Effects of Surface-activated Coal Gangue Aggregates on Properties of Cement-based Materials

Effects of calcined coal gangue （CG） aggregates treated by the surface thermal activation on the flowability and strength, and paste-CG aggregate interfaces of the cement-based material were investigated. The experimental results show that the compressive and flexural strength of the cement-based material with the calcined CG aggregates is much higher than that of the material with the natural CG aggregates, but the flowability of the material with calcined CG is significantly reduced with the calcined time. The strength of the material with the calcined CG aggregates only increases little with the calcined time at the same w/c ratio, but is reduced with the calcined time at the same flowability. The CG aggregates calcined by the surface thermal activation obviously overcomes the disadvantages of fully calcined CG.

Internal Curing Using Water-releasing Material for High Strength Micro-expansive Concrete

Due to its low water content, it is difficult for expansive agent to have an effective expansive effect on high strength concrete to compensate its extensive shrinkage and form a certain expansion. To solve this problem, water-releasing material with water storage and releasing characteristics was incorporated into high strength micro-expansive concrete to provide internal curing, and expansive effect of expansive agent was improved. Migration of water from initially saturated water-releasing material to the surrounding hydrating cement paste was investigated. Based on a given efficient diffusion distance of water stored in water-releasing material, the mass and real water-cement ratio of cured cement paste were estimated. At the same time, the effect of internal curing of water-releasing material on the volume deformation of high strength micro-expansive concrete was investigated.

APPROXIMATE MEANS FOR EVALUATING TENSILE STRENGTH OF HIGH POROSITY MATERIALS

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Properties of Bamboo Charcoal and Cement-based Composite Materials and Their Microstructure

The objective of this work was to study the properties of bamboo charcoal and cement-based composite materials and their microstructure. The pastes with various bamboo charcoals were prepared and the relative properties such as setting times and strength were tested and the microstructures and pore characteristics of pastes with various bamboos were also studied. The experimental results indicated that bamboo charcoal affects the setting times of cement paste, but the introduction of water reducer relieves this condition. Bamboo charcoal also poses an impact on the hardened paste strength. The prominent strength decrease is found when more and larger size bamboo charcoal is mixed into the cement paste. Bamboo charcoal alters the paste microstructure and increases the porosity and pore volume, but it increases the pores with the diameter of less than 50 μm. The pastes with various bamboo charcoals are given with the good functions such as adjusting humidity and adsorption.

Recent developments of the high strength and high ductility nanostructured materials

This talk will summarize the recent work related to a kind of new nanomaterials produced by the SMAT (surface mechanical attrition treatment).The concept of surface nanocrystallization of materials will be presented.In terms of the grain refinement mechanism induced by plastic deformation,a novel surface mechanical attrition(SMA) technique was developed for synthesizing a nanostructured surface layer on metallic materials in order to upgrade the overall properties and performance.The grain refinement mechanism of the surface layer during the SMA treatment will be analyzed in terms of the nanostructure observations in several typical materials.Very high yield stress(5 times of the base material) on the surface layer of the material obtained by the SMAT has been observed.The effect of surface nanostructures on the mechanical behavior and on the failure mechanism of metallic material shows the possibility to develop a new strength gradient composite using co-rolling and nitriding.The role of residual stress induced during the treatment will be investigated and discussed.The developed materials are also porosity free materials which can be used as reference material for the local mechanical behavior investigation technique such as the nanoindentation.A general concept for obtaining high strength and high ductility nanostructured materials will be presented.The exceptional high strength and high ductility steels have developed.The simulation of the mechanisms for improving ductility of high strength nanostructured materials will be presented.The potential applications for the land transportation vehicles(car,bus,train) and wind energy have been investigated.Some examples of concept design for the integration of the advanced nanostructured steels will be presented.

Mechanical model for yield strength of nanocrystalline materials under high strain rate loading

To understand the high strain rate deformation mechanism and determine the grain size,strain rate and porosity dependent yield strength of nanocrystalline materials,a new mechanical model based on the deformation mechanism of nanocrystalline materials under high strain rate loading was developed.As a first step of the research,the yield behavior of the nanocrystalline materials under high strain rate loading was mainly concerned in the model and uniform deformation was assumed for simplification.Nanocrystalline materials were treated as composites consisting of grain interior phase and grain boundary phase,and grain interior and grain boundary deformation mechanisms under high strain rate loading were analyzed,then Voigt model was applied to coupling grain boundary constitutive relation with mechanical model for grain interior phase to describe the overall yield mechanical behavior of nanocrystalline materials.The predictions by the developed model on the yield strength of nanocrysatlline materials at high strain rates show good agreements with various experimental data.Further discussion was presented for calculation results and relative experimental observations.

HIGH TEMPERATURE MATERIALS AND STRENGTH STUDY IN CHINA

In the past half century China has developed and formed her own system ofhigh temperature materials for power, automobile and aero-engine industries in the temperature rangefrom 550 deg C to 1100 deg C. These high temperature materials include heat-resisting steels,iron-base, nickel-iron-base and nickel-base superalloys. Some achievements - in high temperaturestrength study, new technologies and new alloy development are also discussed.

MODIFICATION THE CEMENTIOUS MATERIAL OF ULTRA-HIGH-STRENGTH SLEEPER CONCRETE

This paper presents investigation results on the natural ultra-fine mineral flour of crystalline silica fume (CSF) and porous quartz sand stone (PQSS) which can modify cement mortar strength under hydrothermal synthesis reaction (HSR) in the autoclave-cured condition. The replacement of cement by CSF and PQSS can signifi cantly increase the Jflerural and compressive strength which reach 22MPa and 150MPa respectively and de-crease the porosity oj the cement mortar. The ratio oj fine aggregation, standard sand to cementions material has sig nificant influence on the mortar strength. The mechanisms involved in cement and natural mineral flour and the HSR are presented. CaO/SiO2 ratio ranges from 3. 20 to 1. 11. the main hydrate phase is C2SH and there is not Tober-morite through X-Ray diffraction qualitative analysis. The new and ultra-high strength cementious material as basic material of sleeper concrete can he used in prestressed reinforcement sleeper concrete.

Developing High Strength Pervious Concrete Mixtures with Local Materials

This study focuses on developing pervious concrete mixtures that have higher compressive strengths than conventional pervious concrete. This study also focuses on producing high strength pervious concrete that is also made with locally available materials. The study focused on four aspects of pervious concrete to produce high compressive strengths. These parameters were the effect of the coarse aggregate (type and size), the compaction of the test specimens, the effect of the w/c along with superplasticizers, and lastly the effect of silica fume. This study was completed parametrically in order to isolate each variable in order to see its individual affect. Once an optimum performance was obtained from one variable the best performing mixture was used for the next variable testing. This method allowed for the highest performing mixture to be obtained from each of the investigated variables. The results showed that high strength pervious concrete made with local aggregates, without polymers, and without fibers can be produced in the range of 15.44 MPa - 21.63 MPa. A porosity range 19.1% - 32.9% with a percolation rate range of 5.8 mm/s - 1.9 mm/s was also achieved, with a porosity of 19.4% and percolation rate of 2.6 mm/s for the highest performing mixture.

Strength Acquisition Mechanism of High Temperature Resistant Materials Prepared by Waste Architectural Ceramics

In order to realize the large-scale and high-value utilization of waste architectural ceramics,high-temperature resistant materials based on waste architectural ceramics were prepared with sodium silicate as the binder,clay/bauxite and metakaolin/bauxite as coating materials,and the cold strength obtaining mechanism was explored.The phase composition,the microstructure and the mechanical properties of the high temperature resistant materials based on waste architectural ceramics were tested and analyzed.The results showed that when the heat treatment temperature was between 110-1000℃,the strength of the samples mainly came from the physical adhesion of sodium silicate and fine powder.When the temperature rose to 1100℃,the strength of the sample was improved since the internal low-melting-point components melted and promoted sintering.The addition of clay and bauxite can effectively enhance the flexural strength of the samples when the heat treatment temperature is 1000℃.When the heat treatment temperature rises from 900 to 1000℃,the flexural strength of the samples will be enhanced owing to the formation of silica alumina spinel and mullite from metakaolin.

Fabrication of Aluminium Matrix Composite Using Thixoforming Process for High Strength Material Components

Aluminium-based MMCs(metal matrix composites)have many potential applications in the automotive manufacturing industry,aerospace and military because the aluminum has a low density.Aluminum as a matrix with Al2O3 reinforcement has attracted interest to be developed in order to improve the mechanical property.The study carried out the formation of Al-5%Cu-4%Mg matrix with the reinforcement of Al2O3 by thixoforming process.In this paper,we studied the effect of semisolid thixoforming process on strength of Al-5%Cu-4%Mg matrix.The matrix used here was doped by Al2O3 with the volume fraction from 5%to 20%.It is found that strength of MMCs significantly increases with increasing volume fraction of Al2O3 reinforcement from 5%to 20%.This is due to a good wettability in interface region such as formation of spinel MgAl2O4 phase.Moreover,toughness of MMCs increases by process of semisolid thixoforming due to evolution of microstructure such as globular and fine grain structures.These results indicate that the thixocasting process conducted in this study could increase the value of the matrix hardness and tensile strength,so that such process opens up opportunity for application in the manufacturing industry.

Developing Sustainable High Strength Concrete Mixtures Using Local Materials and Recycled Concrete

This study presents the development of high strength concrete (HSC) that has been made more sustainable by using both local materials from central Texas and recycled concrete aggregate (RCA), which has also been obtained locally. The developed mixtures were proportioned with local constituents to increase the sustainable impact of the material by reducing emissions due to shipping as well as to make HSC more affordable to a wider variety of applications. The specific constituents were: limestone, dolomite, manufactured sand (limestone), locally available Type I/II cement, silica fume, and recycled concrete aggregate, which was obtained from a local recycler which obtains their product from local demolition. Multiple variables were investigated, such as the aggregate type and size, concrete age (7, 14, and 28-days), the curing regimen, and the water-to-cement ratio (w/c) to optimize a HSC mixture that used local materials. This systematic development revealed that heat curing the specimens in a water bath at 50℃ (122oF) after demolding and then dry curing at 200℃ (392oF) two days before testing with a w/c of 0.28 at 28-days produced the highest compressive strengths. Once an optimum HSC mixture was identified a partial replacement of the coarse aggregate with RCA was completed at 10%, 20%, and 30%. The results showed a loss in compressive strength with an increase in RCA replacement percentages, with the highest strength being approximately 93.0 MPa (13,484 psi) at 28-days for the 10% RCA replacement. The lowest strength obtained from an RCA-HSC mixture was approximately 72.9 (MPa) (10,576 psi) at 7-days. The compressive strengths obtained from the HSC mixtures containing RCA developed in this study are comparable to HSC strengths presented in the literature. Developing this innovative material with local materials and RCA ultimately produces a novel sustainable construction material, reduces the costs, and produces mechanical performance similar to prepackaged, commercially, available construction building materials.

Pt-Al₂OM₃Composite Material Designed for Cyclic Production of Optical Glasses under High Temperature Conditions

The article considers one of the possible approaches to the solution of an urgent issue of metal consumption reduction, increase of operating life and maximum operating temperature as well as reduction of irrecoverable losses of platinum products and alloys when operating under high temperature conditions, particularly for glassblowing and single crystal growing crucibles. A two-layered composite material based on platinum-group metals and corundum plasma ceramics is thoroughly investigated. A successful experience of crucibles exploitation, designed for production of high temperature optical glasses from the composite and results of the research on composite material specimens are described.

Effects of the shape and size of rectangular inclusions on the fatigue cracking behavior of ultra-high strength steels

The fatigue cracking behavior of ultra-high strength steels containing rectangular inclusions of small sizes were investigated based on in situ observations by scanning electron microscopy （SEM）. The size and shape of rectangular inclusions affect markedly the initiation site and propagation path of a fatigue crack. Especially, the initiation site of a fatigue crack depends strongly on the angle between the long-axis of a rectangle inclusion and the loading direction, and the length/width ratio of this rectangle inclusion because the residual stress distribution fields vary with these conditions. The results coincide very well with those of finite element analysis.

Numerical Simulation of Warm Forming Behavior of High Strength Aluminum Alloy 7075

Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes.It has been widely used in simulation of sheet metal forming processes at room temperature in the automotive industry.However,material at elevated temperature behaves more differently than at room temperature and specific material parameters and models need to be developed for the simulation of warm forming.Based on the experimental investigation of material behavior of high strength aluminum alloy 7075(AA7075),constitutive equations with strain rate sensitivity at 140,180 and 220 ℃ are developed.Anisotropic yield criterion Barlat 89 is used in the simulation.Warm forming of limit dome height tests and limit drawing ratio tests of AA7075 at 140,180 and 220℃are performed.Forming limit diagrams developed from experiment at several elevated temperatures in the previous study are used to predict the failure in the simulation results.Punch force and displacement predicted from simulation are compared with the experimental data.Simulation results agree with experimental results,so the developed material model can be used to accurately predict material behavior during isothermal warm forming of the AA7075-T6 alloy.

Prediction and Verification of Resistance Spot Welding Results of Ultra-High Strength Steels through FE Simulations

Resistance spot welding (RSW) is the most common welding method in automotive engineering due to its low cost and high ability of automation. However, physical weldability testing is costly, time consuming and dependent of supplies of material and equipment. Finite Element (FE) simulations have been utilized to understand, verify and optimize manufacturing processes more efficiently. The present work aims to verify the capability of FE models for the RSW process by comparing simulation results to physical experiments for materials used in automotive production, with yield strengths from approximately 280 MPa to more than 1500 MPa. Previous research has mainly focused on lower strength materials. The physical weld results were assessed using destructive testing and an analysis of expulsion limits was also carried out. Extensive new determination of material data was carried out. The material data analysis was based on physical testing of material specimens, material simulation and comparison to data from literature. The study showed good agreement between simulations and physical testing. The mean absolute error of weld nugget size was 0.68 mm and the mean absolute error of expulsion limit was 1.10 kA.

Dynamic recrystallization behavior and kinetics of high strength steel

The dynamic recrystallization behavior of high strength steel during hot deformation was investigated.The hot compression test was conducted in the temperature range of 950-1150 °C under strain rates of 0.1,1 and 5 s-1.It is observed that dynamic recrystallization(DRX) is the main flow softening mechanism and the flow stress increases with decreasing temperature and increasing strain rate.The relationship between material constants(Q,n,α and ln A) and strain is identified by the sixth order polynomial fit.The constitutive model is developed to predict the flow stress of the material incorporating the strain softening effect and verified.Moreover,the critical characteristics of DRX are extracted from the stress-strain curves under different deformation conditions by linear regression.The dynamic recrystallization volume fraction decreases with increasing strain rate at a constant temperature or decreasing deformation temperature under a constant strain rate.The kinetics of DRX increases with increasing deformation temperature or strain rate.

Developing Sustainable Ultra High Strength Concrete Mixtures Using Spent Foundry Sand

This study presents the development of ultra high strength concrete(UHSC)that has been made more sustainable by using both local materials from central Texas and spent foundry sand(FS)from the metal casting industry,which has also been obtained locally.This study first describes various trial mixtures tested as well as the specimen preparation techniques investigated that led to the final UHSC-FS mixtures.The developed mixtures were proportioned with local constituents to increase the sustainable impact of the material by reducing emissions due to shipping as well as making UHSC more affordable to a wider variety of applications.The final mixture design constituents were:river sand,locally available type I/II cement,silica fume,and spent FS,which was obtained from a local steel casting company.Multiple variables were investigated,such as the aggregate type and size,concrete age(7,14,and 28-days),the curing regimen,and the water-to-cement ratio(w/cm)to optimize a UHSC mixture that used local materials and FS.This systematic development revealed that heat curing the specimens in a water bath at 50 oC(122 oF)after demolding and then dry curing at 200 oC(392 oF)two days before testing with a w/cm of 0.20 at 28-days produced the highest compressive strengths.Once an optimum UHSC mixture was identified a partial replacement of the fine aggregate with FS was completed at 10%,20%,and 30%.The results showed an increase of compressive strength performance at 10%replacement,followed by no change at 20%,and finally a slight decrease at 30%.Developing this innovative material with local materials and FS ultimately produces a novel sustainable construction material,reduces the costs,and produces mechanical performance similar to prepackaged,commercially,available construction building materials.

Experimental Investigation of the Effect of the Material Damage Induced in Sheet Metal Forming Process on the Service Performance of 22MnB5 Steel

The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in material properties but also causes material damage that may adversely influence the service performance of the material formed.Thus,an investigation is conducted to experimentally quantify such influence for a commonly used steel（the 22MnB5 steel） based on the hot and cold forming processes.For each process,a number of samples are used to conduct a uniaxial tensile test to simulate the forming process.After that,some of the samples are trimmed into a standard shape and then uniaxially extended until fracture to simulate the service stage.Finally,a microstructure test is conducted to analyze the microdefects of the remaining samples.Based on the results of the first two tests,the effect of material damage on the service performance of 22MnB5 steel is analyzed.It is found that the material damages of both the hot and cold forming processes cause reductions in the service performance,such as the failure strain,the ultimate stress,the capacity of energy absorption and the ratio of residual strain.The reductions are generally lower and non-linear in the former process but higher and linear in the latter process.Additionally,it is found from the microstructure analysis that the difference in the reductions of the service performance of 22MnB5 by the two forming processes is driven by the difference in the micro damage mechanisms of the two processes.The findings of this research provide a useful reference in terms of the selection of sheet metal forming processes and the determination of forming parameters for 22MnB5.

FEM simulation of flexible roll forming based on different material models

Flexible roll forming is a new roll forming process that produces parts with variable cross sections. This forming process is proposed to meet the demand of weight reduction of automobile industry. In order to study the mechanisms and material flow rules in this new forming process,the finite element mothod( FEM) model of a nine-step flexible roll forming of an ultra-high-strength steel bumper is established based on deep understanding and reasonable simplification of the process.Given that the material model is an important factor that influences the simulation accuracy,three material models which consist of different yield criteria and hardening models are adopted in the FEM models. Sheet thickness and springback amount calculated with three material models are studied comparatively. According to sheet thickness reduction and springback amounts,it is found that the MKi( Mises yield criterion and kinematic hardening law) model's result is larger than MI( Mises yield criterion and isotropic hardening law) model and HI( Hill's yield criterion and isotropic hardening law) model. Therefore,it is concluded that material models do have influences on the flexible roll forming simulation and need to be determined carefully.