Analysis of notch effect in the apparent fracture toughness and the fracture micromechanisms of ferritic–pearlitic steels operating within their lower shelf

The fracture resistance of materials is generally higher in notched conditions that in cracked conditions. In other words, when the notch radius increases there is also an increase in the apparent fracture toughness, which is that exhibited in notched conditions. This paper presents an analysis of the notch effect on two ferritic–pearlitic steels operating within their corresponding lower shelf, and develops an experimental programme, composed of 28 CT characterisation specimens and 72 CT validation specimens, together with finite elements analysis with the aim of validating the apparent fracture toughness predictions provided by the Theory of Critical Distances. The results have shown how this theory provides reasonable predictions of the apparent fracture toughness of the material The research is completed with the analysis of the evolution of fracture micromechanisms when the notch radius increases, revealing a direct relation between this evolution and the apparent fracture toughness observations

On the assessment of U-shaped notches using Failure Assessment Diagrams and the Line Method: experimental overview and validation

This paper analyses the structural integrity of components containing U-shaped notches by combining Failure Assessment Diagrams and the Line Method correction for notch effects. With this objective, the experimental results obtained in 555 fracture tests are homogeneously evaluated in the same Failure Assessment Diagram, with and without applying the Line Method notch corrections, and covering a wide range of materials such as PMMA, Al7075-T651, four different structural steels (S275JR, S355J2, S460M and S690Q) tested at different temperatures from the lower shelf up to the ductile-tobrittle transition zone, and two rocks (granite and limestone). It is demonstrated that the proposed methodology generally produces significant reductions in the conservatism associated to notch effects, yet providing safe predictions.The authors of this work would like to express their gratitude to the Spanish Ministry of Economy and Competitiveness for the financial support of the projects MAT2010- 15721: ‘Análisis de integridad estructural en defectos tipo entalla’ and MAT2014- 58443: “Análisis del comportamiento en fractura de components estructurales con defectos en condiciones de bajo confinamiento tensional”, on the results of which this paper is based

Dispersión de rayos X aplicado al análisis de nanotubos de carbono, polímeros y nanocompuestos

[EN] In this review we will show that wide and small angle X-ray scattering techniques (WAXS and SAXS respectively) can be a valuable tool to characterize the structure of carbon nanotubes (CNT) and related CNT-polymer nanocomposites at different characteristic length scales. Ranging from single carbon nanotubes to aggregates of CNTs X-ray scattering may offer structural information which can be crucial in order to design new materials based on carbon nanotubes.[ES] En este trabajo de revisión mostramos que las técnicas de dispersión de rayos X a alto y bajo ángulo (WAXS y SAXS respectivamente) pueden ser una herramienta muy valiosa para caracterizar la estructura de nanotubos de carbono (CNT) y nanocompuestos CNT-polímero, en diferentes escalas de longitud. La dispersión de rayos X puede ofrecer información estructural en el rango desde nanotubos de carbono aislados, hasta agregados de CNT. Dicha información puede ser crucial de cara a diseñar materiales basados en nanotubos de carbono.The authors thank the financial support from the MCYT (grant MAT2005-01768), Spain. The help of G. Broza, Z. Roslaniec, K. Schulte, I. Sics, B. H. Hsiao, S. S. Funari in different parts of this work is gratefully acknowledge. M. C. G.-G. and A. N. are also grateful to the Ramón y Cajal Program for the support of this reserach­.Peer reviewe

Analysis of notch effect in load bearing capacity, apparent fracture toughness and fracture micromechanisms of ferritic–pearlitic steels

This paper presents the analysis of the notch effect in two ferritc–pearlitic steels: S275JR and S355J2. The research is based on the development and analysis of an experimental programme composed of 336 CT specimens, combining 6 different notch radii, and testing temperatures from the lower shelf up to the upper shelf of the two materials. The notch effect is analysed through the evolution of both the load bearing capacity and the apparent fracture toughness, and also through the relation between these two variables and the failure micromechanisms. The results reveal a clear notch effect in both materials. In the case of the load bearing capacity, this notch effect has its maximum at lower shelf temperatures. The notch effect in the apparent fracture presents a maximum at the lower temperatures of the ductileto-brittle transition zone. Finally, the Scanning Electron Microscopy fractographies have justified the previous observations

Laser-Induced Periodic Surface Structures on Conjugated Polymers: Poly(3-hexylthiophene)

8 pags.; 11 figs.© 2015 American Chemical Society. In this work, we report on the surface patterning of semiconducting poly(3-hexylthiophene) (P3HT) thin films by means of laser-induced periodic surface structures (LIPSS). Two different laser wavelengths, 266 and 532 nm, and a broad range of fluences and number of pulses have been used in order to optimize the LIPSS morphology. Ripples period and depth can be tuned by laser parameters. In particular, the high optical absorption of P3HT at 532 nm enables the formation of well-ordered nanostructures with periodicities around 460 nm. Near edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopy reveal a good chemical stability of P3HT thin films during LIPSS formation. Conducting atomic force microscopy (C-AFM) performed on the LIPSS reveals a higher electrical conduction in the trenches than in the ridge regions. Resonance Raman spectroscopy and grazing incidence wide-angle X-ray scattering (GIWAXS) indicate a loss of crystallinity of P3HT thin films during LIPSS formation, suggesting melting of the outer polymer surface. This effect produces ridges with molecular order lower than that of the original thin film. As a consequence of this transformation, the electrical conduction in the ridges becomes lower than that in the trenches.The authors gratefully acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness (MINECO) through Projects MAT 2011-23455, MAT 2012-33517 and CTQ 2013-43086-P. A.R.-R. and E.R. are indebted to MINECO for a FPI (BES-2013-062620) and Ramon y Cajal (RYC-2011-08069) contracts, respectively. We thank the Swiss Light Source for beamtime at PolLux, where the NEXAFS experiments were performed. We also thank the ESRF for beamtime at BM26 where in situ GISAXS and GIWAXS experiments were carried out. We thank B. Watts for assistance in using beamline PolLux and G. Portale and W. Bras for beamline support at BM26. P. Müller-Buschbaum and S. Guo are thanked for seminal comments at the beginning of this workPeer Reviewe

Análisis de integridad estructural de aceros ferríticos entallados en la zona de transición dúctil--frágil

Este artículo proporciona una metodología de evaluación de la integridad estructural de aceros ferríticos entallados que operan a temperaturas propias de su zona de transición dúctil-frágil. La metodología se basa en el uso de Diagramas de Fallo y en el concepto de Curva Maestra de Entallas, y queda validada por los resultados obtenidos en su aplicación a 164 ensayos de fractura que combinan dos materiales (aceros S275JR y S690Q), seis tipos de radios de entalla (desde 0 mm hasta 2.0 mm), dos tipos de probeta (CT y SENB), y tres temperaturas diferentes dentro de cada zona de transición dúctil-frágil.This paper provides a structural integrity assessment methodology for the analysis of ferritic steels containing notchtype defects and operating within their ductile-to-brittle transition zone. The methodology, based on the use of Failure Assessment Diagrams and the novel concept of Notch Master Curve, has been applied to 164 experimental results performed on two different steels (S275J and S690Q), six different notch radii (from 0 mm up to 2.0 mm), two different types of specimens (CT and SENB), and three different temperatures within the corresponding ductile-to-brittle transition zone. The results validate the proposed assessment methodology

Aplicación de la curva maestra a un acero S275JR en condiciones entalladas

Este artículo evalúa la aplicación directa de la Curva Maestra para la estimación de la tenacidad aparente a fractura de un acero ferritico-perlítico en presencia de entallas. Para ello, se ha definido un nuevo parámetro denominado temperatura de referencia aparente TºN la cual es diferente de la temperatura de referencia Tº obtenida en fisuras y varía en función del radio de entalla. Para la validación de este modelo, se ha considerado un programa experimental compuesto por 180 probetas CT de acero S275JR. Se han adoptado seis radios de entalla diferentes que varían entre 0mm (fisuras) y 2.0 mm, y se han llevado ensayos en el rango de temperaturas comprendido entre -120ºC y 40ºC. Las predicciones obtenidas con la Curva Maestra se ajustan razonablemente bien a los resultados experimentales, permitiendo así reducir el conservadurismo que supone considerar las entallas como si fuesen fisuras. Además se ha observado que el rango de temperaturas de la zona de transición dúctil-frágil en condiciones entalladas no coincide estrictamente con el correspondiente rango de temperaturas en condiciones fisuradas.This paper evaluates the application of the Master Curve methodology for the prediction of the apparent fracture toughness of ferritic-pearlitic steels in notched conditions. With this purpose, a new parameter is defined named the notch reference temperature TºN, which is different from the reference temperatureTº obtained in cracked specimens and varies with the notch radius. With this purpose, the methodology has been applied to a set of fracture tests on steel S275JR, with notch radii ranging from 0 mm (crack-type defects) up to 2.0 mm and testing temperatures from -120ºC up to 40ºC. The methodology improves significantly the results obtained under the assumption that notches behave as cracks. Besides, it has been observed that temperatures within the ductile-to-brittle transition zone depend on the notch radius

Análisis del efecto entalla en la curva de transición dúctil-frágil del acero S275JR

Este artículo presenta un análisis del efecto entalla en la zona de transición dúctil-frágil del acero ferrítico-perlítico S275JR. Para ello, en primer lugar se determina la temperatura de referencia del material (T0), que resulta ser -26ºC, y en segundo lugar se realizan ensayos de fractura sobre probetas CT a tres temperaturas diferentes dentro del rango de aplicación de la Curva Maestra del material (T0 ± 50ºC). Concretamente, los ensayos se realizan a -10 ºC, -30 ºC y -50ºC, y sobre probetas con seis radios de entalla diferentes que van desde los 0 mm (fisuras) hasta los 2.0 mm. Los resultados muestran un claro efecto entalla en la curva de transición, con un aumento de la resistencia a fractura con el radio de entalla que produce un desplazamiento de la curva de transición dúctil-frágil hacia temperaturas menores, y un aumento de la tenacidad a fractura en el Lower Shelf del material. Finalmente se muestran las predicciones de la Curva Maestra de Entallas, herramienta que permite estimar la tenacidad aparente a fractura de aceros ferrítico-perlíticos entallados en la zona de transición dúctil-frágil del material.Los autores de este trabajo desean agradecer al Ministerio de Ciencia e Innovación del Gobierno de España la financiación del proyecto MAT2010-15721, (subprograma MAT): “Análisis de Integridad Estructural en Defectos Tipo Entalla”, de cuyos resultados se deriva este artículo

Propuesta de curva S-N de diseño para aceros estructurales con bordes rectos cortados por plasma

Este artículo presenta una propuesta de curva de diseño a fatiga para aceros estructurales con bordes rectos cortados por plasma. El corte por plasma se enmarca, junto al oxicorte y al corte láser, dentro de los métodos de corte térmico. En relación con la vida en fatiga de componentes cortados mediante corte térmico la práctica totalidad de las normas de diseño consideran únicamente el oxicorte, sin que exista respaldo normativo para cortes realizados por plasma o por láser. Por este motivo se presenta en este documento un programa experimental de fatiga (S-N) sobre cuatro aceros (S355M, S460M, S690Q y S890Q) con bordes rectos cortados por plasma. Los resultados obtenidos para cada una de las 40 probetas ensayadas se han usado para determinar la correspondiente clase FAT del Eurocódigo, que ha sido validada finalmente con una amplia revisión de los resultados obtenidos en la literatura especializada.This paper presents a proposal of fatigue design curves for structural steels containing plasma cut straight edges. Plasma cutting is, together with flame cutting and laser cutting, one of the thermal cutting technologies. Concerning the fatigue performance of thermally cut structural components, design standards provide design curves for flame cut straight edges, but both plasma and laser cut straight edges are not covered. For this reason this document presents a fatigue experimental program (S-N) with four steels (S355M, S460M, S690Q y S890Q) presenting plasma cut straight edges. The obtained results in the 40 tested specimens have been used to derive the corresponding Eurocode FAT class, which has been finally validated through its application to a wide number of tests found in the literature.Los autores de este trabajo desean agradecer a la Comisión Europea la financiación del proyecto HIPERCUT: “High Performance Cut Edges in Structural Steel Plates for Demanding Aplications” (RFSR-CT-2012-00027), de cuyos resultados se deriva este artículo

Análisis del efecto entalla en la curva de transición Dúctil-Frágil del acero S460M

Este artículo presenta un análisis del efecto entalla en la zona de transición dúctil-frágil del acero ferrítico-perlítico S460M. Con este propósito se determina en primer lugar la temperatura de referencia (T0) del material, dando como resultado -91.8ºC; en segundo lugar se realizan ensayos de fractura sobre probetas SENB a tres temperaturas diferentes (-100 ºC, -120 ºC y -140ºC) dentro del rango de aplicación de la Curva Maestra del material (T0 ± 50ºC), lo cual permite calibrar el valor de la distancia crítica del material (L). Los ensayos se realizan sobre probetas con seis radios de entalla diferentes que van desde los 0 mm (fisuras) hasta los 2.0 mm. Los resultados muestran un claro efecto entalla en la zona de transición, con un aumento de la resistencia a fractura con el radio de entalla. Finalmente se muestran y validan las predicciones de la Curva Maestra de Entallas, herramienta que permite estimar la tenacidad aparente a fractura de aceros ferrítico-perlíticos entallados en la zona de transición dúctil-frágil del material, y que ha sido previamente validada por los autores en los aceros S275JR y S355J2.This paper presents an analysis of the notch effect in the ductile-to-brittle transition zone of ferritic-pearlitic steel S460M. Firstly, the material reference temperature (T0) is obtained, obtaining a value of -91.8ºC. Secondly, SENB fracture specimens are tested at three different temperatures (-100ºC, -120ºC and -140ºC) within the validity range of the material Master Curve (T0 ± 50ºC). The tests are performed on SENB notched specimens containing six different notch radii, from 0 mm (crack-type defect) up to 2.0 mm. The results show a clear notch effect on the ductile-to-brittle transition zone: the larger the notch radius the larger the fracture resistance. Finally, the predictions provided by the Notch Master Curve are presented and validated. This tool allows the apparent fracture of ferritic-pearlitic steels containing notches to be estimated, and it had been previously validated by the authors in steels S275JR and S355J2