Pore space and brittle damage evolution in concrete

AbstractA novel lattice model is proposed for linking experimentally measured porosity of concrete to damage evolution and the emergent macroscopic behaviour. Pore sizes are resolved by X-ray CT and distributed at lattice bonds. The mechanical behaviour of bonds is elastic-brittle with failure criterion dependent on local forces and pore sizes. Bond failures provide the only non-linear effect on the macroscopic response. Results are compared to several experimental load cases. They show good agreement of stress–strain response at lower stress levels and expected differences at peak stresses. The framework allows for future development of models with plasticity and time-dependent effects

The Effect of Sodium Hydroxide on Niobium Carbide Precipitates in Thermally Sensitised 20Cr-25Ni-Nb Austenitic Stainless Steel

Niobium-stabilised austenitic stainless steel (20Cr-25Ni-Nb) has been immersed in sodium hydroxide, which is used as a corrosion inhibitor. The work shows how NbC precipitates may be degraded by use of pH 13 NaOH. Initial electrochemical measurements indicate that there is no benefit to this pretreatment as regards long-term corrosion inhibition, and post corrosion imaging shows the initiation of pitting corrosion at Nb-rich precipitates still present in the microstructure

Cesium and Strontium Contamination of Nuclear Plant Stainless Steel : Implications for Decommissioning and Waste Minimization

Stainless steels can become contaminated with radionuclides at nuclear sites. Their disposal as radioactive waste would be costly. If the nature of steel contamination could be understood, effective decontamination strategies could be designed and implemented during nuclear site decommissioning in an effort to release the steels from regulatory control. Here, batch uptake experiments have been used to understand Sr and Cs (fission product radionuclides) uptake onto AISI Type 304 stainless steel under conditions representative of spent nuclear fuel storage (alkaline ponds) and PUREX nuclear fuel reprocessing (HNO3). Solution (ICP-MS) and surface measurements (GD-OES depth profiling, TOF-SIMS, and XPS) and kinetic modeling of Sr and Cs removal from solution were used to characterize their uptake onto the steel and define the chemical composition and structure of the passive layer formed on the steel surfaces. Under passivating conditions (when the steel was exposed to solutions representative of alkaline ponds and 3 and 6 M HNO3), Sr and Cs were maintained at the steel surface by sorption/selective incorporation into the Cr-rich passive film. In 12 M HNO3, corrosion and severe intergranular attack led to Sr diffusion into the passive layer and steel bulk. In HNO3, Sr and Cs accumulation was also commensurate with corrosion product (Fe and Cr) readsorption, and in the 12 M HNO3 system, XPS documented the presence of Sr and Cs chromates.Peer reviewe

Exploring Hydride Formation in Stainless Steel Revisits Theory of Hydrogen Embrittlement

Various mechanisms have been proposed for hydrogen embrittlement, but the causation of hydrogen-induced material degradation has remained unclear. This work shows hydrogen embrittlement due to phase instability (decomposition). In-situ diffraction measurements revealed metastable hydrides formed in stainless steel, typically declared as a non-hydride forming material. Hydride formation is possible by increasing the hydrogen chemical potential during electrochemical charging and low defect formation energy of hydrogen interstitials. Our findings demonstrate that hydrogen-induced material degradation can only be understood if measured in situ and in real-time during the embrittlement process.Comment: 31 Pages, 18 Figures, Preprin

SKPFM e microcélula eletroquímica para a avaliação do grau de passivação de soldas do aço inoxidável duplex 2101 / SKPFM and electrochemical microcell to the passivation level assessment of welds of 2101 stainless steel

O grau de passivação de juntas soldadas do aço inoxidável duplex 2101 foi avaliado em duas diferentes condições de soldagem TIG e aporte térmico: 2,4 kJ/mm (2,4T) e 1,5 kJ/mm (1,5 T). A caracterização microestrutural foi realizada por microscopia ótica e eletrônica de varredura, e o desempenho em corrosão foi avaliado por ensaios eletroquímicos de corrosão usando uma microcélula eletroquímica. Mapas de potencial de superfície foram obtidas por microscopia de força atômica no modo Kelvin Probe. Os resultados indicaram que o aporte térmico de 1,5 kJ/mm obteve maior resistência à corrosão, uma vez que a microestrutura obteve melhor balanço entre fases austenita e ferrita, e reduzida ocorrência de precipitação de nitretos de cromo. Conclui-se que os resultados obtidos a partir das técnicas de avaliação microestrutural obtiveram forte correlação com os resultados de avaliação eletroquímica e, portanto, a microcélula eletroquímica é uma sensível ferramenta para identificar defeitos em soldas de aço inoxidável duplex 2101

An Experimental Investigation into Strain and Stress Partitioning of Duplex Stainless Steel Using Digital Image Correlation, X-Ray Diffraction, and Scanning Kelvin Probe Force Microscopy

The evolution of microstructure strain partitioning during quasi in situ tensile loading of grade 2205 duplex stainless steel has been investigated. Digital image correlation revealed the development of tensile strain initially in austenite and at interphase boundaries, and further extending into the ferrite with increasing load. Higher resolution digital image correlation observations indicated strain hardening of austenite, followed by deformation of the ferrite. Digital image correlation analysis of a 20% cold-rolled microstructure revealed tensile strain development at interphases, with discrete tensile and compressive strain pockets observed within the austenite. X-ray diffraction measurements indicated the presence of tensile stresses primarily developing in the ferrite, with full-width at half maximum values indicating plastic strain accumulation primarily in the austenite. The effect of tensile loading on Volta potential differences, obtained via scanning Kelvin probe force microscopy, highlighted the development of discrete anodic and cathodic sites with the introduction of strain. A Volta potential roughness parameter (ΨRa) is introduced describing Volta potential changes as a function of strain. This observation supports the concept of an enhanced propensity of local electrochemical activity with increasing applied strain in duplex stainless steel. </jats:p