INCREASING THE DURABILITY OF DETAILS TO WORK UNDER REPEATABLE LOADS

The article presents the results of the development of processes to improve the performance of parts operating under repeated variable loads, taking into account the reasonable parameters of surface plastic deformation (SPD) and cold gas-dynamic spraying of coatings. The influence on the parameters of the working surface layer, the nature of the distribution of the stress-strain state of the surface layer of material and residual compressive stresses, as well as the values of the used resource of plasticity of the surface layer of the workpiece, the parameters of the SPD process. The article shows that the main factor in the formation of residual compressive stresses during SPD is the decrease in the density of the surface layer of the workpiece, which is associated with the use of the plasticity resource. The model of calculation of the used resource of plasticity of material of preparation at SPD which allows to provide the improved quality of a surface layer of details is offered. A method of moving the workpiece layers with maximum hardening and residual compression stresses to the surface of the part by applying a deforming tool of reduced size in the following passes with coating the surface of the part with gas-dynamic spraying before SPD. Cold gas-dynamic coating by spraying, in contrast to most known gas-thermal coating methods that take place under significant temperature effects on the surface of the part, which is unacceptable for surfaces treated by SPD methods, provides a permissible temperature regime for creating special auxiliary coatings while preserving surface properties SPD. The technology of gas-dynamic coating by spraying includes heating the compressed gas (air), directing it into the nozzle and forming in this nozzle supersonic air-powder flow, sprayed material (copper, aluminum), acceleration of this powder material to supersonic speeds and directing it to the surface of the processed product. As a result, a special auxiliary coating (copper or aluminum) is formed on the surface of the product, which improves the parameters of the SPD process.

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INCREASING OF THE DURABILITY OF DETAILS WORKING UNDER REPEATABLE- LOADS

Vibrations in engineering and technology ◽

10.37128/2306-8744-2020-1-1 ◽

2020 ◽

pp. 5-14

Author(s):

Viktor Matviychuk ◽

Oleg Gaidamak

Keyword(s):

Surface Layer ◽

Surface Plastic Deformation ◽

Cold Gas Dynamic Spraying ◽

Surface Plastic ◽

Dynamic Coating ◽

Compressive Stresses ◽

Gas Dynamic ◽

Air Stream ◽

Coating Methods ◽

Cold Gas

The article develops processes of increase the durability of parts operating under repeated loads, by justifying the parameters of surface plastic deformation (SPD) and cold gas-dynamic coating. The influence on the depth of the reinforced surface layer, the nature of the distribution of the stress-strain state of the material and residual compressive stresses, as well as the value of the used plasticity of the metal, the parameters of the SPD process. The hypothesis is substantiated that the main factor in the formation of residual compressive stresses during SPD is the decrease in metal density, which is associated with the use of the plasticity resource. The model of definition of the used resource of plasticity of metals at SPD is developed, that allows to provide qualitative characteristics of a surface layer of details. Methods for shifting the layer with maximum hardening and residual compressive stresses to the surface of the part by using a deformable tool of smaller dimensions in subsequent passes and gas-dynamic coating before SPD. The vast majority of traditional gas-thermal coating methods occur at significant temperature effects on the surface of the part, which is unacceptable for the surface treated by SPD methods. Cold gas-dynamic spraying provides an allowable temperature regime for the creation of special auxiliary coatings while maintaining the properties of the surface treated by SPD methods. The technology of gas-dynamic coating includes heating the compressed gas (air), feeding it into the nozzle and forming a supersonic air stream in this nozzle, introducing a powder material into this stream, accelerating this material in the nozzle by a supersonic air flow and directing it to the surface of the workpiece. As a result, a special auxiliary coating is formed on the surface of the product, which provides optimal parameters of the SPD process.

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IMPROVEMENT OF OFFICIAL CHARACTERISTICS OF THE SURFACE LAYER DETAILS BY APPLICATION OF SURFACE PLASTIC DEFORMATION AND GASODYNAMYNAMYNAMINE

Vibrations in engineering and technology ◽

10.37128/2306-8744-2020-2-10 ◽

2020 ◽

pp. 90-100

Author(s):

Viktor Matviychuk ◽

Oleg Haidamak ◽

Mykola Kolesnik

Keyword(s):

Plastic Deformation ◽

Surface Plastic Deformation ◽

Cold Gas Dynamic Spraying ◽

Thin Plates ◽

Geometrical Parameters ◽

Surface Plastic ◽

Gradual Change ◽

Gas Dynamic ◽

Multi Stage ◽

Cold Gas

The article investigates changes in the characteristics of the surface layers of parts processed by methods of surface plastic deformation (SPD). It is shown that at SPD the strength and hardness characteristics of the material increase and residual compression stresses are formed. On the basis of the study of the stress-strain state of the material at the SPD, its non-monotonicity is established, which is manifested in the gradual change of sign of the components of deformations and stresses. In this regard, a tensor-nonlinear damage accumulation model was used to evaluate the deformability of the material, which takes into account the directional nature of the damage and the anisotropy of the plasticity of the deformed metal. Based on this model, an expression was obtained to determine the plasticity resource used in the case of multi-stage SPD. According to the results of the calculations, it is established that the maximum plasticity resource used in the SPD is at a depth of approximately 0.1 of the diameter of the plastic footprint of the tool, and destruction at full exhaustion of the plasticity resource occurs in the form of peeling of thin plates of appropriate thickness. Recommendations for displacement of the most reinforced layers to the surface of the workpiece are developed, as well as recommendations for limiting deformation by the amount of plasticity resource used. The conducted research allows to assign the optimal modes of SPD at the stage of technological process design. A device for cold gas-dynamic spraying was developed and the possibility of creating antifriction sections using it was investigated. Graphs of dependence of geometrical parameters of the deposited layer on the sputtering distance are constructed and methods and schemes of preparation for deposition of the surface of the workpiece using SPD methods are developed. Experimental cold gas-dynamic spraying was carried out and optimal parameters of the process of spraying of antifriction layers of bronze and metal polymers (pressure, and the temperature of the compressed air and the temperature of the workpiece) on the formed roller surface were determined. A new concept of increasing the contact strength and durability of friction pairs is proposed.

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Relaxation patterns of technological residual voltage in the surface layer of high-strength steel when cyclically loaded

E3S Web of Conferences ◽

10.1051/e3sconf/202124404001 ◽

2021 ◽

Vol 244 ◽

pp. 04001

Author(s):

Georgi Kravchenko ◽

Konstantin Kravchenko ◽

Andrey Smolyaninov ◽

Irina Kudryavtseva

Keyword(s):

Surface Layer ◽

Residual Stresses ◽

Construction Materials ◽

High Strength ◽

Surface Plastic Deformation ◽

Variable Pressure ◽

Surface Plastic ◽

Initial Value ◽

Residual Voltage ◽

Compressive Stresses

Experimentally investigated patterns of changes in technological residual stresses under the influence of variable pressure in the surface layer became 30XNS2A. A mathematical model of relaxation of residual compressive stresses created by surface plastic deformation techniques with symmetrical cyclical bending of samples has been proposed. An empirical expression is proposed for assessing the final value of residual stresses as a result of cyclic loading, depending on the stress amplitude of a symmetric cycle. An expression is given for estimating the coefficient of relaxation rate of residual compressive stresses from their initial value, amplitude of alternating stresses and material properties. The constants of these expressions are determined for various construction materials. The theoretical dependences describe well the obtained experimental data. To predict the level of residual stress realization under operational loading, a formula was obtained to calculate their change as a result of the action of a step loading block with different amplitudes and duration of their action at each of the stages.

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Determining the Quality of the Surface Layer of Low-Stiff Cylindrical Products after Straightening with Transverse Burnishing with Smooth Plates

Proceedings of Higher Educational Institutions Маchine Building ◽

10.18698/0536-1044-2019-12-5-13 ◽

2019 ◽

pp. 5-13

Author(s):

S.A. Zaides ◽

Quang Le Hong

Keyword(s):

Surface Layer ◽

Residual Stresses ◽

Sharp Decrease ◽

Surface Plastic Deformation ◽

Surface Plastic ◽

Surface Layers ◽

Compressive Stresses ◽

Cylindrical Parts ◽

Compressive Residual Stresses

To restore the shape of low-stiff cylindrical parts such as shafts and axles, straightening by transverse bending with the subsequent processing of workpieces by the method of surface plastic deformation based on the transverse burnishing with smooth plates is proposed. The experimental and calculated results are presented to determine the effect of absolute compression on the main characteristics of the quality of the surface layer of parts such as surface roughness and residual stresses. The analysis of experimental data for the evaluation of the parts after straightening by transverse burnishing showed the following positive changes: a sharp decrease in the initial roughness, the formation of equilibrium residual compressive stresses in the surface layers and ensuring stabilization of the accuracy of the processed part in size and shape. Depending on the magnitude of the absolute reduction, the surface quality increases by 2–3 classes, and rather large compressive residual stresses are formed (up to 375 MPa). The results of the work justify recommending the proposed method of straightening by transverse burnishing with smooth plates for implementation into the technology of machine part restoration.

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