Ultra-large aluminum shape casting:Opportunities and challenges

Ultra-large aluminum shape castings have been increasingly used in automotive vehicles,particularly in electric vehicles for light-weighting and vehicle manufacturing cost reduction.As most of them are structural components subject to both quasi-static,dynamic and cyclic loading,the quality and quantifiable performance of the ultra-large aluminum shape castings is critical to their success in both design and manufacturing.This paper briefly reviews some application examples of ultra-large aluminum castings in automotive industry and outlines their advantages and benefits.Factors affecting quality,microstructure and mechanical properties of ultra-large aluminum castings are evaluated and discussed as aluminum shape casting processing is very complex and often involves many competing mechanisms,multi-physics phenomena,and potentially large uncertainties that significantly influence the casting quality and performance.Metallurgical analysis and mechanical property assessment of an ultra-large aluminum shape casting are presented.Challenges are highlighted and suggestions are made for robust design and manufacturing of ultra-large aluminum castings.

Progress in Light-weight High Entropy Alloys

High entropy alloys(HEAs)possess good mechanical properties and a wide range of industrial applications.In this paper,phase formation prediction theory,microstructure,properties and preparation methods of light-weight HEAs(LWHEAs)were reviewed.The problems and challenges faced by LWHEAs development were analyzed.The results showed that many aspects are still weak and require investigation for future advanced alloys,such as clarification of the role of entropy in phase formation and properties of HEAs,improved definition and different generations division of HEAs,close-packed hexagonal(HCP)phase structure prediction and corresponding alloy design and fabrication.Finally,some suggestions were presented in this paper including in-depth research on formation mechanism of multi-component alloy phase and strengthening of large-scale HEA preparation methods via technology compounding and 3D printing technology.Also,there is a need for more research on the in-situ preparation of HEA coatings and films,as well as developing LWHEAs with superior strength and elevated temperature resistance or ultra-low temperature resistance to meet the requirements of future engineering applications.

Preparation of Light-weight Spinel Refractories by Foaming-gel Process

Light-weight magnesium -aluminate spinel materi- als were prepared by foaming-gel process with polyalumi- nium chloride （PAC） as gel. Effect of solid loading in initial slurry on microstructure, porosity, pore size distri- bution, thermal conductivity and mechanical properties was investigated. The results show that the bulk density of the light-weight magnesium -aluminate spinel mate- rials is in the range of O. 7 1.2 g cm-3 ; pore size distribution curves show single-peak characteristics and the mean pore size is in the range of 30. 83 - 61.37 μm ; with the increase of solid loading, the linear shrinkage of the green body during firing and the permanent change in dimensions on heating at l 600 ℃ for 3 h de- crease, but the bulk density increases, the mechanical properties increase obviously; the maximum compressive strength and bending strength reach 35. 25 MPa and 9. 92 MPa, respectively, while the bulk density is 1. 16 g · cm ; and the thermal conductivity at 1 000 ℃ tea- ches 0. 371 W · m-1 . K-1 while the bulk density is O. 7 -3 g · cm

Investigation on microstructures and properties of semi-solid Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5)light-weight high-entropy alloy during isothermal heat treatment process

The Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5)light-weight high-entropy alloy with globular microstructure was fabricated by isothermal heat treatment.The effects of isothermal temperatures and holding times on the semi-solid microstructure evolution were investigated.The results indicate that,with increase of the isothermal temperature,the average grain size increases and the spheroidization time shortens.With prolongation of holding time,the shape factor increases firstly and then decreases,and the average grain size decreases at first and then increases when the isothermal temperature is below 520°C,however it increases gradually at 540℃.The optimal semi-solid microstructure is obtained at 520℃ for 30 min,whose shape factor and average grain size are 0.90 and 56.4μm,respectively.Compared with as-cast Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5) light-weight high-entropy alloy,the compressive strength and plasticity of semi-solid Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5) light-weight high-entropy alloy are increased by 36%and 108%,respectively.The formation of semi-solid microstructures includes three stages:melting separation,spheroidization,and coarsening growth.The sluggish diffusion effect of Al_(80)Mg_(5)Li_(5)Zn_(5)Cu_(5) light-weight high-entropy alloy leads to a low coarsening rate,resulting in slow grain growth.

Principles and Chief Technologies in Developing Light-weighted Worsted Fabrics

More and more light-weighted fabrics are being required by the market, especially for the worsted manufacture.In the past, such fabrics are produced mainly through changing the structure of woven goods or by using finer yarns. But these possibilities are very limited. In this paper, new devices are discussed: (1) on the yarn level- to use single yarns instead of conventional doubled ones, to decrease number of fibers in yarn cross sections beth during spinning and after finishing; (2) on the fiber level - to use finer fibers in blends with wool and modification of the wool fibers; (3) on the macromolecule level - to stretch the macromolecules in alpha keratin, to get super fine wool fibers.

Ultra-thin and light-weight spoof surface plasmon polariton coupler achieved by broadside coupled split ring resonators

Low profile and light weight are very important for practical applications of a spoof surface plasmon polariton（SSPP）coupler, especially at low frequencies. In this paper, we propose and design an ultra-thin, light-weight SSPP coupler based on broadside coupled split ring resonators（BC-SRRs）. The size of BC-SRR can be far less than λ/100 and can extremely well control the reflective phases within a subwavelength thickness. Due to the broadside capacitive coupling, the electrical size of BC-SRR is dramatically reduced to guarantee the ultra-thin thickness of the SSPP coupler. The weight of the SSPP coupler is reduced by a low occupation ratio of BC-SRR in the unit cell volume. As an example, a C-band SSPP coupler composed of phase gradient BC-SRRs is designed, fabricated, and measured. Due to the ultra-small size and low occupation ratio of BC-SRRs, the thickness of the coupler is λ/12 and the surface density is only 0.98 kg/m^2. Both simulation and experiment results verify that the coupler can achieve high-efficiency SPP coupling at 5.27 GHz under normal incidence.

Prickle of Light-Weight Worsted Woven Wool Fabrics

Using the forearm test, the prickle of 26 commercially available light-weight worsted woven wool fabrics and 7 other fiber fabrics were studied under (24±1)℃ temperature and (65±5)% RH conditions. The surface fiber diameter of part of the wool fabrics was measured using a microscope. It was found that most of the light-weight worsted woven wool fabrics gave a prickle sensation under the above conditions. The prickle sensation was significantly correlated with the mean fiber diameter of the surface hairiness. It was also found that the prickle of the light-weight worsted woven wool fabrics was significantly correlated with the number of surface fibers which were coarser than 26 μm diameter.

Effect of Commercial Synthappret BAP Treatment on the Tailorability of Light-Weight Worsted Wool Fabrics

By means of measurement with the FAST instruments, the effect of commercial Synthappret BAP treatment on the tailorability of light-weight wool worsted fabrics has been investigated. It was found that the commercial Synthappret BAP treatment unproved the tailorability of the light-weight wool fabrics mainly by increasing the bending stiffness of the light-weight wool fabrics.

A Study of Thermal Response and Flow Field Coupling Simulation around Hayabusa Capsule Loaded with Light-Weight Ablator

The numerical simulation of flow field around Hayabusa capsule loaded with light-weight ablator thermal response coupled with pyrolysis gas flow inside the ablator was carried out. In addition, the radiation from high temperature gas around the capsule was coupled with flow field. Hayabusa capsule reentered the atmosphere about 12 km/sec in velocity and Mach number about 30. During such an atmospheric entry, space vehicle is exposed to very savior aerodynamic heating due to convection and radiation. In this study, Hayabusa capsule was treated as a typical model of the atmospheric entry spacecraft. The light-weight ablator had porous structure, and permeability was an important parameter to analyze flow inside ablator. In this study, permeability was a variable parameter dependent on density of ablator. It is found that the effect of permeability of light-weight ablator was important with this analysis.

Effects of Spherical Light-weight Aggregates Additions on Workability and Mechanical Properties of Al_2O_3-SiO_2 System Castables

In order to clarify the effect of spherical light-weight aggregates addition on properties of A12 07 - Si02 system castables, adopting ATO mullite traditional light-weight aggregates and ATO mullite spherical light-weight aggre- gates, bauxite homogenization powder, microsilica , cal- cium aluminate cement as main raw materials, light- weight Al2 03 - SiO2 system castables were prepared by replacing conventional light-weight aggregate with spherical light-weight aggregates. The effects of spheri- cal light-weight aggregates addition on workability, me- chanical properties of castables after heated at different temperatures were researched; the microstructure of the aggregates was analyzed by SEM. The result shows that the introduction of spherical light-weight aggregates can significantly improve the flowability and reduce the water addition of the castables. Water demand of the castable is reduced from 18% with the conventional light-weight aggregates to 14% with spherical light-weight aggre- gates. In addition, light-weight castables prepared by spherical aggregates can keep the same workability with- in a wider range of water addition. Therefore, spherical aggregates are user-friendly. The introduction of spheri- cal light-weight aggregates is favorable to packing densi- ty and mechanical properties of castables, such as cold crushing strength, cold modulus of rupture, hot modulus of rupture at 1 200℃.

压型钢板-轻骨料混凝土组合楼板受弯承载力试验研究

通过对压型钢板-轻骨料混凝土组合楼板受弯承载力试验,对其受力性能和变形性能进行研究,并与普通混凝土组合楼板进行对比,以验证《钢-混凝土组合楼盖结构设计与施工规程》(YB 9238-92)及《高层民用建筑钢结构技术规程》(JGJ 99-98)对轻骨料混凝土组合楼板正截面设计计算的适用性,为轻骨料混凝土组合楼板在工程上的应用提供依据。

Utilization of municipal solid waste incineration fly ash in lightweight aggregates

Washing pre-treatrnent of municipal solid waste incineration （MSWI） fly ash blended with shale and sludge was utilized in the manufacture of light-weight aggregates and processed to form ceramic pellets. A formula uniform design was performed to arrange the mixture ratio of the materials. The optimal mixture ratio of the materials was determined by measuring the bulk density, granule strength, and 1 h water absorption of the pellets. It is shown that the optimal mixture ratios of materials, MSWI fly ash, shale, and sludge, are 23.16%, 62.58%, and 14.25% （mass fraction）, respectively. The performance testing indicators of light-weight aggregates are obtained under the optimum mixture ratio： bulk density of 613 kg/m3, granule strength of 821N, and 1 h water absorption of 11.6%, meeting 700 grade light-aggregate of GB/T 17431.2--1998 standard. The results suggest that utilization of MSWI fly ash in light-weight aggregates is an effective method and a potential means to create much more values.

Prediction of hot tearing susceptibility of direct chill casting of AA6111 alloys via finite element simulations

To predict hot tearing susceptibility(HTS)during solidification and improve the quality of Al alloy castings,constitutive equations for AA6111 alloys were developed using a direct finite element(FE)method.A hot tearing model was established for direct chill(DC)casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion.By applying this model to real manufacture processes,the effects of casting speed,bottom cooling,secondary cooling,and geometric variations on the HTS were revealed.The results show that the HTS of the billet increases as the speed and billet radius increase,while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases.This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation,which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.

Stress and deformation due to embankment widening with different treatment techniques

A two-dimensional(2-D) finite element(FE) model was developed to analyze the deformation and stress of embankment on soft ground due to widening with different treatment techniques.It is found that the embankment widening induces transverse gradient change due to differential settlements and horizontal outward movements at the shoulder of the existing embankment.Embankment widening also increases the shear stress along the slope of the existing embankment,especially at the foot of slope.The failure potential due to embankment widening may increase with the increase of widening width when the widening width is smaller than 8.5 m,but may decrease with the increase of widening width as the widening width is greater than 8.5 m.The effectiveness of four ground and embankment treatment techniques,including geosynthetic reinforcement,light-weight embankment,deep mixed columns,and separating wall were compared.The results indicate that these treatments reduce the differential settlements and improve the stability.The light-weight embankment has the most effectiveness among four treatments.By using the fly-ash backfill material in widening,the transverse gradient change decreases from 0.5%-1.3% to 0.26%-0.8% and the maximum horizontal displacement decreases from 2.76 cm to 1.44 cm.

ON TECHNOLOGICAL PR OBLEMS OF FABRICATION OF RELIEF DESIGNS BY ISOMETRIC TRANSFORMATION OF THIN SHEET

Some problems connect ed with production of new light-weight filler type are considered for sandwich layers. Constructively, the filler is the folded structure that can be developed on a plane. This feature makes it possible to produce the filler by isometric t ransformation of thin sheet through local bending without material stretching.Th e main difficulty is that the bending must be carried out along all lines of com plex-shaped marking-out at a time. The problem of shaping can be solved by use of the original shaping device that can be transformed in operation. The herein -presented technology of production makes it possible to fabricate parts with d eep relief using a wide gamut of different materials even as the thin-sheet met al alloys and paper.

Lightweight Mutual Authentication Scheme for Protecting Identity in Insecure Environment

Many improved authentication solutions were put forward, on purpose of authenticating more quickly and securely.However, neither the overuse of hash function,or additional symmetric encryption, can truly increase the overall security. Instead,extra computation cost degraded the performance.They were still vulnerable to a variety of threats, such as smart card loss attack and impersonation attack, due to hidden loopholes and flaws. Even worse, user's identity can be parsed in insecure environment, even became traceable. Aiming to protect identity, a lightweight mutual authentication scheme is proposed. Redundant operations are removed,which make the verification process more explicit. It gains better performance with average cost compared to other similar schemes.Cryptanalysis shows the proposed scheme can resist common attacks and achieve user anonymity.Formal security is further verified by using the widely accepted Automated Validation of Internet Security Protocols and Applications(AVISPA) tool.

Stress-rupture measurements of cast magnesium strengthened by in-situ production of ceramic particles

We have introduced a polymer precursor into molten magnesium and then in-situ pyrolyzed to produce castings of metal matrix composites(P-MMCs)containing silicon-carbonitride(SiCNO)ceramic particles.Stress-rupture measurements of as-cast P-MMCs was performed at 350 ℃(0.69TM)to 450 ℃(0.78TM)under dead load condition corresponding to tensile stress of 2.5 MPa to 20 MPa.The time-to-fracture data were analyzed using the classical Monkman–Grant equation.The time-to-fracture is thermally activated and follows a power-law stress exponent exhibiting dislocation creep.Fractography analysis revealed that while pure magnesium appears to fracture by dislocation slip,the P-MMCs fail from the nucleation and growth of voids at the grain boundaries.

Mechanism of weld-line movement within hydroforming of tailor-welded tube

To reveal the reason of weld-line movement in hydroforming of a tailor-welded tube (TWT) with dissimilar thickness,the stress ratio of axial stress to circumferential stress is derived by mechanical analysis and analyzed between the thicker and thinner tubes,as well as the property of the axial strain. During TWT hydroforming,tensile strain along axial direction happens on the thinner tube. On the contrary,compressive strain happens on the thicker tube. Experiments are conducted to varify the weld-line movement regularity and strain distribution. It indicates that the weld-line moves from the thinner part to the thicker during TWT hydroforming. The thinning ratio of the thinner tube is bigger than that of the thicker tube,especially in the zone near weldline. Stress ratio difference between the thicker tube and the thinner tube is the main reason of weld-line movement and non-uniform thinning ratio distribution.

Epistemic-Based Investigation of the Probability of Hazard Scenarios Using Bayesian Network for the Lifting Operation of Floating Objects

Owing to the increase in unprecedented accidents with new root causes in almost all operational areas, the importance of risk management has dramatically risen. Risk assessment, one of the most significant aspects of risk management, has a substantial impact on the system-safety level of organizations, industries, and operations. If the causes of all kinds of failure and the interactions between them are considered, effective risk assessment can be highly accurate. A combination of traditional risk assessment approaches and modern scientific probability methods can help in realizing better quantitative risk assessment methods. Most researchers face the problem of minimal field data with respect to the probability and frequency of each failure. Because of this limitation in the availability of epistemic knowledge, it is important to conduct epistemic estimations by applying the Bayesian theory for identifying plausible outcomes. In this paper, we propose an algorithm and demonstrate its application in a case study for a light-weight lifting operation in the Persian Gulf of Iran. First, we identify potential accident scenarios and present them in an event tree format. Next, excluding human error, we use the event tree to roughly estimate the prior probability of other hazard-promoting factors using a minimal amount of field data. We then use the Success Likelihood Index Method(SLIM) to calculate the probability of human error. On the basis of the proposed event tree, we use the Bayesian network of the provided scenarios to compensate for the lack of data. Finally, we determine the resulting probability of each event based on its evidence in the epistemic estimation format by building on two Bayesian network types: the probability of hazard promotion factors and the Bayesian theory. The study results indicate that despite the lack of available information on the operation of floating objects, a satisfactory result can be achieved using epistemic data.

An Apparatus for Assessing Lustre of Fabrics

Luster is one of the main factors in assessing fabric appearance. There are many different ways to definite and describe the luster, which result in disorder and discommodious in evaluation. Based on previous work, an apparatus suited for the measure of lustre is developed. Which performed measure the reflection distribution of fabrics automatically. Then the objective judgment can be given by the geniophotometric curve. Finally taking several kind of specimens for example give the results to prove the effectiveness of the device.