Experimental Evaluation of KIEAC of a Carbon Steel Using the Pin-Loaded SENT Geometry

The experimental determination of the threshold stress intensity factor for environment assisted cracking (KIEAC) is described by several standards, which allow the use of different specimen geometries and methodologies for crack length estimation. In some cases, the combination of structure, specimen size, or both, main loading direction, and crack orientations of the component that need to be characterized limit the use of standardized geometries. Consequently, alternative geometries must be used. In this study, fatigue pre-cracked pin loaded single edge notched tension specimens as defined by BS 8571:2018, Method of Test for Determination of Fracture Toughness in Metallic Materials Using Single Edge Notched Tension (SENT) Specimens, were applied for the experimental evaluation of the KIEAC of a carbon steel. The specimens were tested in deaerated substitute ocean water solution saturated with carbon dioxide at 40C and at 1 and 10 bar (100 and 1,000 kPa) under constant load conditions with incremental (step) loading. The crack length during the tests was monitored by direct current potential drop, which was helpful for defining the applied K corresponding to the onset of subcritical crack growth (KIEAC). Additionally, fractographic analysis of KEAC specimens and results from the fracture toughness evaluation of this material in air at room temperature have also been reported

Analysis of the Spb method for geometries where ηpl depends on a/W

Since its proposal, the simplified Spb method has been successfully applied to the fracture toughness evaluation of metallic and polymer materials. However, some points of this methodology remain unclear, like the applicability on standardized geometries in which ηpl depends on the a/W ratio. In order to discuss this and other aspects, theoretical analyses of the Spb method were made and some experimental tests were performed. The theoretical analysis revealed that considerable differences in C(T) and SE(T) geometries could be present when the same ηpl factor for both blunt notched and pre-cracked specimens is used. To minimize these differences, the use of the most general expression of the Spb method in addition to ηpl factors provided by the standards for geometries where ηpl change with a/W is proposed. The proposed experimental methodology, based on the load separation and on ηpl factors provided by the standards, proved to be suitable for C(T) geometry, whereas for SE(T) geometry the results indicate that more research is still needed.Fil: Delgado Ramírez, Egon Rolf. Universidade Federal do Rio de Janeiro; BrasilFil: Perez Ipiña, Juan Elias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Confluencia; Argentina. Universidade Federal do Rio de Janeiro; Brasil. Universidad Nacional del Comahue. Facultad de Ingeniería. Departamento de Mecánica; ArgentinaFil: Castrodeza, Enrique Mariano. Universidade Federal do Rio de Janeiro; Brasil. Politecnico di Milano; Itali

Fracture toughness of high strength seamless pipe steel from SE(T) and SE(B) specimens evaluated by different standards

Recently released, BS 8571:2014 standard offers an alternative for the experimental determination of fracture toughness and resistance curves of metallic materials from SE(T) specimens. Similar in stress conditions and constraint to cracked tubes, specimens in SE(T) geometry should yield less conservative toughness values than conventional high-constraint specimens, such as SE(B) geometry. However, the convention to determine the J-integral fracture toughness proposed in the new BS standard is different from ASTM standards. In this work, SE(T) and SE(B) specimens of similar dimensions of a tough high-strength seamless pipe steel were tested following the BS 8571:2014 and ASTM E1820-16 standards, respectively. Because of the different standardized definitions, SE(T) specimens yield lower fracture toughness than SE(B) specimens, which could lead to more conservative results in structural integrity analysis. This investigation also suggests the introduction of the blunting line concept in the BS 8571:2014 standard in order to minimize this problem.Fil: Filgueiras, Pedro Freire. Vallourec Competence Center Rio; BrasilFil: Menezes, João Teixeira Oliveira de. Universidade Federal do Rio de Janeiro; BrasilFil: Perez Ipiña, Juan Elias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Confluencia; Argentina. Universidad Nacional del Comahue. Facultad de Ingeniería. Grupo de Mecánica de Fractura; ArgentinaFil: Castrodeza, Enrique Mariano. Universidade Federal do Rio de Janeiro; Brasil. Politecnico di Milano; Itali

Fracture toughness of AlSi10Mg alloy produced by direct energy deposition with different crack plane orientations

Three-point bending fracture toughness and tensile specimens were tested at room temperature along different crack plane orientations and loading directions. Before being machined and tested, the printed samples were subjected to heat treatment at 300 °C for 2 h to relieve the residual stresses. Microstructural and fractographic analyses were performed to investigate the fracture mechanisms and the crack propagation paths for each crack orientation. Significant differences in the fracture toughness were observed among the crack plane orientations. Specimens with cracks oriented in the X-Y direction featured the highest fracture toughness values (JIc = 11.96 kJ/m2), whereas the Z-Y crack orientation (perpendicular to the printing direction) performed the lowest fracture toughness values (JIc = 8.91 kJ/m2). The anisotropy in fracture toughness is mainly related to a preferential crack propagation path along the melt pool boundaries. At melt pool boundaries, pores are preferentially placed, coarsening of the microstructure occurs and there is higher Si content, leading to that area being less ductile and less resistant to crack propagation.Validerad;2023;Nivå 2;2023-11-14 (marisr);Funder: EIT (18079);License fulltext: CC BY-NC-ND</p