Vol 19, No 4 (2016)

In the paper presented, we continue the research in the elastic properties of seven-constant tetragonal crystals and nano/microtubes. Our previous study concerned tension of this type of structures, and here we are dealing with their torsion, Poynting’s effect or axial extension under torsion with no tensile force, and torsional stiffness. It is demonstrated that there exists inverse Poynting’s effect: the tubes experience torsion under tension without applying a torque.

Contrary to the common approach of the general relativity, the author uses his invariant integral of physical mesomechanics to model and study the universe at the large scale of about 100 MPc in the Euclidian space. The flatness of the universe proven by numerous probes of the WMAP and PLANCK satellite missions necessitates this approach. From the invariant integral of cosmology, the interaction force of two point masses in the cosmic-gravitational field is derived. This force is proven to be a sum of two terms, the one being the Newtonian gravity and the other the repulsion force caused by the cosmological constant. Both terms make up the right-hand part of the evolution equation of the dynamic universe. Qualitatively in agreement with the FLRW and ACDM models, and WMAP and PLANCK mission data, the exact solution of this equation has provided the history of the early decelerating universe and the asymptotic description of the Big Bang, the expansion at an almost constant rate in the middle age, and the current stage of the accelerated expansion of the universe. The age of the universe is found to be equal to 12.3 billion years. It is shown that neutron stars become stable Black Holes when their masses are greater than 6.7M_sun. Then, it is assumed that the universe not only expands but also revolves, and the evolution equations of the revolving and expanding universe are advanced, with the cosmological constant being defined in terms of the angular velocity of the universe. A singular solution of these evolution equations has described the history of the revolving and expanding universe, at least, up to the age of about ten billion years. Orbital velocities of stars in the Milky Way are calculated to be about 250 km/s independent of the distance of stars from the galaxy center. Using the equation of the fractal dimension of the universe as a power-law fractal, the thickness of a disk-shaped universe is found. The graviton of minimum frequency is hypothesized to be the smallest elementary particle and the building block of everything.

Crack initiation from blunt V-notch borders in ductile A16061-T6 plates is investigated experimentally and theoretically under mixed mode I/II loading. Experimental observations with naked eye during loading indicated large plastic deformations around the notch tip at the onset of crack initiation, demonstrating large-scale yielding failure regime for the aluminum plates. To theoretically predict the experimentally obtained value of the maximum load that each plate could sustain, i.e. the load-carrying capacity, without performing elastic-plastic failure analyses, the equivalent material concept (EMC) is combined with a well-known brittle fracture criterion, namely the averaged strain energy density (ASED) criterion. It is shown that the combined EMC-ASED criterion could successfully predict the experimental results for various V-notch angles and radii.

Deformation and fracture of electroplated Au-Ni coatings subjected to tribological testing under dry conditions were studied. Wear of the coatings is shown to result from macroscopic contact interaction of the specimen with the counterbody, and from abrasive action of microasperities on the counterbody surface and wear particles. The formation mechanisms of wear particles and a transfer layer were investigated, and their contribution to wear of the electroplated Au-Ni coatings was demonstrated. The significance of shear stresses arising at the coating/sublayer interface in coating fracture was substantiated.

The paper studies the localization of plastic deformation and fracture in a material with a porous coating. A dynamic boundary value problem in the plane strain formulation is solved. The numerical simulation is performed by the finite difference method. The composite structure corresponds to the experimentally observed one and is specified explicitly in the calculation. A generation procedure of the initial finite-difference grid is developed to describe the coating structure with adjustable porosity and geometry of the substrate-coating interface. Constitutive equations for the steel substrate include an elastic-plastic model of an isotropically hardening material. The ceramic coating is described by a brittle fracture model on the basis of the Huber criterion which accounts for crack nucleation in triaxial tension zones. It is shown that the specific character of deformation and fracture of the studied composite results from the presence of local tensile regions in the vicinity of pores and along the coating-substrate interface, in both tension and compression of the coated material. The interrelation between inhomogeneous plastic flow in the steel substrate and crack propagation in the coating is studied.

The regular grid generation method was generalized for a 3D region based on the solid mechanics equations that describe deformation of a finite volume. Test calculations of fracture of ceramic composites with inclusions are represented which are based on the developed model of quasi-brittle media with regard to damage accumulation.