Influence Of Yield Stress Research Articles

Influencia de las propiedades mecánicas del acero de alta resistencia en el comportamiento de muros de concreto

The behavior of reinforced concrete walls with high-strength steel (yield strength greater than or equal to 550 MPa [80 ksi]) is evaluated. The influence of yield stress (fy) and the tensile-to-yield strength (ft/fy) are analyzed by means of tests on T-shaped concrete walls. Additionally, the effects of uniform elongation (Esu) and fracture elongation (Esf) are evaluated. Two walls reinforced with Grade 690 or 830 steel (100 or 120) (fy = 690 or 830 MPa [100 or 120 ksi]) and with concrete strength of 55 MPa (8 ksi). Test results were compared with previous tests to validate changes in the Concrete Design Code (ACI 318). The data obtained suggest that walls with high-strength steel have a deformation capacity similar to walls reinforced with conventional steel (fy = 420 MPa [60 ksi]). However, the steel must satisfy ft/fy≥1.2,Esu≤6%yEsf≥10% for the walls to exhibit satisfactory behavior. ILIA: Investigaciones Latinoamericanas en Ingeniería y Arquitectura, No. 01, 2024: 91-99.

Sedimentation of elliptical particles in Bingham fluids using graphics processing unit accelerated immersed boundary-lattice Boltzmann method

Elliptical particles settling in Bingham fluids in a confined, the vertical channel is studied using the immersed boundary-lattice Boltzmann method to understand their sedimentation characteristics. The present elliptical particles-Bingham fluids two-phase systems involve a single particle, a pair of particles, a chain of particles, and a cluster of particles. The graphics processing unit (GPU) is used to improve computational efficiency. Special attention is placed on the influence of yield stress on sedimentation behavior. For a pair of elliptic particles, alongside the drafting–kissing–tumbling (DKT) mode or non-DKT sedimentation mode, a periodic sedimentation mode is found. The results indicate that two elliptic particles keep a kissing state and their trajectories and orientations periodically change during settling in the confined channel. For the elliptic particles chain, the first kissing occurs between the middle and lower particles regarding any Bingham number. Moreover, particles form the cluster for different inclination angles of the particle chain at the Bingham number Bn = 0.02. For the cluster of particles (15×15), the effect of vortex interaction around particles in Newtonian fluids is revealed, and the rheological property of the fluid–particle interaction in Bingham fluids is displayed. Overall, the role of yield stress on the sedimentation of elliptic particles is significant. With the acceleration of GPU, the present method has great potential for modeling large numbers of particles settling in non-Newtonian fluids.

An Incremental Contact Model for Rough Surfaces of Strain-Hardening Solids

The load–area relation of rough surfaces is of great interest in tribology. For elastic–plastic solids with strain hardening, an incremental model is adopted to analyze the contact of rough surfaces, in which the contact is modeled by accumulation of equivalent circular contacts with varying radius. For three typical rough surfaces with various material properties, comparisons with direct finite element calculations demonstrate the efficiency of this incremental contact model. An approximate linear relation between load and contact area is predicted by both methods up to a contact fraction of 15%. The influence of yield stress and strain-hardening exponent on the load-area proportionality is presented. This work gives a simple while effective method to calculate the load-area relation for rough contact of strain-hardening materials.

Elastic-Perfectly Plastic Contact of Rough Surfaces: An Incremental Equivalent Circular Model

Abstract In this paper, an incremental equivalent contact model is developed for elastic-perfectly plastic solids with rough surfaces. The contact of rough surface is modeled by the accumulation of circular contacts with varying radius, which is estimated from the geometrical contact area and the number of contact patches. For three typical rough surfaces with various mechanical properties, the present model gives accurate predictions of the load-area relation, which are verified by direct finite element simulations. An approximately linear load-area relation is observed for elastic-plastic contact up to a large contact fraction of 15%, and the influence of yield stress is addressed.

Formulation of alkali-activated fly ash-slag binders for 3D concrete printing

Printable alkali-activated mixtures, which are homogeneous under pressure and achieve buildability in 3D concrete printing by extrusion-based layer deposition are developed. A baseline mixture of alkali-activated fly ash and slag is modified by using dry constituents such as micro-silica and clay. Carboxymethylcellulose (CMC) is used with the alkaline activating solution as a viscosity modifier. The roles of the different elements in influencing the yield stress, viscosity, and thixotropic buildup in the mixture are evaluated. The influence of yield stress and viscosity in influencing shape retention in printable mixtures is evaluated. Buildability is identified with the thixotropic buildup of elastic modulus and yield stress in the mixture. Phase separation in the mixture under pressure is influenced by the particle size distribution and the viscosity of the activating solution. Mixtures which do not exhibit phase separation under pressure have a narrower distribution of particle sizes, indicated by the Rosin-Rammler fit. Clay and CMC enhance the thixotropic buildup in the alkali-activated mixture and also contribute to achieving homogeneous flow under pressure by mitigating phase separation.

Rheological and thermal properties of aerated sprayed mortar

This paper studies the rheological properties in aerated cement pastes in order to develop an aerated sprayed mortar with low thermal conductivity. For this purpose, different mixtures of cement with additions of metakaolin (MK) and sepiolite (SP) were tested. In addition, influence of yield stress on build-up thickness, as well as expansion speed and pore network were studied using cement pastes aerated with aluminum powder. At the same time, the volume increase during expansion, water retention and yield stress of the fresh foamed cement pastes were studied to characterize the fresh mortar. Results obtained show that the incorporation of siliceous fly ashes (SFA) in ordinary Portland cement together with additions of MK or/and SP provided the largest expansion speed increase and the lowest density of the aerated mortar. Pastes with greater yield stress show higher thermal conductivity but are better to be pneumatically gunited due to its bigger build up thickness. The most suitable paste from all them was selected, sprayed and aerated over ceramic bricks, checking the results on site. Results obtained by means of these tests confirm that is possible to spray an aerated mortar over vertical surfaces. In addition, this mortar has acceptable thermal insulation properties to be used in chambers of building façades and for external wall thermal insulation systems (EWIS).

Finite element investigation of inertia and viscous effects on regularized Herschel–Bulkley flows

Finite element simulations of regularized viscoplastic flows through a planar expansion is performed. The mechanical model is made up of the conservation equations of mass and momentum, coupled with a regularized form of the Herschel–Bulkley viscosity function, based on the Papanastasiou equation. This model is approximated by a three-field Galerkin least-squares method, in terms of the extra-stress tensor, the velocity vector and the pressure field. A sensitivity analysis is performed, aiming at an investigation of the influence of yield stress, shear-thinning and inertia effects on the flow pattern and pressure drop. The results show a strong dependence of the position and shape of the yielded and unyielded regions on Herschel–Bulkley and Reynolds numbers.

Modeling of the flow stress behavior and microstructural evolution during hot deformation of Mg–8Al–1.5Ca–0.2Sr magnesium alloy

Hot compression tests of Mg–8Al–1.5Ca–0.2Sr magnesium alloy were performed on the Gleeble-1500 machine at temperatures of 300, 350, 400, and 450 °C and strain rates of 0.01, 0.1 and 1 s−1. The flow stress behavior and microstructural evolution were followed. The work hardening was derived according to the Laasraoui–Jonas model. An improved approach, which considered the influence of yield stress on flow stress and the effect of grain boundary (GB) migration on the evolution of dislocation density during compression, was used to simulate the microstructural evolution, the flow stress and the volume fraction recrystallized of Mg–8Al–1.5Ca–0.2Sr magnesium alloy. The simulated results are in good agreement with experimental results.

Influence of yield stress and compressive strength on direct shear behaviour of steel fibre-reinforced concrete

This study aims in examining the influence of the paste yield stress and compressive strength on the behaviour of fibre-reinforced concrete (FRC) versus direct shear. The parameters studied are the steel fibre contents, the aspect ratio of fibres and the concrete strength. Prismatic specimens of dimensions 10 × 10 × 35 cm made of concrete of various yield stress reinforced with steel fibres hooked at the ends with three fibre volume fractions (i.e. 0%, 0.5% and 1%) and two aspects ratio (65 and 80) were tested to direct shear. Three types of concretes with various compressive strength and yield stress were tested, an ordinary concrete (OC), a self-compacting concrete (SCC) and a high strength concrete (HSC). The concrete strengths investigated include 30 MPa for OC, 60 MPa for SCC and 80 MPa for HSC. The results show that the shear strength and ductility are affected and have been improved very significantly by the fibre contents, fibre aspect ratio and concrete strength. As the compressive strength and the volume fraction of fibres increase, the shear strength increases. However, yield stress of concrete has an important influence on the orientation and distribution of the fibres in the matrix. The ductility was much higher for ordinary and self-compacting concretes (concrete with good workability). The ductility in direct shear depends on the fibre orientation and is significantly improved when the fibres are perpendicular to the shear plane. On the contrary, for concrete with poor workability, an inadequate distribution and orientation of fibres occurred, leading to a weak contribution of the fibres to the direct shear behaviour.

Influence of yield stress on free convective boundary-layer flow of a non-Newtonian nanofluid past a vertical plate in a porous medium

The effect of yield stress on the free convective heat transfer of dilute liquid suspensions of nanofluids flowing on a vertical plate saturated in porous medium under laminar conditions is investigated considering the nanofluid obeys the mathematical model of power-law. The model used for non-Newtonian nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing boundary-layer equations are cast into dimensionless system which is solved numerically using a deferred correction technique and Newton iteration. This solution depends on yield stress parameter Ω, a power-law index n, Lewis number Le, a buoyancy-ratio number Nr, a Brownian motion number Nb, and a thermophoresis number Nt. Analyses of the results found that the reduced Nusselt and Sherwood numbers are decreasing functions of the higher yield stress parameter for each dimensionless numbers, n and Le, except the reduced Sherwood number is an increasing function of higher Nb for different values of yield stress parameter.

Analytical solution for Newtonian–Bingham plastic two-phase pressure driven stratified flow through the circular ducts

For steady state, stratified, laminar, fully developed two-phase flow which one of them is Newtonian and the other one is Bingham plastic, the motion equations in horizontal pipe with appropriate boundary conditions have been solved analytically. Pressure drop, velocity distribution and location of plug region related to Bingham plastic fluid have been reported. The results show that the non-Newtonian rheological properties have negligible effects on two-phase velocity profile and consequently on pressure gradient in small viscosity ratio of two fluids. With promotion of viscosity ratio, the influence of yield stress on two-phase velocity profile is more considerable.

Relations between fracture toughness, hardness and microstructure of vacuum heat-treated high-speed steel

When modelling the fracture toughness of the investigated AISI M2 high-speed steel, the stress-modified critical strain criterion was used. The very important influence of microstructural parameters such as the volume fraction of undissolved eutectic carbides, their mean diameter, and the mean distance between the carbides, as well as the volume fraction of retained austenite in the matrix, was also taken into account. The influence of yield stress and fracture ductility was expressed in terms of the hardness of the steel. It was found that the plastic zone which develops, during fracture toughness measurements, ahead of the fatigue crack tip, was, as a rule, smaller than the prior austenite grain size, so that, in the case of the investigated high-speed steel, the size of these grains did not have any influence on the measured fracture toughness value. However, importantly, the calculated fracture toughness values, which were derived using a newly developed semi-empirical equation, agreed well with the experimental results obtained by the authors, as well as with results obtained by other authors.

The influence of microstructure on the fracture toughness of AISI M2 high-speed steel

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The effective threshold of fatigue crack propagation in aluminium alloys I. The influence of yield stress and chemical composition

Abstract The thresholds of effective stress intensity range ΔK eff th of a recrystallized and cold-rolled aluminium (pure), and aluminium alloys 6061, 7020 and 7075 were studied. A special technique to determine ΔK eff th very accurately was applied. The measured ΔK eff th value was about 0.85 MPa m1/2 in all alloys. The significant difference in the yield stress (it varies between 30 and 630 MPa) and the chemical composition does not influence ΔK eff th.

The effective threshold of fatigue crack propagation in aluminium alloys. I. The influence of yield stress and chemical composition

Abstract The thresholds of effective stress intensity range ΔK eff th of a recrystallized and cold-rolled aluminium (pure), and aluminium alloys 6061, 7020 and 7075 were studied. A special technique to determine ΔK eff th very accurately was applied. The measured ΔK eff th value was about 0.85 MPa m1/2 in all alloys. The significant difference in the yield stress (it varies between 30 and 630 MPa) and the chemical composition does not influence ΔK eff th.

Axial Fatigue Performance of Cold-Formed Steel Sections

During the expected service life of a transmission tower, the members are subjected to a large number of significant stress fluctuations resulting from alternating wind applications. Fatigue behavior due to repeated loading must therefore be considered in design. This study presents the fatigue-test results of 52 cold­ formed steel members. The experimental program involved the use of five cross-sectional shapes, two test temperatures (-50°C and 25°C), and two steel types, ASTM A715 grade 60 steel and CAN/CSA-G40.21-M 300W. A series of constant amplitude axial fatigue tests were conducted using a loading frequency that ranged from 1-2.5 Hz. All specimens were supported at the ends through bolted connections and were tested under load-controlled condition in a fUlly reversed load-cycle. Stress-strain response was monitored at different stages of the test until failure. A group of SoN and Load-N curves were developed for the purpose of determining the safe endurance limit. The results obtained could be used to establish guidelines for fatigue design of cold-formed steel sections. The experimental program was statistically designed, and was conducted under controlled conditions so that the analysis of the test data would reveal the parameters that were significant in describing the fatigue behavior of the test specimens. Three different types of steel were used to study the influence of yield stress on fatigue life. The types of steel used were ASTM A36, A441, and A514. This provided a range of nominal yield stress that ranged from 248-690 MPa. Nowhere in the available literature has there been an exten­ sive systematic investigation of the axial fatigue behavior of cold-formed steel members. An experimental program (Klipp­ stein 1981) conducted at the U.S. Steel Corporation Research Laboratory, Pittsburgh. Pa., involved 24 beam specimens fab­ ricated from sheet steel. This study indicated that the fatigue life of cold-formed sections was higher than that predicted by fatigue-design curves developed on the basis of tests on hot­ rolled sections. The study also showed that fatigue life is a function of the fabrication details and that it may be decreased substantially if holes or welds are present. Research carried out by Libertiny et al. (1977) has revealed that cold working of sheet-steel can improve the large cycle fatigue resistance, but may result in the degradation of small cycle fatigue resis­ tance.

Finite element analysis of dip coating with bingham fluids

AbstractA finite element analysis of the dip coating process with Bingham fluids is presented. The solution method for the viscoplastic flow problem was based on the augmented Lagrangian method allowing a rigorous treatment of the stress discontinuity. To compute the location of the free surface at equilibrium, an iterative method was used based on the arbitrary Eulerian‐Lagrangian approach in conjunction with mesh smoothing. Numerical predictions were validated against experimental data for the Newtonian limit case. Computations were then performed with Bingham fluids. The influence of yield stress on the meniscus flow Is discussed.

Heat transfer in bioreactors with dense suspension broths

A theoretical correlation for heat transfer in bioreactors, i.e. stirred tanks and bubble columns, with dense suspension broths having a yield stress has been developed. The theoretical predictions show that an increase in yield stress causes a decrease in heat transfer coefficient. At a fairly high degree of turbulence, however, the influence of yield stress is insignificant and the decrease in heat transfer coefficient is mainly attributed to the increase in plastic viscosity. Reasonable agreement is obtained between the predicted and experimental values of the heat transfer coefficient in stirred tanks and bubble columns.

Influence of material strength level on fatigue crack closure

Fatigue crack growth behavior of a medium carbon alloy steel (AISI 4130) has been investigated in two different heat treated conditions. The investigation also examines the influence of material strength level and fracture toughness on fatigue crack growth rate and fatigue crack closure behavior. Compact tension specimens with TL orientation were used. All specimens conformed to ASTM E 647 test requirements. All tests were carried out in constant amplitude tension-tension mode in room temperature environment under load control mode. Crack closure loads were measured by using a clip gage at crack mouth, as per tentative ASTM standard procedure. The results of the present investigation indicates that crack closure in this material does not depend upon the material strength level or K max . In the threshold as well as linear region crack growth rate was found to increase significantly with increase in yield strength and decrease in fracture toughness. However, in the linear region, the influence of yield stress on fatigue crack growth rate was found to be much more compared to threshold region. Crack closure load at threshold did not exhibit any appreciable decrease with increase in yield strength. The threshold was found to decrease with increase in load ratio ( R) and increase in yield strength.

Kinetic Energy Calculations for Non‐Newtonian Fluids in Circular Tubes

ABSTRACTExpressions to calculate the kinetic energy of Herschel‐Bulkley fluids flowing in circular tubes are presented. The influence of yield stress, consistency coefficient and flow behavior index are investigated. An equation ‐ based on theoretical considerations ‐ for determining kinetic energy from a kinetic energy correction factor is developed. Solutions are given in a graphical format to facilitate kinetic energy calculations.