Gonzalez-Ojeda, Roberto
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Preferred name
Gonzalez-Ojeda, Roberto
Official Name
Gonzalez Ojeda, Roberto
Alternative Name
robglez
González-Ojeda, R.
Main Affiliation
ORCID
Scopus Author ID
56314856300
Researcher ID
DTL-2716-2022

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Now showing 1 - 10 of 36
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Superplasticity of ultrafine grained low-carbon HSLA steels

2012 , Verdeja González, José Ignacio , Quintana, María José , García García, José Ovidio , Verdeja González, Luis Felipe , Gonzalez-Ojeda, Roberto , Fernández Fernández, Sara

Steels with ultrafine grained structure may present superplastic behavior at specific temperatures and strain rates that allow the grain boundary sliding mechanisms to be activated. The work presents high temperature tension tests in a low carbon, low alloy steel obtained by advanced thermomechanical controlled rolling processes, showing at 800°C elongations as high as 200%. The microstructure of the steel was analyzed in order to identify ferrite and pearlite grain boundaries, and their interaction after the specimens were deformed, showing intergranular decohesions, restored ferrite grains and elimination of banded structure, which are evidence of superplastic mechanisms in this material which is, in fact, ultrafine grained as demonstrated by quantitative metallographic techniques and grain size distribution analysis.

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Dual-phase ultrafine grained steels produced by controlled rolling processes

2011 , Quintana, María José , Gonzalez-Ojeda, Roberto , Verdeja González, Luis Felipe , Verdeja González, José Ignacio

Double-phase steels are an excellent alternative in the production of automotive parts that require high mechanical resistance, high impact strength and elevated elongation. These materials are produced using low-alloy steels as a basis, reducing costs and resulting in a combination of martensite and ferrite structures with ultrafine grain sizes. These characteristics are accomplished through a strict control of rolling conditions: strain rate, cooling rate and direct quenching. This work presents the results of tension testing of two types of double phased steels, along with microstructural characterization, in order to understand the effect of the advanced thermomechanical controlled rolling processes on the formation of the microstructure and the resulting mechanical properties.

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Cooling efficiency in furnace design

2013-12 , Gonzalez-Ojeda, Roberto , Quintana Hernández, María José , Ruiz Bustinza, Iñigo , García Carcedo, Fernando , Barbés, Miguel Ángel , Florentina Barbés, María

During melting, reduction or thermal treatment of a steel charge, the input of energy (either chemical or electrical) is indispensable to guarantee the viability of the process. Under these circumstances, it will be reasonable to design the furnace lining in such a way that heat loss through the walls is minimized. Nevertheless, it can be proved that, for some situations, it is more efficient to withdraw as much heat as possible from the walls than trying to thermally isolate the system. The work presents recommendations for the design of walls and cooling systems in furnaces obtained by quantitative analysis of temperatures reached in specific locations of the furnace using the nodal wear model. The analysis indicates that the wear process of the lining may be controlled if all the elements that intervene in the process are known.

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Effect of Mo on high entropy Ti-Nb-Zr-Ta alloy: Phase equilibria, microstructure and mechanical properties

2023 , Aranda, Víctor A. , Figueroa, I. A. , Amigó-Borrás, V. , Gonzalez-Ojeda, Roberto , Lozada Flores, Octavio , Vidilli, André Luiz , Barcelos Otani, Lucas , González, Gonzalo

Thermal and mechanical properties of Ti-Nb-Ta-Zr high entropy alloys are often influenced by element content and manufacturing routes, producing significant differences between mechanical properties and microstructure. This work presents a Ti-Nb-Ta-Zr alloy in which Mo is added by adjusting the composition with phase equilibria simulation, improving the mechanical properties based on a mixture of two chemically different solid solutions (BCC1 and BCC2). The materials were produced by arc-melting suction casting. Characterization of the dendritic and interdendritic zones was carried out by means of X-ray spectroscopy, indicating the segregation of Ta and Nb in BCC1 and Zr and Ti in BCC2 phases. The dislocation density increased preferentially in the interdendritic Zr-Ti rich zones. The mechanical properties results were related to the chemical differences between the BCC1 and BCC2 lattice parameters induced by the Mo addition. With Mo segregating between both BCC cells, the resulting microstructure increased the yield strength, being confirmed with the kernel average maps, which showed that, after compression tests, the interdendritic zone accumulated a high density of dislocations, resulting in the segregation of Ti and Zr, affecting the mechanical response of Mo containing alloy. © 2023 Elsevier B.V.

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Dmaic of structural steel parts through FEM and DOE

2016 , Gonzalez-Ojeda, Roberto , Quintana, María José , Verdeja, Luis Felipe

DMAIC in the automotive sector is applied to the design and manufacturing processes of structural steel parts in order to assess variability in mechanical properties of the raw materials, use of different types of steel in the same part, modifications in thickness of the steel sheet and even changes in geometry to produce lighter and stronger parts. The work presents an example of three stamped automotive structural components, mechanically interacting together when deformed under load. Minitab design of experiments module was used to evaluate two level factors, one of them being the thickness of each part, and the other the material properties: DP600, DP780 steel or a boron-based steel alloy. A FEM model of the three parts, with structural supports and loads, was performed to evaluate displacement of the system, max. equivalent stress, strain and total weight, allowing data correlation to determine best practices to accomplish low weight, high stiffness designs. Copyright © 2016 MS&T16®.

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Influence of strain rate and heat treatments on tensile and creep properties of Zn-0.15Cu-0.07Ti alloys

2016 , Quintana, María José , García, José Ovidio , Gonzalez-Ojeda, Roberto , Verdeja, José Ignacio

The use of Cu and Ti in Zn alloys improves mechanical properties as solid solution and dispersoid particles (grain refiners) may harden the material and reduce creep deformation. This is one of the main design problems for parts made with Zn alloys, even at room temperature. In this work the mechanical behavior of a Zn-Cu-Ti low alloy is presented using tensile tests at different strain rates, as well as creep tests at different loads to obtain the value of the strain rate coefficient m in samples parallel and perpendicular to the rolling direction of the Zn strip. The microstructure of the alloy in its raw state, as well as heat treated at 250°C, is also analyzed, as the banded structure produced by rolling influences the strengthening mechanisms that can be achieved through the treatment parameters. © The author; licensee Universidad Nacional de Colombia.

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Open surgery while wearing night vision goggles

2010 , Mosso Vázquez, José Luis , Stetz, Melba C. , Gonzalez-Ojeda, Roberto , Wiederhold, Brenda K. , Arrellín Rosas, Gerardo , Rodríguez Schlögl, Elizabeth María , Mosso Lara, Dejanira

Night vision technology is nothing new. In fact, the military rely significantly on this technology during nighttime operations. A surgeon is like a medical soldier in the battlefield. His/her only mission is that of keeping people alive. Due to many technological advances, patients cannot only train on relaxation while visiting their doctors but also get distracted by playing videogames while waiting for them. Furthermore, this virtual reality experience can be enhanced if the patient wears goggles or Head Mounted Displays under dimmed or absence of lights. The purpose of this study was to test if a surgeon could operate when extending into such a dark condition situation, but in the surgical suite. Therefore, a surgeon performed seven open surgeries on rabbits. All surgeries were performed on the thorax and abdomen regions. Specifically, the surgeon was able to perform these surgeries by wearing on his head a micro camera with infrared light and a night vision goggles. The first assistant used this same system while the scrub nurse and the anesthesiologist did not. There were no complications either during or after these procedures. It is possible to make open surgeries wearing a night vision system. Further approaches should be tested with human volunteers. Keywords: Night Vision Goggles, Open Surgery, Cyber-medicine

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Wear in ultrafine hardmetal mills manufactured by sinter + HIP

2006-12-01 , Ordóñez, Alejandro , Gonzalez-Ojeda, Roberto , Sánchez-Moreno, José Manuel

Ultrafine WC-Co milling tools were wear-tested in finishing machining conditions. Mills manufactured in the laboratory followed the powder metallurgy route for ultrafine grades. Total density in hardmetal grades of 0.2 and 0.4 μm was achieved through the Sinter + HIP technique. Wear in laboratory mills was compared with wear in coarse and ultrafine grade commercial mills. All mills cutting edges suffered wear mainly in the abrasive and chipping form. Chipping was excessive and peculiar in form in the laboratory mills; a slight presence of the fragile η phase was discovered. Laboratory mills showed similar wear to the commercial coarse grades, and much more than that of commercial ultrafine grades. A lack of toughness is suggested due to a small difference in the WC mean grain size, in the Co mean free path (λ) and in its distribution: homogeneous in laboratory mills and heterogeneous in the commercial ones. ©Metal Powder Industries Federation (MPIF)

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Microscale mechanical properties testing and simulation

2018 , Gonzalez-Ojeda, Roberto , Sánchez-Moreno, José M. , Quintana, María José

Characterization of mechanical properties at a micro and nano scale has become increasingly important for manufactured parts, though facilities with accurate and state-of-the-art equipment are scarce, expensive and not always available. For this reason, equipment already in use for traditional characterization can be used to analyze micro and even nano phenomena if calculations and simulations are combined with models representing testing procedures, such as hardness indentation or micro-machining of bending beams. The understanding of the interaction between phases in the material and more accurate finite element models of grains or precipitates with different geometries can contribute in measuring the behavior of very small zones of a manufactured part and design quality control or inspection protocols. © 2018 IEEE.

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Ultrafine-grain Steels: Mechanical Behavior

2016 , Quintana Hernández, María José , Gonzalez-Ojeda, Roberto , MARÍA JOSÉ QUINTANA HERNÁNDEZ;576914

In recent years, both the steelmaking industry and laboratories in different parts of the world, have shown an increasing interest in reaching an industrial-level production of ultrafine grained steels (also known as ultrafine ferrite), which have a grain size d lower than 5 μm, and enhanced mechanical resistance and fracture toughness. At room temperature, the capacity of the material to be deformed during bending or drawing operations (typical of requirements for automotive parts applications) depends on the interaction of a hard and a soft phase in the microstructure. On the other hand, at high temperatures, these steels may show superplastic behavior if deformed at a precise combination of temperature and strain rate.

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