Comprehensive assessment of the strength of the composite fan blade of the main ventilation of the mine

The work is devoted to the development and calculation of the strength of a new composite fan blade of the main ventilation of the mine, including the static and modal analyzes, as well as the stability analysis. The studies took into account the pre-determined aerodynamic loads on the lateral surface of the blade airfoil. The research was carried out by means of the finite element analysis of the thin-walled airfoil structure using the theory of thick multilayer shells. Estimation of the static strength was performed using the Hashin strength criterion. Analysis of the airfoil shell buckling resistance under the action of bending aerodynamic loads was performed using the methods of the linear stability theory. The modal analysis was performed taking into account the prestressed state from the action of static loads. The analysis of the research results testifies to the sufficient static and dynamic strength of the composite airfoil and the possibility of its implementation in a real rotary machine with the correct design of the fastening between the metal part of the blade root and the composite airfoil. The method of designing and analyzing the strength of the fan blade composite airfoil can be used to create new composite elements of turbomachines: the correct selection of thicknesses of different parts of the airfoil allows obtaining a uniform design with rational use of material; the optimal location of the stiffeners inside the airfoil shell avoids its excessive displacement and stress and the buckling effects, as well as achieving the maximal detuning level from the bending natural frequencies of vibrations; the proposed integrated approach to the strength assessment, which takes into account the effect of aerodynamic loads on the blade airfoil in the static analysis and the prestressed state during the modal analysis can significantly improve the accuracy and correctness of calculations. The approach described in the paper is new for low-speed rotary machines, as at present there are no comprehensive methods for designing composite blades of fans and compressors, and there is no mention of specific examples of their implementation in the projects implemented by manufacturers.

HIGH RIGIDITY AND VIBRATION ENDURANCE BAR FOR DEEP HOLES

Different constructions of bars are analyzed in the article, all of which are based on the idea of creating prestressed state in material. Improved construction of bar is proposed for equable spreading of elasticity zone along axis of boring bar.

Model of Fracture Propagation in Hydraulic Isolation of the Wellbore

A model of fracture initiation and propagation along the boundary of a cement plug and a steel casing in a plugged wellbore is proposed. The model allows predicting the conditions of hydraulic isolation failure of a cement plug induced by reservoir pressure. The model describes the stress state of the cement and it’s breakaway from the steel casing caused by the pressure of the pore fluid flowing into the fracture. Numerical experiments show that the fracture propagation velocity and the stability of the hydraulic isolation are sensitive to the reservoir pressure and to the prestressed state of the cement. It is shown also that the quality of cement adhesion to steel and the size of the initial cementing defects have little effect on the initiation conditions and fracture propagation velocity.