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 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

Geometry Effects on Mode I Brittle Fracture in VO-Notched PMMA Specimens

ABSTARCT: This paper gathers experimental and theoretical investigations about both the geometry-dependent fracture initiation angle and the fracture strength in VO-notched polymethyl methacrylate (PMMA) specimens under mode I loading conditions. The numerical analyses revealed that despite the application of pure mode I loading on the geometrically symmetric VO-notched samples, the maximum tangential stress occurs at two points symmetrically placed on either side of the notch bisector line. The experimental tests performed on some specimens showed that a crack does not necessarily propagate along the notch bisector line. Stress-based theoretical studies were then carried out to justify the experimental findings. The conventional maximum tangential stress (MTS) criterion gave weak predictions of the fracture. Therefore, the predictions were checked with the generalized MTS (GMTS) criterion by taking into consideration the higher-order stress terms. It was demonstrated that the GMTS criterion predictions have satisfactory consistency with the experimental results of the crack initiation angle and the fracture strength

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

Environmentally Assisted Cracking Behavior of S420 and X80 Steels Containing U-notches at Two DifferentCathodic Polarization Levels: An Approach from the Theory of Critical Distances

This paper analyzes, using the theory of critical distances, the environmentally assisted cracking behavior of two steels (S420 and API X80) subjected to two different aggressive environments. The propagation threshold for environmentally assisted cracking (i.e., the stress intensity factor above which crack propagation initiates) in cracked and notched specimens (KIEAC and KN IEAC) has been experimentally obtained under di erent environmental conditions. Cathodic polarization has been employed to generate the aggressive environments, at 1 and 5 mA/cm2, causing hydrogen embrittlement on the steels. The point method and the line method, both belonging to the theory of critical distances, have been applied to verify their capacity to predict the initiation of crack propagation. The results demonstrate the capacity of the theory of critical distances to predict the crack propagation onset under the di erent combinations of material and aggressive environments.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 projects MAT2014-58738-C3-3-R and MAT2014-58443-P developed by the University of Cantabria

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”

Influence of the notch length on the estimation of the reference temperature by means of the small punch test

The Master Curve approach has been widely applied to characterize the ductile to brittle transition region of ferritic steels. In order to further optimise the available material to be tested, great efforts have been recently performed to combine it with miniature testing techniques. One of the most promising is the small punch testing technique, currently under standardisation process in Europe. In this paper, small punch modified specimens with a lateral notch for the estimation of fracture toughness have been employed to obtain the reference temperature, T0, of a pressure vessel steel. The influence of the applied notch length has been analysed and a valid range has been proposed. In addition, the validity criterion of the tests for the estimation of T0 has been further verified, confirming its suitability. Finally, results have been compared with those obtained with conventional fracture mechanics specimens and previous works. As a result, a methodology to estimate the reference temperature by means of small punch tests with notch lengths of approximately 4.4 mm has been proposed, turning it into a promising candidate for the characterisation of the transition regime.This research was supported by the project MAT2014-58738-C3-3-R “Efecto del hidrógeno en aceros de media y alta Resistencia: optimización de los métodos de caracterización para la evaluación de la integridad estructural” financed by the Ministry of Economy, Industry and Competitiveness of the Spanish Government

Analysis of Samples Cleaning Methods Prior to Hydrogen Content Determination in Steel

ABSTRACT: There are multiple references to sample cleaning methods prior to hydrogen content determination, or hydrogen spectroscopy analysis, but there is still no unified criteria; different authors use their own "know-how" to perform this task. The aim of this paper is to solve, or at least clarify, this issue. In this work, the most commonly used sample cleaning methods are compared. Then, five different methodologies are applied on certified hydrogen content calibration pins and on high strength steel concrete-prestressing strands and the three main situations regarding hydrogen content in the microstructural net (non-charged, charged, and charged and uncharged) are studied. It was concluded that the HCl solution C-3.5 cleaning method recommended by ASTM G1 introduces large amounts of hydrogen in the samples; but can be useful for eliminating superficial oxides if necessary. The rest of the methods had similar results; but the more complete ones that involve ultrasounds and last longer than 8 min are not appropriated when important diffusion may occur on the samples during their application. Simple methods that involve acetone or trichloroethylene and last around 1 min are preferable for almost all situations as these are faster, easier, and cheaper. As a final recommendation, as trichloroethylene is toxic, the simple acetone method is, in general, the most convenient one for regular hydrogen content analysis.This research was funded by the UNIVERSITY OF CANTABRIA by means of the “Proyectos Puente 2019” grant program. The APC was funded by papers reviews of the authors for MDPI

Analysis of unexpected leaks in AISI 316L stainless steel pipes used for water conduction in a port area

This paper clarifies the causes of a corrosion process observed in austenitic stainless-steel pipes, grade 316L, used for conducting freshwater in a port area. During the pressure test of the installation, before it was put into service, about five months after its construction, a loss of pressure was detected due to leaks of the fluid contained and the presence of corrosion damage on the wall of the tubes, in some cases even passing through the thickness of the tube. An analysis of the chemical composition of the pipe material was carried out, as well as semi-quantitative analysis of the chemical composition of the deposits in the defects, and a culture of sulfate-reducing bacteria (SRB) in Kliguer medium of the stagnant waters within the facility. All this makes it possible to conclude that the observed process fits within the so-called microbiologically induced corrosion (MIC), and, in all probability, it can be affirmed that this process is promoted by the presence and proliferation of sulfate-reducing bacteria (SRB)