Experimental and Numerical Research on Deformation Behavior of Thin-Walled and Large Expansion Ratio Guide Vane Liner in Hydroforming Process

Some tube hydroforming process tests and further research work were conducted to manufacture hollow guide vane liners( made of super alloy GH3030).The relative thickness( t0/ OD) of the tubular blank is approximately 0. 01,and the maximum expansion ratio( Dmax/ OD) of the needed part is more than 40%,and the length to diameter ratio of the expansion regionis more than 3. 0. It is very hard to manufacture this kind of ultra-thin-wall,curved axis and large expansion ratio tubular part without fracture and wrinkles. The success of the process is highly dependent on useful wrinkles with appropriate internal pressure and axial feeding. A simplified finite element model and a theoretical model are used for detecting the deformation behavior and forming laws. Further study results demonstrate that the useful wrinkles do not appear at the same time and middle-wrinkles need bigger axial force than tube-end-wrinkles and feeding-wrinkles. The wrinkles can transfer bigger axial force after its wave peak has come into contact with the die inner surface. The thickness thinning rate of the element at the peak is bigger than that at the trough. With the increase of the axial and hoop stress ratio,the critical buckling stress also increases. Microstructure examination results show that the grain size in the maximum thinning zone has been stretched and refined after the large deformation and annealing treatment.The process is feasible and the finished part is qualified.

Development and evaluation of a hot-rolled 780 MPa steel sheet with an ultra-high expansion ratio

This paper explores the development of a 780 MPa hot-rolled high-strength steel with an ultra-high hole expansion ratio(HER) by using a nanoprecipitation-controlled technology.Systematic analysis and evaluation of an industrially produced steel sheet have been performed to investigate the microstructure, nanoprecipitates, tensile properties, HER,bendability, and forming limit diagram.The newly developed 780 MPa hot-rolled high-strength steel sheet is composed of a fully ferritic microstructure of approximately 5 μm with precipitates of approximately 4-5 nm in ferrite grain interiors.The yield strength and tensile strength can reach above 700 and 780 MPa, respectively.Moreover, the fractured elongation is higher than 19% in the transversal direction, and the average HER exceeds 70%.Furthermore, the newly developed 780 MPa high-strength steel has good bendability reaching R/t=0.2 at 90°.Compared with the conventional 780 MPa high-strength steel, the newly developed 780 MPa high-strength steel exhibits superior forming ability, which is suitable for the production of complex components.High-cycle fatigue indicates that the fatigue limit of the newly developed high-strength steel is 430 MPa under a stress ratio of r=-1,indicating good fatigue properties.The excellent combined mechanical properties of the newly developed 780 MPa high-strength steel are attributed to the grain-refined ferritic microstructure with nanoprecipitates in ferrite grain interiors.

An experimental study of salt expansion in sodium saline soils under transient conditions

Salt expansion in sulfate saline soils that are widely distributed in northwestern China causes serious infrastructural damages under low-temperature conditions. However, the mechanism of salt expansion under low temperatures is not clear. In this study, we conducted a series of cooling experiments combined with salt crystallization to study this mechanism, and employed an ionic model to calculate the supersaturation ratio of the solution. During the experiments, the strength and the process of salt expansion were examined under different cooling rates and various crystal morphologies. The relationship between temperature and supersaturation ratio under transient conditions was also considered. Results indicate that the initial supersaturation ratio of a sodium sulfate solution is closely related to environmental conditions, and that this ratio decreases with slowing the cooling rates and stabilizing the crystal forms. Higher initial supersaturation ratios lead to an increased non-steady-state zone, resulting in less salt expansion. On the other hand, chloride ion content has a distinct influence on the crystallization supersaturation ratio of the sodium sulfate solution, and higher chloride ion content can inhibit salt expansion in sodium saline soils. These findings help explain salt expansion mechanisms in complex conditions such as seasonally frozen soils, and thus help search for improved methods of preventing salt expansion in sulfate saline soils.

Homotopy analysis solutions for the asymmetric laminar flow in a porous channel with expanding or contracting walls

In this paper, the asymmetric laminar flow in a porous channel with expanding or contracting walls is investigated. The governing equations are reduced to ordinary ones by using suitable similar transformations. Homotopy analysis method （HAM） is employed to obtain the expres- sions for velocity fields. Graphs are sketched for values of parameters and associated dynamic characteristics, especially the expansion ratio, are analyzed in detail.

Flow of micropolar fluid between two orthogonally moving porous disks

The unsteady, laminar, incompressible, and two-dimensional flow of a mi- cropolar fluid between two orthogonally moving porous coaxial disks is considered. The extension of von Karman＇s similarity transformations is used to reduce the governing partial differential equations （PDEs） to a set of non-linear coupled ordinary differential equations （ODEs） in the dimensionless form. The analytical solutions are obtained by employing the homotopy analysis method （HAM）. The effects of various physical param- eters such as the expansion ratio and the permeability Reynolds number on the velocity fields are discussed in detail.

Hydrodynamics of gas-solid fluidization of a homogeneous ternary mixture in a conical bed:Prediction of bed expansion and bed fluctuation ratios

Hydrodynamic characteristics of fluidization in a conical or tapered bed differ from those in a columnar bed because the superficial velocity in the bed varies in the axial direction. Fixed and fluidized regions could coexist and sharp variations in pressure drop could occur, thereby giving rise to a noticeable pressure drop-flow rate hysteresis loop under incipient fluidization conditions. To explore these unique properties, several experiments were carried out using homogeneous, well-mixed, ternary mixtures with three dif- ferent particle sizes at varying composition in gas-solid conical fluidized beds with varying cone angles. The hydrodynamic characteristics determined include the minimum fluidization velocity, bed fluctuation, and bed expansion ratios. The dependence of these quantities on average particle diameter, mass fraction of the fines in the mixture, initial static bed height, and cone angle is discussed. Based on dimensional analysis and factorial design, correlations are developed using the system parameters, i.e. geometry of the bed （cone angle）, particle diameter, initial static bed height, density of the solid, and superficial velocity of the fluidizing medium. Experimental values of minimum fluidization velocity, bed fluctuation, and bed expansion ratios were found to agree well with the developed correlations.

Evaluation of factors affecting the edge formability of two hot rolled multiphase steels

In this study, the effect of various factors on the hole expansion ratio and hence on the edge formability of two hot rolled multiphase steels, one with a ferrite–martensite microstructure and the other with a ferrite-bainite microstructure, was investigated through systematic microstructural and mechanical characterization. The study revealed that the microstructure of the steels, which determines their strain hardening capacity and fracture resistance, is the principal factor controlling edge formability. The influence of other factors such as tensile strength, ductility, anisotropy, and thickness, though present, are secondary. A critical evaluation of the available empirical models for hole expansion ratio prediction is also presented.

Optimization Analysis of the Mixing Chamber and Diffuser of Ejector Based on Fano Flow Model

An improved model to calculate the length of the mixing chamber of the ejector was proposed on the basis of the Fano flow model,and a method to optimize the structures of the mixing chamber and diffuser of the ejector was put forward.The accuracy of the model was verified by comparing the theoretical results calculated using the model to experimental data reported in literature.Variations in the length of the mixing chamber L_(m) and length of the diffuser L_(d) with respect to variations in the outlet temperature of the ejector T_(c),outlet pressure of the ejector p_(c),and the expansion ratio of the pressure of the primary flow to that of the secondary flow p_(g)/p_(e) were investigated.Moreover,variations in L_(m) and L_(d) with respect to variations in the ratio of the diameter of the throat of the motive nozzle to the diameter of the mixing chamber d_(g0)/d_(c3) and ratio of the outlet diameter of the diffuser to the diameter of themixing chamber d_(c)/d_(c3) were investigated.The distribution of flow fields in the ejector was simulated.Increasing L_(m) and d_(c3) reduced T_(c) and p_(c).Moreover,reducing p_(g)/p_(e) or d_(g0)/d_(c3) reduced T_(c) and p_(c).The length of the mixed section L_(m2),which was determined on the basis of the Fano flow model,increased as pg increased and decreased as d_(c3) increased.The mixing length L_(m1),which was considered the primary flow expansion,showed the opposite trend with that of L_(m2).Moreover,Ld increased as p_(g)/p_(e) and d_(c)/d_(c3) increased.When the value of d_(c) was 1.8 to 2.0 times as high as that of dc3,the semi-cone angle of the diffuser ranged between 6°and 12°.At a constant dc/dc3,decreasing T_(c) and pc increased Ld.

Perturbation solutions for asymmetric laminar flow in porous channel with expanding and contracting walls

The cases of large Reynolds number and small expansion ratio for the asym- metric laminar flow through a two-dimensional porous expanding channel are considered. The Navier-Stokes equations are reduced to a nonlinear fourth-order ordinary differential equation by introducing a time and space similar transformation. A singular perturbation method is used for the large suction Reynolds case to obtain an asymptotic solution by matching outer and inner solutions. For the case of small expansion ratios, we are able to obtain asymptotic solutions by double parameter expansion in either a small Reynolds number or a small asymmetric parameter. The asymptotic solutions indicate that the Reynolds number and expansion ratio play an important role in the flow behavior. Nu- merical methods are also designed to confirm the correctness of the present asymptotic solutions.

Numerical Modeling on Seismic Performance of Castellated Composite Beam⁃Reinforced Concrete Column Connection

The hybrid structure consisting of castellated composite beam and compound spiral hoop reinforced concrete column take full advantages of steel and concrete material.To popularize the structural form in real conditions,a beam⁃through⁃type beam⁃column connection is proposed.Two 1/2⁃scaled connection specimens were tested and three⁃dimensional finite element models of the beam⁃column connection were set up.The longitudinal reinforcements,concrete beam,and column were simulated by link and solid elements,respectively.The influences of the parameters such as expansion ratio,location of web opening,and original height of steel beam were studied.The results show that connections possessed high initial rigidity.The expansion ratio of steel beam showed more important influence on the connection’s ultimate bearing capacity.For the connection models with steel beam expansion ratio of 1.4,the maximum increment of the ultimate bearing capacity of the connection could reach 28%.In order to prevent the local buckling failure of steel beam from occurring near web opening,the expansion ratio of steel beam should not be greater than 1.3.

Development of a hot-rolled 980 MPa advanced high-strength steel with excellent flangeability and bendability

A new 980 MPa advanced high-strength steel(AHSS) with excellent bendability and flangeability has been studied and industrially produced, typical of tensile strength, fractured elongation, and hole expansion ratio(HER) exceeding 980 MPa, 10%,and 30%,respectively.The 90° V-type bending perpendicular to the rolling direction can satisfy the R/t=1.0 requirement, indicating excellent bendability.Systematic evaluations of industrial trial-produced 980 MPa hot-rolled AHSS have been conducted, including microstructure, tensile properties in three directions, HER,bendability, fatigue limit strength, and forming limit.The microstructure of the newly developed 980 MPa AHSS primarily consists of fine bainite and a small amount of martensite-austenite constituent.The practical yield and tensile strength are higher than 800 and 980 MPa, respectively, with typical elongation of 13% and HER of around 40%.The good combination of the newly developed 980 MPa AHSS is primarily attributed to the fine bainitic microstructure, resulting in excellent flangeability and bendability.In addition, the newly developed 980 MPa AHSS has good fatigue and forming properties, making it suitable for the production of chassis and suspension components.

Hydrodynamics of a bubble-induced inverse fluidized bed reactor with a nanobubble tray

This paper reports on the hydrodynamics of a bubble-induced inverse fluidized bed reactor,using a nanobubble tray gas distributor,where solid particles are fluidized only by an upward gas flow.Increasing the gas velocity,the fixed layer of particles initially packed at the top of the liquid starts to move downwards,due to the rise of bubbles in this system,and then gradually expands downwards until fully suspended.The axial local pressure drops and standard deviation were examined to delineate the flow regime comprehensively under different superficial gas velocities.Four flow regimes(fixed bed regime,initial fluidization regime,expanded regime,and post-homogeneous regime)were observed and three transitional gas velocities(the initial fluidization velocity,minimum fluidization velocity,and homogeneous fluidization velocity)were identified to demarcate the flow regime.Three correlations were developed for the three transitional velocities.As the fine bubbles generated from the nanobubble tray gas distributor are well distributed in the entire column,the bed expansion process of the particles is relatively steady.

Hydrodynamic behaviour of Cellets^(TM)(Ph.Eur./USP)in a spouted bed using image processing method

The hydrodynamic behaviour of the spouted bed in the pharmaceutical industries has been found to be less addressed.The present paper has focused on the hydrodynamic characteristics of a spouted bed where the Cellets^(TM)(Ph.Eur./USP)is adopted as the bed material.Experiments are carried out with three different static bed heights(H_(0))of shallow depth(2D_(i)≤H_(0)<3D_(i))using two different particle sizes.The spouted bed employed with D_(i)/D_(0) of 5 has given the experimental information on external spouting(Ues)by mapping the pressure drop,and fountain height(H_(f))against the superficial gas velocity(U_(g))is rep-resented with the image contours,which show the intrinsic behaviour.All the 1000 μm and 700 μm particles have been found to exhibit symmetric and asymmetric spouting.With increasing U_(g),the fully suspended particles are limited to a certain height in the freeboard region due to the gas-solid cross-flow,which implies the clusters have identified with the image processing method.

Microstructure, property and deformation and fracture behavior of 800 MPa complex phase steel with different coiling temperatures

The microstructure characteristics and properties(especially hole expansion property)of 800 MPa hot-rolled complex phase steel with different coiling temperatures were studied.The microstructure consisted of polygonal ferrite and precipitates when the steel was coiled at 550℃,and when the steel was coiled between 460–520℃,the microstructure was composed of granular bainite and martensite and austenite(M/A)islands.The morphology of the crack was analyzed by scanning electron microscopy,and the in situ scanning electron microscope tensile test was used to find out the fracture mechanism and deformation behavior of the steel with different coiling temperatures.When the steel was coiled at 550℃,the cracks initiated at the ferrite grain boundary and propagated through the grains or along the grain boundaries.When the steel was coiled at 520℃,the cracks first initiated at the junction of ferrite and M/A island and then propagated through the grains.The steel coiled at 520℃ has quite good mechanical properties and relatively high hole expansion ratio.

Effect of promoters on dynamics of gas-solid fluidized bed——Statistical and ANN approaches

In this study, a bubbling fluidized bed column, 99 mm in inside diameter and 960 mm in height, was used to investigate the effect of rod and disc promoters on fluctuation and expansion ratios. Factorial design （statistical approach） and artificial neural network （ANN） models were developed to predict the fluctuation and expansion ratios in this gas-solid fluidized bed with varying gas flow rates, bed heights, particle sizes and densities. The fluctuation and expansion predicted using these statistical and ANN models, for beds with and without promoters, were found to agree well with corresponding experiments. The statistical model was found to be superior to the ANN model due to its ability to take into account both individual and interactive effects. The rod promoters were found to be more effective in reducing bed fluctuation, and in increasing bed expansion at high gas mass velocities.

Effect of Isothermal Annealing on Nano Ti-Carbides Precipitation

Transmission electron microscopy was used to investigate the effect of isothermal holding temperature and time on the nano Ti-precipitates.A holding temperature was varied systematically from 400℃ to 1200℃.The isothermal holding was continued for 30s,300s and 900s,respectively.Nano carbides of (Ti,Nb)C were precipitated significantly at 900℃.The size of carbides was approximately 10nm at 30s holding and increased to 20～30nm at 900s holding.Isothermal holding at 1000℃ showed the increased amount of carbides larger than 100nm.At 800℃,nano (Ti,Nb)C was not observed at 30s and it was examined at 300s.The size of nano (Ti,Nb)C was smaller than that of 900℃.As the isothermal temperature decreased to 700 ℃,the nano (Ti,Nb)C was only seen at 900s holding and the size of carbides was smaller than 10nm.Nano (Ti,Nb)C was disappeared at isothermal holding below 600℃.The kinetics of nano (Ti,Nb)C precipitation were studied as a function of isothermal holding temperature and time,respectively,using the precipitate growth equations.