Role of defect interactions during hydrogen embrittlement in iron: A multiscale perspective

Hydrogen embrittlement (HE) is a phenomenon that affects both the physical and chemical properties of several intrinsically ductile metals. Consequently, understanding the mechanisms behind HE has been of particular interest in both experimental and modeling research. Discrepancies between experimental observations and modeling results have led to various proposals for HE mechanisms. Therefore, in this work we systematically examined the effect of hydrogen on two fundamental HE mechanisms in iron, namely, adsorption induced dislocation emission (AIDE) and hydrogen-enhanced decohesion (HED). In this work, we used density functional theory, atomistic simulations, and continuum Rice-Thompson criterion to systematically investigate: a) the incipient event ahead of a crack tip in single crystals subjected to mode-I loading conditions; b) the cohesive strength of grain boundaries; and c) the energy barrier for a slip transmission across the grain boundary. We observed that the presence of hydrogen 1) reduces the stress intensity factor required for both the dislocation nucleation and the cleavage response for different crack orientations, and 2) increases the energy barrier for slip transmission. Most importantly it was found that the AIDE and HED mechanisms are acting together to cause HE

Numerical investigation of a galvanic structural joint subjected to a mechano- electrochemical loading

Here, we present for the first time, an experimentally validated numerical model for a galvanic couple subjected to a mechano-electrochemical process. The model is capable of tracking moving boundaries of the corroding constituent of the couple by employing Arbitrary Langrangian Eulerian (ALE) method. Results show that, when an anode is under a purely elastic deformation, there is no apparent effect of mechanical loading on the electrochemical galvanic process. However, when the applied tensile load is sufficient to cause a plastic deformation (local internal stress gradient), the local galvanic corrosion activity at the vicinity of the interface is increased remarkably. The effect of other factors, such as electrode area ratios, electrical conductivity of the electrolyte and depth of the electrolyte, are studied. It is observed that the conductivity of the electrolyte significantly influences the surface profile of the anode, especially near the junction

Erosión y desertificación.-Combating desertification strategies in arid land of India

ABSTRACT The present study deals with the current status and process of desertification due to over exploitation and mis-management of natural resources of the Rajasthan. The author try to make some observations on specific indicators of natural resources degradation that have strong impact on the process of desertification. The author have also looked into the climatological phenomenon such as drought. From the above study it is very much clear that to meet out the ever increasing demand of the man and society, the natural resources are being exploited at the rate where no regeneration is possible. Lastly, a brief account of the protective measures that have been taken by government is discussed