Comparative Mechanical Study of Pressure Sensitive Adhesives over Aluminium Substrates for Industrial Applications

The use of adhesives for fixing low-weight elements is showing increasing interest in the industry, as it would reduce the weight of the assembly, costs, and production time. Specifically, the application of pressure-sensitive adhesives (PSAs) to join non-structural naval components to aluminium substrates has not yet been reported. In the present work, a study of the mechanical behaviour of different double-sided PSAs applied on bare aluminium alloy substrates is performed. The influence of surface roughness, surface chemical treatments, and the matrix of the adhesives is studied through different mechanical tests, such as shear, T-peel, and creep. The application of an adhesion promoter improved the mechanical behaviour. Low roughness substrates provided better performance than ground samples. Acrylic foam adhesives were subjected to creep tests, whose results were fitted to a simple mathematical model, predicting the fracture time as a function of the applied load

Experimental and numerical investigation of hybrid laser arc welding process and the influence of welding sequence on the manufacture of stiffened flat panels

La soldadura por arco láser híbrido (HLAW) ha atraído cada vez más atención tanto de la industria como de los laboratorios académicos por su alta eficiencia y calidad de soldadura. El objetivo del presente artículo es desarrollar un método de elementos finitos no lineal para predecir la deflexión inducida por la soldadura y la tensión residual de un panel rígido a escala semiindustrial, utilizando un nuevo modelo de fuente de calor. La nueva fuente de calor híbrida consiste en un modelo matemático de doble elipsoide de Goldak que representa la fuente del arco, combinado con un modelo matemático gaussiano de cono truncado para simular la fuente láser. Para ello, se ha desarrollado un modelo de elementos finitos termoelástico-plástico acoplado tridimensional con ABAQUS utilizando una subrutina numérica adicional de DFLUX escrita en el lenguaje de programación Fortran para simular las distribuciones volumétricas de flujo de calor del proceso HLAW. El método de elementos finitos (FEM) se verifica mediante comparación con mediciones experimentales de muestras de acero naval EH36 de pequeña escala con uniones en T, en configuración a tope en posición de soldadura 2F, soldadas en posición horizontal con penetración total mediante un proceso híbrido de soldadura por arco láser (HLAW). Se observa una buena concordancia entre los resultados numéricos y las mediciones experimentales, lo que confirma que el modelo desarrollado en el presente artículo se puede utilizar eficazmente para predecir el comportamiento de deformación de las estructuras de rigidizadores durante la construcción naval. También se ha estudiado el efecto del cambio de secuencia de soldadura en el panel rígido a escala semiindustrial. Se han investigado cuatro secuencias de soldadura diferentes (SEQ 1,2,3 y 4), para elegir la mejor secuencia de soldadura en cuanto a la magnitud y distribución de las imperfecciones de soldadura (deflexión y tensión residual). Cambiar la secuencia de soldadura tiene un efecto significativo en la distribución y magnitud de la deflexión vertical. Se concluye que la secuencia de soldadura juega un papel importante en la deformación de las estructuras. Un cambio de dirección en la sección media, en combinación con la alternancia de las trayectorias de soldadura entre dos refuerzos consecutivos, conduce a una disminución significativa de la distorsión. El modelo FEM desarrollado ha proporcionado resultados precisos, lo que demuestra que es aplicable para estimar la deformación y la tensión residual inducida por el proceso HLAW en estructuras de construcción naval más grandes. También se puede emplear para optimizar la secuencia de soldadura. La presente contribución forma parte de un proyecto de colaboración entre la Universidad de Cádiz y la Universidad de Alejandría, Egipto, coordinado por el solicitante (J.M. Sánchez Amaya), cuyo principal objetivo es profundizar en el conocimiento y aplicación de las simulaciones FEM a procesos de soldadura. Este proyecto ha sido posible gracias a la financiación, por parte de la Comisión de la Unión Europea, de la beca de programa Erasmus + KA107, que ha permitido cubrir los gastos del viaje de Ahmed Hammad a la UCA. El solicitante (J.M. Sánchez Amaya) ha realizado las siguientes actividades del manuscrito: responsable y coordinador del conjunto de actividades de la colaboración; comparativa y análisis de resultados de las soldaduras HLAW; análisis y discusión de resultados del artículo; y revisión inicial y final del manuscrito

Influence of Surface Pre-treatments on Laser Welding of Ti6Al4V Alloy

In the present study, Ti6Al4V samples have been welded under conduction regime by means of a high power diode laser. The main objective of the work has been to determine the actual influence of the surface pre-treatments on the laser welding process. Thus, six different pre-treatments were applied to Ti6Al4V samples before performing bead-on-plate and butt welding treatments. The depth, width, microstructure, and microhardness of the different weld zones were deeply analyzed. Grinding, sandblasting, and chemical cleaning pre-treatments lead to welds with the highest depth values, presenting high joint strengths. Treatments based on the application of dark coatings generate welds with lower penetration and worse mechanical properties, specially the graphite-based coating

Optimization of the Synthesis Procedures of Graphene and Graphite Oxide

The optimization of both the chemical vapor deposition (CVD) synthesis method to prepare graphene and the Improved Hummers method to prepare graphite oxide is reported. Copper and nickel were used as catalysts in the CVD-graphene synthesis, CH4 and H2being used as precursor gases. Synthesis variables were optimized according to a thickness value, calculated using a homemade Excel-VBA application. In the case of copper, the maximum thickness value was obtained for those samples synthesized at 1050°C, a CH4/H2 flow rate ratio of 0.07 v/v, a total flow of 60 Nml/min, and a time on stream of 10 min. In the case of nickel, a reaction temperature of 980°C, a CH4/H2 flow rate ratio of 0.07 v/v, a total flow of 80 Nml/min, and a time on stream of 1 min were required to obtain a high thickness value. On the other hand, the Improved Hummers method used in the synthesis of graphite oxide was optimized. The resultant product was similar to that reported in literature in terms of quality and characteristics but both time and cost of the synthesis procedure were considerably decreased

A message emerging from development: the repression of mitochondrial β-F1-ATPase expression in cancer

The original publication is available at www.springerlink.com http://dx.doi.org/10.1007/s10863-007-9087-9Mitochondrial research has experienced a considerable boost during the last decade because organelle malfunctioning is in the genesis and/or progression of a vast array of human pathologies including cancer. The renaissance of mitochondria in the cancer field has been promoted by two main facts: (1) the molecular and functional integration of mitochondrial bioenergetics with the execution of cell death and (2) the implementation of 18FDG-PET for imaging and staging of tumors in clinical practice. The latter, represents the bed-side translational development of the metabolic hallmark that describes the bioenergetic phenotype of most cancer cells as originally predicted at the beginning of previous century by Otto Warburg. In this minireview we will briefly summarize how the study of energy metabolism during liver development forced our encounter with Warburg’s postulates and prompted us to study the mechanisms that regulate the biogenesis of mitochondria in the cancer cellThis review article was written while the research activity in the authors’ laboratory was supported by grants from the Ministerio de Sanidad (PI041255), Educación y Ciencia (SAF2005-4001) and Fundación Mutua Madrileña. The CBMSO is the recipient of an institutional grant from Fundación Ramón ArecesPeer reviewe

Noise resistance and shot noise parameters on the study of IGC of aluminium alloys with different heat treatments

In the present paper, the effect of heat treatment on the susceptibility to intergranular corrosion (IGC) of aluminium alloys is analysed. Samples of aluminium alloys AA2024 and AA7075 were first subjected to different heat treatments. Then the susceptibility of these samples to IGC was determined by means of normalized tests, based on the immersion of the samples in an aggressive medium and the subsequent evaluation of the attack, using metallographic analysis. In order to quantity the IGC suffered by the samples, both the degree and the depth of the attacks were measured. In addition, electrochemical noise (EN) signals were recorded during the normalized tests. This technique is especially interesting for the study of corrosion processes of systems with low impedance, such as those faced in this paper, since it does not modify the corrosion potential of the system. Three parameters were used to analyse the EN signals: noise resistance (Rn) and two shot noise parameters, the characteristic charge (q) and the characteristic frequency (fn). Finally, the relationship between the results of the metallographic analysis and those obtained from the analysis of EN signals was established. Unfortunately, a poor correlation between the shot noise parameters and the degree of IGC was found, due to both the high localization and high activities of all systems

The Effects of HLAW Parameters for One Side T-Joints in 15 mm Thickness Naval Steel

The present contribution is the first research reporting full penetration HLAW joints in 15 mm thick EH36 steel butt T-welds with square grooves on 2F welding position by single-sided welding. The effects of welding parameters were investigated to increase the quality of the joints. Conditions leading to defect-free full penetration welds fulfilling naval regulations includes a laser power of 12.5 kW, a welding speed of 1.6 m/min and the vertical laser offset distance from the flange of 1 mm. Advanced characterization of selected welds included a microstructural identification by optical microscopy, SEM, and XRD, revealing the presence of acicular, polygonal and Widmanstatten ferrite, lath martensite, and some retained austenite at FZ. Hardness and microhardness mapping tests showed values of 155 HV at base metal and 200 to 380 HV at the fusion zone connecting the web to the flange

Effect of process parameters on pulsed laser welding of AA5083 alloy using response surface methodology and pulse shape variation

Aluminium alloys exhibit eco-friendly aspects related to global environmental issues, such as almost unlimited recyclability. Nevertheless, some intrinsic characteristics are challenges to explore all their benefits. In the welding process, the high thermal conductivity and low melt point require high control of heat input. Alternatively, the pulsed laser mode provides a sharp beam focus with precise control enabling regulating the energy delivered. In this sense, this present work analysed the effect of pulsed laser welding parameters on 3-mm-thick AA5083 aluminium alloy sheets. Trials targeted to develop sound welds with minimum defect and high penetration depth adopting statistical methods. The optimum parameter arrangement was achieved by varying peak power, spot diameter, and pulse duration. Finally, the best parameter combination was applied using different pulse shapes to mitigate crack formation and pores. As a result, the pulse shape with step-down at the end of each pulse generated crack-free spot welds

Predictive Model and Mortality Risk Score during Admission for Ischaemic Stroke with Conservative Treatment

This work was supported by the "Fundacion Progreso y Salud", in the context of FPS 2020-R&I projects in Primary Care, Regional hospitals and CHARES. Grant number AP-0013-2020-C1-F1 and the APC was funded by the same.Background: Stroke is the second cause of mortality worldwide and the first in women. The aim of this study is to develop a predictive model to estimate the risk of mortality in the admission of patients who have not received reperfusion treatment. Methods: A retrospective cohort study was conducted of a clinical–administrative database, reflecting all cases of non-reperfused ischaemic stroke admitted to Spanish hospitals during the period 2008–2012. A predictive model based on logistic regression was developed on a training cohort and later validated by the “hold-out” method. Complementary machine learning techniques were also explored. Results: The resulting model had the following nine variables, all readily obtainable during initial care. Age (OR 1.069), female sex (OR 1.202), readmission (OR 2.008), hypertension (OR 0.726), diabetes (OR 1.105), atrial fibrillation (OR 1.537), dyslipidaemia (0.638), heart failure (OR 1.518) and neurological symptoms suggestive of posterior fossa involvement (OR 2.639). The predictability was moderate (AUC 0.742, 95% CI: 0.737–0.747), with good visual calibration; Pearson’s chi-square test revealed non-significant calibration. An easily consulted risk score was prepared. Conclusions: It is possible to create a predictive model of mortality for patients with ischaemic stroke from which important advances can be made towards optimising the quality and efficiency of care. The model results are available within a few minutes of admission and would provide a valuable complementary resource for the neurologist.Fundacion Progreso y Salud AP-0013-2020-C1-F