Changes In Strength Properties Research Articles

Identification of temperature and diffusion effects during helium swelling of the surface layer of a TiTaNbV alloy

The article presents the comprehensive analysis results of the connection between structural changes caused by the effects of deformation swelling and softening effects during high-dose irradiation with He2+ ions, alongside determines the kinetics of changes in structural and strength parameters contingent upon irradiation conditions (in the case of irradiation temperature variations). The interest in such studies is due to the need to study the influence of temperature factors on the diffusion mechanisms of implanted He2+ into the damaged layer of a high-entropy TiTaNbV alloy in the case of high-dose irradiation. At the same time, the study of such mechanisms makes it possible to determine not only the radiation resistance of TiTaNbV alloys, but also to expand the general understanding of the influence of the structural features of high-entropy alloys associated with deformation distortion of the crystal structure, which prevents diffusion and migration mechanisms of defect propagation in the damaged layer. During determination of changes in strength properties depending on irradiation conditions, it was found that irradiation temperature growth leads to both a rise in the degree of softening under high-dose irradiation and an increase in the thickness of the softened layer under high-dose irradiation. These changes indicate that at high temperatures, the diffusion of implanted ions is not restrained by structural distortions, which results in their migration to a greater depth exceeding the ion travel depth, which should be considered when designing the use of these alloys in the case of their operation in extreme conditions.

Investigation on the changes of strength properties and ultrasonic pulse velocity of granite and sandstone after high-temperature treatment and liquid nitrogen quenching

Investigation on the changes of strength properties and ultrasonic pulse velocity of granite and sandstone after high-temperature treatment and liquid nitrogen quenching

Study of the Mechanisms of Polymorphic Transformations in Zirconium Dioxide upon Doping with Magnesium Oxide, as Well as Establishing the Relationship between Structural Changes and Strength Properties

The aim of this work is to study the mechanisms of polymorphic transformations in ZrO2 ceramics doped with MgO with different concentrations during thermal isochronous annealing, as well as the effect of the phase composition of ceramics on the change in strength properties and resistance to mechanical stress. Solving the problem of polymorphic transformations in zirconium dioxide by doping them with MgO will increase the resistance of ceramics to external influences, as well as increase the mechanical strength of ceramics. According to the data of X-ray phase analysis, it was found that the addition of the MgO dopant to the composition of ceramics at the chosen thermal annealing temperature leads to the initialization of polymorphic transformation processes, while changing the dopant concentration leads to significant differences in the types of polymorphic transformations. In the case of an undoped ZrO2 ceramic sample, thermal annealing at a temperature of 1500 °C leads to structural ordering due to the partial removal of deformation distortions of the crystal lattice caused by mechanochemical grinding. During the study of the effect of MgO doping and polymorphic transformations in ZrO2 ceramics on the strength properties, it was found that the main hardening effect is due to a change in the dislocation density during the formation of a ZrO2/MgO type structure. At the same time, polymorphic transformations of the m—ZrO2 → t—ZrO2 type have a greater effect on hardening at low dopant concentrations than t—ZrO2 → c—ZrO2 type transformations.

Evaluation the Effects of Waste Glass Powder Mixed with Hydrated Lime on the Unconfined Compressive Strength of Clayey Soil

Stabilization of clayey soil is commonly used to enhance unfavorable engineering properties. The effects of silica additives on soil improvement have been considered recently, and documented research studies on the characteristics of problematic clays stabilized by silica additives are interesting for many researchers. Alternative waste disposal strategies that would be both economically beneficial and environmentally friendly have been identified by this study. In the present study, waste silica-based addition is used to stabilize clayey soil, and the time-dependent changes in strength properties are investigated. Unconfined compressive strength (UCS) tests were conducted on stabilized samples at various curing durations to investigate macro-level properties. The UCS test results revealed that the 7.5% of GP+ 5% L content was optimal for the clayey soil as the strength was increased by 166.06%. The addition of the glass powder with hydrated lime components to the clayey soil resulted in stabilized samples, indicating a dense and compact matrix and reduced soil porosity, which increased the mechanical strength, according to the SEM analysis. This curing reaction technique is very beneficial and economical for geotechnical engineering applications.

Study of the Reinforcement Effect in (0.5-x)TeO2-0.2WO3-0.1Bi2O3-0.1MoO3-0.1SiO2-xCNDs Glasses Doped with Carbon Nanodiamonds.

The purpose of this study is to examine the influence of carbon nanodiamonds on the reinforcement and hardening of telluride glasses, as well as to establish the dependence of the strengthening properties and optical characteristics of glasses on CND concentration. According to X-ray diffraction data, the synthesized glasses have an amorphous structure despite the addition of CNDs, and at high concentrations of CNDs, reflections characteristic of small crystalline particles of carbon nanodiamonds are observed. An analysis of the strength properties of glasses depending on the concentration of the CND dopant showed that an increase in the CND concentration to 0.10–0.15 mol. leads to an increase in hardness by 33–50% in comparison with undoped samples. The studies carried out to determine the resistance to external influences found that doping leads to an increase in the resistance of strength characteristics against destruction and embrittlement, and in the case of high concentrations, the change in strength properties is minimal, which indicates a high ceramic stability degree. The study of the radiation resistance of synthesized glasses found that the addition of CNDs leads to an increase in resistance to radiation damage when irradiated with gamma rays, while also maintaining resistance to high radiation doses. The study of the shielding characteristics found that the addition of CNDs is most effective in shielding gamma rays with energies of 130–660 MeV.

Physicomechanical properties of metal-polymer systems based on polypropylene

The influence of the concentration of nanoparticles of non-ferrous metals (aluminum and copper) on such physicomechanical properties of polypropylene as ultimate tensile stress, tensile yield strength, bending strength, elongation at break, heat resistance, melt flow rate is considered. The optimal concentrations of copper and aluminum nanoparticles have been determined, at which relatively high values of strength indicators are achieved. The influence of sulfuric vulcanization on the regularity of changes in strength properties has been studied.

Analiza MES i zmęczeniowa nawierzchni podatnych na podstawie modelowania rozkładu temperatury

The effect of temperature on asphalt pavement structure is of great importance due to the nature of binder used in the asphalt layers. An equivalent temperature is commonly applied to eliminate the effect of temperature dependence in calculations of mechanical properties of the asphalt and of the pavement. Equivalent temperatures, applied as constant values, are supposed to have the same effect on fatigue behavior of the pavement in the period of one year as the real varying weather conditions. The aim of the presented research was to compare the behavior of the pavement under realistic temperature data throughout a single year with the results of the traditional pavement design method. Temperature data were obtained from a previously established weather station. Binder viscosity and asphalt dynamic modulus were defined based on the temperature profile for asphalt layers divided into 19 sublayers. This subdivision was introduced to better reflect the changes in strength characteristics of the asphalt layers along the depth of the structure. Comparison with the simple calculation using the equivalent temperature method showed that the detailed model outlined in this paper can provide better prediction of the overall pavement structural capacity. The focus of this study is to apply asphalt layer discretization to reflect temperature variation and its influence on changes in strength properties of asphalt mixtures. Temperature at each sublayer was estimated using the German specification, dynamic modulus was determined using the Witczak model, and the structural analysis was performed employing the finite element method.

Study of change in beryllium oxide strength properties as a result of irradiation with heavy ions

The paper presents data on changes in strength properties, including data on microhardness, crack resistance, bending strength and wear of BeO ceramics as a result of irradiation with heavy accelerated ions. The following types of ions were selected as heavy ions: O2+ (28 MeV), Ar8+ (70 MeV), Kr15+ (147 MeV), Xe22+ (230 MeV). Radiation doses were 1013 -1015 ion/cm2 , which make it possible to assess the effect of both single defects arising from radiation, and cluster overlapping defective areas occurring at large radiation doses. During the studies carried out, it was found that an increase in the ion energy and, consequently, in the damaging ability and depth of the damaged area, leads to a sharp decrease in the strength mechanical characteristics of ceramics, which is due to an increase in defective areas in the material of the near-surface damaged layer. However, an increase in irradiation dose for all types of exposure results in an almost equilibrium decrease in strength characteristics and the same trend of change in strength characteristics. The obtained dependencies indicate that the proposed mechanisms responsible for changing the strength properties can, under certain assumptions, be extrapolated to various types of exposure to heavy ions in the energy range (25-250 MeV).

Influence of Sulphate Attack on Properties of Modified Cement Composites

Monitoring the condition of building structures based on composite materials in aggressive environments shows that the deterioration of basic properties occurs under the influence of various factors such as temperature and humidity changes, in addition to changes in the chemical composition of air environment. In addition, the composite materials during the operation must retain not only the mechanical properties laid down at the design stage, but also the electro-physical characteristics, regardless of the type of destructive effects. In the current study, the quantitative assessment of the result of the interaction of an aggressive sulphate-containing medium with composites modified with conductive and dielectric additives was carried out. The effect of sulphate attack on the specific electrical conductivity of cement composites was studied. The nature of the interaction was evaluated by changing the properties of the samples of the developed compositions under the influence of a single-normal solution of sodium sulphate. The analysis was carried out by means of potentiometric titration using the exchange interaction method by fixing the degree of absorption of sulphate ions and determining the concentration of calcium ions in the solution. The measurement of the solution potential allowed determination of the quantitative indicators of the rate of calcium hydroxide leaching from the sample structure, which is necessary to assess the intensity of the destruction process and determine the nature of the change in strength properties. Measurements of the electrical resistivity of samples under the constant influence of sulphate aggression were taken during 28 days of observation. A method for quantifying the effect of a sulphate medium on a cement matrix was proposed that enables the material durability to be predicted. The features of changes in the morphology of structural components after exposure to aggressive solution were determined by physical and chemical methods.

Assessment the Partial Welding Influences on Fatigue Life of S700MC Steel Fillet Welds

Fine-grained steels belonging to the HSLA group (High-Strength Low-Alloy steels) of steels are becoming increasingly popular and are used in both statically and dynamically stressed structures. Due to the method of their production, and thus also the method use to obtain the required mechanical properties, it is really necessary to limit the heat input values for these steels during welding. When applying temperature cycles, HSLA steels in highly heated heat-affected zones (HAZ) reveal intensive grain coarsening and also softening behaviour. This subsequently results in changes in both mechanical and brittle-fracture properties, and the fatigue life of welded joints. While grain coarsening and structure softening have a major effect on the change of strength properties and KCV (Charpy V-notch impact toughness) values of statically stressed welded joints, the effect of these changes on the fatigue life of cyclically stressed welded joints has not yet been quantified. The paper is therefore conceived so as to make it possible to assess and determine the percentage impact of individual aspects of the welding process on changes in their fatigue life. To be more specific, the partial effects of angular deformation, changes that occur in the HAZ of weld, and the notch effect due to weld geometry are assessed.

Study of changes in strength properties along section thickness of high-strength centrifuged and vibro-centrifuged concrete

Improving the efficiency of precast concrete products and structures can be achieved by creating thin-walled products of effective cross-sections from high-strength concrete the formation of which requires application of centrifugal methods of compaction. The paper discusses literature data on the issue of forming the structure of centrifuged concrete by the thickness of the section wall, taking into account different densities of the components of the molded concrete mass under the action of centrifugal forces during mold rotation during concrete compaction at a constant speed. The authors conducted a series of experimental studies to establish the nature of the change in strength properties along the thickness of cross section of products from heavy concrete made by centrifugation and vibrocentrifugation. As a result of experiments, it was found out that the density of samples of centrifuged structures decreases in cross section from the outer layer to the inner one. The greatest values of ultimate strength under axial compression and tension during bending are characterized by the outer layer, the smallest are characterized by the inner layer. The middle layer in terms of strength indicators is close to the average strength of the whole product. A feature of changes in compressive and tensile strength during bending of vibro-centrifuged products and structures compared to centrifuged layers is a smaller difference between the outer and middle layers and a significant difference between the outer and inner layers. It was established that the variability of the structure of high-strength concrete is less pronounced compared to the lower-grade concrete.

Assessment of Material Durability of Steam Pipelines Based on Statistical Analysis of Strength Properties—Selected Models

The paper presents a research method concerning the application of statistical prognostic models for assessment of material durability and operational reliability of steel for steam pipelines, whose operation has exceeded the working time of 100,000 h. Decisions on the admission of long-lived materials to work for power industry results from extensive diagnostic examinations are based on the results of tests of mechanical properties, microstructure degradation, and corrosion processes. Considering the economic reasons and available data published in diagnostic reports, the determination of failure-free operating time of steam pipelines is based on the results of static tensile tests—tensile strength (Rm); conventional yield point (Rp); elongation (A) and Vickers hardness (V), correlated with the operating time and the media type (fresh steam and secondarily super-heated steam) for the most sensitive element of a pipeline, namely the elbow. The results of changes in strength properties during operation are presented in the form of graphs of the analyzed material feature vs. operating time in the range from zero hours (for a new material) to 300,000 h, taking into account the impact of random and systematic disturbances within the adopted tolerance limits. It has been found that because of the R2 factor and significance level in the t-Student test for regression and correlation coefficients, exponential, hyperbolic and quadratic models are best fitted to empirical points. Based on the tensile strength results (Rm), it has been found that the forecast time of the steam pipeline ranges from 193,400 to 258,300 h. Taking the yield strength (Rp) into account, it has been ascertained that the time ranges from 225,000 to 293,000 h, and for the working time forecast of steam pipelines based on Vickers hardness results, it ranges from 192,100 to 246,800 h.

Analysis of failures of bearings of axle box unit with polyamide cages and prospects of increasing their service life

The article analyzes failures of bearings of the axle box unit with polyamide cages and investigates the influence of climatic conditions on operational characteristics of cages. It is determined that the greatest number of defects during the operation of polyamide cages occurs in the following periods: summer-autumn, autumn, winter, winter-spring, spring. The revealed dependence of the operational properties of polyamide samples on weather and climatic conditions in different seasons of the year allows predicting the change in the operational characteristics of the cage and taking measures to restore and improve them. The authors proposed a method of restoration and improvement of operational properties of cages by processing them using a technique of high-frequency electrothermy. Full-scale tests showed the high efficiency of the proposed method, expressed in reducing the weight of the samples as a result of moisture removal, as well as in an ambiguous change in strength properties. Their ambiguity lies in the fact that cages differently restore their original hardness indicators after processing. And in the periods corresponding to winter and winter-spring, it was possible to restore strength indicators to a level even above the original one. For high-frequency processing of polyamide cages, a device has been developed that provides the required coverage of the workpiece electrodes on the upper, lower and inner side surfaces of the partitions. The test of the developed device made is possible to achieve the desired results, expressed in a significant decrease in the relative humidity of the cages and an increase in their strength characteristics by 7.6% of the initial level. All this confirms the practical importance and progressiveness of the developments presented in the work.

The effect of transition metals on the structure and hardening of Al-Mg-Si alloys after cold plastic deformation

The effects of equal-channel angular pressing (ECAP) and rotary swaging (RS) on the change in strength properties during aging at 170 ° C of Al-Mg-Si alloys doped with Sc, Zr and Hf additions was studied. The methods of measuring hardness, electrical resistivity, testing mechanical properties, light and transmission electron microscopy were used. The higher hardening effect compared to the initial state was found in the alloys after ECAP than after RS, whereas the strength properties (tensile strength and yield strength) were higher for alloys subjected to RS than ECAP. Al-Mg-Si alloys with the combined additives of scandium with zirconium and scandium with hafnium showed practically the same values of hardness and strength properties at tensile testing during aging. The reason is in the identical nature of the decomposition of the supersaturated solid solution. It is determined by the sequence of precipitation of the strengthening phase Mg2Si and (Sc1-x, Zrx) Al3 and (Sc1-x, Hfx) Al3 dispersoids which impede the movement of dislocations both in alloys after deformation and after aging.

Weathering and deterioration of geotechnical properties in time of groundmasses in a tropical climate

Weathering and degradation of slope materials govern erosion and stability of slopes over time. Weathering is often ignored or over-simplified in engineering due to absence of time-series of material properties and uncertainty on future environment. The research in this paper investigates the rate of deterioration of geotechnical properties due to weathering over time after excavation of cut slopes in completely weathered material and residual soil in a tropical environment. Three cut slopes are studied with different excavation dates but with similar geological, geotechnical and groundwater conditions, identical slope aspect, and land cover. Index and strength properties are determined by field and laboratory tests. The results show that the hydro-mechanical properties of completely weathered material in cut slopes evolve very rapidly to those of residual soil within time spans of 30 to 90 years in a tropical-humid environment. The properties reduce so much that instability of cut-slopes is inevitable if this reduction is not taken into account during design and excavation of the slopes. Change of strength properties is around 1.1 to 1.3%pt. per year from the original completely weathered material strength at the time of excavation. This is based on simplified linear and logarithmic relationships. The deterioration of geotechnical properties is likely the main reason for many slope failures in cut slopes after many years of stability in the research area of Yên Bái City in Vietnam.

New construction: zero cycle aspects, modern methods and promising materials

This work is aimed at studying the physicochemical processes and establishing the functional dependence of the strength parameters on the sulfur concentration in the composite. The introduction of sulfur in the composite contributes to a change in strength properties, an increase in frost resistance. The dependence of strength on sulfur concentration was studied. The experimental function is determined analytically by solving a system of linear algebraic equations consisting of canonical equations of a given approximating function. The behavior of the dependence of strength on the concentration of nanotubes at two intervals is plotted graphically. Further studies are needed to gain a complete picture of the composite and its characteristics. Nowadays, the results of determining the deformative characteristics are being processed, the impact of the water-cement ratio, the equivalent economic assessment are being studied. At present, an analytical description of the physicochemical and physicomechanical dependencies is being carried out, and an aggregate mathematical model is being built. The results will be presented to the public at subsequent scientific and research conferences.

Microstructure of Soils of Different Geneses and Its Transformation in Constructozems of Moscow

The transformation of microstructure of constructozems was studied in a four-year-long (2012–2016) field experiment with the use of rheological and electron microscopy methods. Field studies were performed in the area of Moscow State University on three variants of artificial human-made soils (constructozems) differing in the structure of their profiles: (1) the control variant with the upper part composed of a homogenized Ap horizon, (2) the layered constructozem composed of a sequence of layers (Ap–peat–sand–Ap), and (3) the constructozem consisting of a mixture of the above-mentioned horizons. Electron microscopy attested to an increase in differentiation of the pore space in the upper Ap horizons in variants 1 and 2: new pores and chambers of different sizes appeared. In the loose porous mass of the peat layer in variant 2, more compact cohesive microstructures were formed. Microaggregation was identified in the upper layer of variant 3. Changes in the spatial arrangement of the solid phase of the soils were reflected in their rheological properties. A gradual increase in stability of structural bonds in the Ap horizon (variant 1) was detected. In variant 2, the underlying peat layer affected the shape of rheological curves in the Ap horizon. In variant 3, changes in strength properties of the mixed soil mass resulted in the formation of rheological behavior of fluid bodies typical of the plowed humus horizons.

Numerical analysis of the energy-intesive components of the vehicle body

The subject of the publication concerns the numerical analysis of the strength parameters of models of thin-walled energy-intensive structures, which include crushed the front struts of vehicle. The impact of the welding process the partial front struts. The results of the analysis of the models of unrepaired and repaired structures, taking into account changes of strength properties in the SWC and weld areas, will be compared in order to estimate the loss of primary strength properties.

Strength Criteria Based on Shear Failure Planes and Test Verification on Loess

Experimental results on loess preliminarily verified shear failure planes under axisymmetric compression stresses as well as their corresponding isotropic strength criteria, which exhibit the inherent natural structure behavior. However, when loading is applied to loess, its natural structure can be destroyed. Induced anisotropy complicates the structural behavior of loess. On the basis of shear failure planes responding to Mohr-Coulomb, Drucker-Prager, and Matsuoka-Nakai criteria, the axisymmetric compression spatially mobilized plane (AC-SMP) was carried out according to the following principles: (1) shear stress is directly proportional to normal stress, (2) failure strength is constant under axisymmetric triaxial compression, and (3) as the location of SMP changes with the rotation of principal stress axes, the isotropic failure criterion of AC-SMP is proposed. Changes in strength properties of loess with vertical microfractures and horizontal isotropy were investigated by true triaxial tests of loess under loading the major principal stress in the vertical and horizontal directions, respectively. True triaxial test results indicate the isotropic failure criteria of AC-SMP in a single direction. Comparison of the strength law under loading in the vertical microfractures direction with that in the horizontal direction displays the anisotropic strength of the natural structure of loess.

Influence of the new construction to settlement of historical building when accounting hardening of medium sand in basement

Currently, a number of difficulties arise in the construction of dense urban areas, as well as in the reconstruction and superstructure of existing buildings and structures. Often when carrying out geological scene investigation, it is not possible to determine the strength parameters of the soil directly under the foundation. In most cases, this leads to understating of its characteristics, which is reflecting in the excessive economic costs resulting from the need to strengthen the existing building structure. However, in many situations, this can be discarded, justifying it by calculations. In this paper is shows the performed series of numerical experiments and were analyzed the changes of existing building foundation settlements, taking into account its long-term exploitation in assessing the impact of new construction. The base had defined by a single-layer half-space with a limited depth of deformation zone and composed of medium-sized sand. PLAXIS 2D software was chosen to create the calculation model. When processing the results, it was possible to identify a certain dependence that allows estimating the maximum settlement of existing building in the impact assessing from new construction taking into account the duration of building operation. The obtained data prove the necessity to take into account the change in strength properties of soils caused by long-term loads action of structures.