Energy-efficient omd processes with complex local loading for the production of machine parts with a given level of properties

The article discusses some new energy-efficient metal forming processes (PMD) with complex local loading of the deformation zone for the production of machine parts with a given level of properties. The place of such processes in the aggregate of all OMD technologies is shown, and their classification is given. The initial data of numerical mathematical modeling of the specified class of processes for a particular case are given, the features of the stress-strain state of the metal in the deformation zone are revealed. In the study, from a theoretical point of view, one of the important practical aspects of these technologies is considered: the effect of the value of axial compression on the shape and size of the deformation zone arising from the action of local loading of the workpiece.

ADDITIONAL CHARACTERISTICS OF HYBRID COMPOSITES FOR FILLING TEETH UNDER LOCAL MOUNTING CLOCKS

For the rational use of materials, it is necessary to have data on their ability to resist deformation and destruction. In particular, in each case it is necessary to have information on the stiffness, strength and resistance to destruction of materials in the specified operating conditions of the elements. To determine such strength characteristics of the material, certain studies are carried out. According to the analysis of literature sources in the study of dental composites mainly determine the tensile strength (bending) and compression [2-10], because it is subjected to restore materials during their operation in the oral cavity. The purpose of the study is to conduct a comparative analysis of the strength of hybrid composites of domestic and imported production during their local loading: Latelux (Latus, Ukraine), TETRIC N-CERAM (Ivoclar Vivadent, Liechtenstein), CHARISMA CLASSIC (Kulzer, Germany). To conduct research, 10 samples of each dental polymer composite were made. Packaging and molding of the material into a specially designed form was performed in laboratory conditions at an air temperature of 18 210 C with their subsequent polymerization with a LED photopolymer lamp Bluephase 20i (G2) (Ivoclar Vivadent). Before the test, the samples were kept for 24 hours at a temperature of 370 C in saline. The samples were loaded on the SVR-5 installation using a ball indenter (ball diameter mm steel SHX15, modulus of elasticity GPa, Poisson's ratio) with a speed of 0.002 mm/s. The purpose of the study is to conduct a comparative analysis of the strength of hybrid composites of domestic and imported production during their local loading. According to the results of experimental studies on the load of PB fracture, the Charisma Classic composite (5.72 ± 0.16 kN) has the highest strength, Latelux (4.23 ± 0.53 kN) the lowest, and Tetric N-Ceram (5, 03 ± 0.71 kN) occupies an intermediate position. To move the indenter, we obtained the following order of materials (in ascending order): Latelux (0.94 ± 0.11 mm); Charisma Classic (1.02 ± 0.04 mm); Tetric N-Ceram (1.03 ± 0.17 mm).

Anisotropic, rate-dependent ductile fracture of Ti-6Al-4V alloy

An extensive experimental campaign was run to investigate the influence of the loading direction, stress state (triaxiality ratio ranging from −0.5 to 1), and strain rate (from 10−3 to 1.5x103s−1) on the ductile fracture of Ti-6Al-4V titanium alloy. Microscopic and macroscopic observations provided some insight into the shear-driven or micro-voiding-controlled damage mechanisms prevailing at low and high triaxiality ratios, respectively. Numerical simulations were run to determine the local loading paths to fracture in terms of plastic strain as a function of stress triaxiality ratio and Lode parameter. The ductility was found to be anisotropic, but only weakly dependent on the strain rate in the considered range. The anisotropy in ductility was different in tension (maximum along DD) and in compression (maximum along ND). The fracture strain decreased with the absolute value of the triaxiality, with a maximum close to zero. No clear correlation with the Lode parameter was found.

Comparative analysis of the strength of restoration polymers of light polymerization for dental restoration using the acoustic emission method: part one

Purpose. Comparative analysis of the strength of hybrid restoration composites of light polymerization during their local loading using the phenomenon of acoustic emission. The following restoration composites were studied: Latelux, Tetric N-Ceram, Charisma Classic. Results. It was determined that the nature of the destruction of all composites is the same: elastic-plastic at the initial stage of the load with a transition to brittle as its further growth. Three types of composite failure are observed: correct, incorrect and mixed. The first predominated during fracture under the action of local loading of the Latelux composite, for Tetric N-Ceram and Charisma Classic materials a mixed type of fracture is characteristic. Conclusions. Analysis of the parameters of the AE signals showed that the signals had the highest amplitude and energy when the Tetric N-Ceram composite was destroyed, and the lowest – Latelux. All dental composites are dominated by high-energy ductile-brittle and brittle fracture, which indicates the spread of micro- and macrocracks of various sizes in materials. Key words: polymer composites, strength, acoustic emission method.

Strain-stress behavior of elastic layer in local loading

The paper studies the problem of a local loading of an elastic layer in 3D perspective. The solution of the boundary value problem subject to a concentrated force is constructed as a combination of two components. The first component is a classical solution of A. Lyav theory of elasticity, the second one is a solution proposed by I.М. Rapoport. The second component is distinctive in that it describes a point edge effect rapidly damping while moving off from the point of force application. This solution is built in a series form, namely, proper decompositions of the auxiliary nonself-adjoint differential operator. The convergence of series is ensured by a rapid growth of eigenvalues. Dying-away to zero at infinity is caused by the exponential law of Macdonald functions damping. The solution of the concentrated force action is used as a kernel to determine displacement vector components, tensors of deformations and strains in the problem of arbitrary local loading of an elastic layer. Eventually, analytical solution of the singular problem makes it possible to reasonably determine the strain-stress state in a local loading zone. Key words: strength, stress-strain behavior, theory of elasticity, differential equations, series, Bessel functions.