Study of Radiation Embitterment and Degradation Processes of Li2ZrO3 Ceramic under Irradiation with Swift Heavy Ions

The work is devoted to the study of radiation damage and subsequent swelling processes of the surface layer of Li2ZrO3 ceramics under irradiation with heavy Xe22+ ions, depending on the accumulation of the radiation dose. The samples under study were obtained using a mechanochemical synthesis method. The samples were irradiated with heavy Xe22+ ions with an energy of 230 MeV at irradiation fluences of 1011–1016 ion/cm2. The choice of ion types is due to the possibility of simulating the radiation damage accumulation processes as a result of the implantation of Xe22+ ions and subsequent atomic displacements. It was found that, at irradiation doses above 5 × 1014 ion/cm2, point defects accumulate, which leads to a disordering of the surface layer and a subsequent decrease in the strength and hardness of ceramics. At the same time, the main process influencing the decrease in resistance to radiation damage is the crystal structure swelling as a result of the accumulation of defects and disordering of the crystal lattice.

Коррелированное накопление микротрещин при ударном повреждении поверхности α-кварца, аморфизованной имплантацией ионами Ar-=SUP=-+-=/SUP=-

The microcrack accumulation in impact damaged -quartz plates prior to and after the Ar+-ion implantation was studied with the acoustical emission (AE) method. The 40 keV implantation doses of 1014 and 1016 ion/cm2 were applied. The statistical analysis of the energy distribution in impact-induced AE time series detected in unirradiated samples showed a random (poissonian type) accumulation of defects which is specific for mechanical destruction of homogeneous brittle materials. The energy distribution in the AE time series excited when damaging the preliminary implanted samples followed a power law typical for the fracture of heterogeneous solids such as rocks, ceramics, etc. The optical photography evidenced a transition from brittle (prior to implantation) to ductile damage formation caused by the disturbed interconnectivity of the crystalline structure in irradiated specimens.

NUMERICAL MODELING OF COMPOSITE FITTINGS FOR CLUTCHING WITH CONCRETE

Reinforced concrete is one of the most common materials in construction. Constructions made of this material have a high bearing capacity; well perceived dynamic and static loads. This is ensured by the adhesion between the reinforcing bar and concrete. The amount of adhesion is made from a number of different factors formed in the region of the conventional surface of interaction of reinforcement with concrete. It is implied that even if any reinforcement is used, materials come into contact over the surface, which can collapse depending on the load. Violation of the clutch causes significant deformation of the structure, which subsequently leads to a loss of the bearing capacity of the element. Therefore, there is a need to study the magnitude of the adhesion between concrete and reinforcement under various influences. This article describes the results of a numerical experiment on pulling out fiberglass reinforcement of a periodic profile from concrete. A mathematical model is constructed, which allows to study the accumulation of defects and the destruction of reinforcement in the area of concrete fixing. The results of numerical studies are considered.

Особенности дефектообразования в наноструктурированном кремнии при ионном облучении

Irradiations of the nanostructured silicon with Si+ and He+ ions were carried out with energies of 200 and 150 keV, respectively. Raman scattering showed destruction of the structure after irradiations and accumulation of defects at different fluences of irradiation. It is shown that monocrystalline silicon films are amorphized under irradiation at 0.7 displacement per atom. However, porous silicon does not completely amorphize at 0.5 displacement per atom, a weak signal is observed in the Raman spectra corresponding to the amorphous silicon phase, and at the same time there is an obvious signal from the crystalline phase of silicon. The size of nanocrystallites in the structure of porous silicon was estimated at different fluences of irradiation.

Introducing a Projection-Based Method to Compare Three Approaches Computing the Accumulation of Geometric Variations

In mechanical design, tolerance zones and contact gaps can be represented by sets of geometric constraints. For computing the accumulation of possible manufacturing defects, these sets have to be summed and/or intersected according to the assembly architecture. The advantage of this approach is its robustness for treating even over-constrained mechanisms i.e. mechanisms in which some degrees of freedom are suppressed in a redundant way. However, the sum of constraints, which must be computed when simulating the accumulation of defects in serial joints, is a very time-consuming operation. In this work, we compare three methods for summing sets of constraints using polyhedral objects. The difference between them lie in the way the degrees of freedom (DOFs) (or invariance) of joints and features are treated. The first method proposes to virtually limit the DOFs of the toleranced features and joints to turn the polyhedra into polytopes and avoid manipulating unbounded objects. Even though this approach enables to sum, it also introduces bounding or cap facets which increase the complexity of the operand sets. This complexity increases after each operation until becoming far too significant. The second method aims to face this problem by cleaning, after each sum, the calculated polytope to keep under control the effects of the propagation of the DOFs. The third method is new and based on the identification of the sub-space in which the projection of the operands are bounded sets. Calculating the sum in this sub-space allows reducing significantly the operands complexity and consequently the computational time. After presenting the geometric properties on which the approaches rely, we demonstrate them on an industrial case. Then we compare the computation times and deduce the equality of the results of all the methods.