Dealing with the Fracture Ductile-to-Brittle Transition Zone of Ferritic Steels Containing Notches: On the Applicability of the Master Curve

ABSTRACT: Characterizing the fracture resistance of ferritic steels operating within their Ductile-to-Brittle Transition Zone (DBTZ) has been successfully addressed through the development of the well-known Master Curve (MC). This tool assumes that fracture, in the presence of crack-like defects, is controlled by weakest-link statistics and follows a three-parameter Weibull distribution. When dealing with notch-type defects, there is no standardized solution to predict the fracture resistance within the DBTZ, but the authors have published some works demonstrating that the MC can also be applied in different ways to characterize ferritic steels containing notches. One of these ways is the direct application of the MC methodology, providing a specific reference temperature (T0N) for each material and notch radius. This work reviews this initial attempt to apply the MC in notched conditions, assessing the validity of the main MC hypotheses (initially valid for cracked conditions) when analyzing notch-type defects and providing experimental validation on steels S275JR, S355J2, S460M and S690Q

Some thoughts about the application of the Master Curve methodology to ferritic steels containing notches

ABSTRACT: The Master Curve (MC) is an engineering tool that allows the fracture toughness of ferritic steels operating within their ductile-to-brittle transition zone to be estimated. It is based on statistical considerations, related to the distribution of cleavage-promoting particles around the crack tip, and assumes that: a) fracture is controlled by weakest link statistics; b) it follows a three parameter Weibull distribution. The authors have previously provided two different approaches for applying the MC in notched conditions. The first one consists of determining the reference temperature (T0) in cracked conditions and applying a subsequent notch correction to estimate the fracture toughness at a given temperature; the second one proposes obtaining directly a notch reference temperature (T0N) for a given notch radius by testing notched specimens. This second approach assumes that both the Weibull parameters (Kmin=20 MPam1/2 and b=4) and the censoring criteria used in cracked conditions are applicable in notched conditions. This paper provides some thoughts about these assumptions with the aim of analysing the applicability of the MC in ferritic steels containing notches, and includes specific validation on steels S460M and S690Q

Analysis of additively manufactured notched PLA plates using failure assessment diagrams

This paper provides a methodology for the estimation of the load-bearing capacity of additively manufactured (AM) PLA plates containing different types of notches (U-notches, V-notches and holes). The methodology is based on the use of Failure Assessment Diagrams (FADs), which are the main fracture-plastic collapse assessment tool provided by structural integrity assessment procedures, such as BS7910 and API 579-1/ASME FFS-1. When analyzing notch-type defects, the FAD methodology requires the application of a notch correction which, in this work, is based on the Theory of Critical Distances (TCD) and the Creager-Paris stress distribution ahead of the crack-tip. The results show that the FAD methodology can be efficaciously applied in this AM polymer, providing safe conservative estimations of critical loads in U-notched and V-notched plates, and accurate slightly unsafe estimations in plates with central hole. The cracking behavior in the different tested plates is a complex procedure generated by a combination of filament failures and debonding processes.This publication is part of the project “Comportamiento en fractura y efecto entalla en compuestos de matriz termopl´astica obtenidos por fabricaci´on aditiva, PID2021-122324NB-I00” funded by MCIN/ AEI /10.13039/501100011033/FEDER “Una manera de hacer Europa”

Master curve evaluation of ANP-5 steel using mini-CT specimens

The nuclear industry demands analyses that make possible the long-term operation of nuclear power plants (i.e., beyond 40 years). In this sense, one of the main challenges to overcome is the restricted amount of material available to extend the surveillance programs. To mitigate this issue, mini-CT specimens have been proposed for the evaluation of the fracture properties of reactor pressure vessel (RPV) materials, and particularly, the corresponding Master Curve. These specimens can be taken from the broken halves of previously tested Charpy specimens. In this work, mini-CT specimens have been employed to evaluate the reference temperature of the RPV ANP-5 steel in non-irradiated conditions. The results were compared with those obtained by means of conventional fracture tests.This project has received funding from the Euratom research and training programme 2020-2024, under grant agreement No. 900014. The significant contribution of the FRACTESUS project members is also acknowledged

FRACture mechanics TEsting of irradiated RPV steels by means of SUb-sized Specimens: FRACTESUS PROJECT

This work presents the overall structure of the FRACTESUS project and the progress carried out so far. The project is part of the EURATOM work programme 2019-2020, topic NFRP-04: Innovation for Generation II and III reactors. The project developments will contribute to the long-term safe operation of nuclear power plants, addressing the goals of the European Union in terms of sustainable and green energy, where the decarbonisation of the energy system is a priority. FRACTESUS intends to demonstrate the reliability of measuring the fracture toughness of reactor pressure vessel steels by means of sub-sized specimens (e.g., 0.16 CT or mini CT specimens). This will allow, among others, to notably increase the number of specimens available in the surveillance programs of the nuclear power plants.This project has received funding from the Euratom research and training programme 2020-2024, under grant agreement No. 900014. The significant contribution of the FRACTESUS project members is also acknowledge

Analysis of additively manufactured PLA containing notches using Failure Assessment Diagrams

ABSTRACT: This paper provides a methodology for the estimation of the load-bearing capacity of additively manufactured (AM) PLA specimens that may be applied to both cracked and notched conditions. The methodology is based on the use of Failure Assessment Diagrams (FADs), which are, in practice, the main fracture-plastic collapse assessment tool provided by structural integrity assessment procedures. When dealing with notch-type defects, the methodology requires, additionally, the application of a notch correction that it is based on the Theory of Critical Distances (TCD) and the Creager-Paris stress distribution ahead of the cracktip. The results show that the FAD methodology (alone, in cracked conditions, or in combination with the TCD in notched conditions) can be successfully applied in this AM polymer.This publication is part of the project “Comportamiento en fractura de materiales compuestos nano-reforzados con defectos tipo entalla, PGC2018-095400-B-I00” funded by MCIN/ AEI /10.13039/501100011033/ FEDER "Una manera de hacer Europa

Environmental fatigue analysis of nuclear structural components: Assessment procedures, loads, and a case study

ABSTRACT: Nowadays, environmental fatigue assessment is mandatory in many countries, in the design and operational stages of nuclear structural components. The analysis of environmental fatigue can be a complex engineering process that is generally performed following national or international procedures. Such procedures are not always based on the same assumptions, and novel analysts may find a confusing variety of documents. Moreover, once a specific procedure has been chosen for the analysis, it is possible to complete the fatigue assessment by using design transients (and loads) or, alternatively, real loads provided by monitoring systems. In this context, this paper provides a comprehensive review of the different environmental fatigue assessment procedures and a brief description of the different types of load inputs (design vs. real data). The work is completed with a case study, in which the (fatigue) cumulative usage factor is estimated in a particular nuclear component by using one of the abovementioned assessment procedures (NUREG/CR-6909) and two options for the load inputsFunding: This research was funded by EURATOM, grant number 662320

Epoxidación de limoneno en fase líquida sobre Ti/KIT-6

RESUMEN: Se evaluó la actividad del material Ti/KIT-6 en la epoxidación de limoneno en fase líquida con hidroperóxido de terbutilo como agente oxidante. La mayor selectividad (60%) se obtuvo a 50 ºC después de 7 h de reacción con una conversión de 23%; otros productos detectados fueron carvona, carveol, 1,2-diol-epoxilimoneno, alcohol perílico y p-menta-2,8-dien-1-ol. Se encontró que el catalizador no se lixivia y que antes de reutilizarlo se debe activar a 550 ºC. El catalizador se caracterizó por análisis químico, DRX, UV-vis e isotermas de adsorción.ABSTRACT: Limonene epoxidation was carried out in the liquid phase using Ti/KIT-6 as the catalyst and tert-butyl hydroperoxide as oxidant. The best selectivity (60%) was obtained at 50 °C after 7 h of reaction, and the conversion was 23%. The main side products were carvone, carveol, 1,2-epoxylimonene diol, perillyl alcohol and p-mentha-2,8-dien-1-ol. The catalyst does not leach under reaction conditions and it can be reused after calcination at 550 ºC. The catalyst was characterized by atomic absorption, XRD, UV-vis and N2 adsorption isotherms

The evolution of the ventilatory ratio is a prognostic factor in mechanically ventilated COVID-19 ARDS patients

Background: Mortality due to COVID-19 is high, especially in patients requiring mechanical ventilation. The purpose of the study is to investigate associations between mortality and variables measured during the first three days of mechanical ventilation in patients with COVID-19 intubated at ICU admission. Methods: Multicenter, observational, cohort study includes consecutive patients with COVID-19 admitted to 44 Spanish ICUs between February 25 and July 31, 2020, who required intubation at ICU admission and mechanical ventilation for more than three days. We collected demographic and clinical data prior to admission; information about clinical evolution at days 1 and 3 of mechanical ventilation; and outcomes. Results: Of the 2,095 patients with COVID-19 admitted to the ICU, 1,118 (53.3%) were intubated at day 1 and remained under mechanical ventilation at day three. From days 1 to 3, PaO2/FiO2 increased from 115.6 [80.0-171.2] to 180.0 [135.4-227.9] mmHg and the ventilatory ratio from 1.73 [1.33-2.25] to 1.96 [1.61-2.40]. In-hospital mortality was 38.7%. A higher increase between ICU admission and day 3 in the ventilatory ratio (OR 1.04 [CI 1.01-1.07], p = 0.030) and creatinine levels (OR 1.05 [CI 1.01-1.09], p = 0.005) and a lower increase in platelet counts (OR 0.96 [CI 0.93-1.00], p = 0.037) were independently associated with a higher risk of death. No association between mortality and the PaO2/FiO2 variation was observed (OR 0.99 [CI 0.95 to 1.02], p = 0.47). Conclusions: Higher ventilatory ratio and its increase at day 3 is associated with mortality in patients with COVID-19 receiving mechanical ventilation at ICU admission. No association was found in the PaO2/FiO2 variation