钢材模型强化参数对构件滞回性能模拟的影响分析

为了考察材料本构模型参数对构件滞回性能模拟的影响,利用通用有限元软件ABAQUS对H形截面钢构件绕强轴压弯的滞回特性进行了数值模拟研究,对比分析了Ramberg-Osgood模型应变硬化指数和两折线模型强化率的参数取值对低周往复荷载作用下构件的极限抗弯承载力、极限后性能模拟结果的影响。分析表明,在所研究的材料强化参数变化范围内,构件极限抗弯承载力的相应变化是有限的;但构件的残余位移、耗能能力等大范围塑性变形阶段的模拟结果对两类材料模型强化参数均表现出很强的敏感性。基于以上分析结果,建议在对构件性能进行全过程数值模拟时应当谨慎地选用材料强化参数,并在必要时补充相应的材料性能试验。

抗撞结构桩基关系研究的不足与措施

通过对土材料模型及参数的确定方法的相关现状进行分析总结,发现用于表征桩基关系的土材料模型及材料参数,无论在试验方法、本构模型遴选,还是模型参数的确定方面都存在不合理现象,同时这也是导致桩基关系不合理的主要成因。保证有限元仿真设计的桩基关系符合抗撞结构的使用要求,并与实际试验安装现场的桩基关系基本一致,即要保证土材料模型及参数与实际试验使用的回填土材料类型及参数的一致性。为此,桩基关系的研究需从桩基试验方法、土材料模型遴选以及模型参数反演3个方面进行完善。针对这3个方面研究存在的具体问题,分别给出了各自潜在的解决方案和未来可能的研究方向。首先,完善子结构级模型的桩基约束条件试验系统,为设计合理的桩基关系提供试验基础;其次,以试验为基础,选择或开发合适的土材料模型后,研究新的反演识别方法,以获取材料模型参数。综合试验到仿真分析的一系列措施,完善桩基关系匹配研究,研究成果对道路交通安全的提升具有极为重要的现实意义。

Effects of initial δ phase(Ni_3Nb) on hot tensile deformation behaviors and material constants of Ni-based superalloy

Effects of initial δ phase（Ni_3Nb） on the hot tensile deformation behaviors and material constants of a Ni-based superalloy were investigated over wide ranges of strain rate and deformation temperature. It is found that the true stress-true strain curves exhibit peak stress at a small strain, and the peak stress increases with the increase of initial δ phase. After the peak stress, initial δ phase promotes the dynamic softening behaviors, resulting in the decreased flow stress. An improved Arrhenius constitutive model is proposed to consider the synthetical effects of initial δ phase, deformation temperature, strain rate, and strain on hot deformation behaviors. In the improved model, material constants are expressed as the functions of the content of initial δ phase and strain. A good agreement between the predicted and measured results indicates that the improved Arrhenius constitutive model can well describe hot deformation behaviors of the studied Ni-based superalloy.

Technological Parameters for Preparation and Granulation of Ammonium Ion-Exchange Material

As a raw material,kaolin was modified to prepare a high-performance ammonium ion-exchange material.According to cation-exchange capacity (CEC) measurement,the prepared ammonium ion-exchange material has an ammonium ion-exchange capacity greater than 75mg/g and can be used to remove ammonia nitrogen in water treatment.A pharmaceutical extruder-rounder was used to study the effects of granulation process.Polyethylene glycol6000 (PEG-6000) was used as the pore-forming agent and calcining temperature of 650℃ was used as the optimal condition.NMR data indicate that 27 Al is mainly converted from hexa-coordinated Al to tetra-coordinated Al during the modification.Compared with 29 Si in the original kaolin,29 Si in the modified kaolin does not have an obvious change.A comparison of the data with Langmuir and Freundlich isotherm models shows a good correlation.The Freundlich model describes the process more accurately,and the adsorption process of ammonia nitrogen in water with the ammonium ion-exchange material closely matches the pseudo-second-order reaction.

Material Parameters of a Structural Steel with Plastic Strain Memory

The present work is concerned with the characterization of hardening parameters for an elasto-plastic continuum model, taking into account the memory effect of plastic strain amplitude, in order to predict the hysteretic responses of a ferritic steel. This elasto-plastic three-dimensional model is based on the internal thermodynamic variables which composed of the nonlinear kinematic hardening and isotropic hardening with the plastic strain memorization. The emphasis is put on the determination of strain memory parameters along with other material parameters of the proposed model in order to better simulate the behavior of the material at different strain range. The material parameters are calibrated with the experimental stabilized loops of stress-strain curves available in the literature. The predicted stabilized loops from the simulation with the determined parameters show good agreement with the experimental results signifying the validity of the considered model.

Research on theory and application of landslide model test

In this paper, a theory of landslide model testing and application in Three Gorges reservoir area were introduced.Based on geo-mechanical model tests, the similarity ratio of similar material parameters, component of similar material and the boundary friction coefficient of the 2D earth landslide model test were derived and stated by theoretical and experimental methods.A model test of the Qianjiangping landslide in Three Gorges reservoir area reveal a two-step trigger mechanism of coexistence between retrogressive landslide and thrust load caused land-slide.

Solidification researches using transparent model materials——A review

A review is given in the paper for solidification researches with transparent model materials. The effective experimental me- thod was first proposed by Jackson and Hunt in 1965. The transparent model materials for solidification researches are a kind of non-faceted crystals known as ＂plastic crystals＂ or ＂globular molecules＂, which have very low entropy of melting as that of metals. According to Jackson＇s theory proposed in 1958, entropy of phase transformation will determine whether the phase interface morphology is smooth or rough in atomic scale, which will lead to faceted or nonfacted phase interface in mi- croscopic and macroscopic scales. Succinonitrile （SCN） and its alloys with water, ethanol, acetone, and NH4C1-H：O solution are most commonly used as transparent model materials for solidification researches of dendritic growth, anisotropy of solid-liquid interfacial energy, crystal nucleation, crystal grain formation, directional solidification, eutectic and peritectic so- lidification, solidification defects formation such as bubble, hot tearing, etc. Among these researches, the most impressive work was the critical test of dendritic growth theories with high purity succinonitrile by Glicksman et al., which gave positive answer to the Ivantsov＇s analysis and negative answer to the ad hoc condition of the maximum velocity hypothesis. The future researches with transparent model materials could be suggested in three aspects： 1） accurate measurement of material proper- ties and alloy phase diagrams in more plastic crystals, especially to find more transparent eutectic and peritectic alloys; 2） accurate measurement of the grain boundary groove shape to obtain precise data of the anisotropy parameters of the interfacial free energy in transparent model materials; 3） to get clear pictures of solidification processes with morphology details in a rela- tively large area, with continuous movement of liquid and particles, in order to give experimental support to numerical simula- tions aimming at accurate description of microstructure formation during solidification of multicomponent alloys under complex conditions of real casting and welding processes.