In this study, laminates based on polyetherimide (PEI) with contents of carbon fibers (CFs) from 55 to 70 wt.% were fabricated by thermoforming (TF) and ultrasonic additive manufacturing (UAM) methods. The UAM laminates with CF contents above 55 wt.% possessed shear strengths lower by 40% in comparison with those of the TF ones, due to insufficient amounts of the binder in the prepregs to form reliable interlaminar joints. For enhancing the shear strength of the laminates with a CF content of 70 wt.%. up to the levels of the TF ones, extra resin layers with thicknesses of 50, 100, and 150 μm were deposited. By ranking the UAM parameters using the Taguchi method, it was possible to increase the shear strengths by 30% as compared to those of the trial laminates. Further improvements were achieved by artificial neural network (ANN) modeling. As a result, the use of the 50 µm thick extra resin layer made it possible to increase the shear strengths up to 50% relative to those of the trial laminates at a CF content of 70 wt.%. This improvement was achieved via minimizing the number of defects at the interlaminar interfaces. The dependences of both mechanical and structural characteristics of the laminates on the UAM parameters were essentially nonlinear. For their analysis and optimization of the UAM parameters, the direct propagation neural networks with the minimal architecture were utilized. Under the ultra-small sample conditions, the use of a priori knowledge enabled us to predict the results rather accurately.

The aim of this study was to investigate microstructure and the mechanical and operational characteristics of thick and thin walls 3D-built by electron beam additive manufacturing (EBAM). In addition, the milling parameters (rotation speed, feed, and cutting width) were optimized based on simultaneous assessments of Ra roughness on the machined surfaces and material removing rate values. The wall dimensions did not exert a noticeable effect on their chemical compositions, as compared with the original wires used for 3D printing. In comparison, the strength characteristics of the wrought steel (cold-rolled plate) were higher due to finer grains, with both ferrite content and dislocation density being greater as well. In the 3D building process, multiple thermal cycles gave rise to the formation of elongated columnar grains, reducing the strength characteristics. The corrosion rate of the wrought steel was almost twice those of the 3D-printed blanks because of the higher content of both ferrite and twins. By assessing the machinability of the EBAM-built blanks using the stationary milling machine, the cutting forces were comparable due to similar mechanical properties (including microhardness). To improve the removing rate values and reduce the cutting forces, it is recommended to enhance the cutting speeds while not increasing the feeds. For the semi-industrial milling machine, both linear multiple regression and nonlinear neural network models were applied. An integrated approach was proposed that rationally determined both additive manufacturing and post-processing parameters based on a combination of express assessment and analysis of the mechanical, operational, and technological characteristics of built products within a single laboratory complex.

In this study, ultrasonic welding (USW) of lap joints of polyetherimide (PEI) plates (adherends) with carbon fiber (CF) prepregs impregnated with PEI was investigated. No energy director (ED) was used, so binder contents were varied in the prepregs to compensate for the lack of the polymer in the fusion zone. In addition, the effect of the USW parameters on the structure and the mechanical properties of the lap-joints were analyzed. The most homogeneous macrostructure, the maintained structural integrity of both the CF-fabric in the prepregs and the lap-joined PEI adherends, as well as the maximum strength properties (tensile strength) were revealed for the USW joints with the minimum polymer content in the prepreg. In this case, rising the USW time from 400 up to 800 ms radically changed the macrostructure of the fusion zone, while the strength properties did not vary significantly (shear stresses were 42–48 MPa). Computer simulation of the influence of the PEI/CF-fabric ratios in the prepregs on the deformation response of the USW joints showed that the prepreg thicknesses and, accordingly, the PEI/CF ratios did not exert a noticeable effect on the strain–stress (tensile) diagrams, while the determining factor was the adhesion level.

To estimate the possibility of using both low-melting TecaPEI and neat PEI films as energy directors (EDs) for ultrasonic welding (USW) of carbon fiber (CF) fabric–polyetherimide (PEI) laminates, some patterns of structure formation and mechanical properties of their lap joints were investigated by varying the process parameters. The experiment was planned by the Taguchi method with the L9 orthogonal matrix. Based on the obtained results, USW parameters were optimized accounting for maintaining the structural integrity of the joined components and improving their functional characteristics. The use of the low-melting EDTecaPEI film enabled US-welding the laminates with minimal damage to the fusion zone, and the achieved lap shear strength (LSS) values of ~7.6 MPa were low. The use of EDSolverPEI excluded thermal degradation of the components as well as damage to the fusion zone, and improved LSS values to 21 MPa. With the use of digital image correlation (DIC) and computed tomography (CT) techniques, the structural factors affecting the deformation behavior of the USW lap joints were justified. A scheme was proposed that established the relationship between structural factors and the deformation response of the USW lap joints under static tension. The TecaPEI film can be used in USW procedures when very high interlayer adhesion properties are not on demand.

In this paper, the tribological characteristics of polyethersulfone-based composites reinforced with short carbon fibers (SCFs) at aspect ratios of 14–250 and contents of 10–30 wt.% are reported for linear metal–polymer and ceramic–polymer tribological contacts. The results showed that the wear resistance could be greatly improved through tribological layer formation. Loading PES with 30 wt.% SCFs (2 mm) provided a minimum WR value of 0.77 × 10−6 mm3/N m. The tribological layer thicknesses were estimated to be equal to 2–7 µm. Several conditions were proposed, which contributed to the formation of a tribological layer from debris, including the three-stage pattern of the changing kinetics of the time dependence of the friction coefficient. The kinetics had to sharply increase up to ~0.4–0.5 in the first (running-in) stage and gradually decrease down to ~0.1–0.2 in the second stage. Then, if these levels did not change, it could be argued that any tribological layer had formed, become fixed and fulfilled its functional role. The PES-based composites loaded with SCFs 2 mm long were characterized by possessing the minimum CoF levels, for which their three-stage changing pattern corresponded to one of the conditions for tribological layer formation. This work provides valuable insight for studying the process parameters of tribological layer formation for SCF-reinforced thermoplastic PES composites and revealing their impact on tribological properties.

The aim of this study was to optimize a set of technological parameters (travel speed, extruder temperature, and extrusion rate) for 3D printing with a PEEK-based composite reinforced with 30 wt.% glass fibers (GFs). For this purpose, both Taguchi and finite element methods (FEM) were utilized. The artificial neural networks (ANNs) were implemented for computer simulation of full-scale experiments. Computed tomography of the additively manufactured (AM) samples showed that the optimal 3D printing parameters were the extruder temperature of 460 °C, the travel speed of 20 mm/min, and the extrusion rate of 4 rpm (the microextruder screw rotation speed). These values correlated well with those obtained by computer simulation using the ANNs. In such cases, the homogeneous micro- and macro-structures were formed with minimal sample distortions and porosity levels within 10 vol.% of both structures. The most likely reason for porosity was the expansion of the molten polymer when it had been squeezed out from the microextruder nozzle. It was concluded that the mechanical properties of such samples can be improved both by changing the 3D printing strategy to ensure the preferential orientation of GFs along the building direction and by reducing porosity via post-printing treatment or ultrasonic compaction.

The objective of this research was to predict the fatigue behavior of polyetherimide-based composites loaded with short carbon fibers 200 μm long under cyclic loads. The weight fraction of the filler was 10, 20, and 30 wt.%, while the maximum stress in a cycle was 55, 65, and 75 MPa. A modified fatigue model based on the obtained experimental results and Basquin equation was developed. The novelty of the results is related to developing a model on the structure–property relationship, which accounts for both the maximum stress in a cycle and the carbon fiber content in the composites. In addition, an “algorithm” for designing such composites according to the fatigue life criterion was proposed. The approach to determine relationships between the composition, structure, and properties of PCMs described in this study can be applied to further expand the model and to improve its versatility in the use of other thermoplastic matrices and fillers. The results of this study can be applied for the design of composites for structural applications with designated fatigue properties.

The study is devoted to computer -aided design of particulate polytetrafluoroethylene-based composites for increasing their thermal conductivity values (as much as possible) with minimal deterioration of the mechanical properties. To solve the issue, an algorithm has been developed and applied using a multi -scale model. It has enabled to fabricate such composites, characterized by both high thermal conductivity and acceptable mechanical properties, via loading the polymer matrix with copper particles of two size ranges, differing by more than an order of magnitude.

The effect of creep development that occurs under cyclic loading of polyetheretherketone (PEEK) is studied, where the cyclic creep parameter is used to quantitatively characterize the structure rearrangement. The magnitude of cyclic creep was calculated from mechanical hysteresis loops. To obtain the dependence of the magnitude of cyclic creep on the amplitude of the external cyclic stress, block loading was carried out with a stepwise increase in the amplitude. It is shown that the mechanism of development of cyclic creep under block loading has a two-stage character. The first stage is responsible for the adaptation of the polymer to an increase in the applied load. The second stage corresponds to stabilization, when the rate of creep development slows down, and its further development stops. It was found that despite the restructuring of the structure and the hardening caused by it, the degree of crystallinity under cyclic loading did not change and amounted to 59%. At the same time, the value of microstresses decreased from 6 to 0.9 MPa. It has been shown that cyclic strain hardening with a block increase in load can lead to an increase in the fatigue life of PEEK (which can reach 90% of the ultimate strength of the material).

The effect of high dose implantation of Ta+ ions (Dion = 5 ' 1016 cm -2) into samples from a TiNi shape memory alloy (SMA) on patterns of deformation and fracture mechanisms under quasi-static uniaxial tensile loads was studied. Using X-ray diffractometry, transmission electron microscopy, and scanning electron microscopy, it was shown that ion implantation resulted in amorphization of the surface layer with a thickness of -100 nm due to the formation of a chemical composition of approximately Ti36Ni41Ta23 (at.%), thermodynamically corresponding to the highest glass forming ability in the Ti-Ni-Ta system. In the implanted surface layer, both the microstructure and crystal structure defects subsystem were modified at a depth of -5 mm. Using the digital image correlation (DIC) method, the dynamics of changes in the integral and local (eyy longitudinal, exy shear and exx transverse) strain components were investigated in the tensile tests of both as-received and implanted TiNi SMA samples. On the basis of the obtained results, both integral and local stress-strain diagrams were plotted. In all studied cases, the main contribution to strain accumulation was made by the eyy and exx strains, which differed significantly for the as-received and implanted TiNi SMA samples. It was concluded that the positive effect of ion implantation was manifested in loading ranges close to the martensitic yield stress (at strain range of 1-6%), despite a noticeable decrease in the ultimate tensile strength and plasticity of the implanted TiNi samples.

The aim of this study was to investigate the tribological characteristics of commercially available high-strength polyphthalamide-based composites with great contents (30–50 wt.%) of both carbon and glass fibers in point and linear contacts against metal and ceramic counterfaces under dry friction and oil-lubricated conditions at various loads and sliding speeds. The lengths of both types of fibers were varied simultaneously with their contents while samples were fabricated from granules by injection molding. When loading PPA with 30 wt.% SCFs at an aspect ratio (AR) of 200, the ultimate tensile strength and the elastic modulus increased up to 142.7 ± 12.5 MPa and 12.9 ± 0.6 GPa, respectively. In the composites with the higher contents of reinforcing fibers PPA/40CCF and AR~1000, the ultimate tensile strength and the elastic modulus were 240 ± 3 MPa and 33.7 ± 1.9 GPa, respectively. Under the applied test conditions, a composite reinforced with 40 wt.% carbon fibers up to 100 μm long at an aspect ratio of ~1000 possessed the best both mechanical properties and tribological characteristics. One of the reasons that should be considered for improving the tribological characteristics of the composite is the fatigue wear mechanism, which is facilitated by the high filling degree, the strong interfacial adhesion, and the great aspect ratio for fibers. Under the oil-lubricated conditions, both friction coefficients and wear rates decreased, so such friction units could be implemented whenever possible. The reported data can be used as practical recommendations for applying fibrous polyphthalamide-based composites as friction unit components.

Thermal expansion mismatch stresses may be a reason for premature failure of sealing and bearing components made of polymer composites that are rubbed against metallic surfaces at elevated temperatures. It is of particular importance for polymer matrix composites loaded with anti-friction inclusions of polytetrafluoroethylene (PTFE) that possesses high coefficient of thermal expansion. In this regard, a study was undertaken to elucidate the effect of the thermal mismatch on wear and friction of amorphous polyetherimide (PEI) matrix loaded with either polytetrafluoroethylene (PTFE) particles (i) or PTFE particles covered with negative thermal expansion zirconium tungstate (ZT) alpha-ZrW2O8 (ii) at temperatures 23 degrees C, 120 degrees C and 180 degrees C. The ball-on-disk testing scheme was used according to standard with AISI 52100 steel balls rubbed against a polymer composite disks at normal force P = 5 N and sliding velocity V = 0.3 m/s. The PEI/PTFE/ZT composite demonstrated a tendency for wear rate (WR) reduction in sliding at 120 degrees C and 180 degrees C as compared to corresponding WR enhancement on the PEI/PTFE. The rationale is provided that the ZT additive effectively reduced thermal expansion of the PTFE in the PEI matrix and thus improved wear resistance of the composite. New thermal expansion-controlled wear and friction instability mechanism has been proposed and discussed.

An approach to detecting discontinuities in carbon fiber-reinforced polymers, caused by impact loading followed by compression testing, was developed. An X-ray sensor-based installation was used, while some algorithms were developed to improve the quality of the obtained low-contrast radiographic images with negligible signal-to-noise ratios. For epoxy/AF (#1) composite subjected to a “high-velocity” steel-ball impact with subsequent compression loading, it was not possible to detect discontinuities since the orientation of the extended zone of interlayer delamination was perpendicular to the irradiation axis. After drop-weight impacts with subsequent compression loading of epoxy/CF (#2) and PEEK/CF (#3) composites, the main cracks were formed in their central parts. This area was reliably detected through the improved radiographic images being more contrasted compared to that for composite #3, for which the damaged area was similar in shape but smaller. The phase variation and congruency methods were employed to highlight low-contrast objects in the radiographic images. The phase variation procedure showed higher efficiency in detecting small objects, while phase congruency is preferable for highlighting large objects. To assess the degree of image improvement, several metrics were implemented. In the analysis of the model images, the most indicative was the PSNR parameter (with a S-N ratio greater than the unit), confirming an increase in image contrast and a decrease in noise level. The NIQE and PIQE parameters enabled the correct assessment of image quality even with the S-N ratio being less than a unit.

The aim of this study was to optimize the ultrasonic consolidation (USC) parameters for ‘PEI adherend/Prepreg (CF-PEI fabric)/PEI adherend’ lap joints. For this purpose, artificial neural network (ANN) simulation was carried out. Two ANNs were trained using an ultra-small data sample, which did not provide acceptable predictive accuracy for the applied simulation methods. To solve this issue, it was proposed to artificially increase the learning sample by including additional data synthesized according to the knowledge and experience of experts. As a result, a relationship between the USC parameters and the functional characteristics of the lap joints was determined. The results of ANN simulation were successfully verified; the developed USC procedures were able to form a laminate with an even regular structure characterized by a minimum number of discontinuities and minimal damage to the consolidated components.

In this study, a methodology was developed for ranking manufacturing technologies of removable complete dentures (RCDs) according to the results of their full-scale mechanical tests. The actuality of the study is motivated by establishing the advantages and drawbacks of 3D-printed RCDs in contrast with ones manufactured via an analog protocol. The RCDs were fabricated via four technological routes that included various combinations of subtractive technologies (hot polymerization/HP and CAD/CAM milling) and additive manufacturing (digital light processing/DLP) ones and the installation of commercially available cosmetic denture teeth (DT). In the mechanical tests, different blocks of teeth (incisors, canines, premolars and molars) were loaded. To solve the ranking problem, it was proposed to interpret the results of the mechanical tests in terms of the reliability, durability and compliance/stiffness criteria. For this purpose, the combined AHP-VIKOR method was applied. In addition, a computer simulation of the mechanical loading conditions and the response of the RCDs was performed based on the finite element method (FEM). As the key conclusion, it was stated that additive manufacturing (AM) methods are competitive and cost-effective techniques for the fabrication of RCDs.

The goal of the study is the fatigue process in polyimide-based composites reinforced with short carbon fibers. Parameters of mechanical hysteresis loops such as the loop area, secant and dynamic moduli were used in the study. Hysteresis loops were constructed using the developed hardware and software system based on the optical method of strain measurements using a digital image correlation (DIC) technique. Methods for calculating the moduli and the parameters of mechanical hysteresis loops is considered. The results of their evaluation and the experimental data on the fatigue behavior of polyimide-based composites reinforced with short carbon fibers are presented. It is shown that an important quantitative measure of the differences in the fatigue behavior of the studied composites is the hysteresis induced energy loss. For a composite with carbonized fibers, the energy loss level per cycle is 35 kJ/m 3 , whereas for a composite with graphitized fibers it is 34% lower (23 kJ/m 3 ). At the same time, the fatigue durability of the latter is - 40 times lower. A decrease both in the secant modulus (up to 11%) and the dynamic modulus (up to 3.5%) was observed in cyclic tests. However, the reduction was twice as much in a composite with carbonized fibers possessing a longer durability. Thus, the DIC-based estimation of mechanical hysteresis loops by the parameters of the secant and dynamic moduli, as well as the loop area can be successfully used to interpret the difference in the fatigue characteristics at the stage of scattered damage accumulation, whereas an unambiguous prediction of the residual life appeared impossible. The problem requires further systematic studying using approaches of the fracture mechanics.

This paper addresses peculiarities in the formation and adherence of a tribofilm on the wear track surface of antifriction PI- and PEI-based composites, as well as a transfer film (TF) on a steel counterface. It is shown that during hot pressing, PTFE nanoparticles melted and coalesced into micron-sized porous inclusions. In the PEI matrix, their dimensions were much larger (up to 30 µm) compared to those in the PI matrix (up to 6 µm). The phenomenon eliminated their role as effective uniformly distributed nanofillers, and the content of 5 wt.% was not always sufficient for the formation of a tribofilm or a significant decrease in the WR values. At the loaded content, the role of MoS2 and graphite (Gr) microparticles was similar, although filling with MoS2 microparticles more successfully solved the problem of adhering to a PTFE-containing tribofilm in the point tribological contact. This differed under the linear tribological contact. The higher roughness of the steel counterpart, as well as the larger area of its sliding surface with the same PTFE content in the three-component PI- and PEI-based composites, did not allow for a strong adherence of either the stable PTFE-containing tribofilm on the wear track surface or the TF on the steel counterpart. For the PEI-based composites, the inability to shield the steel counterpart from the more reactive polymer matrix, especially under the conditions of PTFE deficiency, was accompanied by multiple increases in the WR values, which were several times greater than that of neat PEI.

Low-temperature plasma treatment with atmospheric discharge with runaway electrons (DRE) was shown to be an efficient way to activate carbon fiber’s (CF) surface and subsequently increase its interlayer shear strength (ILSS) values. It was demonstrated that an acceptable ILSS level was achieved after a DRE plasma treatment duration of 15 min. The treatment of CFs resulted in their surface roughness being increased and their functional groups grafting. The XPS data showed a change in the chemical composition and the formation of reactive oxygen-containing groups. SEM examinations of the PPS/CF laminates clearly demonstrated a difference in adhesive interaction at the PPS/CF interface. After the DRE plasma treatment, CFs were better wetted with the polymer, and the samples cohesively fractured predominantly through the matrix, but not along the PPS/CF interface, as was observed for the sample reinforced with the untreated CFs. The computer simulation results showed that raising the adhesive strength enhanced the ILSS values, but reduced resistance to transverse cracking under the loading pin. In general, higher flexural strength of the PPS/CF laminates was achieved with a greater interlayer adhesion level, which was consistent with the obtained experimental data.