Innovative Applications of Ultrafine-Grained Materials

This chapter focuses on multifunctional properties of ultrafine-grained (UFG) metallic materials processed by severe plastic deformation (SPD), such as enhanced mechanical properties, excellent superplasticity, and wear resistance. Based on these multifunctional properties, the potential innovative application for UFG materials processed by SPD is introduced in the next section, including innovative application in micro-forming, nanoimplants, electro-connections, and sport engineering

The compensational boundary method to calculate the projected contact area of nanoindentation in atomistic simulations

The atomistic simulation of nanoidentation has become a powerful method to probe the mechanical behaviour and properties of small volumes of materials. It is crucial to calculate the projected contact area (PCA) accurately in order to obtain a reliable value of nanoindentation hardness. In this work, atomistic simulations of nanoindentation were performed on the Cu(111) and Ag(111) surfaces, and a new compensational boundary method is proposed to calculate the PCA. Compared with other available methods, this method provides a clear physical implication, and works well independently of the contact depth and the deformation behaviour of the material. It is also concluded that the widely-used experimental Oliver–Pharr (O–P) method significantly underestimates the PCA in atomistic simulations, and does not work for shallow nanoindentation at the nanoscale

Molecular dynamics study of the interactions of incident N or Ti atoms with the TiN(001) surface

The interaction processes between incident N or Ti atoms and the TiN(001) surface are simulated by classical molecular dynamics based on the second nearest-neighbor modified embedded-atom method potentials. The simulations are carried out for substrate temperatures between 300–700 K and kinetic energies of the incident atoms within the range of 0.5–10 eV. When N atoms impact against the surface, adsorption, resputtering and reflection of particles are observed; several unique atomic mechanisms are identified to account for these interactions, in which the adsorption could occur due to the atomic exchange process while the resputtering and reflection may simultaneously occur. The impact position of incident N atoms on the surface plays an important role in determining the interaction modes. Their occurrence probabilities are dependent on the kinetic energy of incident N atoms but independent on the substrate temperature. When Ti atoms are the incident particles, adsorption is the predominant interaction mode between particles and the surface. This results in the much smaller initial sticking coefficient of N atoms on the TiN(001) surface compared with that of Ti atoms. Stoichiometric TiN is promoted by N/Ti flux ratios larger than one

Assessing the implications of temperature extremes during the period 1959-2014 on the Inner Mongolia Plateau to sustainable development

The study sought to foster a better understanding of the nature of extreme temperature events and variations, and their implications to sustainable development, based on 16 indices of extreme temperature obtained from 43 meteorological stations on the Inner Mongolia Plateau (IMP). By using linear trend and Mann-Kendall abrupt change tests to investigate temporal variation trends, coupled with spatial distribution patterns and abrupt changes of extreme temperature events, the study revealed that the IMP has experienced extreme warming during 1959–2014 with warm extremes increasing significantly (p < 0.01) and cold extremes apparently decreasing (p < 0.01). The most significant increasing trends of warm extreme indices occurred in the desert steppe area (DSA) and sand desert area (SDA), suggesting that warming trends for night-time indices were larger than for daytime indices, while the most significant decreases in cold extreme indices were detected in forest area (FA) and forest steppe area (FSA). In addition, the significant cold day and cold night indices showed a decreasing trend, while warm day and warm night indices showed an increasing trend across the entire study area. Moreover, the study identified that topography has a large impact on the spatial distribution of extreme temperature indices, as does the type of grassland, and the ubiquity of the heat island effect in constructed urban regions. Finally, the study posits that to mitigate the effects of extreme temperatures, it is imperative to foster adaptive actions based on the principles of sustainable development

A Small World of Neuronal Synchrony

A small-world network has been suggested to be an efficient solution for achieving both modular and global processing—a property highly desirable for brain computations. Here, we investigated functional networks of cortical neurons using correlation analysis to identify functional connectivity. To reconstruct the interaction network, we applied the Ising model based on the principle of maximum entropy. This allowed us to assess the interactions by measuring pairwise correlations and to assess the strength of coupling from the degree of synchrony. Visual responses were recorded in visual cortex of anesthetized cats, simultaneously from up to 24 neurons. First, pairwise correlations captured most of the patterns in the population's activity and, therefore, provided a reliable basis for the reconstruction of the interaction networks. Second, and most importantly, the resulting networks had small-world properties; the average path lengths were as short as in simulated random networks, but the clustering coefficients were larger. Neurons differed considerably with respect to the number and strength of interactions, suggesting the existence of “hubs” in the network. Notably, there was no evidence for scale-free properties. These results suggest that cortical networks are optimized for the coexistence of local and global computations: feature detection and feature integration or binding

Shear fracture mechanism in micro-tension of an ultrafine-grained pure copper using synchrotron radiation X-ray tomography

In order to investigate the early fracture of ultrafine-grained (UFG) pure copper with a partially recrystallized microstructure and simple shear texture, the evolution of surface strain was measured using in situ micro-tension with digital image correlation. The spatial distribution of voids in tensile specimens was revealed after testing using synchrotron radiation X-ray tomography. The results show that the shear fracture behavior is associated with void evolution in UFG copper and this is strongly affected by the simple shear texture produced by equal-channel angular pressing (ECAP). The results have important implications for use in micro-forming

Friction related size-effect in microforming – a review

This paper presents a thorough literature review of the size effects of friction in microforming. During miniaturization, the size effects of friction occur clearly. The paper first introduces experimental research progress on size effects of friction in both micro bulk and sheet forming. The effects of several parameters are discussed. Based on the experimental results, several approaches have been performed to develop a model or functions to analyse the mechanism of size effects of friction, and simulate the micro deep drawing process by integrating them into an FE program. Following this, surface modification, e.g. a DLC film and a micro structure/textured surface, as a method to reduce friction are presented. Finally, the outlook for the size effect of friction in the future is assessed, based on the understanding of the current research progress

Friction related size-effect in microforming – a review

This paper presents a thorough literature review of the size effects of friction in microforming. During miniaturization, the size effects of friction occur clearly. The paper first introduces experimental research progress on size effects of friction in both micro bulk and sheet forming. The effects of several parameters are discussed. Based on the experimental results, several approaches have been performed to develop a model or functions to analyse the mechanism of size effects of friction, and simulate the micro deep drawing process by integrating them into an FE program. Following this, surface modification, e.g. a DLC film and a micro structure/textured surface, as a method to reduce friction are presented. Finally, the outlook for the size effect of friction in the future is assessed, based on the understanding of the current research progress