Term Of Stress Research Articles

A modified cyclic elastoplastic constitutive model considering the variational dynamic recovery term of back stress for FGH95 under asymmetrical cyclic loading

The asymmetric cyclic loading process occurs in aero-engine turbine discs. A constitutive model that accurately describes the cyclic elastoplastic behaviour of the material is important for structural design and low cycle fatigue life prediction of turbine discs. In this paper, the low cycle fatigue test of FGH95 was carried out at 620℃ under 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% and 1.1% strain amplitude with strain ratio equal to 0. The material exhibited cyclic hardening followed by cyclic softening at high strain amplitudes and cyclic softening at low strain amplitudes. The mean stress relaxation rate was similar for each strain amplitude. In addition, the evolution of effective stress and back stress was obtained through the method of internal stress division. Then, the relationship between the change in stress amplitude and the change in internal stress was discussed. The results showed that with cyclic loading, cyclic hardening/softening of FGH95 was affected by the competition mechanism of back and effective stresses. Considering that slip deformation and crystal lattice rotation coexist in plastic deformation, the dynamic recovery term of the Abdel-Karim and Ohno model was used. In order to characterize the different magnitudes of back stress change in materials at different plastic strain intervals, a dynamic recovery term coefficient was introduced to the dynamic recovery term and the critical surface of the back stress. The modified model was used to compare with experimental results. Then, it gives a good description of the material’s mean stress relaxation and strain amplitude variation and gives good agreement on the hysteresis loop.

Oxidation of a conventionally cast Cantor high entropy alloy in an argon flow during creep tests at high temperature

A conventionally cast version of the Cantor alloy (equimolar in Co, Ni Fe, Mn and Cr) was elaborated and samples were cut to carry out three points flexural creep tests according to a (1000, 1050, 1100°C)  (10, 20 and 30 MPa) array to explore the possibility of use in term of temperature and stress. For a majority of cases the deformation rates were too high, revealing a lack of practical interest, except for 10 MPa for which, whatever the temperature tests longer than 100 hours were realized. These tests were all performed under a slow flow of argon o preserve the alloy from oxidation during the tests. In fact, oxygen present as impurity (about 10 ppm) induced a signification oxidation of the samples which were covered by complex oxides involving Mn and Cr in various proportions and for different stoichiometries for the oxygen importance point of view, with thickness not far from what can be obtained in synthetic air for similar conditions.

Investigation of the critical state behavior of unsaturated silty sand with different fine contents in terms of net and effective stresses

This paper investigates the effect of fine content and matric suction on the behavior of silty sand soil through both net and effective stress variables in the critical state soil mechanics framework. For this purpose, a set of CD triaxial tests in saturated and unsaturated states were performed on the samples of sand with different fine contents. The results showed that in term of net stress variables the position of the critical state line (CSL) in stress space for a given non-plastic fine depend on suction. However, these lines approach each other by choosing a proper effective stress relationship. The CSLs in the coordinates of the void ratio in the term of effective stress changed as a function of the non-plastic fine content and matric suction. However, using the concept of the equivalent intergranular void ratio and considering a special mean effective stress variable depending on suction, the CSLs were converged so that a single line can be defined to describe the behavior of the silty sand at the critical state. Finally, the stress-dilatancy relationship of two constitutive models was examined and it was shown that the use of the equivalent state parameter could facilitate the use of these relationships.

Role of Surface-Active Element Sulfur on Thermal Behavior, Driving Forces, Fluid Flow and Solute Dilution in Laser Linear Welding of Dissimilar Metals

Understanding heat and mass transfer and fluid flow in the molten pool is very helpful in the selection and optimization of processing parameters, and the surface-active element has an important effect on the heat and mass transfer in laser welding of dissimilar metals. A three-dimensional (3D) numerical model coupled with a sub-model of surface tension, which considers the influence of local temperature and the concentration of surface-active element sulfur at the gas/liquid surface, is used to analyze the thermal behavior, driving forces, fluid flow, and solute dilution during laser linear welding of 304SS and Ni. The relationship between surface tension, driving forces, and the temperature coefficient of surface tension with the spatial distribution of temperature and the surface-active element sulfur is quantitatively analyzed. The simulation results show that the molten pool is fully developed at 45 ms, and the collision of inward and outward convection, with the maximum velocity reaching 1.7 m/s, occurs at the isotherm with a temperature between 2200 K and 2500 K. The temperature-gradient term and concentration-gradient term of surface shear stress play different roles in different positions of the free surface. The local sulfur concentration changes the temperature sensitivity of the surface tension at different sides of the free surface and further determines the transition of convection. Complex fluid flow promotes solute dilution, and the distribution of solute becomes uniform from the front to the rear of the molten pool. The Ni element is transferred to 304SS mainly at the rear side. The work provides theoretical support for the control of joint quality by changing the content of surface-active elements in dissimilar welding.

Uniaxial compressive behaviour of mortar cylinders reinforced with crimped NiTi shape memory alloy fibres

This study investigated the axial compressive behaviours of cement mortar reinforced with crimped shaped memory alloy (SMA) fibres produced by cold drawing. The performance of the crimped fibre was investigated in term of tensile behaviour, deformation recovery, recovery stress and pullout behaviour. After that, compressive tests of mortar reinforced with two types of SMA fibres, namely, dog-bone-shaped fibres and crimped fibres, were conducted to compare their compressive behaviours. The results showed that both types of SMA fibres increased the compressive strength of mortar, and a 1.0% volumetric ratio of SMA fibres is effective to increase the compressive strength of mortar, whereas a 0.5% volumetric ratio did not significantly increase the compressive strength. The recovery stress of the SMA fibres induced by the shape memory effect does not significantly increase the compressive strength of mortar. However, when crimped SMA fibres with a 1.0% volumetric ratio were heated and recovery stress was induced, they controlled volume expansion more effectively after cracking than crimped SMA fibres without recovery stress. The findings indicate that crimped SMA fibre with recovery stress can provide crack-bridging capacity.

MOTIVATIONAL FACTORS ASSOCIATED WITH SPORTS PARTICIPATION AMONG ATHLETES

Background: Successful athletes are motivated for future-oriented for more achievements. Apprehensive athletes are not as successful as highly motivated athletes. The sport participation is influenced by many factors those contribute in success of athletes. Objective: To explore the motivational factors for sports participation among Pakistani athletes. Methodology: The cross-sectional survey was conducted on both male and female athletes (n=400) between the age of 14 to 40 years, played at the national and international levels at least from one year. The study was conducted at the Pakistan sports board (PSB) from July-December 2018. The non-probability convenience sampling was used in this study. The sports participation scale-6 was used to explore the motivational factors. The data was presented as n(%). Results: the mean age of the participants were 24±5.45 years The results showed that the mean scores of six categories of Sports Motivational Scale (SMS) was 134.69±13.431, which showed that majority of athletes were highly motivated. The result of the study also showed that all subdomain of sports motivation scale positively correlated to total score (p<0.001), while a motivation was negatively associated r=-0.701, p<0.001) with total score of sports motivation scale. Although most of the athletes were normal in term of depression, anxiety, and stress. But depression is negatively correlated (r=-0.09, p=0.04) with sports motivation. Conclusion: This study concluded that most athletes are motivated because hard training improves their performance and other motivational factors are also associated like pleasure, internal satisfaction, and excitement. The least motivational factor was achieving social or material benefits of being an athlete. Keywords: Athlete, motivation, participation, stress.

Perceived Social Support Attenuates the Association between Stress and Health-Related Quality of Life among Adults Experiencing Homelessness.

Health-related quality of life (HRQoL) is defined as a multidimensional subjective assessment of one’s physical and mental health. Homelessness is associated with numerous stressors that can reduce HRQoL. Social support is defined as the availability of individuals, or resources provided by individuals, to cope with stress. Interpersonal social support may be important in buffering HRQoL from the negative implications of stress. Here, we examine this association in a marginalized group known for high rates of physical and mental health comorbidities: adults experiencing homelessness. Participants (N = 581; 63.7% men; Mage = 43.6 ± 12.2) were recruited from homeless-serving agencies in Oklahoma City. Social support was measured with the 12-item Interpersonal Support Evaluation List (ISEL). HRQoL was measured by the Behavioral Risk Factor Surveillance System (BRFSS) survey using self-rated health, the number of poor mental and poor physical health days over the preceding 30 days, as well as the number of limited activity days as the result of poor mental and/or physical health. Perceived stress was assessed using the 4-item Perceived Stress Scale (PSS). The potential moderation effect of social support was examined by assessing the interaction term of social support and stress in a series of linear regression analyses, controlling for sex, age, months homeless, race, education, health insurance status, serious mental illness diagnosis, and recruitment agency/site. There was a significant interaction effect of social support and stress on the prediction of days of poor physical health, days of poor mental health, and days of limited activity (p in all cases ≤ 0.05). Results add to a growing literature on the potentially protective benefits of social support for HRQoL, extend them to a large sample of adults experiencing homelessness in the South, and demonstrate the significance of this moderating effect of social support over and above the influence of several prominent sociodemographic and diagnostic variables. Future work should determine if interventions designed to enhance social support can buffer HRQoL from the deleterious effects of stress among this vulnerable population.

Estimation of the creep crack-tip stress field considering the effect of threshold stress

Because of the presence of second-phase particles or nanoscale particles, a term of threshold stress incorporated into the power-law creep model of some materials, such as magnesium, aluminum, and chromium alloys. The estimation of the creep crack-tip stress field for these materials is notably important to facilitate their exploitation in high-temperature structures. In the present work, a two-term asymptotic expansion of the stress field is developed to predict the creep crack-tip stress field for power-law creep materials with threshold stress. The finite element method is used to verify the accuracy of the two-term asymptotic expansion of the stress field. The simulation results reveal that the two-term asymptotic expansion of the stress field is accurate enough as an engineering method in estimating the creep crack-tip stress field. In addition, the existing estimation method of the time-dependent C-integral of C(t) can be directly implemented in power-law creep materials with threshold stress.

The most appropriate titanium mesh cage size for anterior spinal reconstruction after single-level lumbar total en bloc spondylectomy: a finite element analysis and cadaveric validation study

PurposeThere is little information available regarding the cage diameter that can provide the most rigid construct reconstruction after total en bloc spondylectomy (TES). The aim of this study was thus to determine the most appropriate titanium mesh cage diameter for reconstruction after spondylectomy.MethodsA finite element model of the single level lumbar TES was created. Six models of titanium mesh cage with diameters of 1/3, 1/2, 2/3, 3/4, 4/5 of the caudad adjacent vertebra, and 1/1 of the cephalad vertebra were tested for construct stiffness. The peak von Mises stress (MPa) at the failure point and the site of failure were measured as outcomes. A cadaveric validation study also conducted to validate the finite element model.ResultsFor axial loading, the maximum stress points were at the titanium mesh cage, with maximum stress of 44,598 MPa, 23,505 MPa, 23,778 MPa, and 16,598 MPa, 10,172 MPa, 10,805 MPa in the 1/3, 1/2, 2/3, 3/4, 4/5, and 1/1 diameter model, respectively. For torsional load, the maximum stress point in each of the cages was identified at the rod area of the spondylectomy site, with maximum stress of 390.9 MPa (failed at 4459 cycles), 141.35 MPa, 70.098 MPa, and 88.972 MPa, 42.249 MPa, 15.827 MPa, respectively. A cadaveric validation study results were coincided with the finite element model results.ConclusionThe most appropriate mesh cage diameter for reconstruction is 1/1 the diameter of the lower endplate of the adjacent cephalad vertebra, due to its ability to withstand both axial and torsional stress. According to the difficulty of large size cage insertion, a cage diameter of more than half of the upper endplate of the caudad vertebrae is acceptable in term of withstand stress. A cage diameter of 1/3 is unacceptable for reconstruction after total en bloc spondylectomy.

Design and Research of Double-Layered Cemented Carbide Novel High-Pressure Die

To improve the pressure-bearing capacity, a novel high-pressure die with cemented carbide as the first layer of supporting ring was designed. The novel high-pressure die increases the ultimate load-bearing capacity of the high-pressure die by increasing the pretension of the tungsten carbide cylinder. As the volume of the cemented carbide increases, the difficulty of manufacturing increases, therefore, to reduce the manufacturing difficulty of the cemented carbide supporting ring and reduce the shear stress of the supporting ring, the cemented carbide supporting ring is splited. And through reasonable derivation calculations, the calculation formula suitable for the optimal interference amount of the high-pressure die is obtained. The numerical analysis results show that: when a pressure of 6.2 GPa is applied on the inner wall of the tungsten carbide cylinder, high-pressure die mold that uses cemented carbide as the first layer of support ring (hereinafter referred to as double-layered cemented carbide novel high-pressure die) is lower than the ordinary high-pressure die in term of circumferential stress by 93.34%. In terms of von Mises stress by 21.4%, and term of maximum shear stress by 21.37%. The three principal stress images of the two molds are drawn, which proved that the double-layered hard alloy novel high-pressure die can fully exert the performance of the material and can withstand greater pressure.

Design development and analysis of cylindrical spring with variable pitch for two wheelers

Technological advancements are growing at a rapid rate for comforting mankind. Every sector including manufacturing, aerospace, and automobile are growing in terms of technical enhancements, material development and design innovations. An attempt has been made in this investigation to design the spring system used in the suspension system. A suspension system or shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. In a vehicle, it reduces the effect of travelling over the rough ground, leading to improved ride quality, and increase in comfort due to substantially reduced amplitude of disturbances. Hence, the design of spring in suspension system forms the vital designing component. Here, a spring is designed for which material consideration formed the basis of analysis owing to the impact loads the spring experiences during the working cycle. The spring design combines two basic designs i.e. variable pitch and cylindrical designs to amalgamate the advantages and eliminate the drawbacks of individual designs. A 3D model was generated using SolidWorks software which was further imported in another software i.e. ANSYS to analyze various mechanical parameters. A material study was carried out in terms of mechanical properties for the selection of spring material. The selected material were alloy steel (vanadium chrome spring steel) and high carbon steel (music wire spring steel) which is commonly used. The analysis was carried out by varying the applied load on the spring and it was recorded in term of stress and deformation. It can be inferred that the results of analysis showed spring was designed successfully and fulfilled the motives of two basic spring designs in a single combined spring structure. The result was also in accordance to the previous research which showed alloy steel as a promising material for the springs in the suspension system of the vehicle.

Application of Portable Soil Strength Probe on Bengkalis’ Peat

Peat shear strength measurement in the laboratory is very challenging because undisturbed sampling of very soft peat is very difficult to get. Traditional in-situ test such as standard penetration test (SPT) and cone penetration test (CPT) on peat also have problems i.e. they are very heavy and the measurement is not sensitive on very soft peat. This study described the application of portable soil strength probe on peat. The tool can measure penetration resistance in term of stress and torsion in newton meter. Peat samplings and physical laboratory tests were also conducted. The location of the study is Bengkalis Regency, Riau Province. The result revealed that peat (up to 6-meter depth) at the location is mainly sapric, low ash content with water content more 1000%. Penetration resistance is predominantly 400 kPa. While shear test depicts that peat is mainly frictional with friction angle mainly between 17-21 degrees and very low cohesion i.e. 0.8-3kPa. This study revealed that fibre content correlate moderately with penetration resistance and shear strength. this preliminary work suggested that soil strength probe may be useful for peat characterization.

Liquid metal droplet-enabled electrocapillary flow in biased alternating electric fields: a theoretical analysis from the perspective of induced-charge electrokinetics

The phenomenon of Marangoni chaotic electroconvection of electrolytes induced by liquid metal droplets has been serving as a method of choice for pumping of microfluidics in the past ten years. Although an external additional alternating voltage, usually being sufficiently small, was invariably employed in practical experiments for stabilizing the unidirectional liquid motion caused by a preexisted direct-current electric field, its subtle effect on the superimposed non-uniform surface tension and the final fluid transport state is still theoretically unclear. From the physical perspective of induced-charge electrokinetics, we present herein an analytical criteria for the conditions under which a sessile metal drop can actuate unidirectional liquid motion passing across it affected by a biased alternating voltage signal, wherein a mechanical balance between the linear pump pressure and nonlinear bipolar stress components exerted on the conducting drop surface has been taken into account. For accuracy validation, a numerical model was developed, in which multiple frequency electrochemical polarization was calculated under the Debye–Huckel limit, and coupled to the mechanical problem via inserting the resultant surface tension gradient as a source term of electrocapillary stress at the droplet–medium interface. The analytical solution accords well with the simulation results, in terms of the threshold voltage amplitude for effective liquid transport along the static potential gradient. At last, we demonstrate that the effect of continuous electrowetting can be fully exploited for simultaneous pumping and extraction of microscale impurities in closed fluid loops embedding a network of three-dimensional floating electrode plates for invoking auxiliary dielectrophoretic attraction. These results prove invaluable for achieving a high degree of freedom manipulation of particle and liquid contents in modern microfluidic systems with flexible conducting microdroplets.

Experimental verification of the boundary conditions in the success of the Brazilian test with loading arcs. An uncertainty approach using concrete disks

The present work analyses the reliability of the Brazilian test with loading arcs. A new testing set up has allowed to determine in an effective way the real load of the failure initiation as this moment was not always or correctly detected by the universal testing machine. The instrumentation used is a simple and low-cost method that allows to know the possible pressure distribution in the contact zone as well as the final contact angle. It has been observed that the success of the test depends mainly on the surface finish of the parts involved, their geometric tolerances and the symmetry of the applied load. These boundary conditions have a direct effect in the contact pressure distribution. The possible failure modes observed experimentally have been simulated with the finite element methods. For this, the contact boundary condition has been changed and the possible stress distribution in term of Griffith equivalent stress has been obtained. The numerical analysis allows to study the influence of the initial contact condition on the success of the test and agrees with the experimental results. Furthermore, an uncertainty analysis in the expression of the tensile strength confirms that, when the test is valid, a crack appears suddenly in the central area of the disk, as observed experimentally, so there is no need to determine if the starting point is in the centre. Additionally, it has been observed that the initial crack length depends on the type of pressure distribution in the contact zone. Finally, a series of recommendations are given in order to minimize both the variability of the final contact angle and the risk of premature failure of the Brazilian disk.

The potential utilization of Polyethylene Terephthalate (PET) waste as fine aggregate replacement in asphalt mixture

One of the environmental issues in most regions of Indonesia is the large number of bottles made from poly-ethylene terephthalate (PET) deposited in domestic wastes and landfills. Due to the high volume of these bottles, more than 1 million m3 landfill spaces are needed for disposal every year. The purpose of this experimental study was to investigate the possibility of using PET waste in asphalt concrete mixes as fine aggregate replacement to reduce the environmental effects of PET disposal. Based on the test results, in term of horizontal stress and indirect tensile stiffness modulus (ITSM) the use of waste PET waste increased the performance of the asphalt mixture prepared by the MBA.

Ultimate strength analysis of stiffened plate variation on double bottom of Floating Production Storage Offloading (FPSO)

Double bottom is part of the ship that must be evaluated from the loads for instance wave load acts on side hull and pressure from the outer bottom. The loads must be evaluated and investigated the effect on the double bottom structure. The objective of the present study is to analyze the ultimate strength of stiffened plate variation on the double bottom of the floating production storage offloading. The small section of stiffened plate with attached plating at the double bottom is considered to the analyzed. The numerical analysis is adopted to analyze the model. The stiffened plate is variated with the distance in terms of model breadth. The boundary condition is applied to the model including axial compression load. The behavior of the model is represented by stress and deformation. For the simple analysis, the welding residual stress, crack, and initial imperfection are not taken. The result obtains by the numerical analysis is presented together with the behavior in term of stress and deformation.

Plate deformation analysis on deck structure of jack-up

Any kind of deck on an offshore structure is very important to place everything and doing anything on it. The deck must be strong to withstand any load acting on it not only in vertical but also in a horizontal direction. Besides, many equipment placed in the deck, so that needs to be evaluated for the safety activities. The objective of the present study is to analyze the deck structure of jack-up under axial life load. The small section of the deck is taken and modeled consists of a plate and stiffened plate. The boundary condition is applied to the model including axial compression load. The thickness of the attached plating is simulated and analyzed to obtain the behavior of the model. The behavior of the model is represented by stress and deformation. For the simple analysis, the welding residual stress, crack, and initial imperfection are not taken. There are four cases for boundary conditions with different thickness of the model is analyzed. The result obtains by the numerical analysis is presented together with the behavior in term of stress and deformation.

Ultimate strength analysis of stiffened plate variation on the longitudinal bulkhead of Double Hull Oil Tanker

Loongitudinal bulkhead also gives significant effect to the longitudinal strength of double hull oil tanker. The stiffened plate attached at the longitudinal bulkhead must have enough strength to wishtand the liquid oil which has an impact to the longitudinal bulkhead correspond to longitudinal strength. The objective of the present study is to analyze the ultimate strength of stiffened plate on the longitudinal bulkhead of double hull tanker. The small section of stiffened plate with attached plating at the longitudinal bulkhead is considered to the analyzed. The numerical analysis is adopted to analyze the model. The stiffened plate is variated with the distance in terms of model breadth. The boundary condition is applied to the model including axial compression load. The behavior of the model is represented by stress and deformation. For the simple analysis, the welding residual stress, crack, and initial imperfection are not taken. The result obtains by the numerical analysis is presented together with the behavior in term of stress and deformation.

Study on tropical organic soil stabilization based on biogrouting

Biogrouting is a new environmental friendly stabilization method to stabilize soft soils by applying microorganisms. The microorganisms produce CaCO3, which fill voids of soil particles and bond the particles. This work studied biogrouting of high plasticity tropical organic soil applying Bacillus subtilis bacteria. In order to study the effectiveness of biogrouting using Bacillus subtilis, unconsolidated undrained triaxial and direct shear tests were conducted on the untreated and stabilized soils. The curing time for the stabilized soil specimens were 7, 14 and 28 days before the tests were conducted. In order to study the influence of the amount of Bacillus subtilis, 6 ml and 12 ml of Bacillus subtilis liquid culture was injected into the soil specimens. The soil became stronger as the amount of Bacillus subtilis used increased. The results indicated that the longer curing time and the higher amount of Bacillus subtilis reflected better soil improvement in term of cohesion, friction angle and shear stress. After 28 days of curing time, injection of 6 ml and 12 ml Bacillus subtilis liquid culture increased the effective stress cohesion values by 180% and 270%, respectively.

Experimental Investigation of Concrete Columns Enhanced by PVC Tubes

An experimental investigation of PVC-concrete columns is presented to assess the efficiency of using PVC tube for enhancing strength and ductility of PVC-concrete columns. Study was conducted to assess provided PVC casing confinement mechanism efficiency for enhancing strength and ductility of considered PVC- concrete columns. To investigate the composite mechanism and confining mechanism of the PVC tube, fabricated specimens are tested under uniaxial compression loading in two modes of load application; composite mode and confining mode. The results showed that the composite mode columns exhibit more strength improving than those of confining mode. The upgrading rate in sustained loading resistance of composite mode columns varied from 2.25 to 1.56, while it was 2.07 to 1.55 for confining mode columns. The same comparison is entirely reversed in scope of ductility, where confining mode columns exhibited more axial and lateral deformations than the corresponding composite mode columns. The results are normalized in term of radial stress (fr) and concrete compressive strength (f’e), determined enhanced confined concrete strength (f’ee) could be used to predicate plastic capacity of columns of different mechanism.