Estimating the lower-limit of fracture toughness from ideal-strength calculations

Fracture mechanics is a fundamental topic to materials science.

A Study on Different Bandwidths and Rim Decorations’ Influence on the Mechanical Properties of Graphene Nanoribbon

This paper structured the Graphene Nanoribbon with different bandwidths and rim decorations and obtained the ideal strength and modulus of elasticity based on the calculation under the First Principle. It can be known that the mechanical properties of Graphene Nanoribbon are close to that of graphene, which have less changes with different bandwidth. However, the mechanical properties would be influenced by different decorations which may change the electronic connection state of edge carbon atoms. The results found in this paper can provide some reference for researchers to study the mechanical properties of graphene nanoribbons in the future.

Ultrahigh Strength and Shear-Assisted Decohesion of Sliding Silver Nanocontacts Studied in situ

The behavior of materials in sliding contact is challenging to determine since the interface is normally hidden from view. Using a custom microfabricated device, we conducted in situ, ultrahigh vacuum transmission electron microscope measurements of crystalline silver nanocontacts under combined tension and shear, permitting simultaneous observation of contact forces and contact width. While classically, silver exhibits substantial sliding-induced plastic junction growth, the nanocontacts exhibit only limited plastic deformation despite high applied stresses. This difference arises from the nanocontacts’ high strength, as we find the von Mises stresses at yield points approach the ideal strength of silver. We attributed this to the nanocontacts’ nearly defect-free nature and small size. The contacts also separate unstably, with pull-off forces well below classical predictions for rupture under pure tension. This provides in situ confirmation that shearing reduces nanoscale pull-off forces, consistent with recent theoretical predictions but never before directly observed.

Body composition changes in physically active individuals consuming ketogenic diets: a systematic review

Background To achieve ideal strength/power to mass ratio, athletes may attempt to lower body mass through reductions in fat mass (FM), while maintaining or increasing fat-free mass (FFM) by manipulating their training regimens and diets. Emerging evidence suggests that consumption of high-fat, ketogenic diets (KD) may be advantageous for reducing body mass and FM, while retaining FFM. Methods A systematic review of the literature was conducted using PubMed and Cochrane Library databases to compare the effects of KD versus control diets (CON) on body mass and composition in physically active populations. Randomized and non-randomized studies were included if participants were healthy (free of chronic disease), physically active men or women age ≥ 18 years consuming KD (< 50 g carbohydrate/d or serum or whole blood β-hydroxybutyrate (βhb) > 0.5 mmol/L) for ≥14 days. Results Thirteen studies (9 parallel and 4 crossover/longitudinal) that met the inclusion criteria were identified. Aggregated results from the 13 identified studies show body mass decreased 2.7 kg in KD and increased 0.3 kg in CON. FM decreased by 2.3 kg in KD and 0.3 kg in CON. FFM decreased by 0.3 kg in KD and increased 0.7 kg in CON. Estimated energy balance based on changes in body composition was − 339 kcal/d in KD and 5 kcal/d in CON. Risk of bias identified some concern of bias primarily due to studies which allowed participants to self-select diet intervention groups, as well as inability to blind participants to the study intervention, and/or longitudinal study design. Conclusion KD can promote mobilization of fat stores to reduce FM while retaining FFM. However, there is variance in results of FFM across studies and some risk-of-bias in the current literature that is discussed in this systematic review.

A first-principles study of the relationship between modulus and ideal strength of single-layer, transition metal dichalcogenides

Deformation of single-layer transition metal dichalcogenides (TMDs) can tune their band gap. The regulating range of the band gap is determined by the ideal strengths, which is usually estimated, according...

Ideal Strength and Strain Engineering of Rashba Effect in Two-Dimensional BiTeBr

Achieving large and tunable Rashba effect is of great significance for advancing both the understanding and applications of spintronics. Two-dimensional nanostructures that are expected to sustain large mechanical deformation provide...

Mechanical Properties of DO3 Based on First Principles

The elastic constants, ideal strength, band structure and electronic density state of Fe3Si (DO3) under triaxial tension and triaxial compression were studied using the first principle. The structural parameters calculated at zero pressure are consistent with the experimental results. The dependence of elastic constant and strain can be obtained using static finite strain technique. The ideal triaxial tensile and compressive strength of DO3 were studied by calculating the stress–strain relationship. The micro mechanism that affects the stability of the structure was analyzed using the results of electronic structure calculation. The results showed that the compressive strength of DO3 structure is higher than the tensile strength. When the stress of cell structure exceeds a limit, the covalent bond of Fe–Si is destroyed, resulting in the sudden decrease of G and E and the abnormal change of electronic density of state.