Simulating intergranular hydrogen enhanced decohesion in aluminium using density functional theory

Materials modelling at the atomistic scale provides a useful way of investigating the widely debated fundamental mechanisms of hydrogen embrittlement in materials like aluminium alloys. Density functional theory based tensile tests of grain boundaries (GBs) can be used to understand the hydrogen enhanced decohesion mechanism (HEDE). The cohesive zone model was employed to understand intergranular fracture from energies obtained in electronic structure calculations at small separation increments during ab initio tensile tests of an aluminium Σ11 GB supercell with variable coverages of H. The standard rigid grain shift test and a quasistatic sequential test, which aims to be faster and more realistic than the rigid grain shift method, were implemented. Both methods demonstrated the effects of H on the cohesive strength of the interface. The sequential method showed discrete structural changes during decohesion, along with significant deformation in general compared to the standard rigid approach. H was found to considerably weaken the GB, where increasing H content led to enhanced embrittlement such that, for the highest coverages of H, GB strength was reduced to approximately 20% of the strength of a pure Al GB - it is proposed that these results simulate HEDE. The possibility of finding H coverages required to induce this effect in real alloy systems is discussed in context by using calculations of the heat of segregation of H.

Machine learning potentials for extended systems: a perspective

In the past two and a half decades machine learning potentials have evolved from a special purpose solution to a broadly applicable tool for large-scale atomistic simulations. By combining the efficiency of empirical potentials and force fields with an accuracy close to first-principles calculations they now enable computer simulations of a wide range of molecules and materials. In this perspective, we summarize the present status of these new types of models for extended systems, which are increasingly used for materials modelling. There are several approaches, but they all have in common that they exploit the locality of atomic properties in some form. Long-range interactions, most prominently electrostatic interactions, can also be included even for systems in which non-local charge transfer leads to an electronic structure that depends globally on all atomic positions. Remaining challenges and limitations of current approaches are discussed. Graphic Abstract

Some Thoughts on Modelling Hail Impact on Surfaces

Hail impact-induced erosion has the potential to significantly affect the operational lifetime of structures exposed to extreme weathering environments such as hail events. Computational materials modelling can be used to better understand the erosion behaviour during a hailstone impact, and here the relevant background work is detailed. In this paper, an implementation of an ice impact model, utilising Smooth Particle Hydrodynamics along with a highly strain-rate-dependent material model, is shown, and its results and limitations discussed. An overview is given on the literature on modelling hail events, including the history of experimental work. The various potential modelling methods which have been developed is then given, along with an evaluation of the suitability of the methods to future work in this area.