SHAPE-MEMORY MATERIALS: CRYSTALLOGRAPHIC TEXTURE AND ITS CONSEQUENCES

0002930现在已经充分认识到，形状记忆材料从相或“微观结构”的精细尺度重排中获得其不寻常的和固有的非线性和各向异性性质，并且在伪弹性效应中产生的应变以及在形状记忆效应期间恢复的应变取决于晶体取向。某些形状记忆材料的特殊取向的单晶由于相变可以产生相当大的应变（~ 10%）。 实际的形状记忆材料在本质上通常是多晶的，并且由于它们的热机械加工历史，它们最初是纹理化的。最近人们认识到，形状记忆合金的板、丝和棒的初始晶体学织构在决定这些材料的整体性能方面是至关重要的。由初始纹理引起的明显的各向异性需要适当地占在开发一个强大的计算能力的改进设计的几何形状记忆材料制成的复杂的工程部件。我们将 实验研究了初始织构对形状记忆合金Ti-Ni（块状和薄膜）热机械响应的影响。这种材料越来越多地用作各种应用的功能/智能材料。薄膜形式的Ti-Ni合金是用于微致动器的有前途的材料，因为薄膜中的热传递速率增强。 发展本构方程和计算程序，用于模拟和模拟这些材料中观察到的重要的伪弹性和形状记忆效应。 我们计划开发的数学模型和程序在设计增强热机械性能的部件时应该是有用的。

0002930It is now well recognized that shape-memory materials derive their unusual and inherently nonlinear and anisotropic properties from the fine-scale rearrangements of phases, or ``microstructures,'' and that the strain produced in the pseudoelasticity effect, as well as that recovered during the shape-memory effect, depends on crystal orientations. Specially oriented single crystals of some shape memory materials can produce sizeable strains (~ 10%) due to phase transformations. Practical shape-memory materials are typically polycrystalline in nature, and because of their thermo-mechanical processing history, they are initially textured. It has recently been recognized that the initial crystallographic texture of sheets, wires and rods of shape-memory alloys is crucial in determining the overall properties of these materials. The pronounced anisotropies caused by the initial texture need to be properly accounted for in developing a robust computational capability for the improved design of geometrically-complex engineering components made from shape memory materials. We shall Experimentally study the effects of initial texture on the thermo-mechanical response of the shape-memory alloy Ti-Ni, in both bulk form, and thin films. This material is finding increased use as a functional/smart-material for a variety of applications. Ti-Ni alloys in thin-film form are promising materials for microactuators, because of the enhanced rate of heat transfer in thin films. Develop constitutive equations and computational procedures for modeling and simulation of the important pseudoelasticity and shape-memory effects observed in these materials. The mathematical models and procedures that we plan to develop should be usefulin the design of components for enhanced thermo-mechanical performance.