Monotonic and fatigue performance in bending of fiber-reinforced engineered cementitious composite in overlay system

This paper presents an experimental study and theoretical analyses on the monotonic and fatigue performance in bending of a polyvinyl alcohol (PVA) fiber-reinforced engineered cementitious composite (ECC) overlay system. The influence of the interfacial characteristics between overlay and old concrete substrate on the overall bending performance is investigated. The experimental results show that when ECC is used as overlay material, both load carrying capacity and deformability represented by deflection at peak load of the overlaid beams in flexure are significantly increased compared to those of plain concrete (PC) overlaid beams. The fatigue life of ECC overlaid beams in flexure is not influenced by the layer/base interfacial characteristics, such as smooth cutting surface or sand-blasted rough surface. However, the deformation ability of the overlaid beams, such as deflection at midpoint of beam, in both static and cyclic loading cases are influenced by the interfacial property. The smooth casting surface leads to larger deformation at peak load under monotonic loading and at failure under fatigue loading than the corresponding values for beams with a rough casting surface. The present study demonstrates that reflective cracking failure in pavement overlays can be eliminated by the use of a ductile material such as ECC.     

Evaluation of Critical Binder Properties Affecting the Compactibility of Binary Mixtures

The aim of this study was to identify essential physical and mechanical properties of various binders and to investigate their influence on the tensile strength and porosity of tablets made from binary mixtures with sodium bicarbonate. The binders were characterized according to axial and radial tensile strength after compression into tablets, yield pressure and minimum porosity during compression, and elastic recovery after compression. The addition of a binder generally resulted in an increase in the tensile strength and a decrease in the porosity of the sodium bicarbonate tablets. The location of the binder in the voids between the sodium bicarbonate particles thus decreasing the porosity of the tablet seemed to be an important consideration. Consequently, the addition of binders with a low yield pressure value and a relatively small elastic recovery value (e.g., polyethylene glycol 3000 and polyvinylpyrrolidone) resulted in tablets of low porosity and high tensile strength, especially in the axial direction. The tensile strength of the pure binder also seemed to be important, especially for binders with a lower degree of deformability (e.g., microcrystalline cellulose and pregelatinised starch). The results also indicated the value of using both axial and radial tensile strength measurements in assessing the effect of a dry binder and showed that the importance of different binder properties varied according to the direction of the tablet strength measurements. The results demonstrated that the applied characteristics of the binders used in this study may serve as a useful tool in evaluating the effectiveness of binders.     

Elastohydrodynamics of concentrated suspension with generalized newtonian fluid medium

Lubrication theory is applied to compute the deformation of two approaching particles suspended in a Generalized Newtonian fluid with linear elastic theory estimating deformation and force on the particles with respect to deformability δ. The relative viscosity of concentrated suspension with deformable particles in a Generalized New-tonian fluid is obtained for a simple cubic array configuration by using the results of deformation and force for two particles. Since the deformation of particles generates the freedom of moving particles geometrically, the suspension with deformable particles shows shear thinning behavior.     

水泥石力学变形能力的影响因素实验分析

针对从实验角度计算水泥石在一定井下条件的变形能力研究相对较少的问题,结合弹性耦合力学模型,利用实验结果计算并分析了在一定工况下,水泥浆配方、实验温度、围压、养护时间、水泥环厚度5个方面对水泥石变形能力的影响。结果表明,加入弹韧性材料能够降低水泥环的弹性模量,且加入胶乳后的水泥环力学变形能力较纤维水泥环明显要好;随着养护温度的升高,水泥石的弹性模量减小,从而增加了水泥环的总变形能力;随着围压的增大,水泥环变形能力有减弱趋势;随着水泥环在井下的时间增长,在一定程度上提高了水泥环的力学变形能力;虽然水泥环厚度对水泥石自身性能无影响,但水泥环厚度从38.1 mm减小到19.1 mm,水泥环在井下条件的变形可增大85.5%。     

CaO-MgO-SiO2-Al2O3类夹杂物塑性化对帘线钢加工断丝率的影响

通过分析70 t转炉流程和180 t转炉流程生产的LX72A帘线钢合股断丝率,得出中心偏析相同的条件下,当钢中脆性夹杂物比例由90.7%降至20.5%,也就是塑性夹杂物的比例由9.3%提高79.5%时,平均盘条断丝率由4.20次/t降至2.56次/t。通过采用碱度1.05不含MgO的LF精炼渣,控制钢中Als含量≤0.001%,氧含量≤22×10^-6,可有效地降低钢中脆性夹杂物含量,降低盘条断丝率。     

Improved mechanical properties of V-microalloyed dual phase steel by enhancing martensite deformability

A good combination of ultimate tensile strength(UTS)up to 1365 MPa and total strain to failure(StF)to 15.5％has been achieved due to deformable martensite in the invented vanadium-microalloyed dual-phase(DP)steel,which was manufactured by two-stage annealing of cold rolled steel strip.The employed extensive characterizations revealed that the ductile martensitic phase in this DP steel differ-entiated from ordinarily low-carbon martensitic lath in both morphology and lattice structure.Complex coherent orientation relationships between ferrite,reverse austenite,martensitic phase and vanadium carbide(VC)do exist,leading to a new martensitic transformation mechanism and resultant dual-phase microstructure.Besides,a detailed characterization including essential phase transformation analysis in combination with in situ TEM observation,shows that,all the essential processing including recrystal-lization,reverse austenitic and martensitic transformation,in debt to the particular effects of VC,can be recognized as phase transformations with higher thermodynamic driving force and higher kinetic energy barrier as compared to previously common processing,which actually changes the microstructure and,indirectly leads to higher strength and higher ductility.This synergy of thermodynamics and kinetics can be generalized to improve mechanical properties of present steels.     

型砂退让性的测试方法研究

介绍一种通过测量铸件凝固收缩应力来表示型砂退让性的方法.利用模/数转换器和微机检测手段对多种常用的造型材料进行退让性检测,实时反映浇注后型砂的退让性变化情况, 具有较好的实用价值.     

Equal Channel Angular Deformation （ECAD） of As-Cast AM60 Magnesium Alloy

As-cast AM60 magnesium alloy ingot with grains coarser than those of as-extruded AZ series is more liable to produce cracks under ECAD with severe shear strain. A feasible scheme of equal channel angular deformation (ECAD) for as-cast AM60 magnesium alloy ingot was proposed in this paper. The tests were conducted on Instron machine with hydraulic back-force machine. Through analysing load vs displacement curves, the effects of ECAD processing conditions on deformability and microstructure of as-cast magnesium AM60 billets were discussed. During testing,the back-force employment was helpful to keep ECAD processing more stable. And with back-force, it was observed that the number of ECAD passes in different routes could tremendously affect the deformability and microstructure of magnesium specimens. It was concluded that ECAD processing is entirely feasible for as-cast magnesium AM60 alloy under severe shear strain, and back-force employment, multi-passes deformation and lubrication of graphite paper are the factors primarily beneficial to improvement of deformability and refinement of grained structure. This work provides a way to produce magnesium alloy with fine-grained structure directly from casting ingot by ECAD technique.     

First principles study of influence of alloying elements on TiAl: cleavage strength and deformability

The electronic structure and binding energy of a number of TiAl–X alloy systems (X=V, Cr, Mn, or Si) were calculated using the discrete variational cluster method, based on the local density approximation of the density functional theory. The influence of alloying elements on the cleavage strength and the deformability of TiAl was investigated by means of an atomistically uniaxial loading deformation along the [0 0 1] and the [1 1 0] directions, respectively. The results show that both the cleavage strength and the deformability of TiAl depend on the substitution behaviour of alloying atoms in TiAl. In general, the 3d transition atoms V, Cr, and Mn enhance the cleavage strength and the deformability of TiAl due to an increased number of d-electrons contributing to the d–d bonding, while the atom Al and Si reduce the cleavage strength and the deformability of TiAl because of relatively strong hybridization between the p- and d-electrons.