Monday 09 August 2010

Effect of the gas shielding parameters on the GTAW weldability of Ti-6Al-4V and Ti-3Al-2.5V titanium alloys. S. Aristizábal, L.Varela, y J. Giraldo, Universidad Nacional de Colombia, Colombia.

In this paper, the weldability of titanium alpha-beta alloys Ti-6Al-4V and Ti-3Al-2.5V sheets was studied varying the shielding gas parameters in autogenous bead on plate GTA welds. For this purpose, they were taken two gas nozzle diameters (1/2” and 3/4") and three shielding gas flows (2.5, 6 and 12.5 lpm), to determine the combinations of these variables that produce the best weld properties. The microstructural changes and their effects in weld properties and weld failure modes were analyzed by optical microscopy, scanning electron microscopy, tensile tests and microhardness tests in heat affected zone and fusion zone. The results showed that neither shielding gas flow nor gas nozzle diameter have significant effects in weld metal properties and microstructure within the range of values studied. In this way, using moderate shielding gas flow it is possible to obtain the same weld properties that employing high shielding gas flow, which could reduce the gas consumption. Furthermore, it was noted a considerable reduction in weld ductility for both alloys in comparison with base material and a slight decrease in weld resistance.

Keywords: GTAW or TIG, alpha-beta titanium alloys, shielding gas protection, tensile behavior

Comparative study between AA2024 and AA7075 alloys joints formed by the processes of friction stir welding and riveting. M. Genicolo y M. Alves, Escola Politécnica da Universidade de Sao Paulo, Brasil.

Normally aeronautic structures are made of riveted elements. A driver for this condition is the difficulty related to the aluminum alloys welding process. Nowadays the friction stir welding technology (FSW) is available, which is capable of joining aluminum alloys. Friction stir welding is a solid state joining process where a third material deposition is not required, as well as is not required any electric arc or inert gas atmosphere. The materials to be joined do not reach the melting point, but are subjected to severe plastic deformation, being mixed without melting. The mechanical behavior of welded components is equivalent or better than the behavior of riveted components. This work compares mechanical characteristics of AA2024 alloy and AA7075 alloy joints both for riveting and FSW processes.

Keywords: Aluminum, Stir, Friction, Welding, Riveting

Accumulative roll bonding (ARB) of aluminium 1100 – An innovative approach. E. Lee, O.A. Quintana, M. McGee y J.E. Indacochea, University of IIIinois at Chicago, EE.UU.

Accumulative Roll-Bonding (ARB) is a severe plastic deformation process used to fabricate ultrafine grained metallic materials. This process is applied in the continuous fabrication of multilayered composite sheet metal. The goal is to produce advanced materials with a unique and desirable combination of properties, such as strength and toughness.

This process is a form of solid state bonding where the surfaces of aluminum sheets are brought into sufficiently close proximity for a metallic bond to be formed. Aluminum, however, forms a tenacious and chemically stable oxide film (Al2O3), which makes bonding very difficult. An approach that is used to remove such film is to scratch the faying surface of the aluminum before proceeding with the ARB process. Although this approach has shown some success, there are still regions where the oxide is not completely removed and this can result in lack of bonding. Our study looks at using liquid gallium (Ga) as reactive metal to react with the aluminum forming a low temperature (room temperature) eutectic that will later lead to the formation of a homogeneous single phase across the faying interface following rolling. However, Ga has a propensity to rapidly penetrate the grain boundaries of aluminum, and causing embrittlement. Ga has a high solubility in Al at room temperature; if the amount of Ga exceeds 20 wt. %, it tends to form a eutectic liquid phase with a melting point of about 27°C. It is this excess of liquid Ga that can lead to the severe embrittlement of Al.

In preliminary tests, strips of 1100-Al were cut, degreased with acetone, and a thin film of Ga applied at the faying surfaces. The coupons were then preheated for an appropriate time before rolling. Following the ARB process the coupons again were post heat treated at the same temperature. The samples are being characterized mechanically and metallurgically. Our early results showed that the application of Ga imparted good bonding between the Allayers, compared to samples that were roll bonded without Ga. Peeling tests performed on the coupons corroborate these findings. It has been explained that the level of Ga applied is critical; during processing it was found that the excess of Ga produced embrittlement of the Al
strips and cracks were found in some of the coupons; this also led to decrease in the bonding strength. It was observed that if the heat treating temperature before and after rolling dropped from about 300 °C to 200 °C, the tensile strength i ncreased. This paper provides a detailed metallurgical analysis of the bonding interface and assesses the mechanical properties based on different processing parameters used.

Capacitación de inspectores de soldadura en la modalidad virtual empleando la plataforma educativa Paideia (Welding inspectors virtual training using the Paideia educational platform). P. Lean, Pontificia Universidad Católica del Perú, Perú.

Abstract not available.

Calificación y certificación de inspectores en soldadura y ensayos no destructivos (Welding and NDT inspectors qualification and certification). J. Contreras, Asociación Colombiana de Soldadura y Ensayos No Destructivos, ACOSEND, Colombia.

Abstract not available.

Modern developments in welding education and training and materials testing (Desarrollos modernos en educación y capacitación en soldadura y ensayo de materiales). S. Keitel, C. Ahrens y J. Fuentes Muñoz, GSI SLV Duisburgo, Germany.

La calidad y seguridad de productos técnicos, especialmente en los cuales se realizan tareas de soldadura, es fuertemente influenciada por el factor humano el cual posee un rol muy importante en todos los niveles de ejecución de tareas y responsabilidades.
La capacitación del personal de soldadura es la base de un trabajo bien hecho y de alta calidad. El sistema de cualificación organizado por el IIW (International Institute of Welding) así como sus tecnologías en soldadura son reconocidas y aprobadas en todo el mundo, transformando así positivamente los estándares nacionales e internacionales del personal de soldadura y sus prácticas.

Nuevos conceptos de educación fundados sobre las bases solidas y regulaciones de la IIW en resonancia con los requerimientos de la industria actual, entregan al alumno competencias técnicas listas para ser utilizadas con un mínimo costo de tiempo.

Actualmente las metodologías de enseñanza han sido mejoradas con conceptos en base a multi-media e internet, los cuales entregan al alumno de cursos teóricos mejores herramientas y flexibilidad en su aprendizaje. Cursos con metodologías CBT (Computer-based Training) y BL (Blended Learning) una combinación entre clases presenciales y a distancia, son actualmente de creciente importancia ya que permiten al alumno regular por si solo su velocidad de aprendizaje además del lugar y la hora de aprendizaje, disminuyendo así, costos de viajes y hospedajes.

En el caso de las habilidades manuales que deben ser entrenadas en un soldador, se pueden utilizar técnicas para el entrenamiento de secuencias de movimientos que son conocidas y aplicadas en deportes de alto rendimiento. Es así como por medio de equipos tecnológicos tales como el “Welding Trainer” se puede alcanzar excelentes resultados en el entrenamiento de soldadores.

Por último la creciente complejidad de los procesos de manufactura así como la globalización de la industria actual, exigen, comparables oportunidades para la educación del personal calificado así como de tecnologías de ensayo.

Tuesday 10 August 2010

Effect of grain size on solidification cracking susceptibility of type 347 stainless steel during laser welding. K. Shinozaki, P. Weng, M. Yamamoto, K. Kota, Y. Kohno y T. Komori, Hiroshima University, Japón.

The effect of grain size of base metal on solidification cracking susceptibility has not been quantitatively evaluated yet. We have developed the measuring method of critical strain for solidification cracking with high precision using high speed camera.

In this study, the effect of grain size on solidification cracking susceptibility of Type 347 stainless steel was investigated by using U-type hot cracking test with developed in-situ observation method and the effect of grain size of weld metal on critical strain for solidification cracking was evaluated quantitatively. The grain size of weld metal varied from about 70 to 210µm by changing in the grain size of base metal.

Main results are as follows.
(1) According to the measurement of CST(Critical Strain Temperature), solidification cracking susceptibility increases with an increase in grain size of weld metal.
(2) The area of the grain boundary for each unit area decreases when the grain size increases, and then strain which is applied for grain boundary increases. Moreover critical strain for solidification cracking of grain boundary decreases with grain size. Therefore, it is guessed that the solidification cracking susceptibility increase with an increase in grain size.

Keywords: Solidification cracking, In-situ observation, Type 347 stainless steel, U-type hot cracking test, grain size

Mechanical, tribological and microstructural evaluation of type AWS 5.9 ER 410NiMo martensitic stainless steel welds. J. Escobar, R. Correa, J. Santa, J. Giraldo y A. Toro, Universidad Nacional de Colombia, Colombia.

Welding of martensitic stainless steel is important for hydro-power industry, particularly in plants where the main components are Pelton and Francis turbines. In this work, two welding procedures were developed in order to compare the differences in mechanical properties and cavitation erosion resistance of welded coatings applied using synergic pulsed and spray Gas metal Arc Welding.

Two welding procedures, using AWS 5.9 ER410NiMo filler metal with 1.2 mm of diameter and a shielded atmosphere of Ar-2% 02, were used to weld a single-v-groove butt joint. The tensile strength of the filler metal was measured and indirect cavitation erosion tests according to ASTM G32 (vibratory apparatus) were carried out to compare the welded joints. Dilution measurements were carried out on bead-on-plate weldings and the microstructure of the transverse section of the joints was analyzed to evaluate the differences between the two procedures.

The dilution measurements of pulsed GMAW reported a mean value of 30%, 7% lower than spray GMAW tests. The microhardness measurements of pulsed weldings reported mean values of 420±20 HV300g, 15s. The mechanical tests showed that the yield and maximum tensile strength of pulsed welding was superior in all cases and the measured values were 1127 and 1150 MPa, respectively. The cavitation erosion resistance of samples welded with spray transfer mode was lower than the pulsed welded samples. However, weldings reported in both cases lower cavitation erosion resistance and higher erosion rate than martensitic stainless steel ASTM A743 grado CA6NM extracted from a Bucket of a Pelton turbine.

Keywords: Cavitation erosion tests, Martensitic Stainless steel, Pulsed Gas metal Arc Welding

Efecto de la aplicación de ciclos térmicos sobre un recargue de acero inoxidable martensítico. E. Huape, C. Maldonado, I. Mejía y A. Bedolla, Universidad Michoacana de San Nicolás de Hidalgo, México.

Abstract not available.

Procedimientos para la aplicación de un recubrimiento austenítico con alto Co sobre regiones cavitadas en rodetes pelton de acero inoxidable martensítico ASTM A743 grado CA6NM. E. Hoyos y J. Rodríguez, Universidad Nacional de Colombia, Colombia.

This article presents welding procedures used in the reconstruction of cavitation erosion affected areas in Pelton runners made of ASTM A743 grade CA6NM steel, using an austenitic stainless steel with high Co as filler material (Cavitec ®). Superficial repairs were made specifically in splitters and bucket bottoms.

Electrode diameters, sequences of application and electrical variables for each specific repair area were selected. Two welding procedures were designed for bucket bottoms: one for cavities with a depth less than ~ 8 mm, where Cavitec ® layers were applied directly and a second procedure was used for depths greater than ~ 9 mm, where E410NiMo electrode was used for filling layers and once reached the depth Cavitec ® was used for topcoats. The first procedure was also used in the reconstruction of splitters, where average depth of wear was closer to ~ 4 mm.
Inspection tests were conducted to verify health of deposits obtained using the parameters specified in the procedures and subsequent applications were made directly on the buckets of Pelton runners, on the latter unacceptable porosity were found as determined by the CCH703 Standard, these were repaired using the GTAW process, for which an additional welding procedure was generated. Spot repairs were made on the porosity found using Cavitec ® tubular wire with 0.045"diameter, leaving a sound work surface.

Key Words: Martensitic stainless steel, austenitic stainless steel with high Co, Pelton runner, SMAW, GTAW, porosity.

Metallurgical and mechanical characteristics of X80 steel welded by SMAW, gravity and underwater, and robotic FCAW processes. A. Arce, A. Bracarense, T. Mendes y J. Mendes, Universidade Federal de Minas Gerais, Brasil.

A review of welding and weldability of the X80 high strength low alloy steel has been made when welding manually and with a gravitational system with basic electrode, underwater and in air and with self protected tubular wire with robot. The comparative study of microstructural and mechanical properties of welded joints, with emphasis on the heat affected zone (HAZ) coarse grain region has set the best specifications. The welding procedures were capable to provide appropriate mechanical properties, hardness and impact resistance. These good characteristics were associated with the presence of bainitic structure in the coarse grain region in the case of welding manually and using a gravitational system with basic electrode, and with self protected tubular wire using a robot. The underwater welding results gave high values of hardness and low resistance to impact and were associated with the presence of martensite structure in the coarse grain region. The results allowed to develop a welding program and weldability study for X80 high strength low alloy steel used in gas and oil pipelines and offshore structure.

Key-words: X80 steel, Pipelines, Welding and Weldability, High Strength Low Alloy Steel.

Effects of preheat temperature on microstructure of MAG weld metal for 950 MPa class steel. K. Ikeuchi, M. Takahashi, A. Muraoka y S. Ahmed, Osaka University, Japón.

The microstructure and mechanical properties have been investigated for the weld metal of 950 MPa class steel that was produced by MAG welding in the shielding gas of Ar + 5%CO2 at preheat temperatures Tp of room temperature to 673 K. The major optical microstructure observed in the weld metal produced at Tp of room temperature consisted of a plate structure with a small amount of granular structure. As the preheat temperature was increased, the area of granular structure increased at the expense of the lath structure. The weld metal microstructure observed with a TEM consisted mainly of lath and non-lath structures involving the retained austenite. The lath structure, which was dominant at Tp of room temperature to 423 K, involved retained-austenite films less than 100 nm in thickness at lath boundaries. The non-lath structure became dominant as the preheat temperature was increased, and it consisted of a ferrite matrix a few µm in size that involved coarser retained austenite of complicated morphologies. The ferrite matrix of the non-lath structure showed similar morphological features to those of the granular structure observed in the optical microstructures. With a rise in the preheat temperature, the hardness and tensile/yield strength of the weld metal decreased, while the toughness and ductility increased. These effects of the rise in the preheat temperature on the mechanical properties can probably be attributed to the increased content of the granular or non-lath structure. The effects of the solidification segregation of Ni and Mn on the microstructure were also discussed on the basis of microstructures revealed by Lepera’s etching.

Keywords: Weld metal, High strength low alloy steel, 950 MPa class steel, MAG welding, Microstructure, Mechanical properties, Retained austenite.

Estudio de la unión soldada por arco sumergido de un acero microaleado con niobio y vanadio para aplicaciones estructurales. M. Saavedra, L. Béjar- Gomez y A. Medina-Flores, Universidad Michoacana de San Nicolás de Hidalgo, México.

El acero que se utilizó para la realización de este trabajo es experimental del tipo estructural, fabricado por fundición y tratamiento termomecánico, microaleado con 0.02% de niobio, 0.06% de vanadio y 0.06% de carbono, se desarrolló para aplicaciones estructurales en donde se requieren elevados valores de resistencia. La resistencia a la tensión del acero fue de 440 MPa. Su microestructura fue de grano fino y de tipo ferrítico perlítico. Este acero se soldó en posición plana por el proceso de arco sumergido, tomando en consideración que se trata de un proceso de amplia aplicación en la industria. El objetivo de este trabajo fue hacer un análisis de las propiedades mecánicas de la unión soldada del acero microaleado con niobio y vanadio, así como estudiar la microestructura de la unión en el metal de depósito, zona afectada térmicamente y en el material base. Otro aspecto fundamental fue valorar las propiedades mecánicas del metal base y del depósito, fortaleciendo el estudio con el análisis de los perfiles de dureza y las microestructuras encontradas en las diferentes regiones de la unión soldada.

Palabras clave: Acero microaleado, unión soldada, proceso de arco sumergido, microestructura de la unión, propiedades de la unión.

Welding and overlay procedures of dissimilar steel welding joints in the nuclear industry. A. Arce, A. Bracarense, L. Lourenco, G. Marconi, M. Dutra, M. de Abreu, M. Pessoa y Gabriela Ribeiro, Universidade Federal de Minas Gerais, Brasil.

This work presents the GTAW welding of dissimilar ferritic steel type A508 class 3 and austenitic stainless steel type AISI 316 L using Inconel® 600 (A182 and A82) and overlay covering with Inconel® 690 (A52) as filler metal. Dissimilar welds with these materials without defects and weldability problems such as hot, cold, reheat cracking and Ductility Dip Crack were obtained. Comparables mechanical properties to those of the base metal were found and signalized the efficiency of the welding procedure and thermal treatment selected and used. This study evidences the importance of meeting compromised properties between heat affected zone of the ferritic steel and the others regions presents in the dissimilar joint, to elaborate the dissimilar metal welding procedure specification and weld overlay. Metallographic studies with optical microscopy and Vickers microhardness were carried out to justified and support the results, showing the efficiency of the technique of elaboration of dissimilar metal welding procedure and overlay. The results are comparables and coherent with the results found by others. Some alternatives of welding procedures are proposed to attain the efficacy. Further studies are proposed like as metallographic studies of the fine microstructure, making use, for example, of scanning electron microscope (SEM adapted with an EDS) to explain looking to increase the resistance to primary water stress corrosion (PWSCC) in nuclear equipments.

Key-words: Dissimilar weld metal, weld overlay, welding procedure, nickel based alloys

The effect of altitude on FCAW-S. G. Guaytima, G. Malaisi, B. Narayanan y M. Quintana, Techint Ingeniería y Construcción, Argentina.

The exploitation of gas deposits in Peru brought about the construction of premises to obtain and transport gas. The complex and varied geographic locations of deposits posed a challenge to Techint, which in late 2007 headed PLNG Construction. This project comprised the construction of an API 5L Grade X70 408 Km long gas pipeline linking the Chiquintirca Plant in the Amazon jungle border and the Pacific coast of Peru, passing through mountain chain Los Andes. From the beginning, this project posed numerous challenges from the design and construction point of view which involved working at an extreme altitude (up to 4,900 MASL). This accomplishment granted TECHINT access to the Guinness World Records Book as the highest pipeline in the world.

Altitude not only hinders logistics and welder’s performance, but also has an impact on welding processes. TECHINT is highly experienced in the construction of pipelines at high altitude and it has dealt with various projects that crossed the Cordillera de Los Andes in South America.

From the early stage of this project, altitude was known to negatively affect weldability. TECHINT worked closely with Lincoln Electric Company to develop a solution for this project. Key points for the success of this project were: Selection of proper welding process, production of customized welding consumables more resilient to changes in atmospheric pressure at high altitudes, and tailored welding procedures.

In order to simulate the welding at high altitudes, a pressure controlled chamber was built at the Lincoln Electric R&D facility in Cleveland, Ohio USA, to make the proper choice of welding consumables easier.

This work describes TECHINT’s experience during PLNG construction and describes the development of best practice guidelines for pipeline construction at high altitudes.

Key words: high altitude welding, pipeline welding, self-shielded FCAW.

Analysis of the FCAW-DWOA welding applied to the naval industry. F. Gonsalves, T. dos Santos, F. Leslie y E. de Magalhaes, Universidade Federal do Pará, Brasil.

The technique FCAW-DWOA (Double Wire Arc Only) tiene great advantages compared with the FCAW process. This study aims to examine welded joints by the techniques and FCAW FCAW-DWOA in semi-flat position and held in an industrial environment, presenting the results of sanity superficial analysis of economic characteristics and geometric. In the bead passes used the wire electrode AWS Class E71T-1, three levels of feed rate (6, 8 and 10 m / min) with and without addition of cold wire AWS ER70S-6 (in FCAW-DWOA ) in two independent procedures, one with the addition of cold wire diameter of 0.8 mm, and the other with 1.0 mm, the ratios of speeds of feeding wires 6 / 2, 8 / 3 and 10 / 4 f / min. For the analysis of health were good results where all welds showed no damage length. The characterization was economically significant improvements with the implementation of the FCAW-DWOA already related geometric features tended to decrease penetration and increased lateral reinforcement.

Low hydrogen downhill welding electrodes for high strength pipelines. M. Jones y J. Ogborn, The Lincoln Electric Company, EE.UU.

With the increasing strength levels and stringent project requirements of modern pipe steels, low hydrogen SMAW electrodes are frequently specified for the field construction of pipelines. The productivity benefits gained by welding downhill have been recognized by industry as evidenced by the availability of commercial products and literature citations since the 1970?s. Thus, a low hydrogen downhill (LHD) electrode provides an attractive value proposition to pipeline contractors. In recognition of their growing demand, the latest AWS A5.5:2006 specification introduces a new Exx45-P2 classification for the low hydrogen downhill-welding pipeline electrodes. Where LHD electrodes were previously classified as Exx18-G and thus had fairly open limits on weld metal composition, the new Exx45-P2 classification limits the weld metal chemical composition. The classification also calls for test methods that are more relevant to the application. This paper presents the design approach used to develop and the test results of the first electrode in the market that meets this new AWS classification. The new electrode is also the first LHD electrode that meets the requirements of the optional H4R AWS designator.

Key words: Pipeline welding, SMAW electrodes, low hydrogen downhill, low hydrogen vertical down, hydrogen induced cold cracking, high strength pipe steel, E8045-P2, E9045-P2, E10045-P2

Numerical modeling for mechanical and thermal analysis of residual stresses from the welding process. T. Vidal Valente y J. de Almeida, Universidade de Brasilia, Brasil.

It is usual in the construction or maintenance of mechanical elements, to join or repair parts by means of welding processes. . Such processes cause a number of changes in the base material due to the high temperature gradient generated in the process, and produce heat affected zones, (HAZ), which are susceptible to failures. The effect of temperature on material generates a thermo expansion, followed by a subsequent contraction due to cooling. This phenomenon generates a field of residual stresses which is usually responsible for failure fatigue. Therefore it is important to estimate the magnitude of the residual stresses to take control of a failure. The analytical study of such problem is very complex and the corresponding analytical solution is often inexistent in the case of big structures such as a turbine runner. In this work, a numerical analysis method is employed to estimate the problem solution. The finite element software ANSYS was used to model the effects of a welding repair carried out on a Francis turbine runner blade. The method of analysis is of direct type, i.e. built a numerical model of transient process and not a linear input of heat generated by the welding, and has parameters for the variation in thermal properties such as enthalpy and thermal conductivity depending on the temperature. They are also used to the phenomena of convection and radiation conditions as a control for temperature. With this model is obtained the temperature field in the region, which is used as loading for mechanical analysis, which is supported by experimental parameters of stress-strain, modulus of elasticity and coefficient of thermal expansion as a function of temperature. That way you get the residual stresses generated by the process of welding.

Keywords: Fatigue, welding, computation analysis and finite element.

Computational simulation of a Weld joint failure process using the Gurson-Tvergaad model. H. Kunert, J. Otegui y P. Venturino, Universidad Nacional de Mar del Plata, Argentina.

Este trabajo presenta los métodos y resultados de un modelado numérico realizado para ratificar o rectificar resultados experimentales y pericias de laboratorios llevados a cabo como parte de un Análisis de Causa Raíz de incidentes registrados en un gasoducto enterrado en zona montañosa y clima selvático. El gasoducto estaba sometido a un estado biaxial de tensiones causado por presión interna y tracción axial debida principalmente a inestabilidad del suelo. Las fisuras se propagaron por la Zona Afectada por el Calor (ZAC) de las soldaduras circunferenciales.

El modelado numérico incluye no linealidades materiales y geométricas, y utiliza el método de elementos finitos para resolver la ecuación diferencial subyacente. Emplea diferentes modelos materiales: el de Von Mises como recurso clásico y el de Gurson-Tvergaad con un enfoque más novedoso. El primero da resultados muy exactos para estados triaxiales compresivos. No es exacto con alta triaxialidad en tracción, donde eventuales impurezas, poros o huecos crecen y coalescen. Para este problema Gurson presentó en 1977 una modificación del modelo de Von Mises apto para metales porosos, luego Tvergaad modificó los parámetros para lograr resultados más acordes a los reales. En el trabajo se verifica que el estado de cargas sufrido por el sistema se corresponde adecuadamente con el modelo de Gurson-Tvergaad. Los resultados del modelado coinciden con los ensayos de laboratorio realizados.

Palabras clave: Soldadura, Falla, Tensión Biaxial, FEM, gasoducto.

Fracture toughness testing of ductile weld metal by using normalization method. N. Gubeljak, J. Landes, J. Donoso, M. Chapeti y J. Predan, University of Maribor, Eslovenia.

The fracture behavior can be described with the combination of standard normalization method and observation of plastic region at the crack tip (size and shape) during fracture test. In this paper it is postulated that the fracture toughness resistance of the material can be described by using standard (ASTM E-1820-01) normalization method in spite of the fact that values of fracture resistance are out of standard range. Due to this, fracture toughness tests of weld metal using existing procedures according to standards may give invalid results for the critical crack initiation toughness or fracture resistance curve in terms of the J-integral or the critical crack-tip opening displacement, CTOD. In such cases, the measured high toughness is the consequence of the gross yielding of a significant volume of un-cracked ligament, and can be measured only by using surface displacement measurement techniques. The results show that standards based on recording load vs. few measured clip gauge points and displacement are insufficient. The normalization method seems a good alternative measurement and analysis technique which indirectly correlates to surface displacement measurements, especially in case of miniature mechanical testing.

Keywords: Fracture toughness testing, Normalization method, Weld metal.

Wednesday 11 August 2010

Effect and characterization of surfaces by atmosferic plasma treatments: wettability and adherence - J. Abenojar, M. Martinez, N. Encinas y J. del Real, Universidad Carlos III de Madrid, Spain.

El plasma se produce tras aplicar una descarga de energía a un gas para reorganizar las estructuras electrónicas de las especies (átomos y moléculas) y así producir especies excitadas e iones. Los plasmas atmosféricos se generan a través de corrientes eléctricas en la mayoría de los casos. El campo eléctrico transmite la energía a los electrones del gas (que son las especies cargadas más móviles).
Los tratamientos con plasma son aplicaciones capaces de modificar químicamente la superficie del material hasta una profundidad de micras o, a lo sumo, milímetros. Por este motivo, se pueden utilizar tratamientos con plasma con distintos objetivos: limpieza superficial, hacer recubrimientos, activación de superficial, mejorar la biocompatibilidad, entre otros.
Este trabajo tiene como objetivo estudiar superficies tratadas con plasma atmosférico y su caracterización, mediante técnicas como son: espectroscopia de fotoelectrones emitidos por rayos-X (XPS), espectroscopia de infrarrojo (FTIR-ATR), ángulo de contacto, rugosidad y microscopia electrónica de barrido (MEB). Las superficies tratadas serán poliméricas (polietileno, polipropileno, ABS, policarbonato) y cerámicas (cristal). En los resultados se puede destacar que la eficacia del tratamiento depende del material utilizado.

Palabras clave: Tratamientos superficiales; Energía superficial; Plasma atmosférico.

Solución analítica de la temperatura transitoria de un cuerpo semi-infinito sometido a una fuente de calor en 3-D en el proceso de arco sumergido. A. Ghosh y S. Chattopadhyaya, Government College of Engineering and Textile Technology, India.


Arreglos de fase - en dónde estamos?. R. Leon y M. Moles, NDT Innovations-Olympus NDT, Perú-Canadá.


Técnicas de sensoramiento no invasivo para el monitoreo de la calidad en el proceso de soldadura GMAW. E. Huanca y S. Crisóstomo, Universidade de Brasilia, Brasil.


Un nuevo y mejorado sistema de inspección AUT de soldadura circunferencial. R. Leon y M. Moles, NDT Innovations-Olympus NDT, Perú-Canadá.


Inspección de tuberías de diámetro pequeño. R. Leon y M. Moles, NDT Innovations-Olympus NDT, Perú-Canadá.


Formación de partícula y desprendimiento de metal de los alambres en el proceso de rociado de doble arco. W. Tillmann, S. Momeni y M. Abdulgader, Technische Universitat Dortmund, Alemania.


Determinación de las propiedades del arco eléctrico en la superficie del material base para el desarrollo de procesos y equipos de soldadura con electrodo no consumible. J. Fuentes, U. Füssel y J. Zschetzsche, GSI SLV Duisburgo, Alemania.


Microestructura de recubrimientos de vidrios metálicos depositados mediante rociado por plasma. A. Kobayashi, T. Kuroda, H. Kimura y A. Inoue, Osaka University, Japón.


Cálculo de la soldadura por puntos. M. Stipkovic, C. Correa, M.A. Stipkovic y G. Ferreira, Universidade de Sao Paulo, Brasil.


Simulación de ciclo térmico y evaluación de la tenacidad en uniones soldadas de acero SUMITEN. V. Aguero y C. Fosca, Pontificia Universidad Católica del Perú, Perú.


Influencia del aporte de calor en la evaluación de grietas en juntas soldadas de acero API X80 a través del ensayo Tekken. R. Perea y R. Trevisan, Universidade Estadual de Campinas, Brasil.


Comportamientos en medios agresivos de adhesivos elásticos. . Martínez, J. Abenojar y M. Pantoja, Universidad Carlos III de Madrid, España.


Implementación del criterio de falla de juntas unidas por adhesivos. R. Rodriguez, C. Souza, P. Sollero, E. Albuquerque y M. Rodrigues, Universidade Estadual de Campinas, Brasil.


Efecto y caracterización de superficies mediante tratamientos de plasma atmosférico: mojabilidad y adherencia. J. Abenojar, M. Martinez, N. Encinas y J. del Real, Universidad Carlos III de Madrid, España.


Análisis cinético y de curado mediante DSC de diferentes resinas epóxicas. G. García, J. Abenojar, M. Martinez y J. del Real, Universidad Nacional de Colombia, Colombia.