349 research outputs found
Microstructure modelling of hot deformation of Al–1%Mg alloy
No full textThis study presents the application of the finite elementmethod and intelligent systems techniques to the
prediction of microstructural mapping for aluminium alloys. Here, the material within each finite element
is defined using a hybrid model. The hybrid model is based on neuro-fuzzy and physically based components
and it has been combined with the finite element technique. The model simulates the evolution of
the internal state variables (i.e. dislocation density, subgrain size and subgrain boundary misorientation)
and their effect on the recrystallisation behaviour of the stock. This paper presents the theory behind
the model development, the integration between the numerical techniques, and the application of the
technique to a hot rolling operation using aluminium, 1 wt% magnesium alloy. Furthermore, experimental
data from plane strain compression (PSC) tests and rolling are used to validate the modelling outcome.
The results show that the recrystallisation kinetics agree well with the experimental results for different
annealing times. This hybrid approach has proved to be more accurate than conventional methods using empirical equations
Machine learning aided nanoindentation: A review of the current state and future perspectives
No full textThe solution of instrumented indentation inverse problems by physically-based models still represents a complex challenge yet to be solved in metallurgy and materials science. In recent years, Machine Learning (ML) tools have emerged as a feasible and more efficient alternative to extract complex microstructure-property correlations from instrumented indentation data in advanced materials. On this basis, the main objective of this review article is to summarize the extent to which different ML tools have been recently employed in the analysis of both numerical and experimental data obtained by instrumented indentation testing, either using spherical or sharp indenters, particularly by nanoindentation. Also, the impact of using ML could have in better understanding the microstructure-mechanical properties-performance relationships of a wide range of materials tested at this length scale has been addressed.The analysis of the recent literature indicates that a combination of advanced nanomechanical/microstructural characterization with finite element simulation and different ML algorithms constitutes a powerful tool to bring ground-breaking innovation in materials science. These research means can be employed not only for extracting mechanical properties of both homogeneous and heterogeneous materials at multiple length scales, but also could assist in understanding how these properties change with the compositional and microstructural in-service modifications. Furthermore, they can be used for design and synthesis of novel multi-phase materials
Contrapunteos de Lydia Cabrera
No full textEven today in the history of Cuban anthropology, little attention is paid to the writer and anthropologist Lydia Cabrera, who has only recently begun to be part of the list of intellectuals in official Cuban culture. However, because of her work and life trajectory, Cabrera can be considered the modern founder of studies on Afro-Cuban religions.
The main purpose of this text is to analyse Lydia Cabrera’s ethnographic work based on the idea that there was a ‘counterpoint’, a dialogue, a metaphorical game, between the liminal identity of the author herself – manifested in a racial, cultural, gender, social and political sense – and her interest and dedication to the contribution of slaves and the population of African origin to the history, culture and, ultimately, the identity of their Cuban homeland.Todavía hoy en la historia de la antropología cubana se presta poca atención a la escritora y antropóloga Lydia Cabrera, quien solo muy recientemente ha empezado a formar parte de la nómina intelectual de la cultura cubana oficial. Sin embargo, en función de su obra y trayectoria vital puede considerarse a Cabrera como la fundadora moderna de los estudios sobre las religiones afrocubanas.
El objeto central de este texto es analizar el trabajo etnográfico de Lydia Cabrera a partir de la idea de que existe un contrapunteo, un diálogo, un juego metafórico, entre la identidad liminar de la propia autora -manifiesta en un sentido racial, cultural, de género, social y político- y su interés y dedicación a la aportación de los esclavos y la población de origen africano a la historia, a la cultura y, en última instancia, a la identidad misma de su patria cubana
Measurement of residual stress in thermal spray coatings by the incremental hole drilling method
No full textThe experimental measurement of residual stresses originating within thick coatings deposited by thermal spray processes onto solid substrates plays a fundamental role in the preliminary stages of coating design and process parameters optimization. The main objective of the present investigation was to determine the residual stresses by means of the incremental hole drilling method in order to perform the measurement of the stress field through the thickness of two different HVOF Nickel-based coatings. The holes through the coatings were carried out by means of a high velocity drilling machine (Restan). A finite element calculation procedure was used to identify the calibration coefficients necessary to evaluate the stress field. The Integral method was used for the analysis of non-uniform through-thickness stresses. The results for both coatings indicate that the nature of the residual stresses is tensile and their values are between 150-300 MPa. (c) 2006 Elsevier B.V. All rights reserved
OBREGON, Alvaro (Gral.); CABRERA, Luis (Lic.)
No full textFile originally titled “Gen. Alvaro Obregón. File number 5. Subject: B.A. Luis Cabrera. Letter signed by Clemente Reynoso on April 29-919”. Clemente Reynoso is a pseudonym of Gen. Alvaro Obregón, used when answering a letter written by B.A. Luis Cabrera, Secretary of Finance and Public Credit. In said letter, Cabrera addresses three issues: How friends are made using an elevated position. How those friends are “political dead weight” and why the author himself did not make friends by using his position as Secretary of Finance and Public Credit. Clemente Reynoso analyzes the three points, harshly criticizing Cabrera. (This letter can also be found in series 11020700, file C-20, “CABRERA, Luis”, in the Alvaro Obregón database and in series 13010201 “Documents in a Lock Box. CABRERA, Luis; Clemente REYNOSO”, file 10/7 from this same Database). / Cédula titulada originalmente "Señor General Alvaro Obregón. Expediente número 5. Asunto: Lic. Luis Cabrera. Carta firmada por Clemente Reynoso al. Abril 29-919". Clemente Reynoso es un seudónimo del Gral. Alvaro Obregón, quien contesta una carta del Lic. Luis Cabrera, Secretario de Hacienda y Crédito Público, en la que Cabrera aborda tres asuntos: Cómo se fabrican amigos estando en un puesto elevado. Cómo esos amigos son el "lastre político" y por qué no fabricó amigos usando el puesto de Secretario de Hacienda y Crédito Público. Clemente Reynoso analiza los tres puntos criticando duramente a Cabrera. (Esta carta se encuentra también en la serie 11020700, expediente C-20, "CABRERA, Luis" del Fondo Alvaro Obregón y en la serie 13010201 "Documentos en Caja. CABRERA, Luis; Clemente REYNOSO", expediente 10/7 de este mismo Fondo)
OBREGON, Alvaro (Gral.); CABRERA, Luis (Lic.)
No full textFile originally titled “Gen. Alvaro Obregón. File number 5. Subject: B.A. Luis Cabrera. Letter signed by Clemente Reynoso on April 29-919”. Clemente Reynoso is a pseudonym of Gen. Alvaro Obregón, used when answering a letter written by B.A. Luis Cabrera, Secretary of Finance and Public Credit. In said letter, Cabrera addresses three issues: How friends are made using an elevated position. How those friends are “political dead weight” and why the author himself did not make friends by using his position as Secretary of Finance and Public Credit. Clemente Reynoso analyzes the three points, harshly criticizing Cabrera. (This letter can also be found in series 11020700, file C-20, “CABRERA, Luis”, in the Alvaro Obregón database and in series 13010201 “Documents in a Lock Box. CABRERA, Luis; Clemente REYNOSO”, file 10/7 from this same Database). / Cédula titulada originalmente "Señor General Alvaro Obregón. Expediente número 5. Asunto: Lic. Luis Cabrera. Carta firmada por Clemente Reynoso al. Abril 29-919". Clemente Reynoso es un seudónimo del Gral. Alvaro Obregón, quien contesta una carta del Lic. Luis Cabrera, Secretario de Hacienda y Crédito Público, en la que Cabrera aborda tres asuntos: Cómo se fabrican amigos estando en un puesto elevado. Cómo esos amigos son el "lastre político" y por qué no fabricó amigos usando el puesto de Secretario de Hacienda y Crédito Público. Clemente Reynoso analiza los tres puntos criticando duramente a Cabrera. (Esta carta se encuentra también en la serie 11020700, expediente C-20, "CABRERA, Luis" del Fondo Alvaro Obregón y en la serie 13010201 "Documentos en Caja. CABRERA, Luis; Clemente REYNOSO", expediente 10/7 de este mismo Fondo)
Nanoindentación de capas finas de ZrW
No full textDoble titulacióEl objetivo de este proyecto es de determinar el mejor modelo analítico para
caracterizar el comportamiento mecánico (modulo elástico y dureza) de una capa fina de
ZrW depositada sobre un sustrato de sílice. Para el modulo elástico, los modelos
estudiados son: Rar et al., Bec et al, Saha y Nix. Para la dureza, el estudio será realizado
con los modelos siguientes: Jönsson y Hogmark, Chicot y Lesage, Korsunsky et al.,
Puchi-Cabrera.
El estudio se hace sobre seis materiales, que son en realidad variaciones de
composición química de aleaciones de ZrW, con estructuras microscópicas diferentes.
Serán designados por la intensidad de corriente utilizada durante la deposición con
magnetrón sputtering (0,15A - 0,30A – 0,32A – 0,34A – 0,36A - 0,50A).
El modelo de Saha y Nix da los mejores resultados para una modelización del
modulo elástico. El modelo de Jönsson y Hogmark da mejores resultados para la dureza,
aunque satisfactorio para todos los materiales aunque en algunos casos, el modelo de
Puchi-Cabrera se revela mejor”
Nanoindentación de capas finas de ZrW
No full textDoble titulacióEl objetivo de este proyecto es de determinar el mejor modelo analítico para
caracterizar el comportamiento mecánico (modulo elástico y dureza) de una capa fina de
ZrW depositada sobre un sustrato de sílice. Para el modulo elástico, los modelos
estudiados son: Rar et al., Bec et al, Saha y Nix. Para la dureza, el estudio será realizado
con los modelos siguientes: Jönsson y Hogmark, Chicot y Lesage, Korsunsky et al.,
Puchi-Cabrera.
El estudio se hace sobre seis materiales, que son en realidad variaciones de
composición química de aleaciones de ZrW, con estructuras microscópicas diferentes.
Serán designados por la intensidad de corriente utilizada durante la deposición con
magnetrón sputtering (0,15A - 0,30A – 0,32A – 0,34A – 0,36A - 0,50A).
El modelo de Saha y Nix da los mejores resultados para una modelización del
modulo elástico. El modelo de Jönsson y Hogmark da mejores resultados para la dureza,
aunque satisfactorio para todos los materiales aunque en algunos casos, el modelo de
Puchi-Cabrera se revela mejor”
Nanoindentación de capas finas de ZrW
No full textDoble titulacióEl objetivo de este proyecto es de determinar el mejor modelo analítico para
caracterizar el comportamiento mecánico (modulo elástico y dureza) de una capa fina de
ZrW depositada sobre un sustrato de sílice. Para el modulo elástico, los modelos
estudiados son: Rar et al., Bec et al, Saha y Nix. Para la dureza, el estudio será realizado
con los modelos siguientes: Jönsson y Hogmark, Chicot y Lesage, Korsunsky et al.,
Puchi-Cabrera.
El estudio se hace sobre seis materiales, que son en realidad variaciones de
composición química de aleaciones de ZrW, con estructuras microscópicas diferentes.
Serán designados por la intensidad de corriente utilizada durante la deposición con
magnetrón sputtering (0,15A - 0,30A – 0,32A – 0,34A – 0,36A - 0,50A).
El modelo de Saha y Nix da los mejores resultados para una modelización del
modulo elástico. El modelo de Jönsson y Hogmark da mejores resultados para la dureza,
aunque satisfactorio para todos los materiales aunque en algunos casos, el modelo de
Puchi-Cabrera se revela mejor”
Influence of tip defect and indenter shape on the mechanical properties determination by indentation of a TiB2–60%B4C ceramic composite
No full textInstrumented indentation is very useful to determine the elastic modulus and hardness of materials. To obtain reliable values of the mechanical properties, the measurement of the indenter displacement into the material must be very precise. In practice, the frame compliance of the instrument and the indenter tip defect are among the most influential parameters. In microindentation, the frame compliance term must be calculated for each analysis. On the other hand, the tip defect can lead to a wrong estimation of the contact area, which is involved in both the elastic modulus and the hardness calculations. The present work is mainly focused on the influence of the tip defect on the determination of the mechanical properties of a composite TiB₂–60% B₄C hard material using Berkovich, Vickers, Knoop and spherical indenters. This composite system was obtained by sintering in vacuum, employing a pulsed electric current, without any sintering additives. It has been shown that the tip defect greatly affects the results related to the mechanical properties of the system under study, even for low defect sizes, which are usually neglected in practice. After correction, the elastic modulus of the TiB₂–60% B₄C is found to be equal to 490 GPa whatever the indenter shape used. This result corroborates the value of 500 GPa found for this system by employing the resonance frequency method according to the ASTM Standard e1876-99. For analyzing the hardness-load dependence, the representative parameter of the Proportional Specimen Resistance model becomes null when the tip defect is introduced into the hardness calculation. Additionally, this parameter is found to be directly proportional to the tip defect size, suggesting a special attention when characterizing the indentation size effect of materials. Finally, the Meyer hardness found for the TiB₂–60% B₄C is close to 20 GPa.sponsorship: Professor Puchi-Cabrera gratefully acknowledges the financial support of the Conseil Regional Nord-Pas de Calais, France, through the International Chair program 2011 and Professor Staia acknowledges the financial support from Ghent University (BOF). (Conseil Regional Nord-Pas de Calais, France, Ghent University (BOF))status: Publishe
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