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Combined experiments and computational modelling are used to increase understanding of the suitability of the Single-Edge Notch Tension (SENT) test for assessing hydrogen embrittlement susceptibility. The SENT tests were designed to provide the mode I threshold stress intensity factor ($K_{\text{th}}$) for hydrogen-assisted cracking of a C110 steel in two corrosive environments. These were accompanied by hydrogen permeation experiments to relate the environments to the absorbed hydrogen concentrations. A coupled phase-field-based deformation-diffusion-fracture model is then employed to simulate the SENT tests, predicting $K_{\text{th}}$ in good agreement with the experimental results and providing insights into the hydrogen absorption-diffusion-cracking interactions. The suitability of SENT testing and its optimal characteristics (e.g., test duration) are discussed in terms of the various simultaneous active time-dependent phenomena, triaxiality dependencies, and regimes of hydrogen embrittlement susceptibility.

We combine welding process modelling with deformation-diffusion-fracture (embrittlement) simulations to predict failures in hydrogen transport pipelines. The focus is on the structural integrity of seam welds, as these are often the locations most susceptible to damage in gas transport infrastructure. Finite element analyses are conducted to showcase the ability of the model to predict cracking in pipeline steels exposed to hydrogen-containing environments. The validated model is then employed to quantify critical H$_2$ fracture pressures. The coupled, phase field-based simulations conducted provide insight into the role of existing defects, microstructural heterogeneity, and residual stresses. We find that under a combination of deleterious yet realistic conditions, the critical pressure at which fracture takes place can be as low as 15 MPa. These results bring new mechanistic insight into the viability of using the existing natural gas pipeline network to transport hydrogen, and the computational framework presented enables mapping the conditions under which this can be achieved safely.

First principles electronic structure calculations have been carried out on ordered double perovskites Sr_2B'B"O_6 (for B' = Cr or Fe and B" 4d and 5d transition metal elements) with increasing number of valence electrons at the B-sites, and on Ba_2MnReO_6 as well as Ba_2FeMoO_6. The Curie temperatures are estimated ab initio from the electronic structures obtained with the local spin-density functional approximation, full-potential generalized gradient approximation and/or the LDA+U method (U - Hubbard parameter). Frozen spin-spirals are used to model the excited states needed to evaluate the spherical approximation for the Curie temperatures. In cases, where the induced moments on the oxygen was found to be large, the determination of the Curie temperature is improved by additional exchange functions between the oxygen atoms and between oxygen and B' and B" atoms. A pronounced systematics can be found among the experimental and/or calculated Curie temperatures and the total valence electrons of the transition metal elements., Comment: 8 pages, 11 figures. Submitted to the Physical Review B

Magnetization and Mossbauer studies have been performed on the polymer coated magnetite nanoparticles with particle size from 5.1 to 14.7 nm. The maximum in the temperature dependence of magnetization (TM) is found to be inconsistent with the particle size (DTEM). The effective magnetic anisotropy (Kan) is found to increase with the decrease of DTEM, which is attributed to the increase of surface anisotropy. The absence of coercivity and remanence of magnetization noticed well above TM indicates the superparamagnetic behaviour, which has also been observed in the temperature dependent Mossbauer results. The temperature dependence of hyperfine field is found to follow similar dependence of saturation magnetization for bulk magnetite.