We have offered the methods of the operative evaluation of a breaking stress in testing strength on compression of heavy concrete of grade 400 with the use of fractal formalism. The methods are based on the setting of the relations of the values of a breaking stress and fractal measurement of concrete: 1. Areas with crushed stone prevailing (R2 = 0.7224); 2. Areas with sand prevailing (R2 = 0.6102); 3. Pin holes (R2 = 0.6874). During fractal experimenting the indexes of breaking were increased from 391.63 to 515.13 kH in reducing fractal dimension of areas 1 from 1.866 to 1.588; areas 3 from 1.826 to 1.684 and internal quality (boundary of its elements) from 1.617 to 1.353. Increase of fractal dimension was fixed only for areas containing sand (areas 2) from 1.755 to 1.944. These results make possible to apply fractal dimension as the indicator of structural changes of concrete in the prediction of its properties. In fractal modelling the accuracy of the results depends on the option of the task way for space metric that is proved by the obtained linear model (R2 = 0.9254), which describes the connection between the elements of macrostructure and strength criterion of concrete. Such methods provide a satisfactory in practical purposes operative prediction for the values of breaking stress of concrete of grade 400 with significant reduction of time and money expenditures on full-scale testing and the application of microscopy.

The large-scale use of conveyor belts in coal mines is of special importance in safety considerations.In the operation of rubber cable conveyor belts, the cable base becomes damaged, reducing the belt strength.Studies of d-m-ge and the effect on strength characteristics of conveyor belts, and development of standards of admissible wear and tear, are essential for reducing hazard and increasing belt service life.A rubber cable conveyor belt is a thin plate reinforced by densely placed lengthwise cables.The bonding material is rubber, which has a lower hardness comprable to that of the cable.The theoretical basis for calculatlon of such a lamlnated structure has been developed in [1][2][3].The calculation of the stressed state for a d--umged rubber cable conveyor belt is described in [4].Of the more recent publications, [5, 6] should be mentioned.The equations for the study of a stressed state of a d--mged rubber cable conveyor belt ( Fig. 1) are deduced on the basis of the following assumptions: (i) in each cable, a tensile stress Gi(y), kg/cm, arises which is variable lengthwise; (2) only the shear stress zi(y) , kg/cm, is considered in rubber layer; (3) the belt is in a plane stressed state. The shear strain in the rubber interlayer is found from the expression ~,,(y) _ vi+1(Y)--vi(~).(1) h where 71(Y) is shear strain; Vi(Y) is the elastic displacement along the cable, cm; and h is the width of the rubber interlayer, cm. Hooke's law assumes the formwhere E is the elasticity modulus of the cable, kg/cm2; D is the cable diameter, cm; and G is the rubber shear modulus, kg/cm~The equilibrium equations expressed in ter~s of displace~ents have (see, e.g., (2) and (3)) the following appearance:

Introduction. Different approaches are used to study the structure and properties of structural steels. The properties of steels are determined using traditional methods (physical methods, field tests, X-ray analysis, microscopy, etc.). Structure studies are also carried out using traditional methods based on Euclid's integer geometry. A similar approximation of structural elements by Euclid's figures leads to a decrease in the accuracy of forecast models due to the complex shape of its elements. The reason for this is the fractality (fine dimensionality) of most elements of the material structure. The paper proposes an approach based on a combination of expert and fractal assessments when creating a forecast model for the quality of construction steel. Materials and methods. Construction steel 20 in the mode of factory delivery was studied. The steel had a ferrite-pearlite structure. Mechanical tests and determination of chemical composition were carried out in accordance with the existing regulatory documents (DSTU 7809). The content of pearlite in steel ranged from 10 to 18 %, depending on the amount of carbon. Ferrite occupied the entire other part of the area of the slide examined under the Neophot-2 optical microscope. The results of the experiment. Expert assessment was used to predict mechanical indicators of strength with the aim of reducing material and time costs for conducting field tests with metal samples. The effect of the ferrite-pearlite structure on the mechanical characteristics of strength was investigated by comparing the fractal evaluations of the structure with the indicators of mechanical tests. It has been established that an increase in the fractal dimension of pearlite has a positive effect on the growth of strength indicators of steel 20. A similar effect is, in a certain way, associated with the change in the shape of pearlite grains in the process of changing the amount of carbon in steel within the limits of regulatory documents. Conclusions. For structural steel 20, models for assessing its mechanical characteristics were obtained using the fractal dimensions of structural elements and expert assessments. Coefficients of pairwise correlation of regression equations are recorded in the range of 0.65...0.85. The obtained results can be used to forecast strength indicators of steel, which is especially relevant when assessing its residual resource during operation.

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