Papers by Keyword: Plastic Deformation

Abstract: Polymethylmetharylate (PMMA) has been widely used for aircraft canopies and transparent structural components, and processed into various parts through vacuum forming. In this study, the effects of forming speed and deformation characteristics on thickness uniformity during high-temperature vacuum forming of PMMA were analyzed. First, creep tests and high-temperature tensile tests were conducted at the specimen level to quantitatively distinguish between creep deformation and plastic deformation. Creep tests were performed under constant temperature and load conditions, and strain was measured through Digital Image Correlation. For plastic deformation analysis, tensile tests at room temperature and elevated temperatures were carried out to compare yield strength and elongation changes. To analyze thickness uniformity during the forming process, rectangular-shaped parts were fabricated using vacuum forming under various conditions where temperature and forming speed are key variables. After forming, thickness uniformity and surface transparency of the products were measured. Additionally, internal structural changes according to forming speed and temperature conditions were analyzed, and a comprehensive evaluation of material stability was performed.

Abstract: In the framework of sustainable manufacturing and circular economy, the reuse of metallic components at the end of their first life (EoL) is a promising strategy to reduce energy consumption and material waste, but it requires an accurate assessment of residual plastic deformation, which strongly affects structural integrity and remaining formability. Conventional full-field techniques such as Digital Image Correlation (DIC) require a reference image of the undeformed state, which is generally unavailable for EoL components. To address this limitation, this work investigates a deep learning–based, reference-free approach for strain estimation directly from a single image of the deformed surface. The method relies on a convolutional neural network architecture derived from VGG-16, trained to regress the in-plane principal strains and their orientation from local image subsets of the surface texture using a synthetically generated dataset based on real material textures and realistic imaging conditions. The trained model is applied to high-resolution optical images of pre-deformed steel and aluminum components from regions subjected to different deformation histories, with partial validation provided by finite element simulations and conventional DIC measurements. Preliminary results show that the proposed approach can distinguish regions with different levels of plastic deformation and provide strain maps consistent with independent mechanical assessments, demonstrating its potential as a rapid, non-destructive tool for deformation mapping and classification of EoL components to support remanufacturing and reuse decisions.

Abstract: This paper presents a metallographic and fractographic study of AISI 304 austenitic stainless steel subjected to mechanical loading in the sensitized condition. Static three-point bending tests and impact tests were carried out to evaluate how sensitization affects the mechanical response and fracture behaviour of AISI 304. The study compares the initial state of the material with its condition after sensitization at 700 °C for 10 h, with emphasis on changes in plastic deformation and fracture mechanisms. Microstructural evaluation was performed using light microscopy, while Vickers microhardness measurements provided insight into local mechanical changes. Fractographic analysis using scanning electron microscopy revealed differences in fracture surface morphology. Results demonstrate a decrease in microhardness, reduced impact energy, and noticeable differences in fracture morphology following the sensitization treatment, indicating that the heat treatment influences both the mechanical response and failure behaviour of AISI 304.

Abstract: A theoretical analysis of low-temperature plastic deformation processes and acoustic relaxation in the high-entropy alloy Al_0.5CoCrCuFeNi has been conducted. Within the framework of proposed dislocation model it was established the key types of dislocation defects in the alloy's lattice structure; types of barriers that hinder the movement of dislocation lines (strings); and mechanisms of thermally activated movement of various dislocation line elements through these barriers at room and low temperatures. Using this model, quantitative estimates have been derived for significant dislocation characteristics and their interaction with barriers, such as the distance between local obstacles in the slip plane ∼ 4 nm, the Peierls stress for dislocations in an easy slip system 4 · 10⁶ Pa, and more. Additionally, an estimated speed of sound 3.4 · 10³ m/s based on the proposed model aligns well with the direct experimental data. The empirical estimates for the energy per unit length of a dislocation ∼ 10^-8 J/m and the linear mass density ∼ 10^-15 kg/m are consistent with modern continuum dislocation theory. A detailed examination of the structure of the alloy Al_0.5CoCrCuFeNi was carried out using X-ray diffraction and Energy Dispersive Spectroscopy techniques. Numerical estimates of the dislocation density ∼ 5 · 10¹⁵m^-2 were obtained through Williamson-Hall analysis of X-ray diffraction patterns. It was found to correlate with the estimates overall length of dislocation segments per unit volume which effectively interacts with elastic vibrations of the sample ∼ 4 · 10¹³m^-2, as determined from acoustic relaxation measurements.

Abstract: The study investigates the kinetics of plastic deformation propagation in a welded joint of 10G2FB steel after submerged arc welding. A metallographic analysis of the microstructure of the weld seam, fusion zone, and heat-affected zone was performed. Tensile testing and electron microscopy studies were conducted to determine the mechanisms of plastic deformation and crack initiation. It was found that the fusion zone is the most vulnerable to the formation of deformation defects, which can affect the durability of the structure. Recommendations for optimizing welding parameters to improve the mechanical properties of welded joints are proposed.

Abstract: The restoration parts made metallic materials by the method hot die forging is considered. Technological processes for restoring parts by hot stamping have a number advantages: shaping occurs in dies a simple design, existing forging and pressing equipment is used with the use standard automation and mechanization tools. In the process restoration parts by hot plastic deformation, it is possible to restore the shape and dimensions the worn surface, as well as to obtain the required microstructure the metal the restored part, which makes it possible to increase its service life due to subsequent thermo mechanical processing. A study was made the reasons for the loss performance the ball pins the torque rod, designs dies were developed for the restoration worn solid parts by the method hot forging. Parts are restored by creating targeted metal flows into the wear area using hot plastic deformation. It has been established that the hardness the metal in the middle part the restored part "Ball pin" increased by 30 ... 32% in relation to serial parts. When heated to the temperature forging and deformation the metal, the internal damage the metal accumulated inside the part is restored. This allows you to increase the durability the restored parts by 26…30%.

Abstract: The goal of this research is to examine the influence of temperature affects the forging of a rectangular billet of AISI 4120 alloy steel using the 3D Deform version 11 software. The simulation was performed with 0.3 coefficient of friction on a metal forming (lubricated) process and the part is intended for application in aerospace and oil and gas industries. Three modules of deform software were defined to execute the simulation: pre-processing, simulation, and post-processing. The pre-processing in forging employed standard data— material selection, billet drawing, top and bottom dies design, meshing and simulation control. After 120 steps, the post-process estimation of deformation temperature, effective strain and stress, total velocity, and total displacement were obtained on the billet of material at temperatures of 800^o C, 1000^o C, and 1200° C. The results show that when forging temperatures climb, effective strain and stress decrease, total displacement and velocity decrease, and the final temperature increases.

Abstract: In large-sized metal structures, various stress concentrators are often present, which affects the operation of the material. These are intermittent bonds, holes, welded joints, material defects, etc. As a result of overloads under the action of an external cyclic load on structures in the area of stress raisers, the cycle asymmetry, the level of maximum stresses and deformations increase. In this case, the determination of the limit values of the stress cycles can be performed using a diagram of the limit stress amplitudes. The paper presents an engineering method for calculating the limiting stress amplitudes and constructing Hay’s diagrams. It is based on the use of mathematical models of classical linear and structural-mechanical fracture mechanics. Analytically and by calculation, the validity of the method is shown, which consists in determining the endurance limits and limiting stress amplitudes under high-cycle loading in a wide range of variation of the cycle asymmetry coefficient for ferrite-pearlite steels with a yield strength of up to 400 MPa. Thus, a generalized calculation method has been developed for determining the endurance limits for high values of cycle asymmetry and cycle stresses. The error of the method is estimated in the area of low-cycle load. The influence of constant and average load in a cycle on the endurance limit has been investigated both for high-cycle and low-cycle loading. The proposed approach allows to construct Smith and Hay’s fatigue diagrams for the tensile region, taking into account the structural characteristics of the material and the error allowed for engineering calculations.

Abstract: The influence of plastic deformation on the change of the relative number of luminescence centers of Mn²⁺ ions with various local surroundings in ZnS single crystals at various wavelengths of the excitation light has been thoroughly studied. Taking into account that the emission of each individual photoluminescence band is due to the emission of manganese luminescence centers with a certain type of local symmetry, the use of the decomposition of the experimental photoluminescence spectra of Mn²⁺ ions in ZnS single crystals into individual bands and the subsequent analysis of changes in the photoluminescence spectra of each individual band allowed a detailed study of the effect of dislocation move on quantitative changes in emitting manganese luminescence centers of various types.

Abstract: The mechanorheological viscoelastic plastic model was used to study the effect of impact speed on the dynamics of mechanical interaction of a spherical body with the surface. An analysis of the impact process made it possible to draw some conclusions. The impact interaction time depends on the impact speed and mechanical properties of the material. The impact time decreases with an increase in the impact speed, a decrease in plasticity, and an increase in elasticity. With an increase in the impact speed, the impact time decreases. During the experiment, the initial impact speed increased 10 times. During the impact interaction, the body deformation increased 6-7 times. According to the calculations, the average body deformation speed also increased 10 times. As a result, the time for travelling a distance equal to the elastic and plastic deformation when loading bodies and the elastic deformation when unloading bodies decreased. The total deformation is composed of elastic and plastic components. With an increase in the impact speed, the plastic component increases, which decreases the unloading time due to a decrease in the elastic component. The impact time is an important characteristic of the dynamic process of interaction. Therefore, when identifying theoretical models to the real processes, these parameters should be congruent. To improve the modeling accuracy and reliability for various technological processes under dynamic loads, it is necessary to take into account various factors.