B. N. Semenov

Novel Shrinkage-Free Structural Ceramic Materials for Gas Turbine Applications

The paper presents results of development of the novel shrinkage-free, adaptable to machining and easily welded alumo-boron-carbide silicon materials that experience the cermet stage during their manufacturing. A specific feature of the like ceramics is their double-stage sintering process when, after the original stage, a metal-ceramic blank has a sufficient strength and is easily machined by conventional metal-cutting tools. In addition, such materials are electrically conductive, therefore, the elasto-erosion treatment technique can be applied. Subsequently, a machined part is finally sintered, whereas all the geometries remain actually unchanged due to the shrinkage absence. Prior to the final sintering, all separate parts can be joined by the diffusion welding with the seam strength being 5–10% different from the strength of the main part. The paper provides an insight into the processes and results of tests of the representative selections of samples of four types of the structural ceramics that are experiencing the cermet stage during the process of their formation. Also, ceramic parts for the CGTE hot passage are demonstrated.Copyright

Stability loss in an infinite plate with a circular inclusion under uniaxial tension

Loss of stability under uniaxial tension in an infinite plate with a circular inclusion made of another material is analyzed. The influence exerted by the elastic modulus of the inclusion on the critical load is examined. The minimum eigenvalue corresponding to the first critical load is found by applying the variational principle. The computations are performed in Maple and are compared with results obtained with the finite element method in ANSYS 13.1. The computations show that the instability modes are different when the inclusion is softer than the plate and when the inclusion is stiffer than the plate. As the Young’s modulus of the inclusion approaches that of the plate, the critical load increases substantially. When these moduli coincide, stability loss is not possible.

Deformation and fracture processes in graphene nanoribbons with linear quadrupoles of disclinations

The deformation and fracture processes in graphene nanoribbons containing linear quadrupoles of disclinations are investigated by the method of molecular dynamics. Special attention is given to estimating the effect of the curvature formed by disclinations and free boundaries in graphene nanoribbons with linear quadrupoles of disclinations on their mechanical characteristics (the stress–strain curve, the strength at the single-axis tension, and the degree of plastic deformation).

The Stability of the Plates with Circular Inclusions under Tension

This paper deals with the problem of local buckling caused by uniaxial stretching of an infinite plate with a circular hole or with circular inclusion made of another material. As the Young’s modulus of the inclusion approaches that of the plate, the critical load increases substantially. When these moduli coincide, stability loss is not possible. This paper also shows the difference between them when the inclusion is softer than the plate and when the inclusion is stiffer than the plate. Computational models show that instability modes are different both when the inclusion is softer than the plate and when the inclusion is stiffer than the plate. The case when plate and inclusion have the same modulus of elasticity, but different Poisson’s ratio is investigated too. It is also discussed here the case when a plate with inclusion is under biaxial tension. For each ratio of the modulus of elasticity of plate versus inclusion it’s obtained the range of the load parameters for which the loss of stability is impossible.

The Influence of Defects and Inclusions on Capacity for Work of Thin Plates

Some problems of strength and stability of thin constructions with defects and inclusions, which are of vital importance for nano- and microtechnology, are investigated. The attention is paid to the estimation of the number of defects influencing the capacity for work of nanosized plated and shells. The influence of surface effect is taken into account.

Deformation and Fracture in Graphene with Divacancies of the 555-777 Type

The deformation and fracture of graphene sheets containing 555–777 defects have been investigated by molecular dynamics simulations. Each such defect is a divacancy forming a localized configuration of three pentagonal and three septangular cells of carbon atoms in a hexagonal graphene lattice. An emphasis is made on the influence of 555–777 defects in graphene on its mechanical characteristics (stress–strain curve, uniaxial tensile strength, and maximum elastic strain).