Quasi-static Tensile Tests Research Articles

Investigation on the microstructure evolution and mechanical properties of electromagnetic rail material in a launch environment

The failure issue of electromagnetic railgun rails is a widely researched problem, but effective research methods are lacking in studying the microstructure of rail materials. The high current and high strain rate tensile (HCHST) testing platform was designed to simulate the high current density and high strain rate deformation service conditions of pure copper rails used in electromagnetic guns. The microstructural and mechanical properties of commercially pure copper were analyzed using TEM and EBSD under high current density (2680 A/mm2) and various high strain rates (ε̇=3404s−1,ε̇=6808s−1)using the HCHST test platform. The obtained results were then compared with those obtained from the as-received state and the quasi-static current-assisted tensile (QCAT) test. The findings indicate that the deformation mechanism of pure copper specimen under HCHST is similar to that of QCAT, where dislocation and slip are the main mechanisms. However, distinct differences in microstructure were observed. Specifically, a significant number of dislocation walls were present in the grains under QCAT, whereas numerous dislocation cells were formed in the grains under HCHST. In the high-current density environment of 2680 A/mm2, as the strain rate increased, the number of dislocation cells increased while their size decreased. The grains became extremely refined, and the KAM value also increased. Furthermore, the Vickers hardness of pure copper significantly improved after undergoing the HCHST. Based on the experimental findings, it was observed that during the service process of the pure copper rail in electromagnetic railguns (under the influence of high current density and high strain rate deformation), the surface of the rail material experienced significant dislocation entanglement. This resulted in a significant increase in the strength and hardness of the surface of the rail with high strain rate deformation. However, the uneven distribution of strength and hardness throughout the surface layer of the rail eventually made it more susceptible to deformation and failure.

Research on dynamic deformation behavior and constitutive relationship of hot forming high strength steel

To accurately characterize the dynamic deformation mechanical properties of hot forming steels 6Mn6 and 22MnB5 under collision conditions, quasi-static tensile tests (0.001s−1) and Hopkinson compression bar tests (∼2000s−1, ∼3000s−1, ∼4000s−1) were conducted to analyze the influence of strain rate on the material mechanical properties. Based on the experimental results, four constitutive models including Johnson-Cook (JC), modified JC (m-JC), Cowper-Symond (CS), and Khan-Huang (KH) models were established for both 6Mn6 and 22MnB5. Additionally, a modified model based on the Swift-Voce strain hardening model coupled with the Cowper-Symond model was proposed. A numerical simulation model for compression bar tests was developed using JC and m-JC models. The experimental results indicate that both hot forming steels exhibit strain rate sensitivity, with 6Mn6 performed a more pronounced effect than 22MnB5. The average absolute error (AARE) and correlation coefficient (R) of the m-JC and CS models were 0.99 and 0.29 %, 0.95 and 0.4 %, respectively. The dynamic deformation behavior of 6Mn6 and 22MnB5 at high strain rates was accurately predicted. Comparing with the JC model, the utilization of the m-JC user subroutine has resulted in a significant improvement in simulation accuracy by 58 % and 84 % for these two materials, which laying a solid foundation for high-precision vehicle collision simulation.

Experimental and numerical investigation of adhesively bonded kfrp/steel double strap joints incorporating eggshell powder-toughened epoxy adhesive

Due to the environmental concerns, the application of natural FRPs to replace synthetic fibre as a strengthening material has increased. Kenaf fibre-reinforced polymer (KFRP) has comparable specific strength with glass fibre-reinforced polymer (GFRP). Moreover, epoxy resin is widely used as a matrix of composites and adhesives; however, it has low shear strength. Improvement of epoxy properties is therefore required, for example, by incorporating biofiller such as eggshells from household waste, which contain calcite, to improve its shear strength. Testing series includes variations of KFRP bond length, KFRP thickness and eggshell filler volume fractions. All the DSJ specimens underwent a two-stage testing process, experimentally and numerically. In Stage 1, experimental work was performed on the specimens through quasi-static tensile tests, following the ASTM D3528–96. In Stage 2, numerical studies were conducted to predict the strength using the extended finite element method (XFEM) within ABAQUS CAE. Subsequently, the strength prediction from developed 2-D FEA models was validated by the experimental datasets. All testing specimens exhibited KFRP rupture mode. For all the studied overlap lengths, the joint strength increased with the increase of the studied composite's adherend thickness (1 - 4 mm); however, the overlap length reached the optimum at the overlap length of 80 mm, where beyond that overlap length, the joint strength tended to decrease. The maximum joint strength is achieved with a combination of 80 mm bond length and 4 mm KFRP thickness, resulting in a 226.5% enhancement compared to the baseline (composite thickness of 1 mm, with adhesive without filler). Moreover, it was found that volume fraction of 5% eggshell was the optimum. The strength prediction was performed using an extended finite element method (XFEM), In general, there were good agreements in both experimental datasets and XFEM models, with discrepancies of less than 16.1% (averaging less than 8%). The FEA modelling approaches are promising for predicting the joint strength of KFRP/steel DSJ.

Developing austenitic high-manganese high-carbon steels for biodegradable stent applications: Microstructural and mechanical studies

Fully degradable stents that temporarily support healing tissue can solve potential long-term complications associated with permanent implants. In this study, we investigate austenitic high-manganese high-carbon steels as promising candidates for such biodegradable stent applications. The microstructural characteristics and mechanical properties of the Fe–Mn–C steels were systematically analysed to assess their suitability for this purpose. A series of four austenitic Fe–Mn–C steels with varying manganese (15 and 30 wt%) and carbon (0.6–1.0 wt%) content were processed by vacuum induction casting, annealing and hot forging. Microstructural analysis was performed, and the hot forged materials were further evaluated using ultrasound, macro hardness, and (stopped) quasi-static tensile tests to assess stent-related parameters. In contrast to the as-cast state, the hot forged steels exhibited high chemical homogeneity, as was found by energy-dispersive X-ray spectroscopy (EDXS). Electron backscatter diffraction (EBSD) revealed comparability between the four steels regarding their annealing twin fractions and grain size distributions. An austenitic microstructure was revealed for all modifications by transmission X-ray diffraction (XRD), except Fe–15Mn–0.6C, which displayed a minor ε–martensite fraction. Reducing manganese from 30 to 15 wt% resulted in favourable effects, including a higher Young's modulus, lowered offset yield strength, and an increased ultimate tensile strength due to larger strain hardening while preserving a high total elongation. However, reducing the carbon content to 0.6 wt% diminished the mechanical performance due to reduced solid solution strengthening and the ε–martensite formation. Among the investigated steels, the novel Fe–15Mn–0.8C alloy exhibited the most attractive combination of the studied properties for potential stent applications.

Experimental and Numerical Analysis of Aluminum-Polyethylene Composite Structure Subjected to Tension and Perforation Under Dynamic Loading for a Wide Range of Temperatures

The aim of this work consists of identifying the material behavior of Alucobond composite structures subjected to ballistic impact. The composite is made of Aluminum alloy AW5005 and LDPE (low-density polyethylene). The mechanical properties of these materials are described in term of strain rate and temperature dependencies. Quasi-static tensile and compression tests for Alucobond are performed at four different strain rates, i.e. 0.0001 0.001, 0.01, and 0.03 s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${s}^{-1}$$\\end{document}. Moreover, in dynamic regime the used strain rate ranges in compression and perforation tests are (104\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${10}^{4}$$\\end{document}s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${s}^{-1}$$\\end{document} ≤ ε˙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\dot{\\varepsilon }$$\\end{document} ≤ 105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${10}^{5}$$\\end{document}s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${s}^{-1}$$\\end{document}) at temperatures ranging from room temperature 20 °C to 100 °C. Various parameters influence the behavior of the Alucobond structure under impact: the geometry and the mechanical properties of the projectile, the initial impact velocity, and the thermomechanical behavior of the target. Numerous quasi-static and dynamic original test results (traction and perforation over a wide range of strain rates at room temperature and high temperature) are presented. Numerical simulations, particularly using the finite element (FE) method with the ABAQUS explicit code, are also effective supplements for theoretical and more detailed experimental investigations, which were carried out to analyze the dynamic behavior of impacted structures.

Modified constitutive models for Inconel 718 considering current density and temperature in electrically assisted forming process

Electrically Assisted Forming (EAF) technology has obvious advantages in material forming. To develop an effective constitutive model considering electrical effects, room temperature and electrically assisted quasi-static uniaxial tensile tests were conducted using ultrathin nickel-based superalloy plates with a thickness of 0.25 mm. The research focused on the two most widely recognized effects: the Joule thermal and the electric athermal effects. The mechanism of current action can be divided into two scenarios: one considering the Joule thermal effect only, and the other considering both effects simultaneously. Two basic constitutive models, namely the Modified-Hollomon model and the Johnson-Cook (J-C) model, were selected to be optimized through the classification of two different situations, and four optimized constitutive models were proposed. It was found that the J-C model with simultaneous consideration of the Joule thermal effect and electric athermal effect had the best prediction effect by comparing the results of these four models. Finally, the accuracy of the optimization model was verified by finite element simulation of the electrically assisted stretching optimization model. The results show that the constitutive model can effectively predict the temperature effect caused by the Joule heat effect and the athermal effect of current on the material.

Quasi-static mechanical behavior of 2.5D woven variable thickness composites

Many special-shaped structural parts have begun to be prepared in aerospace and other fields using 2.5D woven composites. Therefore, two kinds of 2.5D woven variable-thickness composites are designed by reducing the number of yarn layers, called outer reduction yarn woven composites (ORYWC) and inner reduction yarn woven composites (IRYWC). Both variable thickness regions comprise five independent parts, each occupying one or two layers of yarn reduction. In addition, the microstructure of ORYWC and IRYWC is measured using X-ray computed tomography, and the mechanism of geometric deformation during weaving and molding is discussed. Finally, the quasi-static tensile test is conducted to compare and analyze the longitudinal stiffness, tensile strength, and damage mechanism of ORYWC and IRYWC. The results show that the longitudinal stiffness of the five parts of the two structures maintains little difference. The average stiffness and tensile strength of IRYWC decrease by 4.82% and 10.65% compared with ORYWC.

Machine learning-based assessment of hygrothermal aging performance in CFRP-aluminum alloy adhesive bonded structures

ABSTRACT Adhesive bonding is an effective technique for connecting fiber reinforced composites (FRPs) and plays a crucial role in determining load transfer capability and overall structural safety. However, long-term exposure to temperature and moisture can degrade adhesive joints, highlighting the significant importance of accurately predicting their durability when designing reliable adhesive structures. This study aims to address the industry’s demand and academic interest by proposing a convenient and accurate prediction method to evaluate the durability of adhesive structures subject to complex stresses. Laboratory accelerated aging experiments were conducted on butt joints (experiencing pure normal stress) and shear joints (experiencing pure shear stress). Quasi-static tensile tests and adhesive FTIR tests were performed to establish a dataset of adhesive functional group absorbance and failure strength under single stress conditions. To compare and assess the predictive performance of different models for aging behaviors, Artificial Neural Network (ANN), Support Vector Regression (SVR) and Random Forest (RF) models were selected. The model hyperparameters were further optimized using the Genetic Algorithm (GA). The results demonstrated that the ANN model exhibited superior correlation and accuracy compared to the SVR, and RF. The characteristic importance analysis revealed that the hydrolysis and post-curing of adhesives were the primary factors affecting joint performance under hygrothermal environments. By incorporating environmental degradation factors and defining initial failure criteria, the CZM constitutive model was modified and a predictive method was established for assessing the hygrothermal aging behavior of CFRP/aluminum alloy bonding structures. This method effectively eliminates the effect the intricate aging process (e.g. aging time, aging conditions) and establishes a direct correlation between the molecular structure of adhesive and the macroscopic mechanical properties of the bonded joint, which serves as a valuable reference and guidance for the safety design of automotive composite material bonding structures throughout their entire lifespan.

Analysis of fracture state and fatigue life of high modulus carbon fiber wrapped composite barrel

High-modulus Carbon Fiber-reinforced Polymer composites are widely used in critical industries due to their exceptional mechanical properties. However, the fatigue and fracture of high modulus carbon fiber materials are currently poorly studied. For this purpose, the NOL ring fatigue tensile testing is referenced and improved to investigate the performance and service life of high-modulus carbon fiber wound barrels. NOL ring specimens, made of M40 carbon fiber material, are subjected to quasi-static tensile and fatigue tests. The fracture state and characteristics of high modulus materials during fatigue are analyzed. Two-parameter Weibull distribution function is used to analysis statistically the fatigue life results of composite samples. Then, the life curve is drawn for different stress amplitudes. Additionally, the fiber fracture surface is observed under a high-power microscope. The fiber fracture model under brittle fracture is established. The results indicate that the fracture characteristics and mechanisms of high-modulus materials differ from those of high-strength materials, necessitating different fatigue life assessment methods. The fatigue failure of high modulus fibers exhibits brittle fracture similar to quasi-static loss, with flat fracture surfaces and minimal cumulative damage. The failure mechanism is accompanied by brittle fractures with a small amount of fiber pulled out.

Influence of vacuum annealing on mechanical characteristics of focused ion beam fabricated silicon nanowires

This paper describes the influence of vacuum annealing on the mechanical characteristics of silicon (Si) nanowires (NWs) fabricated using focused ion beam (FIB) technologies. Two types of Si NWs having a cross-sectional one-side length or diameter ranging from 19 to 447 nm are prepared using the direct milling and Ga ion doping functions of FIB. The Si NWs prepared are annealed at 400–700 °C in high vacuum for 10 min, followed by quasi-static uniaxial tensile testing using a microelectromechanical system based tensile test system in a scanning electron microscope. All the Si NWs fracture in a brittle manner. Young's modulus of submicrometer-sized Si NWs shows both annealing and specimen size influences in the range from 120 to 170 GPa, whereas that of nano-sized Si NWs shows only annealing influence in the range from 60 to 110 GPa. Tensile strength scatters greatly, ranging from 1.0 to 7.2 GPa, which increases with increasing the NW size. A transmission electron microscope and an atomic force microscope suggest that, by annealing, recrystallization happens in the damaged layer introduced by FIB milling and the NW surface morphology changes due to its recrystallization and gallium (Ga) ion evaporation. Fracture origin is discussed through the comparison between surface roughness and crack length estimated by the Griffith theory of brittle fracture.

Effects of High Temperature and Different Salt Solutions on Basalt Fiber-Reinforced Composites’ Bonded Joint Durability Impact

Fiber-reinforced composites are widely used in industrial development due to their excellent performance, and the study of basalt fiber-reinforced resin (BFRP) as a new type of economical and environmentally friendly material is highly valued, since harsh environments can affect the durability of bonded joints. In this paper, the Araldite® 2015 adhesive for BFRP–BFRP single lap joints (SLJs) was selected as the subject of study and the joints were analyzed in aging experiments in three environments: deionized water (DW), 3.5% NaCl solution, and 5% NaCl solution at 80 °C for 0 days (no aging), 10 days, 20 days, and 30 days. Using Fick’s second law to describe water absorption in joints and materials, the comparison shows that the water absorption in the joints occurs primarily in the adhesive. Differential scanning calorimetry (DSC) was used to characterize the decrease in the glass transition temperature (Tg) of the adhesive at each failure point, and the thermogravimetric analysis (TGA) tests showed that moisture and heat led to the degradation of the polymer material in the joint. The failure strength of the joints in quasi-static tensile tests was positively correlated with the moisture content of the solution, and the changes in the absorption peaks of the functional groups of the adhesive after aging were observed. The comprehensive macro-micro failed section analysis showed that the water molecules damage the chemical properties of the adhesive, meaning that the adhesive and BFRP binding ability is decreased. The proportion of failure section tear decreased with the extension of the aging time, and a high temperature induced water evaporation and an adhesive post-curing reaction. The change in the failure mode is a result of the combined effect of the post-curing effect and hydrolysis reaction, which is validated by the results of the Fourier infrared spectroscopy (FTIR). This study contributes to an in-depth understanding of the effect of moisture and heat on the residual properties of bonded joints.

Excellent dynamic properties and corresponding deformation mechanisms in a microband-induced plasticity steel with dual-heterogeneous structure

A dual-heterogeneous structure with dual phases and heterogeneous grains was designed in a high Mn microband-induced-plasticity (MBIP) steel. The heterogeneous structured sample exhibits similar dynamic shear yield strength, while exhibiting enhanced dynamic uniform shear strain and dynamic shear toughness by 36 % and 47 %, respectively, as compared to the homogeneous structured sample. The strain hardening mechanisms contributing to the excellent dynamic shear properties in the heterogeneous structured sample have been revealed. Firstly, the superior hetero-deformation-induced hardening capability of the heterogeneous structured sample arises from a higher density of geometrically necessary dislocations induced in each phase. Secondly, a pronounced strain rate effect is observed in body-centered cubic (BCC) grains and face-centered cubic (FCC) ultra-fine grains, leading to an elevated level of strain rate sensitivity. Finally, the MBIP effect is also observed in FCC coarse grains under dynamic loading. Moreover, the MBIP effect in FCC ultra-fine grains is more likely to occur at high strain rates due to the emergence of single-wall domain boundaries, which is not observed during quasi-static tensile testing. The present results provide new routes for designing impact-tolerant structures in advanced metals and alloys.

Integrity evolution during dissimilar welding of TWIP steel

The integrity evolution induced by manufacturing involving dissimilar TWIP and mild steel weld spots was investigated. Focus was given to the effect of manufacturing parametrization on controlling the dilution of the alloying elements and the resulting weld integrity. Samples manufactured with different conditions were characterized by chemical and phase composition, morphology, and mechanical properties. The findings showed that the distribution of chemical composition and metallurgical features are sensitive to the welding parameters. The influence of manufacturing on weld morphology was noticed. Manganese distribution is affected by the welding cycle, thus leading to austenite destabilization and brittle behavior upon a quasi-static tensile shear strength test. A processing set was proposed to control manganese dilution and martensite transformation.

Design of a Wearable Real-Time Hand Motion Tracking System Using an Array of Soft Polymer Acoustic Waveguides.

Robust hand motion tracking holds promise for improved human-machine interaction in diverse fields, including virtual reality, and automated sign language translation. However, current wearable hand motion tracking approaches are typically limited in detection performance, wearability, and durability. This article presents a hand motion tracking system using multiple soft polymer acoustic waveguides (SPAWs). The innovative use of SPAWs as strain sensors offers several advantages that address the limitations. SPAWs are easily manufactured by casting a soft polymer shaped as a soft acoustic waveguide and containing a commercially available small ceramic piezoelectric transducer. When used as strain sensors, SPAWs demonstrate high stretchability (up to 100%), high linearity (R2 > 0.996 in all quasi-static, dynamic, and durability tensile tests), negligible hysteresis (<0.7410% under strain of up to 100%), excellent repeatability, and outstanding durability (up to 100,000 cycles). SPAWs also show high accuracy for continuous finger angle estimation (average root-mean-square errors [RMSE] <2.00°) at various flexion-extension speeds. Finally, a hand-tracking system is designed based on a SPAW array. An example application is developed to demonstrate the performance of SPAWs in real-time hand motion tracking in a three-dimensional (3D) virtual environment. To our knowledge, the system detailed in this article is the first to use soft acoustic waveguides to capture human motion. This work is part of an ongoing effort to develop soft sensors using both time and frequency domains, with the goal of extracting decoupled signals from simple sensing structures. As such, it represents a novel and promising path toward soft, simple, and wearable multimodal sensors.

Mechanical and thermal properties of W-20Cu alloy for packaging HgCdTe IRFPA detector at cryogenic temperatures

Tungsten-copper alloy, as an electronic packaging material with excellent comprehensive performance, is widely used in the cooled packaging dewar structure of HgCdTe infrared focal plane detector. Thermodynamic properties (Coefficient of Thermal Expansion (CET), Thermal Conductivity (TC), Specific Heat Capacity (SHC)), mechanical properties and microstructure of W-20 wt% Cu(W-20Cu) are investigated in the range of 300 K ∼ 4.2 K, respectively. The quasi-static tensile tests are carried out on an electronic universal testing machine to obtain the typical stress–strain curves and mechanical properties of W-20Cu. The yield strength (YS), ultimate tensile strength (UTS), elongation and shrinkage of the specimens are measured. Besides, the Scanning Electronic Microscopy (SEM) are applied to observe the microstructure of W-20Cu alloy. The results demonstrate that W-20Cu alloy has outstanding thermal properties of high strength and hardness, high specific heat and low heat capacity and expansion coefficient. Tensile properties of the alloy significantly improve at extremely low temperature, and compared with 300 K, the YS and UTS of W-20Cu increase by 30.68 % and 11.27 % at 77 K. At 4.2 K, the YS increase by 44.49 %, and the UTS increase by 17.20 %, while the plasticity and fracture toughness have a sharp reduction from 300 K to 4.2 K. All specimens exhibit brittle fracture characteristics. With the increase of W crystals cleavage ratio and W-W continuity, the microstructure continuity and uniformity are improved. The number of plastic dimples of Cu phase decreases and the dimples become shallow slightly.

Stereolithography for manufacturing of advanced porous solids

The aim of this paper is focused on benefits of stereolithography (SLA) technology for the fabrication of the lightweight lattice structures with potential for load-bearing function and high absorption of impact energy. SLA is an additive manufacturing technology employing the principle of liquid resins curing moderated by radiation of a wavelength from ultra-violet band where resulting material parameters are tunable by setting of the curing process. The batches of samples manufactured using three different resins were subjected to quasi-static uni-axial tensile and compression tests. Acquired data were processed to derive deformation behaviour expressed as stress-strain diagrams and fundamental material properties. Based on the knowledge obtained from the mechanical tests, the setup of the fabrication parameters, the most suitable resin for manufacturing of the lattice structures and the overall suitability of SLA technology for the fabrication of advanced porous materials, were determined.

Numerical and theoretical prediction of foreign object damage on AM355 simulated blade validated by ballistic impact tests

Foreign object damage (FOD) of aeroengine blade was a critical concern in aeroengine maintenance due to its potential impact on airworthiness. This study investigated FOD of simulated blades made of high-strength steel AM355 through a combination of experiments, finite element (FE) simulations, and theoretical analysis. Firstly, mechanical tests were conducted, including the quasi-static tensile tests at different triaxialities and temperatures, as well as Split-Hopkinson pressure bar (SHPB) tests. Experimental results showed that AM355 was sensitive to strain rate, with a 30.7% increase in yield strength observed at a strain rate of 3864 s−1. Then, a Johnson–Cook (J-C) model with failure criterion was developed and validated through FE analysis. The mechanical performance of AM355 was compared to that of TC4. Lastly, FOD tests accompanied by corresponding numerical simulations were conducted via the laboratory air gun device and the developed J-C model. The predicted notch morphologies and sizes agreed well with experimental observations, with the notch depth linearly increased with the increase of the projectile velocity. Finally, a FOD theory prediction model was developed through a spring-mass model based on Winkler's elastic-plastic foundation. The theoretical predictions were in good agreement with the numerical and experimental results, providing valuable insights for FOD assessment of real aeroengine blades.

STUDY ON THE VISCOELASTOPLASTIC PROPERTIES OF POLYTETRAFLUOROETHYLENE AND NANOCOMPOSITES WITH INCREASED WEAR RESISTANCE BASED ON IT. PART 1. MATERIALS, TEST PROGRAMS AND BASIC PROPERTIES

This is the first (introductory) article in a series of articles devoted to a comprehensive experimental study and modeling of the viscoelastoplastic properties of polytetrafluoroethylene and a number of composites with increased wear resistance based on it, obtained in recent years in the laboratories “Technology of Polymer Nanocomposites” and “Polymer Composites for the North” of the Ammosov North-Eastern Federal University by introducing layered silicates (mechanically activated kaolin and serpentine, magnesium spinel) and short basalt or carbon fibers as fillers. Data from quasi-static tensile tests of these materials under different loading programs are presented: a family of stress-strain curves (until failure) at different strain rates, loading and unloading curves at different strain rates, creep and recovery curves for different stress levels, etc. The basic scalar characteristics of materials are determined (instantaneous modulus, yield strength, stress and strain at failure depending on the loading rate, etc.), the influence of the composition and proportion of fillers on them, and their strain rate sensitivity are analyzed. After mechanical tests, changes in the microstructure of PTFE and composites with different filler contents in the destruction zones of the samples were studied using a scanning electron microscope. An initial analysis of the volume of test data accumulated over 2 years revealed high deformability of materials, pronounced hereditary properties, the ability of materials to creep (flow) under constant load and accumulate irreversible (plastic) deformation, very high strain rate sensitivity, a strong influence of small amounts of fillers on the structure and mechanical properties. A more detailed presentation of the entire volume of test data and effects found, a systematic study of the viscoelastoplastic properties of these materials with different filler contents and their detailed comparative analysis as well as detection of connection with wear resistance are the topics of subsequent articles in the series in 2023-2025.

Compressive and tensile behaviours of 3D hybrid auxetic-honeycomb lattice structures

Lattice structures have the potential for application in tensile conditions. However, limited studies have addressed tensile behaviours of such structures and compared them with their compressive behaviours. In this paper, re-entrant structure as the foundation was selected to develop new 3D hybrid auxetic honeycomb lattice structures, each characterized by a unique unit cell configuration that features interconnected centre auxetic honeycomb, differentiating it from 2D hybrid auxetic honeycomb structures. A series of uniaxial quasi-static tensile and compressive tests, followed by simulations were conducted on these structures to investigate and compare their energy absorption characteristics. The results show that there were significant differences between these structures in terms of their mechanical behaviours under tension and compression. Especially, the smallest value of energy absorption under tensile load was 86% higher than the largest value under compressive load. The stiffnesses of these lattice structures under tensile loading were about 84–122 times of those of the identical corresponding structures when they were compressed. Meanwhile, the progressive stretching, buckling and collapse mechanisms observed in these structures exhibited excellent stiffnesses and energy absorptions under tensile and compressive load compared to traditional 3D auxetic as the basic structure. The outer frame structure of lattice structures had a direct influence on Poisson's ratio. The work indicates that the stiffness and energy absorption of the traditional 3D auxetic structure can be enhanced by embedding auxetic and honeycomb umbrella shaped elements.

Miniaturized S-shaped flexible magnetic pulse welding coil design for engineering applications

Magnetic pulse welding (MPW) as a new solid-phase welding technology in the manufacturing field has vast application prospects. However, the application of MPW in engineering is severely limited by the large working area required for existing coils resulting in poor flexibility of the process. In this paper, a highly flexible, miniaturized S-shaped stereoscopic coil was proposed to reduce the working area required for the MPW process. The required working area was reduced to 32 × 30 mm. Numerical simulations were performed to determine the most suitable coil cross-section size. In addition, the feasibility of the coils was verified by welding AA5052 aluminum alloy and 316 L stainless steel through the new stereoscopic coils. Quasi-static tensile testing, laser microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS) were used to characterize the mechanical properties of the joints, weld interface morphology and element diffusion, respectively. It was revealed through simulation that the impact velocity of the new stereoscopic coil during MPW (342 m/s) was slightly higher than that of the conventional flat coil (327 m/s) at the same discharge energy. This indicated that the coil could achieve reliable welding. The AA5052-316 L joint welded by the new stereoscopic coil was demonstrated to be reliable by experiments. Furthermore, microscopic observation revealed that two effective bonding regions were formed at the interface. In addition, continuous interfacial waves and element diffusion were observed at the welding interface. Finally, the typical parts of AlFe double-cap beam structure were successfully welded by using a new stereoscopic coil. The coil is beneficial to broaden the application field of MPW.