Fundamental role of local curvature of crystal structure in plastic deformation and fracture of solids

It is shown that strain-induced defects of all kinds are nucleated in local curvature zones of the interfaces between 3D-crystals and 2D-planar subsystem similar to a laser pumping mechanism. Mobile curvature solitons are generalized wave structural carriers of plastic flow. Fracture is the structural phase decay of a crystal in the zones of very high curvature

Influence of porosity on the deformation behaviour of systems with nanostructured thermal barier coatings

Based on the principal concepts of physical mesomechanics that take into account reversible structural-phase transformations in the rotational-wave flows at the interfaces, a new modification of the multilevel discrete-continuous method of excitable cellular automata (ECA) has been developed. The new modification explicitly takes into account the porosity and the nanocrystalline structure. Also, algorithms for calculating the local moments of forces and the angular velocities of microrotations arising in a structurally heterogeneous medium have been implemented. The model has been complemented by the dissipation conditions expressed for mechanical energy flows. On the basis of the method of excitable cellular automata, some numerical experiments on thermal loading of three-layered compositions with the intermediate layers of different structures have been carried out. It is shown that nanostructuring of the intermediate sublayer and the introduction of nanoporosity gives rise to a positive effect on the relaxation ability of thermal barrier coatings

Material fragmentation as dissipative process of micro rotation sequence formation: Hybrid model of excitable cellular automata

The authors have developed a multi-level model of energy propagation along interfaces between the various structural elements of a solid with taking into account mutual energy transformations of various kinds. They have also designed a computer simulation tool based on the excitable cellular automaton (ECA) method. An algorithm for calculating the local moments of forces has been developed for the case of material rotation and torsion. The relationship for the accumulated elastic energy is supplemented with a dissipation term. Numerical experiments have been carried out on high-energy impact on polycrystalline copper specimens with different grain sizes. The paper shows that during the nanostructuring of material surface layer, the dissipation of elastic energy gives rise to the rotation of structural elements. This makes it possible to prevent the occurrence of stress concentrators with peak values typical of coarse-grained specimens and reducing their mechanical properties

Deformation and fracture of a layered VT6-based material under shock loading

In the work, we investigate in detail the mechanisms of plastic deformation, structure transformations and fracture in layered VT6-based material under shock loading

Determination of fracture toughness for small-sized specimens with ultrafine grain structure

The results of changing the fracture toughness of materials are given for the VT6 titanium alloy. Its coarse grain structure was reduced down to ultrafine structure by forging. The specific energy of fracture [gamma] for the small-sized chevron-notched specimens was found thanks to the new technique. It is shown that severe plastic deformation reduces [gamma] at room temperature. The structure of the surface fracture of the VT6 alloy’s ultrafine grain structure can be conceived as local zones of strong deformed material with a high concentration of pores. Such kind of structure cannot be formed only by means of crystallographic shears along close-packed planes. That fact proves the cardinal role of rotational modes of deformation in the origination and formation of a crack at various scale levels

Molecular dynamics study of cluster structure and properties of rotational waves in solid nanostructures

The paper reports a molecular dynamics analysis of rotary properties of a transformational wave generated due to compressive influence. Studies are performed in the time interval prior to the onset of elastic precursor reflection from the free boundary. It is shown that the leading front of a rotary wave coincides with the transformational wave front. The rotary wave velocity for copper is determined, being equal to 1300 m/s. The values of angular moment projections onto the coordinate axes in a plane perpendicular to wave propagation are found to be symmetrical, and their total sum equals zero

Molecular dynamics study of cluster structure and properties of rotational waves in solid nanostructures

The paper reports a molecular dynamics analysis of rotary properties of a transformational wave generated due to compressive influence. Studies are performed in the time interval prior to the onset of elastic precursor reflection from the free boundary. It is shown that the leading front of a rotary wave coincides with the transformational wave front. The rotary wave velocity for copper is determined, being equal to 1300 m/s. The values of angular moment projections onto the coordinate axes in a plane perpendicular to wave propagation are found to be symmetrical, and their total sum equals zero

Magnetron deposition of metal-ceramic protective coatings on glasses of windows of space vehicles

Transparent refractory metal-ceramic nanocomposite coatings with a high coefficient of elasticrecovery and microhardness on the basis of Ni/Si-Al-N are formed on a glass substrate by the pulse magnetron deposition method. The structure-phase states were investigated by TEM, SEM. It was established that the first layer consists of Ni nanograins with a fcc crystalline lattice, the second layer is two-phase: 5-10 nm nanocrystallites of the AlN phase with the hcp crystalline lattice in amorphous matrix of the Si3N4 phase

Magnetron deposition of metal-ceramic protective coatings on glasses of windows of space vehicles

Transparent refractory metal-ceramic nanocomposite coatings with a high coefficient of elasticrecovery and microhardness on the basis of Ni/Si-Al-N are formed on a glass substrate by the pulse magnetron deposition method. The structure-phase states were investigated by TEM, SEM. It was established that the first layer consists of Ni nanograins with a fcc crystalline lattice, the second layer is two-phase: 5-10 nm nanocrystallites of the AlN phase with the hcp crystalline lattice in amorphous matrix of the Si3N4 phase