Distribution of SiC_p in Al and Al-Cu Alloy Centrifugally Cast with Electromagnetic Stirring

The SiCp/(AI-Cu) alloy and pure Al matrix composites have been prepared by the centrifugal casting with electromagnetic stirring. There are two particle-depleted zones formed in the samples without electromagnetic stirring. Electromagnetic stirring may result in a homogeneous distribution of fine SiC particles in the AI-Cu alloy, whereas it has little effect on the segregation in pure Al matrix. The results also show that the particle segregation is influenced by particle size and the coarse particles are more readily segregated than the fine ones.

Solidification microstructure of centrifugally cast Inconel 625

Centrifugal casting is a foundry process allowing the production of near net-shaped axially symmetrical components. The present study focuses on the microstructural characterization of centrifugally cast alloys featuring different chemical compositions for the construction of spheres applied in valves made of alloy IN625 for operation at high pressure. Control of the solidification microstructure is needed to assure the reliability of the castings. Actually, a Ni-base superalloy such as this one should have an outstanding combination of mechanical properties, high temperature stability and corrosion resistance. Alloys such as IN625 are characterised by a large amount of alloying elements and a wide solidification range, so they can be affected by micro-porosity defects, related to the shrinkage difference between the matrix and the secondary reinforcing phases(Nb-rich carbides and Laves phase). In this study, the microstructure characterization was performed as a function of the applied heat treatments and it was coupled with a calorimetric analysis in order to understand the mechanism ruling the formation of micro-porosities that can assure alloy soundness. The obtained results show that the presence of micro-porosities is governed by morphology and by the size of the secondary phases, and the presence of the observed secondary phases is detrimental to corrosion resistance.

Numerical model and experimental observation for distribution of SiC_p in electromagnetic-centrifugally cast composites

A two-phase numerical model coupled with heat transfer was presented to describe the radial distribution of SiC particles on centrifugally-cast metal matrix composite,and a transverse static magnetic field was concurrently imposed to induce electromagnetic stirring of the melt as it revolved with the mold.Meanwhile,experimental observations were also carried out to examine the radial distribution of SiC particles in pure aluminum.The effects of the imposed magnetic field,particle size and the matrix metals were discussed.The computational results show that the particles tend to be congregated by the centrifugal force,and both increasing the imposed magnetic field and decreasing the particle size tend to result in even distribution of the particles.With the magnetic field varying from 0 to 1 T and the particle size from 550 to 180 μm,a uniform distribution of the particles in the aluminum matrix can be obtained among the computational results.The matrix metal can also influence the particle distributions due to the difference in physical properties of metals.Experimental observation shows similar tendency of particle distributions in aluminum matrix influenced by magnetic field and particle size.However,the chilling effect from the mold wall results in an outer particle-free zone,which is not involved in the numerical model.

MODELING OF 'BANDING' MICROSTRUCTURE FORMATION IN CENTRIFUGALLY SOLIDIFIED Ti-6Al-4V ALLOY

Numerical investigations of the ＇banding＇ microstructure formation during solidification of Ti-6Al-4 V alloy in the centrifugal casting are conducted using a multi-scale model, which combines the finite difference method （FDM） at the macroscale with a cellular automaton （CA） model at the microscale. The macro model is used to simulate the fluid flow and heat transfer throughout the casting. The micro model is used to predict the nucleation and growth of microstructures. With the proposed model, numerical simulations are performed to study the influences of the nucleation density, mould rotation speed, and casting size upon the ＇banding＇ microstructure formation. It is noted that changing the nucleation density has a minor effect on the microstructure formation. The rotation speed promotes the formation of ＇banding＇ microstructure, which is more noticeable for larger size castings. The ＇major mechanism responsible for this ＇banding＇ phenomenon is the spatial variation in cooling rates created by centrifugal force.

Investigation of the block toppling evolution of a layered model slope by centrifuge test and discrete element modeling

Primary toppling usually occurs in layered rock slopes with large anti-dip angles.In this paper,the block toppling evolution was explored using a large-scale centrifuge system.Each block column in the layered model slope was made of cement mortar.Some artificial cracks perpendicular to the block column were prefabricated.Strain gages,displacement gages,and high-speed camera measurements were employed to monitor the deformation and failure processes of the model slope.The centrifuge test results show that the block toppling evolution can be divided into seven stages,i.e.layer compression,formation of major tensile crack,reverse bending of the block column,closure of major tensile crack,strong bending of the block column,formation of failure zone,and complete failure.Block toppling is characterized by sudden large deformation and occurs in stages.The wedge-shaped cracks in the model incline towards the slope.Experimental observations show that block toppling is mainly caused by bending failure rather than by shear failure.The tensile strength also plays a key factor in the evolution of block toppling.The simulation results from discrete element method(DEM)is in line with the testing results.Tensile stress exists at the backside of rock column during toppling deformation.Stress concentration results in the fragmented rock column and its degree is the most significant at the slope toe.

Microstructure and Hot Tearing Sensitivity Simulation and Parameters Optimization for the Centrifugal Casting of Al-Cu Alloy

Four typical theories on the formation of thermal tears:strength,liquid film,intergranular bridging,and solidifica-tion shrinkage compensation theories.From these theories,a number of criteria have been derived for predicting the formation of thermal cracks,such as the stress-based Niyama,Clyne,and RDG(Rapaz-Dreiser-Grimaud)criteria.In this paper,a mathematical model of horizontal centrifugal casting was established,and numerical simulation analysis was conducted for the centrifugal casting process of cylindrical Al-Cu alloy castings to investigate the effect of the centrifugal casting process conditions on the microstructure and hot tearing sensitivity of alloy castings by using the modified RDG hot tearing criterion.Results show that increasing the centrifugal rotation and pouring speeds can refine the microstructure of the alloy but increasing the pouring and mold preheating temperatures can lead to an increase in grain size.The grain size gradually transitions from fine grain on the outer layer to coarse grain on the inner layer.Meanwhile,combined with the modified RDG hot tearing criterion,the overall distribution of the castings’hot tearing sensitivity was analyzed.The analysis results indicate that the porosity in the middle region of the casting was large,and hot tearing defects were prone to occur.The hot tearing tendency on the inner side of the casting was greater than that on the outer side.The effects of centrifugal rotation speed,pouring temperature,and preheating temperature on the thermal sensitivity of Al-Cu alloy castings are summarized in this paper.This study revealed that the tendency of alloy hot cracking decreases with the increase of the centrifugal speed,and the maximum porosity of castings decreases first and then increases with the pouring temperature.As the preheating temperature increases,the overall maximum porosity of castings shows a decreasing trend.

Numerical Simulation and Entropy Production Analysis of Centrifugal Pump with Various Viscosity

The fluid’s viscosity significantly affects the performance of a centrifugal pump.The entropy production method and leakage are employed to analyze the performance changes under various viscosities by numerical simulation and validated by experiments.The results showed that increasing viscosity reduces both the pump head and efficiency.In addition,the optimal operating point shifts to the left.Leakage is influenced by vortex distribution in the front chamber and boundary layer thickness in wear-ring clearance,leading to an initial increase and subsequent decrease in leakage with increasing viscosity.The total entropy production Spro,Total inside the pump rises with increasing viscosity.The different mechanisms dominate under varying conditions:Turbulent dissipation dominates at low viscosity.Under high-viscosity conditions,energy loss is primarily caused by direct dissipation Spro,D and wall entropy production Spro,W.This study provides a deeper and more objective understanding of the energy characteristics of centrifugal pumps handling fluids of various viscosity,potentially aiding in optimizing pump design and improving energy conversion efficiency.

Centrifuge modeling of a large-scale surcharge on adjacent foundation

This study investigates the ground and structural response of adjacent raft foundations induced by largescale surcharge by ore in soft soil areas through a 130g centrifuge modeling test with an innovative layered loading device.The prototype of the test is a coastal iron ore yard with a natural foundation of deep soft soil.Therefore,it is necessary to adopt some measures to reduce the influence of the large-scale surcharge on the adjacent raft foundation,such as installing stone columns for foundation treatment.Under an acceleration of 130 g,the model conducts similar simulations of iron ore,stone columns,and raft foundation structures.The tested soil mass has dimensions of 900 mm×700 mm×300 mm(lengthwidthdepth),which is remodeled from the soil extracted from the drilling holes.The test conditions are consistent with the actual engineering conditions and the effects of four-level loading conditions on the composite foundation of stone columns,unreinforced zone,and raft foundations are studied.An automatic layer-by-layer loading device was innovatively developed to simulate the loading process of actual engineering more realistically.The composite foundation of stone columns had a large settlement after the loading,forming an obvious settlement trough and causing the surface of the unreinforced zone to rise.The 12 m surcharge loading causes a horizontal displacement of 13.19 cm and a vertical settlement of 1.37 m in the raft foundation.The stone columns located on both sides of the unreinforced zone suffered significant shear damage at the sand-mud interface.Due to the reinforcement effect of stone columns,the sand layer below the top of the stone columns moves less.Meanwhile,the horizontal earth pressure in the raft foundation zone increases slowly.The stone columns will form new drainage channels and accelerate the dissipation of excess pore pressure.

Experimental Analysis of Radial Centrifugal Pump Shutdown

Centrifugal pumps are widely used in the metallurgy,coal,and building sectors.In order to study the hydraulic characteristics of a closed impeller centrifugal pump during its shutdown in the so-called power frequency and frequency conversion modes,experiments were carried to determine the characteristic evolution of parameters such as speed,inlet and outlet pressure,head,flow rate and shaft power.A quasi-steady-state method was also used to further investigate these transient behaviors.The results show that,compared to the power frequency input,the performance parameter curves for the frequency conversion input are less volatile and smoother.The characteristic time is longer and the response to shutdown is slower.The quasi-steady-state theoretical head-flow curves match the experimental head-flow curves more closely at low flow rates when the frequency conversion input is considered.Moreover,in this case,the similarity law predicts the hydraulic performance more accurately.

Blade Wrap Angle Impact on Centrifugal Pump Performance:Entropy Generation and Fluid-Structure Interaction Analysis

The centrifugal pump is a prevalent power equipment widely used in different engineering patterns,and the impeller blade wrap angle significantly impacts its performance.A numerical investigation was conducted to analyze the influence of the blade wrap angle on flow characteristics and energy distribution of a centrifugal pump evaluated as a low specific speed with a value of 69.This study investigates six impellermodels that possess varying blade wrap angles(95°,105°,115°,125°,135°,and 145°)that were created while maintaining the same volute and other geometrical characteristics.The investigation of energy loss was conducted to evaluate the values of total and entropy generation rates(TEG,EGR).The fluid-structure interaction was considered numerically using the software tools ANSYS Fluent and ANSYSWorkbench.The elastic structural dynamic equation was used to estimate the structural response,while the shear stress transport k–ωturbulence model was utilized for the fluid domain modeling.The findings suggest that the blade wrap angle has a significant influence on the efficiency of the pump.The impeller featuring a blade wrap angle of 145°exhibits higher efficiency,with a notable increase of 3.76%relative to the original model.Variations in the blade wrap angle impact the energy loss,shaft power,and pump head.The model with a 145°angle exhibited a maximum equivalent stress of 14.8MPa and a total deformation of 0.084 mm.The results provide valuable insights into the intricate flow mechanism of the centrifugal pump,particularly when considering various blade wrap angles.

Numerical analysis on seismic performance of underground structures in liquefiable interlayer sites from centrifuge shaking table test

When an underground structure passes through a liquefiable soil layer,the soil liquefaction may pose a significant threat to the structure.A centrifuge shaking table test was performed to research the seismic response of underground structures in liquefiable interlayer sites,and a valid numerical model was obtained through simulation model test.Finally,the calibrated numerical model was used to perform further research on the influence of various distribution characteristics of liquefiable interlayers on the seismic reaction of underground structures.The key findings are as follows.The structure faces the most unfavorable condition once a liquefiable layer is located in the middle of the underground structure.When a liquefiable layer exists in the middle of the structure,the seismic reactions of both the underground structure and model site will increase with the rise of the thickness of the liquefiable interlayer.The inter-story drift of the structure in the non-liquefiable site is much smaller than that in the liquefiable interlayer site.The inter-story drift of the structure is not only associated with the site displacement and the soil-structure stiffness ratio but also closely associated with the slippage of the soil-structure contact interface under the condition of large deformation of the site.

Improvement of microstructure and mechanical properties of Al−Cu−Li−Mg−Zn alloys through water-cooling centrifugal casting technique

The microstructure and mechanical properties of as-cast Al−Cu−Li−Mg−Zn alloys fabricated by conventional gravity casting and centrifugal casting techniques combined with rapid solidification were investigated.Experimental results demonstrated that compared with the gravity casting technique,the water-cooling centrifugal casting technique significantly reduces porosity,refinesα(Al)grains and secondary phases,modifies the morphology of secondary phases,and mitigates both macro-and micro-segregation.These improvements arise from the synergistic effects of the vigorous backflow,centrifugal field,vibration and rapid solidification.Porosity and coarse plate-like Al13Fe4/Al7Cu2Fe phase result in the fracture before the gravity-cast alloy reaches the yield point.The centrifugal-cast alloy,however,exhibits an ultra-high yield strength of 292.0 MPa and a moderate elongation of 6.1%.This high yield strength is attributed to solid solution strengthening(SSS)of 225.3 MPa,and grain boundary strengthening(GBS)of 35.7 MPa.Li contributes the most to SSS with a scaling factor of 7.9 MPa·wt.%^(-1).The elongation of the centrifugal-cast alloy can be effectively enhanced by reducing the porosity and segregation behavior,refining the microstructure and changing the morphology of secondary phases.

Effect of the Density of Molten Metal on the Raining Phenomenon in Horizontal Centrifugal Casting

In this work the influence of the density of the molten metal on the emergence of the raining phenomenon in the horizontal centrifugal casting process is numerically studied. Transient 2D numerical simulations were carried out using Computational Fluid Dynamics software. Three molten metals with different density, namely aluminum, iron and lead, and three angular frequencies, namely 50, 66 and 77 rad/s were considered. It is found that the density of the molten metal significantly affects the emergence, transient or permanent, of the rain phenomenon. However, the magnitude and duration of the rain phenomenon depend on the angular frequency of the rotating mold. Likewise, since gravitational forces affect the metal according to its density, the value of the critical rotation speed of the mold is also affected.

Evaluating the impact of delayed centrifugation on protein profiles analyzed by LC/MS in serum and plasma samples

The pre-analytical steps in blood-based liquid biopsy,involving sample collection techniques and storage conditions,play a critical role in ensuring the integrity and reliability of collected samples.These steps have a directly impact on the accuracy and reliability of test results and are therefore of utmost importance.Mass spectrometry(MS)-based proteomics is an exceptionally powerful tool in the field of liquid biopsy.It enables the comprehensive analysis of the protein content within biological specimens,providing valuable insights into the underlying mechanisms and pathogenesis of diseases.In this study,we aim to explore the variations in the protein landscape between serum and plasma specimens and evaluate the impact of delayed centrifugation on LC/MS-analyzed protein profiles.We seek to provide recommendations on optimal pre-analytical protocols for MS-based proteomics studies.This will enhance the accuracy and reliability of liquid biopsy for precision medicine,ultimately leading to improved patient outcomes.

Effects of temperature on fracture behavior of Al-based in-situ composites reinforced with Mg_2Si and Si particles fabricated by centrifugal casting

An aluminum-based in-situ composites reinforced with Mg2Si and Si particles were produced by centrifugal casting A1-20Si-5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on fracture behavior of the composite were investigated. The results show that the average fraction of primary Si and Mg2Si particles in the composites is as high as 38%, and ultimate tensile strengths （UTS） of the composites first increase then decrease with the increase of test temperature. Microstructures of broken specimens show that both the particle fracture and the interface debonding affect the fracture behavior of the composites, and the interface debonding becomes the dominant fracture mechanism with increasing test temperature. Comparative results indicate that rich particles in the composites and excellent interface strength play great roles in enhancing tensile property by preventing the movement of dislocations.

Flow equation and similarity criterion during centrifugal casting in micro-channel

Liquid metal filling flow process in the microscale during the centrifugal casting process was studied by means of similar physical simulation. The research was focused on derived similarity criterion. Based on the traditional flow equations, the flow equation and the Bernoulli＇s equation for liquid metal flows in micro-scale space were derived, which provides a mathematical model for numerical simulation of micro-scale flow. In the meanwhile, according to the micro-flow equation and the similarity theory, the similarity criterion for the physical simulation of the mold filling behaviors was presented under centrifugal force field, so as to achieve the visual observation and quantitative analysis of micro-flow process.

CENTRIFUGAL TEST STUDY ON THE BEHAVIOR OF SOFT CLAY AT SEA BOTTOM UNDER THE ACTION OF WAVE FORCE

The importance of studying the behavior of the soil at the sea bottom under the action of wave force has arisen with the development of offshore engineering.In this paper,the behavior of the soft clay under the action of wave forces is studied by performing centrifugal tests.The soil profile and the wave characters were simulated in the centrifugal model cell according to the typical environmental conditions of the oil fields in the Bohai gulf.Test results show that the soft clay layer will be seriously softened near the upper surface under the maximum wave height and slightly affected in the deeper layer,and that no liquefaction was recorded in the silty sand sublayer during the test.It is proven that the centrifugal test is a valid technique for simulating the interaction between soil and wave.

Similar physical simulation of microflow in micro-channel by centrifugal casting process

By means of similar physical simulation, liquid metal filling flow pattern in the microscale during the centrifugal casting process was studied. It was found that, in microscale, the flow channel with the maximum cross-sectional area was filled first, and the micro flow channels with 0.1 mm in diameter were filled when the rotational speed was increased to 964 r/min. The total fluid energy remained constant during the mould filling, and the changes of cross-sectional area only occurred in the microflow channels with 0.3 mm in diameter. Filling velocity increased with processing time, and a peak value was achieved rapidly, followed by a gentle increase as the process proceeded further. The time required to achieve the peak filling rate decreased dramatically with increase of rotational speed.

基于RFPA-Centrifuge的顺层边坡稳定性数值试验分析

基于离心加载法的原理,应用岩石破裂过程分析RFPA2D软件对某露天矿边坡的变形及破坏过程进行了数值试验研究,再现了边坡失稳的动态过程。根据数值试验所得出的模拟结果,分析得出了该边坡最危险滑动面的形成机制。为边坡失稳的预测及防治提供科学依据。

冷却风扇气动性能及噪声模拟与试验验证

为评估冷却风扇气动性能及噪声,以某摩托车用轴流式冷却风扇为研究对象,应用计算流体力学和计算声学方法,采用流体分析软件STAR-CCM+和噪声分析软件Virtual Lab对风扇性能及噪声开展研究,并与风扇性能和噪声试验数据对比验证计算模型的可靠性。结果表明:轴流式冷却风扇风量仿真值与实测值变化趋势一致,最大误差约为4.9%,总体平均误差约为2.94%。轴流式风扇转速4213 r/min及风压0 Pa时,噪声仿真值与试验值的误差为9.7%,误差低于10%,可满足工程需求。类似研究方法应用于发电机组用离心式风扇风量及噪声预测研究中,经分析得出离心式风扇入口风速试验值与仿真值间最大误差为9.17%,最小误差为5%;1 m远场噪声监测点的噪声声压级仿真值为66 dB(A),实测声压级为75 dB(A),两者差异为9 dB(A),误差约为13.6%,原因是实测噪声值中含有电机驱动系统运转的噪声。研究结果可为轴流式及离心式风扇的气动性能及噪声评估提供方法参考。