No 2 (2022)

Polymer composite materials (PCM) reinforced with glass fibers are very important in many industries due to their unique properties (high chemical resistance and specific strength) with the economic efficiency of use. At the same time, the application of glass fabrics as reinforcing elements ensures high manufacturability. However, unlike crystalline materials, polymer composite materials are subject to the complex process of destruction, which requires the application of non-destructive control methods to get information about the nature of the resulting damage and the kinetics of their accumulation. The paper studies the deteriorations formed in the fiberglass samples molded using T-11-GVS-9 glass fabric and DION 9300 FR binder within static bending deformation accompanied by the acoustic emission (AE) method. In this work, the authors solved the problem of identifying the nature of damages in fiberglass using the Fourier spectra of the recorded AE signals. The authors used the clustering method to estimate their formation and development kinetics. Clustering was performed based on the Kohonen self-organizing map (SOM) algorithm using the values of peak frequencies of the Fourier spectra calculated for the recorded AE signals under static bending deformation of a fiberglass sample up to failure. To ensure the separability of the resulting damages according to the AE parameters, the authors used the loading rate that was ten times lower than that calculated according to the state standard. The study established that the application of frequency representation of AE signals recorded during the fiberglass destruction is effective when solving the task of identifying the nature of the resulting damages. As a result of the study, the authors found that the process of delamination formation during the bending of multilayer laminated plastics acts as a critical mechanism of destruction leading to a significant loss of the polymer composite strength properties.

Magnetic shape memory alloys are a specific subtype of shape memory materials. The magnetic deformation phenomenon causes the high research interest in these alloys. Thus, in one of the most promising alloys based on Ni–Mn–Ga, using a magnetic field, it is possible to achieve changes in a single crystal size by up to 10 % due to the reorientation of the magnetic field in magnetic domains. The high magnetic deformation is directly related to the high mobility of twin boundaries separating two domains. In this work, the authors used a composite piezoelectric oscillator at a frequency of about 100 kHz to determine the influence of such defects as dislocations and twin boundaries on the mechanical characteristics of Ni₄₉Mn₃₀Ga₂₁. The authors investigated the features of temperature dependences of internal friction in the samples before and after deformation and provided the amplitude dependences of these characteristics. In the studied single-crystal martensitic phase, the transition from the tetragonal phase to the orthorhombic phase was detected at 235 K. In the Ni–Mn–Ga tetragonal phase, the formation of new defects contributes to the more pronounced and early onset of amplitude-dependent internal friction. At lower loads, the successive stages occur associated with the processes of dislocations and twin boundaries movements inside the Cottrell clouds, dislocations and twin boundaries movement outside the Cottrell clouds, and supposedly, the slowdown of dislocations and twin boundaries movement due to their interaction. As well as internal friction, the authors studied the change in Young’s modulus. Its decrease at all temperatures is most pronounced in the samples with the defective structures. The study identified that in the orthorhombic phase, it is possible to observe the internal friction dependence on the deformation amplitude at a lower load due to an increase in the twin boundaries mobility with increasing temperature.

Despite the increasing automation of the process of designing and manufacturing metal products, their failure remains a common phenomenon. The metallographic examination is appointed, which can only be carried out at a proper level by the specialized accredited organizations to identify the causes of such incidents. A metallographic examination is a tool that acts as feedback between the output quality of products and the entire chain of numerous operations during production. The purpose of this work is, using a practical example, to demonstrate the possibility and special significance of the conclusions of the metallographic examination for the development of the product manufacturing technology. Using the high-speed plasma spraying method, the authors applied the NiCrBSi coating to the surface of the locomotive wheel pair axle to increase its wear resistance. The life bench tests of the axle revealed the main fatigue crack, the tests were stopped, and the axle was artificially broken completely. The analysis of metal quality, including chemical composition, mechanical properties (strength, ductility, and impact hardness), microstructure, metal purity according to the non-metallic inclusions, and parameters of a surface layer hardened by rolling, showed its full compliance with the regulatory documentation. The thickness and hardness parameters of the NiCrBSi coating also corresponded to the declared ones. According to the fractographic analysis, the fatigue fracture was initiated at multiple points, which was a characteristic sign of a common objective reason for the insufficient strength of a product not associated with some random factor. The metallographic examination identified that the main reason for the failure of a wheelset axle is the coating’s insufficient fatigue strength. The numerous fatigue microcracks that originated in the coating grew into the base metal and led to the fatigue macrocracks formation at different height levels. The merging of these cracks led to widespread fatigue fracture surface formation.

A provision of location tolerances and their retention in the postoperative period is one of the main hard-hitting process tasks when producing long-length low-rigidity shaft-type parts. Mixed treatment – tensile straightening or thermal-power treatment is one of the technological methods intended to provide this group of geometrical indicators, including axle linearity. The efficiency improvement of this technology is impossible without knowing the features of the formation of plastic deformations distribution along the length of long-length blank parts. The paper considers the application of an optical method for controlling deformation on the surface using the method of digital image correlation at axial deformation of cylindrical parts. The work describes an experimental device for optic control of deformations when loading a specimen using digital cameras. The authors studied the influence of various modes of paint deposition to a sample (deposition rate, distance, deposition mode – continuous or pulsed) on the features of a produced speckle in the form of random distribution of mixed-size paint spots over the specimen surface; obtained histograms of the intensity distribution of various speckles. The authors carried out the experiments to identify deformations based on the technology of the local gradient digital image correlation method for the specimens of polymer tubes with different speckle types. The study identified the distribution of the deformation over the length of samples within the deformable area selected for analysis with the specified degree of smoothing provided by choice of correlation kernel size and the choice of its displacement step for fixing deformation processes with a precise error. The authors obtained distributions of axial deformations along the length of specimens and errors of deformations determination depending on a speckle nature. The study specifies necessary speckle parameters ensuring minimal error for long-length samples up to 200 mm in length and appropriate technology for paint depositing. It is a speckle with a wide range of spot sizes rarefied with their locations and the Gaussian filter image smoothing before the analysis.

One of the key challenges in additive manufacturing of plastic goods using the Fused Filament Fabrication (FFF) technology is to ensure their strength. The low strength of polymer materials and the distinct anisotropy of their mechanical properties limit the use of 3D printing as an alternative to the traditional small-scale production technologies. The most promising solution to the goal of increasing the strength of printed goods is the application of continuous fiber reinforcement. Several additive manufacturing devices and software products that allow preparing a control program for 3D printing with reinforcement are known, however, having all their advantages, they, like conventional printed products, have a wide spread in strength in various directions (in the plane of a layer and perpendicularly to it, in the direction of growing). In this paper, the authors propose using the continuous fiber reinforcement along the three-dimensional trajectories to smooth out the anisotropy of the products’ properties in the FFF technology and ensure wider possibilities for using them in the production of final goods. In the course of work, a 3D printer with the ability to print using five degrees of freedom and software for preparation of control programs were upgraded for the printing process with laying continuous fiber; printing modes with reinforcement were developed; samples were produced for standard static bending tests. The experiments show that reinforcement improves the printed specimen’s strength, and the proposed three-dimensional reinforcement technique ensures the lower flexing strength compared to standard flat reinforcement with uniaxial laying of fibers, though, the destruction of 3D reinforced specimens occurred without evident delamination.

The paper presents the comparative analysis of the structure and mechanical properties (microhardness) of the surface layers of the hypoeutectic Al–11Si alloy and hypereutectic Al–20Si alloy exposed to electroexplosive alloying (treatment mode: aluminum foil mass is 58.9 mg; Y₂O₃ powder mass is 88.3 mg; the discharge voltage is 2.6 kV). During the research, the authors identified that the Al–11Si alloy initial structure mainly consists of the Al solid solution grains. Eutectic grains are located along the grain boundaries and at the joints of aluminum grain boundaries. In the Al–11Si alloy, the aluminum grain size varies from 25 μm to 100 μm, and the Al–Si eutectic grain size varies within 10–30 μm. The hypereutectic composition Al–20Si alloy in the initial state is characterized by the presence of primary silicon inclusions predominantly of a plate-like shape. The sizes of these inclusions reach 120 μm. After electroexplosive alloying, in the Al–11Si alloy, the author identified the formation of a multilayer structure consisting of a highly-porous coating irregular in thickness, a liquid-phase alloying layer, and a heat-affected layer. The modified layer thickness for the Al–11Si alloy varies in the range of 33–60 μm, and for the Al–20Si alloy, the modified layer thickness varies within 20–100 μm. The microhardness value of the initial hypoeutectic Al–11Si alloy was 64 HV0.05, for the hypereutectic Al–20Si alloy – 71 HV0.05. It can be noted that the microhardness of the Al–11Si alloy surface layer exceeds the initial material microhardness more than 2.5 times. In the Al–20Si alloy, the surface layer microhardness exceeds the one of the initial material more than twice. With the increase of the distance from the modification surface, the microhardness decreases and reaches the initial alloy value at the depth of ≈90 μm.