Effect of melt-to-solid volume ratio and preheating temperature on Mg/Al bimetals interface by centrifugal casting

Compound casting is an efficient method for bonding dissimilar metals,in which a dramatic reaction can occur between the melt and solid.The centrifugal casting process,a type of compound casting,was applied to cast Al/Mg dissimilar bimetals.Magnesium melt was poured at 700 °C,with melt-to-solid volume ratios(Vm/Vs) of 1.5 and 3,into a preheated hollow aluminum cylinder.The preheating temperatures of the solid part were 320,400,and 450 °C,and the constant rotational speed was 1,600 rpm.The cast parts were kept inside the casting machine until reaching the cooling temperature of 150 °C.The result showed that an increase in preheating temperature from 320 to 450 °C led to an enhanced reaction layer thickness.In addition,an increase in the Vm/Vs from 1.5 to 3 resulted in raising the interface thickness from 1.2 to 1.8 mm.Moreover,the interface was not continuously formed when a Vm/Vs of 3 was selected.In this case,the force of contraction overcame the resultant acting force on the interface.An interface formed at the volume ratio of 1.5 was examined using scanning electron microscopy(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS),and the results demonstrated the formation of Al_(3)Mg_(2),Al_(12)Mg_(17) and(δ+Al_(12)Mg_(17)) eutectic structures in the interface.

A Modified Bi-Directional Evolutionary Structural Optimization Procedure with Variable Evolutionary Volume Ratio Applied to Multi-Objective Topology Optimization Problem

Natural frequency and dynamic stiffness under transient loading are two key performances for structural design related to automotive,aviation and construction industries.This article aims to tackle the multi-objective topological optimization problem considering dynamic stiffness and natural frequency using modified version of bi-directional evolutionary structural optimization(BESO).The conventional BESO is provided with constant evolutionary volume ratio(EVR),whereas low EVR greatly retards the optimization process and high EVR improperly removes the efficient elements.To address the issue,the modified BESO with variable EVR is introduced.To compromise the natural frequency and the dynamic stiffness,a weighting scheme of sensitivity numbers is employed to form the Pareto solution space.Several numerical examples demonstrate that the optimal solutions obtained from the modified BESO method have good agreement with those from the classic BESO method.Most importantly,the dynamic removal strategy with the variable EVR sharply springs up the optimization process.Therefore,it is concluded that the modified BESO method with variable EVR can solve structural design problems using multi-objective optimization.

Combined effects of volume ratio and nitrate recycling ratio on nutrient removal,sludge characteristic and microbial evolution for DPR optimization

The optimization of volume ratio(V_(An)/V_(A)/V_(0))and nitrate recycling ratio(R)in a two-sludge denitrifying phosphorus removal(DPR)process of Anaerobic Anoxic Oxic-Moving Bed Biofilm Reactor(A^(2)/O-MBBR)was investigated.The results showed that prolonged anaerobic retention time(HRT An:1.25→3.75 hr)exerted favorable effect on chemical oxygen demand(COD)removal(57.26%→73.54%),poly-β-hydroxyalkanoates(PHA)synthesis(105.70→138.12 mg COD/L)and PO_(4)^(3-)release(22.3→38.9 mg/L).However,anoxic retention time(HRT A)and R exhibited positive correlation with PHA utilization(43.87%-81.34%)and denitrifying phosphorus removal(DPR)potential(NO_(3)-/PO^(3-)_(4):0.57-1.34 mg/mg),leading to dramatical TN removal variations from 68.86%to 81.28%.Under the V An/V A/V O ratio of 2:6:0,sludge loss deteriorated nutrient removals but the sludge bioactivity quickly recovered when the oxic zone was recovered.The sludge characteristic and microstructure gradually transformed under the dissolved oxygen(DO)control(1.0-1.5→1.5-2.0 mg/L),in terms of sludge volume index(SVI:194→57 m L/g VSS),median-particle-size(D 50:99.6→300.5μm),extracellular polymeric substances(EPS)(105.62→226.18 mg/g VSS)and proteins/polysaccharides(PN/PS)ratio(1.52→3.46).Fluorescence in situ hybridization(FISH)results showed that phosphorus accumulation organisms(PAOs)(mainly Cluster I of Accumulibacter,contribution ratio:91.79%-94.10%)dominated the superior DPR performance,while glycogen accumulating organisms(GAOs)(mainly Competibacter,contribution ratio:82.61%-86.89%)was responsible for deteriorative TN and PO_(4)^(3-)removals.The optimal HRT A and R assembled around 5-6.5 hr and 300%-400%based on the PHA utilization and DRP performance,and the oxic zones also contributed to PO_(4)^(3-)removal although it showed low dependence on DO concentration and oxic retention time(HRT_(0)).

Destructive and non-destructive evaluation of concrete for optimum sand to aggregate volume ratio

Aggregates are the biggest contributor to concrete volume and are a crucial parameter in dictating its mechanical properties.As such,a detailed experimental investigation was carried out to evaluate the effect of sand-toaggregate volume ratio(s/a)on the mechanical properties of concrete utilizing both destructive and non-destructive testing(employing UPV(ultrasonic pulse velocity)measurements).For investigation,standard cylindrical concrete samples were made with different s/a(0.36,0.40,0.44,0.48,0.52,and 0.56),cement content(340 and 450 kg/m^(3)),water-to-cement ratio(0.45 and 0.50),and maximum aggregate size(12 and 19 mm).The effect of these design parameters on the 7,14,and 28 d compressive strength,tensile strength,elastic modulus,and UPV of concrete were assessed.The careful analysis demonstrates that aggregate proportions and size need to be optimized for formulating mix designs;optimum ratios of s/a were found to be 0.40 and 0.44 for the maximum aggregate size of 12 and 19 mm,respectively,irrespective of the W/C(water-to-cement)and cement content.

Diagnostic Value of Quantitative Parameters of DCE-MRI in Endometrial Carcinoma and Its Correlation with Clinicopathological Factors

In the study,108 patients with endometrial cancer were selected as the observation group,and 105 patients with benign endometrial lesions were selected as the control group.After DCE-MRI examination,it was found that the volume transfer constant(K^(trans)),rate constant(K_(e))and extracellular space volume ratio(V_(e))in the observation group were higher than those in the control group(P<0.05).The area under curve(AUC)of combined K^(trans),K_(e) and V_(e) values in the diagnosis of endometrial cancer was 0.841.The values of K^(trans),K_(e )and V_(e) were positively correlated with the clinical stage and the degree of muscular invasion,but negatively correlated with the degree of differentiation(P<0.05).The results of the study suggested that DCE-MRI quantitative parameters have a certain value in the differential diagnosis of endometrial cancer,which helped to further distinguish the degree of muscular invasion,clinical stage,and differentiation of endometrial cancer patients.

Experimental and Numerical Analysis of the Relationship between Pressure and Drip Rate in a Vertical Polypropylene Infusion Bag

Vertical infusion(self-emptying)bags used for Intravenous infusion are typically obtained by moulding a soft envelope of polypropylene.In normal conditions a continuous flow of liquid can be obtained with no need to use a pump.In the present study,the relationship between air pressure effects and the drug drip rate have been investigated experimentally and numerically.After determining relevant experimental data about the descending height of liquid level,the dropping speed and pressure,the ordinary least square method and MATLAB have been used to reconstruct the related variation and interrelation laws.Numerical simulations have been performed to determine the best gas-liquid volume ratio and improve the overall performances of these bags.According to these results,that the biggest effect on the drip rate is produced by the diameters of the used needles.

Influence of notch volume on mechanical properties of a novel high-strength and high-toughness steel

The effect of notch volume on the mechanical behavior of a novel high-strength and high-toughness steel with negative Poisson’s ratio effect(called NPR steel)was studied.First,the quasi-static tensile test of NPR steel with different notch volumes was carried out,and its failure characteristics and mechanical properties parameters were studied.Then,the modified Johnson-Cook(J-C)constitutive model with coupled notch volume ratio was proposed.The model was validated based on three-dimensional finite element numerical simulations.The results show that the engineering stress–strain curve of NPR steel has no yield platform,and has the mechanical properties of high strength,high elongation,and high energy absorption.Notch volume significantly affects the mechanical properties of NPR steel.The elongation,yield strength,tensile strength,and energy absorption characteristics of steel bar gradually decrease with the increase in notch volume.The notch volume ratio V^{*},a characteristic parameter describing the notch volume of reinforcement,is defined,and the quantitative relationship between this parameter and mechanical parameters is established,which can accurately characterize the mechanical properties of specimens with different notch volume ratios.Based on the true stress–strain curves with different notch volume ratios,a constitutive model with modified Johnson-Cook model parameters is proposed.The finite element results show that the modified J-C model can accurately fit the quasi-static tensile mechanical behavior of NPR steel.

Estimation of the minimum miscibility pressure for CO_(2)ecrude-oil systems by molecular dynamics simulation

CO_(2)injection is an effective enhanced oil recovery technique for energy security with the benefits of carbon neutrality.To reach the maximum oil recovery,the miscible condition between CO_(2)and oil needs to be maintained in the reservoir,which requires the operation pressure to be higher than the minimum miscibility pressure(MMP).There are two types of MMPs:the first-contact MMP(FC-MMP)and the multi-contact MMP(MC-MMP).In this study,molecular dynamics simulations were performed for the CO_(2)eoil interface system using two simplified digital oil models:a Bakken dead oil with four lumping components and a live-crude-oil model with 50 types of oil molecules but with no asphaltenes and heavy oil fractions.The vanishing interfacial tension method was used to predict the MMP.Different CO_(2)eoil volume ratios were considered to mimic the different degrees of vaporization.To estimate the MMP accurately and rapidly,the interfacial tension in the low-pressure regime was used for the prediction.Consequently,different MMPs were obtained,where the MMP value increased with increasing CO_(2)eoil volume ratio.FC-MMP can be predicted when the CO_(2)eoil volume ratio is sufficiently high.When the CO_(2)eoil volume ratio was approximately 9e10,MMP was closest to the actual MC-MMP value.The condensing and vaporizing mechanism was also studied at the molecular scale.Because pure CO_(2)was used,only the vaporizing effect on MMP occurred.It was found that the intermediate C2eC6 components have the main effect on the MMP calculation.This study can help to establish a computational protocol to estimate FC-MMP and MC-MMP,which are widely used in reservoir engineering.