Hot deformation behavior of low carbon steel during compression at elevated temperature

Hot compression tests of low carbon steel were carried out on Gleeble-3500 system in the temperature range from 750 to 900 ℃ and in the strain rate range from 0.001 to 1.0 s-1, and the associated microstructural evolution was studied by observations with a metallographic microscope. The results show that the stress-strain curves exhibit a peak stress at critical strain, after which the fl ow stresses decrease monotonically until reaching high strains, showing a dynamic fl ow softening. The peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation. The fl ow stress increases with increasing strain rate and decreasing deforming temperature. The fl ow stress can be described by constitutive equation in hyperbolic sine function and can also be described by a Zener–Hollomon parameter Z. With increasing deformation temperature and decreasing strain rate, the grain size as well as the volume fraction of the recrystallized grains increase. The safe region for hot working of the alloy has been determined according to the processing map and microstructure at the true strain of 0.5, which is the deformation temperature of 840-940 ℃ and the strain rate of 0.001-1.0 s-1.     

Hot Deformation Behavior of Mg2[KG-*2]B2[KG-*2]O5 Whiskers Reinforced Al Composite

The hot deformation behavior of Mg2B2O5w/Al composite was investigated by compression test at different temperatures and different strain rates. The constitutive equation was established by taking peak stresses as the function of temperatures and strain rates. It was found that the hyperbolic sine law creep equation is in good agreement with the experimental results and can be applied to all flow stresses under various deformation conditions. The apparent activation energy of the composite is 138. 64 kJ /mol, which is approximately equal to that of lattice self-diffusion of pure Al.     

FEM analysis of vacuum hot bulge forming of Hastelloy C-276 thin-walled cylindrical workpiece

A stress relaxation test has been carried out for Hastelloy C-276 at temperature of 800 ~C and initial stress level of 250 MPa. Based on the experimental stress relaxation curve, the relationship between creep strain rate and stress has been derived. Then, a set of creep constitutive equations has been built and the values of constants arising in the constitutive equations have been determined by fitting the creep strain rate-stress curve. Close agreement between computed results and experimental ones is obtained for stress relaxation data. The creep constitutive equation set has been integrated with the commercial FE （finite element） solver MSC.Marc via the user defined subroutine, CRPLAW, for the vacuum hot bulge forming process modelling of Hastelloy C-276 thin-walled cylindrical workpiece. The temperature field, the radius-direction displacement field and the stress-strain field are calculated and analyzed. Furthermore, the bulging dimension and the final internal diameter of workpiece are predicted and the test results verify the reliability of the finite element method.     

磁弹性理论中的守恒定律和路径无关积分

守恒定律与路径无关积分是传统力学中的重要工具,在位错、断裂力学和其他缺陷理论中具有重要的应用价值。由于力场和磁场的共同作用,以及磁弹性材料本身的耦合性质,所以磁弹性体具有更为广泛的守恒定律和路径无关积分。文中通过定义4种不同的热力学函数,应用电磁场理论中的能量矩概念,建立了磁弹性理论中对偶形式的守恒定律,并由这些对偶形式的守恒定律得到了相应的路径无关积分。文中建立的守恒定律和路径无关积分,对研究磁弹性体中的缺陷理论将起到十分重要的作用。     

高斯曲率内蕴公式的几种形式的推导方法

考虑曲面上高斯曲率内蕴公式的表示问题,运用曲面基本方程的矩阵表示法,给出了高斯曲率是内蕴量的直接的显式公式,并指出这种内蕴公式与Brioschi的表示公式是明显一致的;给出了高斯曲率简化公式的推导来源,揭示出了高斯曲率隐式公式的发现过程.     

中国团餐企业资产与收益现状研究

中国餐饮业发展飞速,团餐业的发展尤为突出。文章通过对2011、2012年50家团餐骨干企业的资产总额、利率情况、营业收入及单位人口创收等收益情况的比较研究,认为我国团餐企业处于中等规模,对资源的充分使用还有较大发展空间,盈利与竞争能力较强,同时可以得出团餐行业的总体创收趋势及投资回报速度尚可的结论。     

基于试验非拟合混凝土本构方程

目的建立混凝土单轴拉伸和压缩应力-应变方程．方法基于混凝土单轴拉伸和压缩的试验数据,研究应力-应变变化规律,抛弃传统的拟合方法,直接由混凝土基本性能（初始弹性模量、峰值应力、峰值应变和应变软化性态）导出应力-应变方程．结果全程应力-应变方程由强化方程和软化方程给出,在峰值应力之前,强化方程为单调增且二阶导数为负的曲线,与试验结果曲线相符．在峰值应力之后,用不同的软化方程表示试验软化曲线．结论笔者提出的混凝土本构方程与很多实验数据相符,方程中的参数具有明显的力学意义,形式简单,便于理解,能很好的应用于混凝土本构关系的研究中．     

Combined damaged elasticity and creep modeling of ceramics with wedge splitting tests

During the crack propagation in common refractory ceramics at high temperatures, creep may occur in the wake of a process zone and in front of a crack tip. To account for this phenomenon, an integrated material constitutive model was developed by combining the mechanical behavior following isotropic damaged elasticity concept and Norton-Bailey creep. The post peak fracture behavior followed the bilinear softening law and a simple criterion was defined to consider the creep asymmetricity in uniaxial tension and compression. The material constitutive model was applied to inversely identify mode I fracture parameters with wedge splitting tests of an alumina spinel material at 1200 °C. It showed that the mean ratio of the nominal notch tensile strength to the actual tensile strength was 1.93 and the mean pure fracture energy was 297.6 N/m. In addition, the creep contributed 12.9% on average into the total fracture energy.     

利用变频调速器对砂布砂纸生产线进行恒张力控制

本文根据弹性力学中的虎克定律，结合砂布砂纸生产特点，分析计算了生产线中基体、应变、速度、张力、转速等参数之间的关系，建立了砂布砂纸生产线中传动辊转速（频率）运动方程。然后利用此规律通过交流变频调速器对电机转速的控制，实现了砂布砂纸生产线的恒定张力控制。系统控制简捷、稳定，调节方便，节约能耗，重复性好，实用性强。     

工业纯铝高温流变行为的实验研究

为了深入了解连续铸轧这一融合了“铸造”和“轧制”两个工艺过程条件下的流变行为与简单铸造+热加工(热轧)组合条件下流变行为的差异,在Gleeble-1500热模拟机上对铸造工业纯铝高温压缩流变行为及其影响因素进行了系列的模拟实验研究,得到了不同变形条件下铸造工业纯铝高温压缩成形过程中的流变曲线;通过多元线性回归分析得到了其应力-应变本构方程;并与铸轧过程物理模拟实验研究的结果进行了对比分析,结果表明:在相同变形条件下铸造工业纯铝高温压缩变形流变应力小于铸轧过程的流变应力,且随着应变速率的增大,它们之间的差值更大。