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

Prediction of fracture loads in PMMA specimens using the Equivalent Material Concept and the Theory of Critical Distances combined criterion

This paper provides a methodology for the prediction of fracture loads in notched materials that combines the Equivalent Material Concept with the Theory of Critical Distances. The latter has a linear-elastic nature, and requires material (critical distance) calibration in those cases where the non-linear material behaviour is significant. The calibration may be performed by fracture testing on notched specimens, finite elements modelling or a combination of fracture and simulation. In any case, it may constitute a major issue when applying the Theory of Critical Distances on an industrial level. The proposed methodology sets out to define an equivalent linear-elastic material on which the Theory of Critical Distances may be applied through its basic formulation and without any previous calibration of the corresponding critical distance. It has been applied to PMMA Single Edge Notch Bending specimens, providing accurate predictions of fracture loads.The authors of this work would like to express their gratitude to the Spanish Ministry of Science and Innovation for the financial support of the project MAT2014-58443-P: “Análisis del comportamiento en fractura de componentes estructurales con defectos en condiciones debajo confinamiento tensional”, on the results of which this paper is based

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

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

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

Estimación de la carga de rotura en probetas entalladas de aluminio AL7075-T651 mediante el uso del concepto del material equivalente combinado con el criterio de la densidad de energía de deformación

El principal objetivo de este artículo es la aplicación del criterio de la Densidad de Energía de Deformación (SED), combinado con el Concepto de Material Equivalente (EMC) para predecir la carga de rotura de probetas CT de la aleación de aluminio Al7075-T651 que contienen entallas en U. Con este propósito, se han realizado 24 ensayos de fractura combinando 6 radios de entalla diferente, que cubren desde probetas fisuradas (0 mm) hasta probetas de 2 mm de radio de entalla. Las probetas fisuradas se han empleado para obtener las propiedades de fractura del material y el resto de los ensayos, se han usado para comprobar y comparar la carga de fractura obtenida experimentalmente con las predicciones que devuelven los métodos mencionados anteriormente: SED, SED-EMC. Los resultados teóricos de las predicciones de la carga de rotura para el material imaginario obtenido mediante el empleo del EMC, concuerdan con los resultados experimentales derivados de las muestras reales

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

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

Critical distance default values for structural steels and a simple formulation to estimate the apparent fracture toughness in u-notched conditions

The structural integrity assessment of components containing notch-type defects has been the subject of extensive research in the last few decades. The assumption that notches behave as cracks is generally too conservative, making it necessary to develop assessment methodologies that consider the specific nature of notches, providing accurate safe predictions of failure loads or defect sizes. Among the different theories or models that have been developed to address this issue the Theory of Critical Distances (TCD) is one of the most widely applied and extended. This theory is actually a group of methodologies that have in common the use of the material toughness and a length parameter that depends on the material (the critical distance; L). This length parameter requires calibration in those situations where there is a certain non-linear behavior on the micro or the macro scale. This calibration process constitutes the main practical barrier for an extensive use of the TCD in structural steels. The main purpose of this paper is to provide, through a set of proposed default values, a simple methodology to accurately estimate both the critical distance of structural steels and the corresponding apparent fracture toughness predictions derived from the TCD.The authors of this work would like to express their gratitude to the Spanish Ministry of Science and Innovation for the financial support of the Project MAT2014-58443-P: “Análisis del comportamiento en fractura de componentes estructurales con defectos en condiciones de bajo confinamiento tensional”, on the results of which this paper is based