Characterization of Ternary NiTiPd High-Temperature Shape-Memory Alloys under Load-Biased Thermal Cycling

While NiTiPd alloys have been extensively studied for proposed use in high-temperature shape-memory applications, little is known about the shape-memory response of these materials under stress. Consequently, the isobaric thermal cyclic responses of five (Ni,Pd)_49.5Ti_50.5 alloys with constant stoichiometry and Pd contents ranging from 15 to 46 at. pct were investigated. From these tests, transformation temperatures, transformation strain (which is proportional to work output), and unrecovered strain per cycle (a measure of dimensional instability) were determined as a function of stress for each alloy. It was found that increasing the Pd content over this range resulted in a linear increase in transformation temperature, as expected. At a given stress level, work output decreased while the amount of unrecovered strain produced during each load-biased thermal cycle increased with increasing Pd content, during the initial thermal cycles. However, continued thermal cycling at constant stress resulted in a saturation of the work output and nearly eliminated further unrecovered strain under certain conditions, resulting in stable behavior amenable to many actuator applications.     

采用有限元和热光弹方法分析扁形钢锭模的热应力

采用有限元和热光弹方法分析２６．６ｔ扁形钢锭模的热应力分布规律,设计出比较合理的钢锭模结构,提高了钢锭模的使用寿命,从而降低了炼钢成本。     

采用有限元和热光弹方法分析[1]扁形钢锭模的热应力

采用有限元和热光弹方法分析26.6t扁形钢锭模的热应力分布规律,设计出比较合理的钢锭模结构,提高了钢锭模的使用寿命,从而降低了炼钢成本。     

The Effect of Aluminum Additions on the Microstructure and Thermomechanical Behavior of NiTiZr Shape-Memory Alloys

The microstructure, thermal cycling, and mechanical behavior of Ni_48.5Ti_31.5?x Zr₂₀Al _x (x?=?0, 1, 2, 3) alloys were studied in the solution-treated and aged condition using microscopy techniques, differential scanning calorimetry, and compression tests. The microscopy techniques used include optical, scanning, and transmission electron microscopy, and three-dimensional, atom?Cprobe microscopy. The results of this study indicated a strong dependence of the transformation behavior on alloy chemistry and thermal cycling. The aluminum additions served to decrease transformation behaviors from 351?K to 596?K (78?°C to 323?°C) and reduce thermal stability. Additionally, aluminum was shown to increase the plateau stress in the aged condition, whereas the formation of coarse-grained intermetallic phases caused the embrittlement of the microstructure, reducing its ductility. The addition of Al resulted in the refinement of the coarse, lenticular precipitates identified as Ni₄(Ti,Zr)₃.     

20辊森吉米尔轧机板形调控性能研究

运用通用有限元软件ANSYS建立了具有多种辊间接触状态的20辊森吉米尔轧机辊系三维弹性变形的有限元模型,合理解决了对辊间接触压扁变形的建模,实现了对此较复杂辊系变形的正确求解.以国内某厂森吉米尔轧机为对象,结合现场实际数据,成功实现了运用通用有限元软件ANSYS求解20辊森吉米尔轧机的辊系三维弹性变形,进而分析了森吉米尔轧机的板形调控性能.     

Experimental Study of the Biaxial Cyclic Behavior of Thin-Wall Tubes of NiTi Shape Memory Alloys

Combined torsion-tension cycling experiments were performed on thin-wall tubes (with thickness/radius ratio of 1:20, similar to that found for stents) of nearly equiatomic NiTi shape memory alloys (SMAs). Experiments were controlled by axial displacement and torsional angle with step loading involving torsional loading to a maximum strain, followed by tensile loading, and reverse-order unloading. The superelasticity of the material is confirmed by pure torsion and tension experiments at the test temperature. The evolution of equivalent stress-strain curves as well as the separated tensile and torsional stress-strain curves during cycling is analyzed. Results show that the equivalent stress increases greatly with a small amount of applied axial strain, and the equivalent stress-strain curves have negative slopes in the phase transformation region. The shear stress drops when the torsional strain is maintained at its maximum value and the tensile strain is increased. The shear stress increases with decreasing tensile strain, but it cannot recover to the original value after the complete unloading of the tensile strain. Attention is also paid to dissipated energy density and characteristic stress evolutions during cycling.     

Modelling a Skin-Pass Rolling Process by Means of Data Mining Techniques and Finite Element Method

 An experience is presented using the finite element method (FEM) and data mining (DM) techniques to develop models that can be used to optimize the skin-pass rolling process based on its operating conditions. A FE model based on a real skin-pass process is built and validated. Based on this model, a group of FE models is simulated with different adjustment parameters and with different materials for the sheet; both variables are chosen from pre-set ranges. From all FE model simulations, a database is generated; this database is made up of the above mentioned adjustment parameters, sheet properties and the variables of the process arising from the simulation of the model. Various types of data mining algorithms are used to develop predictive models for each of the variables of the process. The best predictive models can be used to predict experimentally hard-to-measure variables (internal stresses, internal strains, etc) which are useful in the optimal design of the process or to be applied in real time control systems of a skin-pass process in-plant.     

Influence of Composition and Thermomechanical Training Process on the Transformation Behavior and Shape Memory Properties of NiTi Based Alloys

The effects of composition, specially the Cu element and thermomechanical training process on the transformation and one way shape memory behavior (OWSM) of NiTi based alloys were investigated using differential scanning calorimetry and microstructural analysis. The hot rolled strips with different compositions were trained under various applied pre-strains by bending test at martensitic state. It was found that the presence of Cu in the NiTi alloy results in an improvement of the OWSM effect by reducing the transformation hysteresis and forming the longer martensitic variants with lower interfacial energy than the NiTi binary alloys. Increasing the applied pre-strain and the number of thermomechanical training cycles caused OWSM effect to decrease. Although the transformation temperature increased at the higher applied pre-strain, it was reduced during the thermomechanical training process.     

Finite Element Method (FEM) Calculations of Stress-Strain Behavior of Alpha-Beta Ti-Mn Alloys: Part I. Stress-Strain Relations

By use of a NASTRAN¹⁸ Computer Program, the Finite Element Method (FEM) has been employed to calculate the effect of particle size, matrix, and volume fraction on the stress-strain relations of α-β titanium alloys. It was found that for a given volume fraction, the calculated stress-strain curve was higher for a finer particle size than for a coarse particle size within the range of the strains considered, and this behavior was seen for all the different volume fraction alloys considered. For a 50:50 vol pct α-β alloy, the stress-strain curve withβ, the stronger phase, as the matrix was higher than that with α, the softer phase, as the matrix. The calculated stress-strain curves for four different vol pct α alloys were compared with their corresponding experimental curves, and in general, good agreement was found. Whenever there were discrepancies, they were discussed by comparing the morphology of the mesh used in the calculations with the morphology of the actual materials.     

Validation of Analytical Multiparameter Homogenization Models for Out-of-Plane Loaded Masonry Walls by Means of the Finite Element Method

The linear elastic analysis of in-plane and out-of-plane loaded masonry walls is still significant under service loads and is required by codes of practice, therefore the knowledge of the homogenized mechanical properties of masonry is of relevant interest. The aim of this paper is to discuss the problem of the out-of-plane loaded masonry walls in detail and to assess the accuracy and reliability of different homogenization approaches presented in the technical literature, with particular interest in recent explicit formulas obtained through an asymptotic model (as reported by Cecchi and Sab in 2002). Several meaningful comparisons are presented for different types of new and historical masonry structures currently employed in Italy. The validation of the analytical models is carried out by means of a three-dimensional (3D) finite-element (FE) out-of-plane homogenization. A final structural comparison among analytical models, FE out-of-plane homogenization, and a computationally expensive heterogeneous 3D FE model is discussed for a simply supported square panel laterally loaded.     

浅析NiTi形状记忆合金的疲劳机理

由于NiTi形状记忆合金具有可逆的热弹性马氏体相变效应等不同与一般金属的特性，使得其疲劳机理也不同于一般的工程材料。为此，本文侧重分析了温度变化对NiTi形状记忆合金疲劳机理的影响和应力诱发马氏体相变等特征相变过程，以及相关的研究方法与主要结果，将为进一步研究其疲劳过程及增韧工艺提供理论参考依据．     

中间包夹杂物运动行为的数模研究

利用数学模型研究了中间包内钢水中夹杂物运动的规律,采用自编的计算机软件,对马钢板坯和异型坯中间包夹杂物的运动进行了仿真计算,结果表明,中间包内夹杂物直径＞100um时,都能在中间包内上浮,而＜5um的小颗粒夹杂则很难在中间包内上浮,90％以上都随着钢水流出中间包。加入挡墙后,直径＞50um的夹杂物都能在中间包内上浮排出。大大提高了钢水的清洁度。本文提供了一种研究中间包夹杂物运动的方法,并认可采用挡墙控制钢水流动,可有效地排除钢水中的夹杂物。     

TIG焊接热循环对AZ31B镁合金硬度的影响

以AZ31B镁合金为研究对象，采用TIG焊方法进行焊接，考察了焊接热循环对镁合金的硬度的影响。测量、比较、分析了焊缝、热影响区、母材的硬度。结果表明，表面处理过程（研磨、抛光、侵蚀液体及工艺等）对镁合金硬度的影响很大，直接影响到“焊接工艺-硬度”之间关系。与母材相比，由于焊缝的冷却速率高，组织细小，硬度较高。热影响区的组织虽比母材粗大，但硬度与母材相近。焊缝区不同部位的硬度存在一定差异。     

异步轧制的过程的有限元模拟

应用弹塑性有限元商用软件Marc对二辊异步轧制过程进行了分析计算。给出了变形过程中的力学参数如应力，应变等变化状态，是确了异步轧帛的变形和受力状态，为轧制过程机械性能参数的合理化设置提供了依据。     

轧制过程宽展问题的有限单元法分析

本文根据刚塑性有限单元法,采用20节点曲六面体等参单元对平辊轧制过程进行了分析。求得金属三维流动的速度场,以及在稳态轧制时轧件的外轮廓形状等,并与实验结果进行了比较。     

Origin of Microstructural Irreversibility in Ni-Ti Based Shape Memory Alloys during Thermal Cycling

Different microstructures of Ni-Ti- and Ni-Ti-Fe-based shape memory alloys were subjected to thermal cycling: dipping in liquid nitrogen, for approximately 5 minutes, and then bringing it back to room temperature or austenite (cubic: B2) ↔ martensite (monoclinic: B19′) reversible solid-state phase transformation. Direct electron backscattered diffraction (EBSD) observations could bring out aspects of microstructural irreversibilities: namely, changes in grain size, misorientation buildup, and presence of retained martensite. The average changes in grain size (Δd) differed by almost 2 to 4 times between different microstructures. The highest Δd was typically observed in structures having maximum clustering of fine (d < 5 μm) grains. The sample with highest Δd was also subjected to multiple thermal cycling. Although Δd scaled linearly with d after the first thermal cycle, the scatter increased during subsequent thermal cycles. Grain or orientations deviating from the linear behavior were clearly anisotropic crystallographically. With repeated thermal cycling, the patterns of changes in Δd, austenite misorientation, and retained martensite content were similar. A phenomenological model or hypothesis, based on 40 deg á 001 ñ leftlangle {001} rightrangle orientation relationship between austenite and martensite phases, was proposed to address the observed patterns of microstructural irreversibility.     

控流装置对中间包夹杂物运动行为的影响

采用拉格朗日颗粒轨迹模型,应用计算流体动力学方法,对中间包夹杂物颗粒运动轨迹及去除率进行了模拟研究。计算结果表明：控流装置的设置可显著改善夹杂物流向,延长停留时间,提高夹杂物去除率。夹杂物去除率随夹杂颗粒当量直径的变大而提高。控流装置对50μm以下夹杂颗粒去除率提高较多。本实验所设计的几种控流装置中,采用导流隔墙的中间包夹杂物去除效果最好。     

T型管液压成形过程的有限元分析

应用动态显式有限元法,建立了T型管液压成形分析模型,对不同加载条件下的模拟结果进行对比,分析了轴向载荷的作用,探讨了最佳载荷曲线的确立原则.     

有限元法分析钢包吊钩的强度

应用有限元法分析了片式吊钩的应力情况,包括最大接触应力及最大拉伸应力的位置和数值。分析了多片式铆接结构的优缺点,为改进和设计新的吊钩提供参考。