No 3 (2014)

The methodology and results of experimental study by Sachs method of residual stresses in thick-walled cylinders of steel grade 45 (0.45% C) with 5 mm diameter hole, outer diameter of 15 mm, height of 50 mm after compression and tension mandrelling, which is performed with allowances that ensure high accuracy of the mandrelled holes are presented in the article.It is found that the transition from the compression configuration to the tension one increases axial and radial residual strains and reduces hoop residual strains on the surface of the hole and outer surface of the cylinder, and increases the largest in absolute value residual stresses in these areas: hoop stresses – from 285 to 320 MPa; radial stresses – from 105 to 115 MPa; axial stresses – from 20 to 60 MPa.It is shown that the nature of the residual stress distribution in cylinders does not depend on the mandrelling configuration.

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The instrument of technological inheritance mechanics is developed to design strengthening technological processes, providing specified operation characteristics of machine parts. The key issue, that determinate the accuracy of the developed technological solutions, is the adequacy of calculating the mechanical state in the deformation actual processes that occur in the metal surface layer during processing. The traditional approach to solving the problems of contact interaction of the workpiece and the tool has several drawbacks that lead to the possibility of significant errors in the calculation. An approach to the solution of the contact problem by incorporating a system of equations of the finite element approximation of the contact surface is offered in the paper. An example of the calculation in the elastic formulation for linear triangular element is given. It is noted that the proposed solution has a number of advantages in comparison with a solution that can be obtained using commercial CAE-systems that use the finite element method to calculate the stress-strain state.

The influence of the heating temperature during the heat treatment of the alloy tube billets 58Сu-34Zn-3Mn-2Al after extrusion on the quantity of α-phase is investigated, and an analysis of the distribution of α-grains in the cross section of billets is carried out. It is established that the most uniform distribution is achieved by α-grains after heating the pipe blanks to 450 ° C, holding for 3 hours with the next air cooling. As a result of the work, the causes of uneven distribution of α-phase is found, also a recommendation for its reduction throughout the length of pipes is given. A correlation between the amount of α-phase, after extrusion and after aging is marked. The possibility of using software packages SIAMS type 700 when calculating the amount of α-phase is analyzed.

The structure and mechanical properties of Ni3Al intermetallic are studied. The materials are fabricated according to different schemes, which combined mechanical activation of Ni and Al powders, self-propagating high temperature synthesis (SHS) and spark plasma sintering (SPS). It is found that Ni3Al intermetallics, fabricated by SPS using three different routes, have relative density of about 97 % and high values of mechanical properties compared to similar materials, obtained by conventional methods. Microhardness of the sintered samples range from 6100 to 6300 MPa. The value of flexural strength of all sintered samples is equal to 800 MPa. Spark plasma sintering of 86.71 % wt. Ni and 13.29 % wt. Al powders at 1100 °C leads to the formation of the material with the highest level of tensile strength equal to 400 MPa. This process was the most fast and efficient. It combines the chemical interaction of reagents with the sintering process.

Nowadays the most part of the machine elements is subjected to different technological effects on the stage of production. These effects are intended to improve the operational characteristics of the machine elements. One of such effect is the formation of the ceramic coating on the product surface. Ceramic coating has very high wear resistance, low coefficient of friction, but its operational characteristics in conditions when the sample with coating is subjected to loading with variable sign are unknown. The method of investigation of relationships of inelastic deformation of the samples with nonhomogeneous structure of metal alloy Д16АТ in conditions of periodic loading are suggested in the paper. The research methodology includes a step-stress test in the cycle, and registration of the effects of non-equilibrium strain. The study represents the comparative analysis of samples with removed and modified surface layer. Layer is modified by micro-arc oxidation (MAO) and removed by chemical etching in alkaline sodium hydroxide solution (15% NaOH). It is proved that the samples with coating demonstrate higher stress under which irreversible phenomena occur in comparison with the samples with removed surface layer. It is shown that the stress at which there are irreversible phenomena in coated specimens is 20% higher than that of the samples with a removed surface layer.