialities. Using ABAQUS/Standard and LS-DYNA numerical codes, experimental data are matched. This method allows the researcher to obtain critical data of equivalent plastic strain and triaxility, which allows for more precise calibration of the Johnson-Cook fracture model. Such enhancement allows study of the fracture behaviour of the material across its usage temperature range.