Effect of graphene on the fracture behaviour of 3D printed PLA SENB specimens

ABSTRACT: This paper analyses the effect of graphene addition on the fracture behaviour of 3D printed PLA SENB specimens containing crack-like defects. The addition of graphene is assumed to improve the tensile behaviour of 3D printed PLA material, but the integrity of structural components strongly depends on the material fracture resistance. Tensile and fracture SENB specimens have been tested with different raster orientations (0/90, 30/-60 and 45/-45), showing that the effect of graphene addition (1 wt. %) is very sensitive to the raster orientation: this effect is significant for raster orientation 45/-45 and very limited for 0/90 (with 30/-60 providing intermediate results).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 PGC2018-095400-B-I00 “Comportamiento en fractura de materiales compuestos nano-reforzados con defectos tipo entalla”

Assessment of notched Polyvinyl chloride (PVC) tubular beams using the Theory of Critical Distances and Finite Element analysis

ABSTRACT:This paper combines the Theory of Critical Distances (TCD) and Finite Element Analysis (FEA) to provide estimations of fracture loads in Polyvinyl chloride (PVC) tubular beams containing notch-type defects. The methodology is, however, theoretically applicable to any kind of material and component developing a predominant linear-elastic behavior. FEA is used to determine the stress field at the notch tip, which is then combined with one of the TCD failure criteria (the Point Method, PM) to derive the corresponding critical load. The results prove that this methodology provides reasonable 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 PGC2018-095400-B-I00 “Comportamiento en fractura de materiales compuestos nano-reforzados con defectos tipo entalla”, on the results of which this paper is based

Analysis of submerged small punch test under static load for its employement in hydrogen embrittlement situations on high and medium strength steels

En este trabajo se analizan dos aceros de media y alta resistencia bajo escenarios de fragilización por hidrógeno, mediante el empleo de ensayos Small Punch (SPT) sumergidos bajo carga estática sobre probetas pre-cargadas en hidrógeno. Se llevan a cabo ensayos de tracción a baja velocidad (SSRT) normalizados, y los ensayos SPT anteriormente citados. Se comprueba para estos escenarios una propiedad indicada en el código de buena práctica más orientada a fluencia, que indica que el valor de la velocidad de deformación en un ensayo SSRT y de desplazamiento de punzón en un SPT tienen valores numéricos semejantes cuando el tiempo de rotura en ambas situaciones es similar. Finalmente se proponen metodologías para determinar las velocidades de propagación en ambiente agresivo mediante el empleo de ensayos SPT.In this work two steels, of medium and high strength, are analyzed under hydrogen embrittlement scenarios using submerged Small Punch tests (SPT) under static load, on specimens pre-charged in hydrogen. Standard slow strain rate tests (SSRT), and the aforementioned SPT tests are performed. For these scenarios, it was checked a property proposed in the code of practice, mainly focused on SPT creep tests. It indicates that the deformation rate in a SSRT and punch displacement in an SPT have similar numerical values when the breaking times in both tests are alike. Finally, practical methodologies are proposed to determine propagation rates in an aggressive environment using SPT tests.The authors of this paper would like to thank the Spanish Ministry of Economy and Competitivity for the support received for the development of the research projects MAT2011-28796, and MAT2014-58738

Dispositivo para la realización de un ensayo miniatura de punzonado en condiciones de sumersión en una solución líquida

Dispositivo para la realización de un ensayo miniatura de punzonado, con alineación de cargas y minimización de los rozamientos, que permite la caracterización mecánica de una probeta sumergida en un líquido y comprende: un dispositivo de ensayo que comprende a su vez: la probeta objeto de ensayo situada entre una matriz de opresión y una matriz de apoyo; un punzón de cabeza semiesférica; la matriz de opresión que presenta una abertura configurada para servir de guía al punzón; la matriz de apoyo que presenta una abertura configurada para permitir la deformación de la probeta; y al menos un elemento de apriete; un sistema transmisor de esfuerzos que comprende dos tramos configurados para transferir la fuerza generada por la máquina de ensayos a cada uno de los dos extremos del dispositivo de ensayo; un recipiente configurado para albergar en su interior un líquido en el que sumergir totalmente la probeta, que comprende dos aberturas en dos de sus laterales enfrentados configuradas para, durante el ensayo, situar el conjunto dispositivo de ensayo y sistema transmisor de esfuerzos a lo largo del eje comprendido entre las dos aberturas; un soporte configurado para sustentar el dispositivo de ensayo, el sistema transmisor de esfuerzos y el recipiente.Solicitud: 201400788 (07.10.2014)Nº Pub. de Solicitud: ES2534613A1 (24.04.2015)Nº de Patente: ES2534613B2 (13.08.2015

Analysis of notch effect in 3D-printed ABS fracture specimens containing U-notches

In this paper a fracture assessment in additive manufactured acrylonitrile butadiene styrene (ABS) fracture specimens containing U-notches is performed. We performed 33 fracture tests and 9 tensile tests, combining five different notch radii (0 mm, 0.25 mm, 0.50 mm, 1 mm and 2 mm) and three different raster orientations: 0/90, 30/-60 and 45/-45. The theory of critical distances (TCD) was then used in the analysis of fracture test results, obtaining additional validation of this theoretical framework. Different versions of TCD provided suitable results contrasting with the experimental tests performed. Moreover, the fracture mechanisms were evaluated using scanning electron microscopy in order to establish relationships with the behaviour observed. It was demonstrated that 3D-printed ABS material presents a clear notch effect, and also that the TCD, through both the point method and the line method, captured the physics of the notch effect in 3D-printed ABS. Finally, it was observed that the change in the fracture mechanisms when introducing a finite notch radius was limited to a narrow band behind the original defect, which appeared in cracked specimens but not in notched specimens.This research received funding from the Spanish Ministry of Science and Innovation, grant PGC2018-095400-B-I00 “Comportamiento en fractura de materiales compuestos nano-reforzados con defectos tipo entalla”

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

Structural integrity assessment of additively manufactured ABS, PLA and graphene reinforced PLA notched specimens combining Failure Assessment Diagrams and the Theory of Critical Distances

ABSTRACT: Failure Assessment Diagrams (FADs) are a widely used engineering tool for the analysis of structural components containing cracks, and are included in recognised structural integrity assessment procedures such as BS7910 and API 579 1/ASME FFS 1. Their consistency and reliability has been demonstrated over the years through numerous laboratory validation tests and industrial applications. Nevertheless, both their theoretical definition and their subsequent validation have been performed in metallic materials and, therefore, their use in other types of materials still requires theoretical support and experimental validation. Moreover, FADs have been initially defined for the analysis of crack-like defects, whereas there are many situations where the defects that are, or might be, responsible for structural failure are not necessarily cracks. This is the case of (non-sharp) defects with a finite radius on their tip, which here will be referred to as notches. Simultaneously, additive manufacturing (AM) is an emergent technology that allows practically any type of geometry to be fabricated through a relatively simple process. One of the main AM techniques is fused deposition modelling (FDM), which consists in the extrusion of heated feedstock plastic filaments through a nozzle tip. The resultant printed materials have rather particular properties that are very dependent on the printing parameters and on the final state of internal defects. Concerning AM polymers and polymer-matrix composites, their use as structural materials, beyond their main current use in prototyping, requires the development of specific structural integrity assessment procedures. This paper provides FAD analyses for three additively manufactured (FDM) materials containing U-shaped notches: ABS, PLA and graphene reinforced PLA. The results show that the FAD methodology may be applied for the estimation of fracture loads in these particular materials, as long as linear-elastic fracture toughness values are used.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

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

Coupling Finite Element Analysis and the Theory of Critical Distances to Estimate Critical Loads in Al6060-T66 Tubular Beams Containing Notches

ABSTRACT: This paper validates a methodology for the estimation of critical loads in tubular beams containing notch-type defects. The methodology is particularized for the case of Al6060-T66 tubular cantilever beams containing U-shaped notches. It consists in obtaining the stress field at the notch tip using finite element analysis (FEA) and the subsequent application of the theory of critical distances (TCD) to derive the corresponding critical load (or load-bearing capacity). The results demonstrate that this methodology provides satisfactory predictions of fracture loads.This research received funding from the Spanish Ministry of Science and Innovation, grant PGC2018-095400-B-I00 “Comportamiento en fractura de materiales compuestos nano-reforzados con defectos tipo entalla”

Use of the small punch test under static load in hydrogen embrittlement situations. Analysis of the test curve

En este trabajo se analiza un acero de alta resistencia bajo escenarios de fragilización por hidrógeno mediante los últimos avances en el empleo de las técnicas Small Punch en escenarios frágiles. En una primera etapa se fundamenta porqué el ensayo Small Punch (SPT) puede ser una alternativa simple y económica cuando el empleo de ensayos normalizados en ambiente no es viable. A continuación se llevan a cabo ensayos SPT sumergidos bajo carga estática sobre probetas previamente cargadas en hidrógeno. Con ello se comprueba que esta tipología de ensayos SPT da como resultado curvas de que comparten similitudes con las del Small Punch Creep Test, la cual es analizada en profundidad. A partir de ello se lleva a cabo una análisis de la evolución de la probeta a lo largo del ensayo, y se propone un posible camino de trabajo futuro para la determinación de la velocidad de ensayo SPT idónea en condiciones de fragilización por hidrógeno.In this work, a high strength steel is analyzed under hydrogen embrittlement scenarios, employing the latest advances in the use of Small Punch techniques in brittle scenarios. In a first stage it is analyzed why the Small Punch (SPT) test can be a simple and economical alternative method when the use of normalized tests in environment is not viable. Subsequently, SPT tests carried out under static load using pre-charged specimens in hydrogen. It is shown that this type of SPT test give as a result curves that share similarities with those of the Small Punch Creep Test, which is analyzed in depth. From this, an analysis of the evolution of the specimen is carried out throughout the test, and a possible way for the determination of the suitable SPT punch rate in hydrogen embrittlement scenarios is proposed as a future work.The authors of this paper would like to thank the Spanish Ministry of Economy and Competitivity for the support received for the development of the research projects MAT2011-28796, and MAT2014-58738