We are the first to perform experiments on strengthening plasma coatings on a cylindrical surface by friction stir processing with two oppositely located tools. A 65Kh25G13N3 steel powder (Fe–23.7

The content of oxygen and nitrogen has been determined in plasma coatings sprayed from the powder of Co and its alloys Co–32Ni–21Cr–8Al–0.5Y and Co–27.9Cr–7.04Al–3.25Si–2Y (wt

Due to their low density, corrosion resistance and strength properties, composite materials made of carbon fiber reinforced plastics, or carbon plastic (CP), successfully compete with metals, but are inferior to them in impact strength. The idea of the work was to increase the impact strength and additionally reduce the density of CP products by introducing ultra-high molecular weight polyethylene (UHMWPE) rovings with high tensile strength, impact strength and low density. CP, consisting of rovings with carbon fibers (CF), was additionally reinforced with D800 and SK75 rovings with UHMWPE fibers. CF and UHMWPE rovings were mixed in different proportions and unidirectional, hybrid (three-component) samples were made with two types of HT-2 and L285 epoxy matrices. In addition to hybrids, two-component samples were made with each of the CF, D800 and SK75 rovings separately. The number of rovings in the volume of hybrid samples was changed with a step of 25 %, obtaining the ratio between the amount of CF and UHMWPE rovings 0.25/0.75, 0.50/0.50 and 0.75/0.25. The required number of rovings with such ratios was calculated using the CF and UHMWPE constants of the rovings. The impact strength, density, and bending strength of the samples were determined. The density of the samples was determined by the calculation method, also using the roving constants. The results of testing the strength of hybrids were compared with the indicators of the CP strength. With an increase in the number of UHMWPE rovings, the bending strength and density of hybrids decreased at different rates compared to CP, and the impact strength sharply increased, then dropped sharply. The density of the hybrids decreased by about 8 % with each step, and the rate of decrease in bending strength was approximately twice the rate of decrease in their density. The impact strength of hybrids containing 25 % and 50 % UHMWPE rovings increased on average by 3.28 and 3.4 times, respectively.

The potential of improving the impact strength and reducing the density of carbon-fiber-composite products (CFCs) is explored as a function of the content of introduced ultra-high-molecular-weight polyethylene (UHMWPE) roving. The roving feature high tensile and impact strength and low density. The carbon fiber composite consists of carbon-fiber (CF) roving. It is additionally reinforced using D800 and SK75 roving with UHMWPE fibers. CF and UHMWPE roving are mixed in different ratios to make unidirectional hybrid (three-component) samples in two types of epoxy matrices (HT-2 and L285). In addition to hybrids, two-component samples are made using individual CF, D800, and SK75 roving. The amount of roving in the volume of hybrid samples is changed with a 25

The formulation and solution of the problem of determining safety stocks in a linear technological chain consisting of suppliers in a network structure is considered. It is assumed that the conditions for the production of suppliers in terms of throughput are quite sufficient to ensure deliveries on time in the required volume. The allocated volume of resources in the supplier’s production system for these purposes cannot be predetermined precisely. It is a random variable that changes in a certain interval, which is actually confirmed statistically. Reducing losses from downtime of technological equipment is ensured by the creation of reserve stocks. For solving the problem the method of dynamic programming is used, which allows one to determine the optimal values of safety stocks analytically.

The article considers the production subsystem as an element of the technological chain of a production system of any structure. Improvement of business efficiency involves optimizing key integration processes and coordinating the interaction of subsystems and links in technological chains. Each subsystem participates in the production of final products and is both a consumer and a supplier of products. The influence of various factors on the production process, including random ones, is the cause of violations of the time standards for product movement, which is expressed in deviations of the actual timing of the launch and release of planned accounting units from the planned standards. The concepts are introduced: late start-up in the subsystem - input deficit, delay transfer to the time of planned start - up in a neighboring subsystem along the technological chain-residual deficit. The solution of the subsystem is analyzed taking into account the amount of deficit transmitted along the technological chain. The function of costs for regulating external instability is defined, which includes two parameters: the value of the input deficit and the value of the residual deficit. If there is a residual deficit, compensation for the cost of reserving a neighboring subsystem along the chain is carried out in accordance with the linear function of the penalty and should be sufficient to neutralize it in this subsystem. A solution to the problem was obtained and a policy for regulating the remaining deficit was formulated.

The effect of rigid and flexible matrices on the properties of carbon fiber reinforced plastics has been studied using the impact break method at different rates of loading the composite material (CM). It has been established that the strain of CM under static loading conditions has a smooth character and is generally tensile. For this reason, CM with a plastic matrix under static loading conditions has higher properties, such as the maximum specific absorbed-in-fracture energy α = 154 J/cm2 and the maximum strength σ = 524 MPa at a greater relative strain ε = 6%. The fracture mechanism of carbon fiber reinforced plastics (CFRPs) abruptly changes upon an impact. The fracture of CMs is initiated by an impact at the first moment of its action. The entire process of CM strain until fracture is accompanied by fiber filament breaks. Load fluctuations occur due to filament breaks and are reflected in the strain curves in the form of peaks. The processes of filament break and crush are superimposed on the overall process of multistage CM tensile strain at a higher level. The accumulation of fiber crushes and breaks decreases the strength of CMs. This leads to fast fracture at lower strain in comparison with the case of static loading conditions. The specific absorbed-in-fracture energy α of CFRPs with a flexible matrix decreases upon an impact by a factor of 3.4, from 154 to 45 J/cm2, relative to the specific absorbed-in-fracture energy of CM in the static case; the material is fractured at a smaller relative strain ε = 1.7% and a lower strength σ = 496 MPa.

The paper presents a method making it possible to reveal the minimum cross-sectional area, maximum volume fraction of filaments (fibers) of a roving, and minimum volume fraction of the interfilament gaps of a dry roving, which are independent parameters (constants) of roving. Each kind of roving taken separately has parameters relevant only to it (technical data). Practical application of the method is demonstrated by examples of determination of these data for rovings of carbon (CF) and ultrahigh-molecular-weight polyethylene (UHMWPE). The ratio of the cross-sectional areas of the resin-impregnated and dry roving depends on the amount of matrix within the interfilament gaps and is a constant, which is assigned by the impregnation technology. The constants of rovings are a base for calculation of the reinforcement factors for components of composite. The constants make it possible to simplify the calculation of the number of rovings at prespecified concentration of reinforcement components in hybrid composites made of unidirectional fibers. Examples of utilization of the constants for the calculation of volume, required quantity, density, and volume fractions of reinforcement components in composites made of unidirectional fibers are presented. The difference of degree between actual volume fractions of fibers in the rovings and ideal values calculated for hexagonal and tetragonal spacing of fibers is revealed too.

A method making it possible to calculate the density and matrix volume fraction of two-component and hybrid composites reinforced with unidirectional rovings of carbon fibers (CF) and ultrahigh-molecular-weight polyethylene (UHMWPE) fibers is presented. Experimentally found constants of the rovings were used in calculation. The values of calculated density and matrix volume fraction were compared with an actual data of samples. The samples were obtained by resin impregnation of the rovings at free air. The impregnation was implemented simultaneously with laying of the rovings. This procedure does not permit saving the prespecified sample volume without volume control. The effects of volume deviations on the actual density of sample and the actual volume fraction of matrix were investigated on the samples with uncontrolled and controlled volume. The roving volume fractions and concentrations of hybrid and two-component composites were specified as the basic data of calculations. The actual densities of samples, as well as the value of matrix volume fractions, were compared with the calculated ones. The experimental data are in good agreement with the calculated data.

A new approach toward understanding failure mechanisms of anisotropic fiber-reinforced composite materials due to low velocity impact is discussed. The dependence of failure mechanisms and mechanical properties of such composites on loading velocity are examined by Impact Break method. It has been shown experimentally that especially large change in the CM properties occurs in the transition from static to impact loading conditions. CM destruction was observed at the first moment of a shock load application. The relaxation of the stresses in CM and the energy dissipation from breaking fibers are limited the short duration of impact value equal to 1-2 ms. Failure mechanism is based on the fibers stretching and stress-wave propagation through the CM under impact. The processes of multi-breaking and crushing of the filaments are imposed on the process of multi-stage stretching deformation. It led to decrease CM properties as compared with that under static. In a static situation, the deformation of CM is mostly stretching deformation. It gradually grows as the load increases. It has been found out that specific absorbed-in-fracture energy of CFRP and OFRP under impact loading conditions is significantly reduced by factors of 3.7 and 3.2, respectively, as compared with that under static ones. As a result, the choice of CM to create structures based only on the static properties of the material does not guarantee the impact resistance of structures upon low-velocity impact.

The effect of pretreatment and plasma preheating of Ti-substrate on shear strength of three-dimensional capillary porous Ti-coating was studied. After sandblasting the shear strength of the plasma sprayed coating was 200 ± 2 MPa, and after additional matting it was 68 ± 4 MPa. The use of plasma preheating of the substrates for 9 seconds decreased difference between values of the shear strength to 249 ± 17 MPa and 229 ± 16 MPa, respectively. After plasma spraying the microhardness of the surface layer of the substrate was 4.34 ± 0.35 GPa, the microhardness of the boundary between the coating and the substrate was 8.08 ± 0.45 GPa, and the microhardness of the coating was 3.48 ± 0.25 GPa. High shear strength of the coating was attributed to the activation of the substrate by means of plasma preheating and hardening of the boundary between the coating and the substrate by oxides and nitrides.

The shear strength of a three-dimensional capillary-porous (TCP) Ti coating was investigated as a function of the time of preheating by a plasma jet. The substrates were used after sandblasting with alumina particles and additionally treated with glass beads. Heating the substrate with plasma for 10 seconds minimizes the difference in shear strength for these two substrate treatment options, respectively, 249.4 MPa and 229.8 MPa. The microhardness of the initial Ti 1.86 GPa, near the interface between the substrate and the coating, it increases to 4.34 GPa. The microhardness at the middle of the thickness of the coating was 3.48 GPa, and the interface has a microhardness of 8.08 GPa. The shear strength of TiT + HA coatings was 90.7 MPa. High values of microhardness and shear strength of Ti coating Tiare explained by activation of the substrate by heating and hardening of the joint zone due to doping with oxygen, nitrogen and the contribution of the relief and the specific surface of the substrate.

Plasma spraying of composite coatings is developed and investigated. Three-dimensional capillary porous titanium (3DCP Ti) coatings with a thickness of 1 mm are sprayed using a wire. Hydroxyapatite (HA) coatings with a thickness of 0.08–0.35 mm are sprayed on 3DCP Ti coatings at a temperature of 300–550°C. The joint between the coating and plastic is analyzed at shear. The plastic simulates bone tissue that grows into the coating surface. The heating of the 3DCP Ti coating to 550°С when the HA coating is being sprayed increases the shear strength of the coating with respect to the plastic to 9.8 MPa. Modeling approximations are proposed for the shear of the joint between the coating and the plastic.

The mechanical properties and fracture mode of polymer composite materials reinforced with fibers of high-performance polyethylene are investigated. It is found that plasma treatment (activation) of the fibers increases the composite strength. This effect is explained by the formation of chemically active centers on the surface of treated fibers, the strength of the fiber-matrix joints in which is higher. These centers can be seen through an optical microscope as white stripes. The changes observed are connected with a unique fibril-porous structure of the fibers as well as peculiarities of cross-cut craze propagation throughout the fibers.