Decrease In Ultimate Strength Research Articles

Mechanical properties of bridge steel Q420qE at elevated temperatures

High-temperature mechanical properties of bridge steels, which were rarely investigated, are the foundation for fire resistance analysis and design of bridges. This study investigates the high temperature mechanical properties of Q420qE bridge steel by using steady-state tensile test method. Results indicate that this steel shows no yield plateau at both room temperature and elevated temperatures. Compared with the same grade structural steels, the decrease in elastic modulus and yield strength of Q420qE with increasing temperature are slower. However, the decrease of ultimate strength is more rapid, with a maximum difference on reduction factor being about 0.327 (41.92 %). The mainstream fire resistance design standards exhibit limitations in predicting the high temperature mechanical properties of Q420qE steel. Furthermore, predictive equations of mechanical property reduction factors of Q420qE at elevated temperatures were proposed, and constitutive model of Q420qE at elevated temperatures was recommended.

Effect of temperature on the mechanical properties of aluminum polycrystal using molecular dynamics simulation

The initial temperature has a considerable effect on aluminum polycrystals' physical stability and mechanical performance, with the possibility to optimize their mechanical properties for practical applications. Thus, using a molecular dynamics technique, the effect of temperature on the mechanical properties of aluminum polycrystals is studied. Stress-strain curves, ultimate strength, and Young's modulus were all measured at temperatures of 300, 350, 400, and 450 K. The findings from MD simulations show that the initial temperature significantly affects the physical stability and mechanical performance of designed aluminum polycrystals. The aluminum polycrystal experiences a numerical increase in ultimate strength and Young's modulus from 6640 to 74.072 to 7.055 and 79.226 GPa, respectively, when subjected to the optimal initial conditions of 350 K. With further increasing temperature to 450 K, ultimate strength and Young's modulus decrease to 6.461 and 74.413 GPa, respectively. The observed decrease in ultimate strength and Young's modulus of the aluminum polycrystal as the temperature increased from the optimal condition of 350 K–450 K can be attributed to the weakening of interatomic attraction forces at higher temperatures. This reduction in interatomic bonding strength resulted in decreased material stiffness and resistance to deformation, leading to lower ultimate strength and Young's modulus values. This study's novelty lies in its comprehensive assessment of the initial temperature's effects on the mechanical performance of aluminum polycrystals, providing valuable insights for practical applications and advancing beyond previous efforts in the literature.

О НЕОБХОДИМОСТИ УТОЧНЕНИЯ РАСЧЕТНОЙ МЕТОДИКИ ОЦЕНКИ ПРЕДЕЛОВ ОГНЕСТОЙКОСТИ МЕТАЛЛИЧЕСКИХ КОНСТРУКЦИЙ С УЧЕТОМ ПРОДОЛЖИТЕЛЬНОСТИ ИХ ЭКСПЛУАТАЦИИ

The paper discusses the issue of estimating the fire resistance limits of metal structures taking into account the duration of their operation. The results of the study of the influence of the duration of operation on the mechanical characteristics of steel structures, such as the ultimate strength, the yield strength and the relative elongation are presented. The study was conducted on a steel structure with a service life of more than 80 years. The results of static tensile mechanical tests showed that the ultimate tensile strength for the steel specimens in question is at a minimum level (a decrease in ultimate strength of 10–15 % or more). The conceptual opinion about the necessity of taking into account the change of strength and yield strength when assessing the fire resistance limits of steel structures of different service life has been expressed.

Механические характеристики стальных конструкций длительного срока эксплуатации при пожаре

The problem of fire resistance of metal building structures with a long service life is considered. The results of a study of the influence of a long service life of steel structures on the physical, chemical and mechanical characteristics (tensile strength, yield strength, relative elongation) at the elevated temperatures in relation to a steel structure with a service life of 92 years are presented. The steel structure was operated under stress conditions — bending under the load of a reinforced concrete flight of stairs. Due to long-term use, traces of the corrosion process are noticeable on its surface over its entire area. The results of the chemical analysis of test samples № 1, 2 are presented. According to GOST 27772—2021, it can be established that the steel under study corresponds to the standard content of the chemical composition of steel of strength class C345, with the exception of a 2-fold increased S content and an insufficient amount of manganese content. With increased sulfur content, steel becomes less strong and the steel resistance to brittle fracture decreases. This is confirmed by earlier work, which showed that increased sulfur content helps to reduce the mechanical characteristics of steel by 2 times. For the first time, the tests were carried out to assess changes in the mechanical characteristics of long-term steel structures under conditions of increased temperature (fire). A comparative analysis of the results of studies of mechanical tests at elevated temperatures for various steel grades was performed. It was established that for the studied samples of steels № 1, 2, long-term natural exposure at temperatures of 500 °C and 600 °C, the yield strength decreases by 23 % and 46 %, and the ultimate strength decreases by 42 % and 50 %, respectively. A tendency for a more intense loss of mechanical characteristics for steel structures of long-term natural aging under fire conditions was revealed.

Quantifying the Microstructure and Mechanical Property Differences between Bulk and Thin-wall Additively Manufactured Inconel 718

Multiple thermal excursions and rapid, uncontrolled cooling rates are inherent to additive manufacturing (AM). Differences in thermal conductivity between solidified metal and uncoalesced powder leads to disparate microstructures and properties near areas of high geometrical complexity relative to bulk regions. To quantify this effect for Inconel 718 (IN718) a series of micro-tensile dogbones were printed in 0.6 mm and 0.8 mm thicknesses using a contour + hatching strategy with either an aligned or rotated beam path and compared to a larger ‘bulk’ sample from the same print. The driving hypothesis for this study is that the lower cooling rates observed for areas in the thin-wall regime results in a coarser microstructure but with reduced texture and a resulting increase in strength due to a more uniform microstructure especially in the rotated case. Samples were characterized via micro-tensile testing and scanning electron microscopy. It was observed that thin-wall samples possessed significantly smaller grains than the Bulk samples (31.45 μm vs > 255.96 μm) by preventing the epitaxial growth of columnar grains that span many build layers as was observed in the Bulk samples. This difference led to the Bulk samples possessing an average ductility 30% higher than the thin-walls but a decrease in ultimate strength of over 25%. Quantifying and accounting for the geometry-dependent variability of microstructure and properties such as is shown in this study will be necessary to optimally design and build geometrically complex AM parts.

Finite Element Analysis of Sn-58Bi Shear Test

Finite element analysis (FEA) of quasi-static single lap shear test was conducted to study the mechanical properties of Sn-58Bi in terms of deformation, strain, stress, yield strength and ultimate strength. The study generated results of simulated behaviour of low temperature Sn-Bi solder alloy to address the demand of low temperature solder alloys in the electronic industry. The geometry was constructed in SolidWorks based on ASTM D1002 standard before being imported to ANSYS. The simulation was conducted at shear velocity of 0.1, 0.5, 1 and 1.27 mm/min and temperature of 138, 178, 208 and 238 °C using ANSYS. The simulation results were compared with the corresponding experimental results. Simulation results showed that an increase in shear velocity caused a decrease in ultimate strength and an increase in ductility of Sn-58Bi. As the velocity increased from 0.5 to 1.27 mm/min, the ultimate strength decreased from 339.87 to 291.24 MPa. This is predicted due to the Bi-rich layer within the lamellar structure of Sn-Bi alloy. An increase in temperature caused an increase in ultimate strength and brittleness in Sn-58Bi due to the trans-granular propagation of brittle failures along the weak Bi-abundant phase. As the temperature increased from 138 to 238°C, ultimate strength increased from 290.46 to 298.93 MPa.

Influence of the Addition of Alumina Nanofibers on the Strength of Epoxy Resins

The paper describes the effect of the addition of alumina nanofibers on the mechanical properties of the epoxy resin. Alumina nanofibers functionalized with epoxypropyl functional groups are used in this work. The dependence of the mechanical characteristics on the amount of the additive, as well as the features of its distribution in the material, is investigated. In the work, nanocomposites were obtained, which are epoxy resin with aluminum oxide nanofibers. The mechanical properties of the samples were studied by bending tests and differential mechanical analysis (DMA). It has been shown that the addition of alumina nanofibers leads to an increase in ultimate flexural strength. The maximum of this increase is near the percolation threshold of alumina nanofibers in epoxy resin. With the addition of 0.2% alumina nanofibers, the ultimate flexural strength increases from 41 to 71 MPa. It is shown that after exceeding the percolation threshold of nanofibers, the ultimate strength decreases. In this case, the elastic modulus increases from 0.643 to 0.862 GPa. DMA is shown that the glass transition temperature decreases with increasing amount of the additive. This indicates a decrease in the molecular weight of the polymer. By implication, this suggests that the hardener connects the epoxypropyl functional groups on the nanofibers and the epoxy groups in the resin, and as a result of this process, the nanofibers become natural polymer chain length limiters. The data obtained from mechanical testing and differential mechanical analysis can be used to strengthen epoxy resins in polymer composite materials and molding compositions.

Phase transitions and mechanical behavior of Ti-3wt.%Nb alloy after high pressure torsion and low-temperature annealing

The influence of microstructure and phase transitions on tensile strength, plasticity and microhardness of a Ti-3wt.%Nb alloy subjected to high pressure torsion (HPT) followed by annealing is studied in this work. The initial state of the alloy was the α-solid solution with a small amount of the β-precipitates. The characterization of microstructure and phase transitions has been performed using scanning and transmission electron microscopy as well as X-ray diffraction. During HPT, the grain refinement took place and the α-phase partially transformed into ω-phase. The tensile test of the HPT-deformed sample showed an almost two-fold increase of ultimate strength in comparison with the initial state, as well as lower plasticity. During the short-term annealing of the deformed state up to 250 °C, the grain size slightly increased, the density of the crystal structure defects decreased and ω-phase transformed back to the α-phase. Such microstructural changes led to an important growth of plasticity and a slight decrease in ultimate strength of the HPT-deformed alloy.

Ultimate strength and fracture failure of hull stiffened plates based on plastic accumulation under cyclic loading

Relying on nonlinear finite element analysis of ANSYS software, the ultimate strength and fracture failure of hull stiffened plates based on plastic accumulation have been studied under cyclic compression and compression-tension load. In addition, the shakedown is also preliminarily discussed. According to different cyclic load patterns, the influence of material models such as elastic-perfectly plastic, isotropic hardening, and Chaboche model on plastic accumulation, ultimate strength, and fracture characteristics of stiffened plates is mainly researched. Studies have shown that material models have a significant impact on the plastic accumulation region, plastic accumulation speed, and the ultimate strength of hull stiffened plates under cyclic loading. As the number of cycles increases, plastic accumulation will cause hull stiffened plates to fracture or reach a shakedown state. When the Chaboche model is adopted, the plastic accumulation speed of hull stiffened plates under cyclic loading is the slowest, and the decrease in ultimate strength is the most moderate. For the cyclic load amplitude and pattern selected in this study, when plastic accumulation causes stiffened plates to fracture, its ultimate strength drops to 24–55% of the first compressive ultimate strength.

Finite Element Analysis of Steel Plates with Rectangular Openings Subjected to Axial Stress

Steel plates with openings are among the important ship structural components used in the ship’s hull to withstand the hydrostatic forces of the ocean, which cause sagging and hogging moments at the ship’s bottom. The existence of openings on plates can cause structural rupture, stress concentration and a decrease in ultimate strength. This research is aimed at investigating the influence of selected parameters on the ultimate capacity of steel plates with rectangular holes subjected to axial stress, using ANSYS finite element analysis (FEA) under its non-linear static structural programme. The main parameters investigated in this paper are the plate thickness, opening aspect ratio, number of openings, position of openings, and the boundary condition of the plate. The influence of these parameters on the stress of plates and their deformation was evaluated. The comparison of the numerical simulation with the well-established analytical method using the Navier solution and Roark’s Formulas showed a good agreement.

Evolution of the Structure and Properties of Cu–6% Nb Microcomposite Wire during Long-Term Temperature Tests

The electrical conductivity, mechanical strength and crystal structure of Cu–6 wt % Nb microcomposite wire upon exposure to a temperature of 450°C for up to 2000 hours are investigated. Structural changes are compared with the ultimate strength and electrical conductivity. Several mechanisms of strength degradation with different time constants are identified. Within long times, the ultimate strength decreases by 32% from the initial value while the electrical conductivity increases by no more than 2%. Strength degradation is accompanied by the relaxation of microstresses in the copper matrix and structural changes in the nanoscale niobium component.

The Influence of Size Effect on Strength and Deformation Characteristics of Different Types of Rock Samples

This paper presents the results of the experimental study of the influence of sizes effect on the strength and deformation characteristics of samples of hornfels, limestone, sandstone, siltstone and ore-bearing rocks. Tests were performed on cylindrical samples of three sizes of diameters - 10, 30 and 60 mm under uniaxial compression and tension loading. The results of the study demonstrated that the values of ultimate strength decrease when the size of samples increases for the samples of cornea, limestone, sandstone and siltstone. The ultimate strength increases with increasing of sample size for ore-bearing rocks containing viscous inclusions. The samples of smaller size of ore-bearing rocks exhibit a brittle character of the fracture for all types of rocks, and the viscosity of fracture increases with increasing size of samples. the obtained regularities were analysed from the positions of otwo types of size effect (volume and surface).

Experimental investigation on timber-glass double-lap adhesive joints reinforced with nylon fabric

Adhesive technology is widely used and studied in different fields. This joining method allows to join different materials, assembling lightweight and solid structures. However, joints are usually the most vulnerable part of a structural system. A method of reinforcing adhesive joints is the insertion of elements inside the adhesive layer, to improve the mechanical performance of the joint both in terms of ultimate strength and stress distribution. In this paper, the effect of nylon fabric reinforcement inside the adhesive layer of timber-glass adhesive joints, according to different positions, is studied and discussed. Two different epoxy adhesives have been used in double-lap adhesive joints between treated and untreated timber (i.e. mahogany) and float glass adherends. Shear tests carried out on both reinforced and unreinforced joints showed a generalised increase in terms of ductility of the reinforced configuration accompanied by a decrease in ultimate strength.

L-shaped concrete-filled steel hollow-section columns under diagonal cyclic loading

L-shaped concrete-filled steel hollow-section (CFSHS) columns have the potential to be widely used as corner columns, and have the advantage of creating larger usable areas in buildings. However, few experimental tests of this kind of column under diagonal cyclic loading have been reported. Tests on eight L-shaped CFSHS columns with equal legs were conducted to study their hysteretic behaviour; the test variables were: loading angle, concrete compressive strength, axial load level and presence or absence of stiffeners. The failure process and modes, stiffness degradation, ductility and energy dissipation were observed, and lateral load–displacement hysteretic curves and envelope curves were plotted. The results show that L-shaped CFSHS columns have generally good hysteretic behaviour and that the displacement ductility coefficients are in excess of 3 in most cases. Columns with a loading angle of 45° have >10% decrease in ultimate strength but a slightly higher ductility than columns with a loading angle of 0°. The ultimate strength, ductility and energy dissipation of columns all decrease with increasing axial load levels. Discontinuously welded stiffeners can improve the ultimate strength and ductility, but the amplitude is limited. Finally, a finite-element model was developed; the predicted results agree well with the test results.

Progressive Collapse Analysis of Intact and Damaged Ships under Unsymmetrical Bending

This study examined the hull girder strength of intact and damaged ships by adopting the incremental-iterative method for progressive collapse analysis, which was extended to the general case of the unsymmetrical bending of beams with an arbitrary cross-section. The sources of an unsymmetrical loading, including rotation of the loading plane and section asymmetry caused by structural damage, are described. A fast and robust procedure is presented to determine the translation and rotation of the instantaneous neutral axis at each curvature increment when applying Smith’s progressive collapse analysis method. A series of analyses were conducted on a double hull VLCC and a bulk carrier, considering various loading plane angles and damage conditions. The decrease in ultimate strength and the influences of rotation of the instantaneous neutral axis and ship heeling are discussed. The proposed method can be used for a rapid and rational assessment of the hull girder strength under adverse conditions.

Characterization of mechanical and wear properties of ABS/SiO2 nanoparticles

Objective: In this present work, the SiO2 nanoparticles as filler materials and ABS as a matrix material taken for the injection molding process to prepare the specimens, after that, to study the enhancement of mechanical properties and wear performance of composite materials. Method/Findings: SiO2 nano particles are added to Acrylonitrile Butadiene styrene(ABS) polymer composites at various weight fractions. It is also found that tensile strength, hardness, and wear properties improved in reinforcement. A pin-on-disc type friction and wear monitor (ASTM G99) was employed to evaluate wear behavior of ABS/SiO2 polymer composites. In this experimental study, the input process parameters such as load, sliding distance, and speed are considered and optimized for the composite materials’ properties. Tensile tests and wear tests were conducted to examine, and the properties of the material were studied. Morphology of the fractured material was studied using SEM analysis. The wear debris observed to explore the flacks and groves of the content during wear test for this study Orthogonal array (L9) and control parameters. Applications/Improvements : The significant contributions of this work are the decrease of ultimate strength with increasing content of SiO2 in the composites, and the sliding speed conversed to 45.51% of the wear rate variation. Mechanical and wear properties of ABS/SiO2 nanoparticles polymer composites were studied further. Keywords: ABS; SiO2 Nanoparticles; tensile; hardness; wear; SEM

Evolution of microstructure and mechanical properties of the high-speed train bearing under different service periods

The microstructure and mechanical properties of high-speed train bearing are significantly influenced by the harsh service environment during the long-term service process, which is crucial for the safety and service life of bearing. In this paper, the outer ring of high-speed train bearing is taken as the research object. The microstructure of the outer ring under different service periods was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) combined with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The mechanical properties were measured by the MTS testing machine and microhardness tester. The evolution of microstructure and mechanical properties of the high-speed train bearing outer rings under different service periods was investigated by comparative analysis. The results show that, with the increase of the service period, the bainite in bearing outer ring become coarser, the number of acicular carbides increases, and size of microcracks increases. Moreover, the dislocation density and microhardness near the inner-surface of the outer ring increases slightly. However, both yield strength and ultimate strength decrease with the increase of the service period.

Experimental study on compressive behavior of concrete-filled GFRP tubular stub columns after being subjected to acid corrosion

This paper presents the results of axial compression tests of concrete-filled GFRP tubular (CFGT) stub columns after being subjected to acid corrosion. Fifty-four specimens subjected to acid corrosion and nine specimens untreated with acid solutions are axially tested. The main parameters considered in this study include the wall thickness of GFRP tube, concrete strength, PH value of acid solution, and immersion duration. CFGT stub columns after being subjected to acid corrosion are all failed with the fracturing of GFRP tube and crushing of core concrete. The ultimate strength of the CFGT stub columns corroded by acid solution decreases remarkably compared with those without acid corrosion. The longer the immersion duration, the lower the ultimate strength of the acid corroded CFGT stub columns. Immersion duration has the greatest influence on the percentage decrease of ultimate strength of the acid corroded CFGT stub columns, followed by the PH value of acid solution. However, the effects of the wall thickness of GFRP tube and concrete strength on the percentage decrease of ultimate strength can be neglected. Additionally, the finite element models are also developed for the acid corroded CFGT stub columns by the ABAQUS software and are verified with the experimental results.

Characterization of closed-die forged AZ31B under pure axial and pure shear loading

Extruded AZ31B was closed-die forged at a relatively low temperature of 250 °C. Quasi-static axial and shear tests in addition to cyclic pure axial and cyclic pure shear tests were performed to characterize the uniaxial response of the forged parts. To examine the effect of forging on the mechanical behavior of the material, quasi-static and fatigue response of the starting extruded AZ31B was also studied under axial loading. The forging process refined the grain structure and modified the crystallographic texture of the extruded AZ31B. The intensity of texture and the orientation of c-axis in the forged part were found to be controlled by the extent and the direction of plastic deformation, respectively. The modified microstructure resulted in insignificant effect on yield strength, slight decrease in ultimate strength, and enhanced failure strain of the forged AZ31B under axial loading. However, the forged AZ31B exhibited superior yield strength, similar ultimate strength, and lower failure strain under shear loading. The cyclic axial strength of the forging was similar to the starting extruded material under high strain amplitudes, but slightly superior under lower strain amplitudes, due to the development of a smaller tensile mean stress. The half-life hysteresis response for the forged material was asymmetric under large axial strain amplitudes, but it was symmetric under cyclic shear loading. This difference is originated from activation of twinning/ detwinning deformation under cyclic axial loading, while dislocation slip is the dominant deformation mechanism during cyclic shear loading. Fatigue fracture surface of forged AZ31B depicts that fatigue cracks were initiated from multiple locations under both cyclic axial and shear loadings.

Heat Treatment Map of Al2Ca-added AlSi11MnMg Pressure-Cast Alloy Plotted by Full Factorial Design of Experiment and Analysis of Variance

The methods of design of experiment (DOE), analysis of variance (ANOVA) and response surface (RS) are used to study the effect of heat treatment on the microstructure and mechanical properties of a novel AlSi11MgMn pressure-cast alloy with an addition of Al2Ca. After the high-pressure casting, the specimens are solution treated at 490°C for 15 min and quenched in cold water. After the solution treatment, the morphology of the eutectic silicon changes, the elongation increases, and the yield strength and the ultimate strength decrease. The effect of the aging temperature and time on the tensile mechanical properties is studied by 4 × 4 full factorial design of experiment. The response surface is plotted for the ultimate and yield strengths and for the elongation; three equations predicting satisfactorily the mechanical properties of the alloy as a function of the aging temperature and time are derived.