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(1) Background: The paper addresses the effect of carbon fibers (CFs) treatment by low-temperature plasma with runaway electrons on the deformation behavior of the polyetheretherketone (PEEK)-layered composites. (2) Methods: The effect of the interlayer adhesion on the mechanical response of the composites was assessed through the tensile and three-point bending tests. In addition, computer simulations of the three-point bending were carried out with the use of the finite element analysis (FEM) with varying conditions at the “PEEK–CF layers” interface. (3) Results: DRE–plasma treatment during the optimal time of t = 15 min led to formation of a rougher surface and partial desizing of a finishing agent. The shear strength of the layered composites increased by 54%, while the tensile strength and the flexural modulus (at three-point bending) increased by 16% (up to 893 MPa) and by 10% (up to 93 GPa), respectively. (4) Conclusions: The results of the numerical experiments showed that the increase in the stiffness, on the one hand, gave rise to enlarging the flexural modulus; on the other hand, a nonlinear decrease in the strength may occur. For this reason, the intention to maximize the level of the interlayer stiffness can result in lowering the fracture toughness, for example, at manufacturing high-strength composites.

High-strength PI and PEI polymers differ by chemical structure and flexibility of the polymer chains that ensure lower cost and higher manufacturability of the latter. The choice of a particular polymer matrix is of actuality at design of antifriction composites on their basis. In this study, a comparative analysis of tribological behavior of PI and PEI- based composites was carried out with linear contact rubbing. The neat materials, as well as the two- and three-component composites reinforced with chopped carbon fibers, were investigated. The third components were typically used, but were different in nature (polymeric and crystalline) being solid lubricant fillers (PTFE, graphite and MoS2) with characteristic dimensions of several microns. The variable parameters were both load and sliding speed, as well as the counterface material. It was shown that an improvement of the tribological properties could be achieved by the tribological layer formation, which protected their wear track surfaces from the cutting and plowing effects of asperities on the surfaces of the metal and ceramic counterparts. The tribological layers were not formed in both neat polymers, while disperse hardening by fractured CF was responsible for the tribological layer formation in both two- and three component PI- and PEI-based composites. The effect of polymer matrix in tribological behavior was mostly evident in two-component composites (PI/CF, PEI/CF) over the entire P⋅V product range, while extra loading with Gr and MoS2 leveled the regularities of tribological layer formation, as well as the time variation in friction coefficients.

A modified Mori–Tanaka model to predict the average mechanical characteristics for dispersedly reinforced materials considering the physical nonlinearity, especially plasticity, of its constituents is proposed. A comparison of theoretical results with experimental data showed that this modification provides a sufficiently high accuracy of calculated estimates for parameters of the stress-strain state of such materials.

The paper proposes a simple two-layer model to assess the behavior of a heat-loaded thermal barrier coating–substrate system with neglect of thermally grown oxide and bond coat. The model includes solutions of boundary value problems of thermal conduction, thermoelasticity, stability, and stress-strain state after stability loss, and it also provides for coating delamination from the substrate after stability loss. It is shown that when the coating–substrate system is exposed to intense heat, the coating experiences compressive stresses which can cause a loss of its stability. When the coating losses its stability on the elastic substrate, chess-board extrusion and intrusion regions with respective tensile and compressive zones arise in the system. At a critical stress intensity, the system losses its continuity at the coating–substrate interface, and the coating delaminates from the substrate in tensile zones. The zones of delamination at the coating–substrate interface are arranged periodically.

Previously, an algorithm based on two control parameters was applied to computer aided design of materials, and here the algorithm is extended to three parameters controlling the effective physicomechanical properties of polymer matrix composites: (i) the average particle size of a polymer powder, (ii) the length of reinforcing fibers, and (iii) the level of fiber–matrix adhesion. The use of these control parameters is dictated by the possibility of their ranging in terms of degrees of influence on effective material characteristics. The algorithm with built-in experimental data is applied to design a composite with specified properties on the example of ultrahigh molecular weight polyethylene reinforced with milled or chopped glass fibers. The form of data presentation shows the whole range of the three parameters which provides the desired result.

Abstract The paper presents the results on application of Lamb waves based technique for impact damage detection and severity identification. The PZT network operates in the round-robin mode changing the actuator and sensor roles of the transducers in order to detect the response of the system in the presence of damage. The monitoring is performed via the analysis of three parameters: change of the amplitude (dA), change of the energy (dP) and cross-correlation (NCC) of the signals in baseline and damaged state. Testing of laminate CFRPs shows that the damage location is estimated with an error of 5–15 mm, while the computed Damage index is linearly dependent on the applied impact energy. For honeycomb CFRPs the NCC parameter do not provide accurate results, however, other parameters allow identification within the 5–20 mm error and reflect accurate data on the severity of the damage.

TEM and X-ray diffraction studies were carried out to examine changes in the structure, phase composition, and defect substructure in the head of a differentially hardened rail after 691.8 and 1411 million gross tons (MGT) of traffic. The rail material was examined along the central axis of the head and along the gauge corner radius at distances of 0, 2, and 10 mm from the tread surface. The redistribution of carbon atoms was quantitatively analyzed. It was shown that long-term operation of rails is accompanied by two simultaneous processes related to the evolution/degradation of the structure and phase composition of lamellar pearlite colonies, namely, cutting and cold dissolution of cementite lamellae. The first process involves the cutting of carbide particles and the subsequent dragging of their fragments, which causes changes only in their linear dimensions and morphology. The second process is the fracture of cementite lamellae in pearlite colonies due to the migration of carbon atoms from the cementite lattice to dislocations, which creates favorable conditions for a structural-phase transformation in the rail metal. The reason of this is the low average binding energy of carbon atoms with dislocations (~0.6 eV) and with iron atoms in the cementite lattice (~0.4 eV). Cementite nanoparticles were revealed in the ferrite matrix; their appearance was accompanied by dislocation glide and deformation-induced decomposition of carbon solid solution in α-iron. The curves of the change in the total yield strength versus the distance to the tread surface along different directions in the rail head were plotted. The carbon content in the structural elements of rail steel was estimated. It was found that carbon in the initial state is mainly contained in cementite particles, while in rails subjected to traffic loading it is located, along with cementite particles, at crystal structure defects (dislocations, grain boundaries, subgrains). In the surface layer of steel, carbon is also present in the crystal lattice of α-iron. The results on the redistribution of carbon atoms are interpreted using the concept of interstitial bifurcation structural states in lattice curvature zones.

(1) Background: this study deals with design of an automated laboratory facility based on a servo-hydraulic testing machine for estimating parameters of mechanical hysteresis loops by means of the digital image correlation (DIC) method. (2) Methods: the paper presents a description of the testing facility, describes the grounds for calculating the elastic modulus, the offset yield strength (OYS) and the parameters of the mechanical hysteresis loops by the DIC method. (3) Results: the developed hardware-software facility was tested by studying the fatigue process in neat polyimide (PI) under various amplitude tension-tension loadings. It was found that the damage accumulation was accompanied by the decrease in the loop areas, while failure occurred when it reduced by at least ~5 kJ/m3. (4) Conclusions: it was shown that lowering the loop area along with changing the secant modulus value makes it possible to estimate the level of the scattered damage accumulation (mainly at the stresses above the OYS level). It was revealed that fractography data, namely the pattern and sizes of the fatigue crack initiation and propagation zones, did not correlate well with the dependences of the parameters of the hysteresis loops.

The fatigue properties of neat polyimide and the “polyimide + 10 wt.% milled carbon fibers + 10 wt.% polytetrafluoroethylene” composite were investigated under various cyclic loading conditions. In contrast to most of the reported studies, constructing of hysteresis loops was performed through the strain assessment using the non-contact 2D Digital Image Correlation method. The accumulation of cyclic damage was analyzed by calculating parameters of mechanical hysteresis loops. They were: (i) the energy losses (hysteresis loop area), (ii) the dynamic modulus (proportional to the compliance/stiffness of the material) and (iii) the damping capacity (calculated through the dissipated and total mechanical energies). On average, the reduction in energy losses reached 10–18% at the onset of fracture, whereas the modulus variation did not exceed 2.5% of the nominal value. The energy losses decreased from 20 down to 18 J/m3 (10%) for the composite, whereas they reduced from 30 down to 25 J/m3 (17%) for neat PI in the low-cycle fatigue mode. For high-cycle fatigue, energy losses decreased from 10 to 9 J/m3 (10%) and from 17 to 14 J/m3 (18%) for neat PI and composite, respectively. For this reason, the changes of the energy losses due to hysteresis are of prospects for the characterization of both neat PI and the reinforced PI-based composites.

The effect of a lattice curvature on impact toughness at low temperatures is studied for the 09Mn2Si and 10Mn2VNbAl high-strength low-alloy (HSLA) steels having different compositions of doping elements. It is shown that the formation of the lattice curvature (several degrees/micrometer), in particular by helical rolling, significantly increases the low-temperature impact toughness of the HSLA steels, regardless of the alloying element compositions. This means that the observed effect could be characteristic of other HSLA steels subjected to complex thermo-mechanical treatment with the formation of the lattice curvature of a certain degree. Authors suggest that the perlite $$\rightarrow $$ bainite phase transformation develops under helical rolling at a temperature of $$\sim $$ $$850\,^\circ \hbox {C}$$ . As a result, bainite is formed in the lattice curvature zones characterized by the presence of interstitial mesoscopic structural states where random rotational deformation modes could develop. This drastically improves the low temperature impact toughness of the HSLA steels and contributes to enhance their fatigue life and wear resistance.

The cross-sectional curvature and shape (inner and outer) of a cylindrical surface formed by turning have an effect on the roughness parameter—the arithmetic mean deviation of the Ra profile. The main regularities in this influence are analyzed in this article. The authors investigated specially designed test specimens using their own method, which excludes the influence of other parameters on the roughness forming process. The diameters of the cylindrical surfaces of test specimens were selected taking into account the spindle rotation speed of the lathe. As a result, these surfaces were machined at practically the same cutting speed when performing the final processing step. The Grebbs criterion was used to evaluate the uniformity of surface roughness obtained experimentally.

The structure, mechanical and tribological properties of the PEI- and PI-based composites reinforced with Chopped Carbon Fibers (CCF) and loaded with commercially available micron-sized solid lubricant fillers of various nature (polymeric-PTFE, and crystalline-Gr and MoS2) were studied in the temperature range of 23–180 (240) °C. It was shown that tribological properties of these ternary composites were determined by the regularities of the transfer film (TF) adherence on their wear track surfaces. The patterns of TFs formation depended on the chemical structure of the polymer matrix (stiffness/flexibility) as well as the tribological test temperatures. Loading with PTFE solid lubricant particles, along with the strengthening effect of CCF, facilitated the formation and fixation of the TF on the sliding surfaces of the more compliant PEI-based composite at room temperature. In this case, a very low coefficient of friction (CoF) value of about 0.05 was observed. For the more rigid identically filled PI-based composite, the CoF value was twice as high under the same conditions. At elevated temperatures, rising both CoF levels and oscillation of their values made it difficult to retain the non-polar PTFE transfer film on the sliding surfaces of the PI-based composite. As a result, friction of the ceramic counterpart proceeded over the composite surface without any protecting TF at T ≥ 180 °C. For the sample with the more flexible PEI matrix, the PTFE-containing TF was retained on its sliding surface, providing a low WR level even under CoF rising and oscillating conditions. A similar analysis was carried out for the less efficient crystalline solid lubricant filler MoS2.

This research addresses the development of a formalized approach to dental material selection (DMS) in manufacturing removable complete dentures (RDC). Three types of commercially available polymethyl methacrylate (PMMA) grades, processed by an identical Digital Light Processing (DLP) 3D printer, were compared. In this way, a combination of mechanical, tribological, technological, microbiological, and economic factors was assessed. The material indices were calculated to compare dental materials for a set of functional parameters related to feedstock cost. However, this did not solve the problem of simultaneous consideration of all the material indices, including their significance. The developed DMS procedure employs the extended VIKOR method, based on the analysis of interval quantitative estimations, which allowed the carrying out of a fully fledged analysis of alternatives. The proposed approach has the potential to enhance the efficiency of prosthetic treatment by optimizing the DMS procedure, taking into consideration the prosthesis design and its production route.

The optimal mode for ultrasonic welding (USW) of the “PEEK–ED (PEEK)–prepreg (PEI impregnated CF fabric)–ED (PEEK)–PEEK” lap joint was determined by artificial neural network (ANN) simulation, based on the sample of the experimental data expanded with the expert data set. The experimental verification of the simulation results showed that mode 10 (t = 900 ms, P = 1.7 atm, τ = 2000 ms) ensured the high strength properties and preservation of the structural integrity of the carbon fiber fabric (CFF). Additionally, it showed that the “PEEK–CFF prepreg–PEEK” USW lap joint could be fabricated by the “multi-spot” USW method with the optimal mode 10, which can resist the load per cycle of 50 MPa (the bottom HCF level). The USW mode, determined by ANN simulation for the neat PEEK adherends, did not provide joining both particulate and laminated composite adherends with the CFF prepreg reinforcement. The USW lap joints could be formed when the USW durations (t) were significantly increased up to 1200 and 1600 ms, respectively. In this case, the elastic energy is transferred more efficiently to the welding zone through the upper adherend.

Since the inelastic strain development plays an important role in the low-cycle fatigue (LCF) of High-Performance Polymers (HPPs), the goal of the research was to study the effect of an amorphous polymer matrix type on the resistance to cyclic loading for both polyimide (PI)- and polyetherimide (PEI)-based composites, identically loaded with short carbon fibers (SCFs) of various lengths, in the LCF mode. The fracture of the PI and PEI, as well as their particulate composites loaded with SCFs at an aspect ratio (AR) of 10, occurred with a significant role played by cyclic creep processes. Unlike PEI, PI was less prone to the development of creep processes, probably because of the greater rigidity of the polymer molecules. This increased the stage duration of the accumulation of scattered damage in the PI-based composites loaded with SCFs at AR = 20 and AR = 200, causing their greater cyclic durability. In the case of SCFs 2000 µm long, the length of the SCFs was comparable to the specimen thickness, causing the formation of a spatial framework of unattached SCFs at AR = 200. The higher rigidity of the PI polymer matrix provided more effective resistance to the accumulation of scattered damage with the simultaneously higher fatigue creep resistance. Under such conditions, the adhesion factor exerted a lesser effect. As shown, the fatigue life of the composites was determined both by the chemical structure of the polymer matrix and the offset yield stresses. The essential role of the cyclic damage accumulation in both neat PI and PEI, as well as their composites reinforced with SCFs, was confirmed by the results of XRD spectra analysis. The research holds the potential to solve problems related to the fatigue life monitoring of particulate polymer composites.

(1) Background: The paper addresses the computer simulation and prediction of the service life of the base of removable complete dentures (RCDs) under typical loads caused by biting and chewing food. For this purpose, the finite element method (FEM) was used. It is assumed that various blocks of teeth, such as incisors, canines, premolars and molars, are subjected to cyclic impacts during a human life. (2) Methods: Both symmetric and asymmetric mastication (two- and one-sided loads, respectively) cases were considered. The load level was assumed to be 100 N, which corresponds to the average muscular compression force of typical human jaws. (3) Results: The FEM analysis of the stress–strain state evolution for RCDs under cyclic loads was carried out. Maps of equivalent lines were drawn for the denture base in terms of its durability. A multi-axial criterion was implemented to determine the number of cycles prior to failure by the mechanism of a normal opening mode crack. The FEM-based assessment of the service life of RCDs enabled us to establish the critical stress concentration areas, thereby allowing for further planning for the correction of an occlusal scheme or teeth inclinations. As a result, the service life of RCDs under cyclic loading can be improved. (4) Conclusions: An algorithm for designing RCDs in the case of edentulism based on the FEM simulation using commercial software as part of the procedure is proposed.

—The hardness and the tribological properties of the AK10M2N silumin subjected to irradiation by a high-energy pulsed electron beam with an energy density of 35 J/cm2 are studied. As compared to the as-cast state, the microhardness of the surface layers increases by ≈20% (up to ≈1.2 GPa), the friction coefficient decreases by a factor of ≈1.3 (down to 0.42), and the wear parameter decreases by a factor of ≈6.6 (down to 0.74 × 10–3 mm3/(N m)). These changes are shown to be caused by the dissociation of silicon and intermetallic compounds in the surface layer during irradiation by a high-energy pulsed electron beam.

The manuscript is devoted to the investigation of microstructure, static and fatigue tensile properties of commercially pure titanium grade 2 in two states with coarse grains (CG ≈ 25 µm) and ultra-fine grains (UFG ≈ 0.2 µm). During mechanical tests, the in situ monitoring was conducted by means of acoustic emission and digital image correlation. Scanning electron microscopy was employed for fracture surface observations. The results of the tensile tests show significant growth in ultimate strength and decrease of ductility due to grain-boundary strengthening. Fatigue tests revealed that the high amount of defects (grain boundaries, dislocations, etc.) in UFG suppress plastic deformation and leads to earlier crack initiation, however, at the macrocrack growth stage, these impurities are obstacles for the transgranular mechanism of fracture. The experimental data obtained allow one to get the appropriate understanding of the mechanisms responsible for the variation of mechanical properties and fracture patterns as well as to attain quantitative estimation of strain localization induced by the grain refinement.

Laminated composites based on polyetheretherketone (PEEK) and polyimide (PI) matrices were fabricated by hot compression. Reinforcing materials (unidirectional carbon-fiber (CF) tapes or carbon fabric) and their layout patterns were varied. Stress–strain diagrams after three-point flexural tests were analyzed, and both lateral faces of the fractured specimens and fractured surfaces (obtained by optical and scanning electron microscopy, respectively) were studied. It was shown that the laminated composites possessed the maximum mechanical properties (flexural elastic modulus and strength) in the case of the unidirectional CF (0°/0°) layout. These composites were also not subjected to catastrophic failure during the tests. The PEEK-based composites showed twice the flexural strength of the PI-based ones (0.4 and 0.2 GPa, respectively), while the flexural modulus was four times higher (60 and 15 GPa, correspondently). The reason was associated with different melt flowability of the used polymer matrices and varied inter- (intra)layer adhesion levels. The effect of adhesion was additionally studied by computer simulation using a developed two-dimensional FE-model. It considered initial defects between the binder and CF, as well as subsequent delamination and failure under loads. Based on the developed FE-model, the influence of defects and delamination on the strength properties of the composites was shown at different stress states, and the corresponding quantitative estimates were reported. Moreover, another model was developed to determine the three-point flexural properties of the composites reinforced with CF and carbon fabric, taking into account different fiber layouts. It was shown within this model framework that the flexural strength of the studied composites could be increased by an order of magnitude by enhancing the adhesion level (considered through the contact area between CF and the binder).

The aim of this work was to design and optimize compositions of three-component composites based on polyetheretherketone (PEEK) with enhanced tribological and mechanical properties. Initially, two-component PEEK-based composites loaded with molybdenum disulfide (MoS2) and polytetrafluoroethylene (PTFE) were investigated. It was shown that an increase in dry friction mode tribological characteristics in metal-polymer and ceramic-polymer tribological contacts was attained by loading with lubricant fluoroplastic particles. In addition, molybdenum disulfide homogenized permolecular structure and improved matrix strength properties. After that, a methodology for identifying composition of multicomponent PEEK-based composites having prescribed properties which based on a limited amount of experimental data was proposed and implemented. It was shown that wear rate of the “PEEK + 10% PTFE + 0.5% MoS2” composite decreased by 39 times when tested on the metal counterpart, and 15 times on the ceramic one compared with neat PEEK. However, in absolute terms, wear rate of the three-component composite on the metal counterpart was 1.5 times higher than on the ceramic one. A three-fold increase in wear resistance during friction on both the metal and ceramic counterparts was achieved for the “PEEK + 10% PTFE + 0.5% MoS2” three-component composite compared with the “PEEK + 10% PTFE”. Simultaneous loading with two types of fillers slightly deteriorated the polymer composite structure compared with neat PEEK. However, wear rate was many times reduced due to facilitation of transfer film formation. For this reason, there was no microabrasive wear on both metal and ceramic counterpart surfaces.

In this study, the authors have analyzed the effect of nanosized particles of titanium carbonitride Ti-C-N and non-stoichiometric nitride TiN1–x on the structure and properties of coatings on 09Mn2Si steel formed by arc welding, utilizing MP-3 electrodes. It was shown, that adding of TiN1–x modifying powders into the weld pool effectively increased the fatigue durability and impact toughness at negative temperatures.

The structure and mechanical properties of ductile ferrite-pearlite 09Mn2Si steel after helical rolling (HR) were studied. It has been shown that five passes of the helical rolling (with a gradual temperature decrease at each pass) resulted in a finely dispersed structure formation in the rod surface layer (up to ∼1 mm thick). This indicated the development of intensive plastic deformation there. At the same time, a lamellar structure consisting of thin elongated ferrite grains has formed in the underlying layers. The largest strain hardening was evident in the surface layer up to 3 mm thick. A yield tooth and plateau were evident on plastic flow curve. The length of the yield plateau was increased up to 2 times compared to as-received steel. This was accompanied with tensile strength increasing by 30%, while the elongation at break decreased. Data of cyclic testing have shown that fatigue life of the HR-treated samples increased by 3.8 times. The highest fatigue durability was characteristic for specimens cut out from the core of HR processed rod.

The paper is devoted to solving the problem of excluding areas of irregularities in material surface images. To solve this problem, we propose an algorithm for automatic mask construction with identifying the areas with material, areas without material, and crack areas; this combines image processing methods (pattern search, threshold flood filling, boundary search) with crack detection algorithms. It is demonstrated that this algorithm is applicable to experimental images with a large number of frames in a series.

It was shown that an increase in impact toughness of the Ti-6Al-4V alloy (including at low temperatures) was associated with two mechanisms. The first one was the suppression of the discontinuity nucleation due to the dynamic nature of the structural rearrangement provided by interstitial mesoscopic nanoscale structural states (IMNSS) under the crystal lattice curvature conditions as well as plastic distortion. The second mechanism was the ductile material extrusion in the superplastic flow mode (down to T=–70°C). This enabled to extensively deform specimens without failure (in fact, in the superplastic flow mode) upon impact bending. It was discussed that the development of deformation defect flows was realized according to the mechanism of the structural-phase transformation.

Ultrasonic impact treatment (UIT) is intended for improving surface properties of metals and alloys due to the combined structure modification. Application of electrical pulses (electropulsing—EP) combined with ultrasonic surface straining allows to increase the depth of the modified surface layer and to improve physical-mechanical properties of alloys under the treatment. A clear explanation of this effect has not been developed yet. The paper deals with modeling the process of combined mechanical-electrophysical treatment (UIT + EP) of titanium alloy composite “Ti-6Al-4V + TiC”. Ultrasonic impact treatment was modeled by applying pulsed mechanical loads with the use of a hard–alloy striker. It is shown that the complementary electric current exposure made it possible to enhance the effect of ultrasonic impact treatment. In so doing, the strain in local treated regions was enlarged. It was revealed that the application of the combined treatment made it possible to locally modify effective mechanical properties, in particular, an elastic modulus was decreased, while tensile strength and the elongation at break were enlarged.

In this study, a structural and functional analysis was conducted to investigate antifriction multicomponent polymer composites on the basis of ultrahigh-molecular polyethylene (UHMWPE) developed as feedstocks for additive manufacturing of friction parts operating under extreme conditions. The aim was to make UHMWPE extrudable by selecting appropriate polymer plasticizers. An algorithm is proposed for the development of extrudable UHMWPE-based composites with a minimum amount of experimental data available. The algorithm determines the control parameters that provide required characteristics of multicomponent polymer materials and thereby ensure the achievement of desired tribological, mechanical and processing properties. The dependence of the experimentally determined characteristics versus the control parameter values is analyzed, and corresponding response surfaces are constructed in the state space. The surfaces reveal the range of the control parameter values that ensure the achievement of specified properties. The algorithm is applied to select an optimal composition of the ternary “UHMWPE+ 17 wt% HDPE-g-SMA + 12 wt% PP” mixture, whose tribological and mechanical behavior is similar to that of unfilled UHMWPE, but the melt flow is good enough for 3D printing. A comparative study is carried out on structural, mechanical and tribological properties of the multicomponent “UHMWPE+ 17 wt%HDPE-g-SMA+ 12 wt% PP” composites fabricated by FDM printing and hot pressing. It is shown that the tribological and mechanical properties of 3D-printed extrudable UHMWPE-based composites exceed the properties of composites obtained by compression sintering, which is due to the formation of more homogeneous permolecular structure with increased crystallinity. The tribological characteristics of the 3D-printed composites are studied under various friction test conditions (P*V). The composites are proposed as suitable for friction parts operating in a wide range of speeds and loads.

It was shown that loading with carbon and glass fibers results in increasing mechanical properties of polyimide (PI) based composites. Upon annealing and subsequent treatment of the fibers with a silane-coupling agent the tensile strength of the composites increased compared to loading with the unmodified fillers. The ultimate reason was increasing degree of interphase adhesion. It was shown that loading with carbon and glass fibers increased wear resistance of the composites. When testing over a ceramic counterpart, the wearing of the composites was slightly evident. In this regard, one can recommend application of these composites to operate in friction units in ceramic-polymer tribological conjugations.

The mechanical and tribological properties of PEEK-based composites reinforced with chopped carbon fibers have been studied. It has been shown that blending in a paddle mixer with bottom horizontally blade positioning did not result in carbon fibers agglomeration (in the form of “pellets”). Use of this mixing method allowed increasing the elastic modulus (at 3-point bending) of PEEK-based carbon composites by 15–25%, while flexural strength enlarged by 27–42% as compared to gravity blending or mixing with a top vertical blade positioning. Loading the PEEK with chopped carbon fibers reduced the friction coefficient by 1.3 times, while the wear rate decreased by 3 times.

The mechanical and tribological properties of “Polyimide (PI) – PTFE” composites (loaded with various size particles and fibers) at testing against metal and ceramic counterpart have been studied. It is shown that at fine PTFE powder (fluorolite) content equal to 10 wt. % the mechanical properties of the composite are comparable with ones of neat PI due to the uniform filler distribution in the matrix. At the same time, wear resistance of the composite increases up to 100 times due to transfer film formation on a counterpart surface. The composite “PI + 10 wt. % fluorolite” is recommended for antifriction applications for metal-polymer and ceramic-polymer tribological friction units.

The purpose of this review is to summarize data on the structure, mechanical and tribological properties, and wear patterns of composites based on high-performance polymers (HPPs) intended for use in friction units. The review includes three key sections, divided according to the tribological contact schemes regardless of the polymer matrix. In the second part, the analysis of composites is carried out in point contacts. The third section is devoted to the results of studies of HPP-based composites in linear ones. The fourth section summarizes information on flat contacts. Particular attention is paid to the formation of transfer films (TFs) in the contacts and their influence on the tribological patterns of the studied rubbing materials. As a conclusion, it is noted that the challenge of experimental methods for analyzing TFs, stated by K. Friedrich, is effectively solved in recent studies by the XPS method, which enables us to accurately determine their composition. Although this determination is completed after the tribological tests, it allows not only a more accurate interpretation of their results considering specific conditions and loading schemes, but also the ability to design HPP-based composites that form required TFs performing their preset functions.

Dynamics of destruction of epoxy composites with different contents of nanoparticles of ultra-dispersed diamond is investigated. Epoxy diane oligomer ED-20 was employed as the basic bonding agent i...

Mechanical and tribotechnical properties of polyetheretherketone (PEEK) composites filled with carbon nanotubes/nanofibers (CNT/CNF) and short carbon fibers (SCF) were studied. It is shown that mechanical properties vary slightly when loading CNF/CNT. Enforcement by SCF gives rise to increasing elasticity modulus up to 2 times. Loading of 0.3 wt. % CNF/CNT ensures enlarging wear resistance of PEEK composites by 2 times. At the SCF loading 30 wt. % the wear resistance might be increased by 8 times. The prospects of use antifrictional PEEK nano- and microcomposites in additive manufacturing for fabricating complex shape parts are discussed.

The structure, mechanical and tribological properties of the polyimide-based composites reinforced with chopped carbon fibers (CCF) and loaded with solid-lubricant commercially available fillers of various natures were investigated. The metal- and ceramic counterparts were employed for tribological testing. Micron sized powders of PTFE, colloidal graphite and molybdenum disulfide were used for solid lubrication. It was shown that elastic modulus was enhanced by up to 2.5 times, while ultimate tensile strength was increased by up 1.5 times. The scheme and tribological loading conditions exerted the great effect on wear resistance of the composites. In the tribological tests by the ‘pin-on-disk’ scheme, wear rate decreased down to ~290 times for the metal-polymer tribological contact and to ~285 times for the ceramic-polymer one (compared to those for neat PI). In the tribological tests against the rougher counterpart (Ra~0.2 μm, the ‘block-on-ring’ scheme) three-component composites with both graphite and MoS2 exhibited high wear resistance. Under the “block-on-ring” scheme, the possibility of the transfer film formation was minimized, since the large-area counterpart slid against the ‘non-renewable’ surface of the polymer composite (at a ‘shortage’ of solid lubricant particles). On the other hand, graphite and MoS2 particles served as reinforcing inclusions. Finally, numerical simulation of the tribological test according to the ‘block-on-ring’ scheme was carried out. Within the framework of the implemented model, the counterpart roughness level exerted the significantly greater effect on wear rate in contrast to the porosity.

The fracture of V-notches with end holes made of tungsten-copper functionally graded material under mode I has been studied in this paper. The averaged strain energy density over a well-defined control volume was employed to predict the fracture loads. A numerical approach was used to determine the outer boundary of the control volume. Mechanical properties such as elasticity modulus, Poisson’s ratio, fracture toughness KIc, and ultimate tensile stress have been considered to obey the power law function through the specimen width.

Results of the analysis of acoustic-emission signals generated due to ultrasonic waves propagating in a polymer composite material and registered with piezoelectric and fiber-optic sensors are presented. The fiber-optic sensors were arranged into an adaptive interferometer based on using a dynamic hologram formed in a photorefractive crystal. Reducing the setpoint fading has made it possible to improve the noise immunity and sensitivity of the measurement system when using an adaptive interferometer on a photorefractive crystal. Optical fibers in the interferometer’s measurement system served as sensors of ultrasonic waves and were built into a polymer composite material when the sample was manufactured. The sample was a rectangular plate made of a multilayer fiberglass material. It has been discovered that the sensitivity of the adaptive interferometer makes it possible to detect acoustic- emission signals generated by a Hsu–Nielsen source. When determining the speed of sound in the polymer composite material, peculiarities of registering a group wave by fiber-optic sensors have been established that are due to the anisotropy of the medium the wave propagates in and the distributed character of sensor placement in the studied composite material. The wavelet transform has been used to separate the informative component of the wanted signal.

It is shown that, under an electroexplosive spraying of coatings of various systems, the dynamic rotation of the particles deposited is the basis for forming a vortex hierarchically organized structure in both the coating and upper layers of the substrate, including their interface. This causes dispersion of all the structural elements of the cover, their mutual penetration into each other, and the absence of a sharp interface between the coating and the substrate. The impact of multiple shocks on the deposited coating by a highenergy plasma jet from the discharge of a plasma accelerator creates the forged structure in the material, which is characterized by high strength, wear resistance, and relaxation capability.

The structure and mechanical properties of 09Mn2Si steel of the main pipeline “Kysyl–Syr–Mustakh–Yakutsk” cut out from a linear part fragment of the pipe with the outer diameter of 530 mm and a wall thickness of 7 mm at the region “Berge–Yakutsk” after 37 years of operation were investigated. It was revealed that values of the basic mechanical properties of the steel have not changed as compared with the emergency reserve one. In doing so the impact toughness was shown to be the most sensitive parameter indicating the degradation processes development. At testing temperature of 20 °C it has decreased by 1.48 times whereas at T = –70 °C by 2.42 times. One of the main reasons of the steel degradation is the strain aging which gives rise to the dislocation structure and microstructure modification that substantially impairs its resistance to brittle fracture. A scheme to characterize mechanical properties degradation of the 09Mn2Si steel in the structural state under investigation is suggested.

The effect of the microstructure parameters as well as the testing temperature on the impact toughness of 17Mn1Si steel has been studied. The interrelation between the testing temperature during impact bending and deformation and fracture energy consumption has been studied. The relation between fracture energy characteristics at high-rate impact bending and the microstructure of the steel has been established. It is shown that the decrease of the testing temperature leads to almost linear reduction of the impact toughness.

Effect of interface profile as well as mechanical properties of Substrate onto stability loss of thermal barrier coating under thermal impact is studied with the use of FEM simulation. It is shown that the interface boundary profile exerts little effect on the temperature distribution in the thermal barrier coating-substrate system. When solving the problem of the stressed-deformed state under the influence of temperature (thermal impact), the effect of the boundary conditions on stresses is high, whereas the impact of the interface profile on the value of precritical stresses is insignificant. When solving the problem of TBC stability, the presence of a complex profile of the contact surface is taken into account by introducing rib stiffeners that support the coating. The complex profile of the “coating-substrate” interface boundary increases the critical stresses of the coating stability loss and changes the stability loss pattern. The anisotropy of the coating material strain-strength properties results in the change in the pattern of the stability loss, though the general effect of the coating thickness and the foundation stiffness on the stability loss pattern remains unchanged. The stress-strain state differences before and after the coating stability loss are qualitative.

Some mechanical and tribotechnical properties of perspective thermoplastic polyetheretherketone matrix (PEEK) based composites loaded with polytetrafluoroethylene (PTFE) and molybdenum disulfide (MoS2) microparticles under dry sliding friction conditions were investigated in order to find efficient combined solid lubricant filler. It is shown that polytetrafluoroethylene is an efficient solid lubricant for PEEK matrix (wear resistance of the composite increases by 8 times for metal–polymer tribo-pair, while it makes 15 times for ceramic–polymer friction pair). Simultaneous adding the molybdenum disulfide and PTFE particles with the content of the latter less than 0.5 wt % ensures maximum wear resistance of the composite while keeping the strength properties at the level of neat PEEK.

Mechanical and tribological properties of polyimide (PI) based composites with solid lubricant fillers (polytetrafluoroethylene (PTFE) and molybdenum disulfide) were studied at testing over various counterparts (metallic and ceramic). It is shown that PTFE is an efficient solid lubricant filler for polyimide which increases wear resistance of the composites up to 100 times as compared to neat polymer due to the formation of a transfer film on the metallic counterface. At the same time, despite its solid lubricating “status” molybdenum disulfide particles acts as microabrasive decreasing wear resistance under dry sliding friction, while at the content of 5 wt % MoS2 loading does not ensure maintenance of mechanical properties at the level of neat polymer. Two-component composite “PI + 15 wt % PTFE” is recommended as an efficient antifriction material for metal-polymer and ceramic-polymer friction pairs.

The paper presents a next stage in the development of excitable cellular automata method which allows one to model energy flow propagation in a loaded solid under external mechanical and thermal-dynamic loads. At this stage the method is proposed for assessing the probability of crack initiation near geometric stress concentrators. Patterns of various mechanical characteristics distribution on the specimen surfaces are given, as well as the time dependence graphs of the average values of these parameters in the vicinity of notch tip. Some aspects of the notch shape effect over the deformation patterns as well as prospects of the proposed approach development are discussed.