НАПРЯЖЕННОЕ СОСТОЯНИЕ ПЛОСКИХ ОБРАЗЦОВ С НАПЫЛЕННЫМСЛОЕМ ПРИ ИСПЫТАНИЯХ НА ИЗГИБ

Abstract

The subject of study is the analysis of the stress state during bending, both in the elastic and elastic-plastic stages, of a flat sample with a sprayed layer having different mechanical properties (elastic modulus and yield strength) than the substrate material. The goal is to select options for coatings of small (soft layer), neutral and large (hard layer) stiffness concerning the base metal, which has a lower yield strength, with different ratios of their thicknesses (0.2, 0.4 and 0.6). Tasks: to analyze the distribution of normal stresses, to determine the most loaded points on the surface of the sprayed layer and on the lower surface of the substrate, to determine the conditions and causes of the appearance of cracks in the sprayed layer and plastic deformations in the substrate. The methods used are computer simulations and analytical calculations. The following results were obtained. The nature of the distribution of normal stresses substantially depends on the ratio of the thicknesses of the sprayed layer and the substrate and does not change with their proportional increase or decrease. The most loaded points in the section where the normal stresses reach maximum values are the points on the surface of the sprayed layer and on the bottom surface of the substrate. The level of maximum normal stresses both in the sprayed layer and the substrate significantly exceeds (by 2 orders of magnitude) the tangents. That is, they are the main cause of the appearance of cracks in the sprayed layer and plastic deformations in the substrate. At the same time, the results of calculations using analytical formulas based on the laws of solid mechanics and computer simulations are the same, which confirms the adequacy of the modeling. The level of stresses at a constant thickness of the substrate is affected by both the relative thickness of the sprayed layer and its rigidity. The maximum stresses in the sprayed layer decrease with an increase in its relative thickness and increase with an increase in its relative rigidity. Соnclusion. The results obtained by various methods of theoretical studies allow us to determine the directions of improvement of equipment, technological methods of selecting modes, active materials for producing sprayed layers with high quality for assemblies and parts of various configurations and different materials of products and sprayed with the material. The findings of the work can be used in practice in the development of technological maps of the processes of deposition. The scientific novelty of the obtained results consists of the following: methods for studying the stress state of flat samples with a sprayed layer during bending tests have been improved; for the first time, the results of the influence of a set of characteristics of the deposition conditions on the strength characteristics of the sprayed layer on the substrate were obtained.