Non-Linear Homogenization of Porous Anisotropic Materials: Applications to Plastic and Magnetic Shape-Memory Alloys

该奖项的研究目标是调查孔隙率的影响，并在两种不同类型的运动约束材料系统中开发本构模型。第一种类型的实例包括低对称性金属，例如镁和锆合金，其名义上是不可压缩的多晶聚集体，但是当存在孔隙时，其可以经历显著的体积应变。第二种类型的例子包括磁性形状记忆合金，如镍-锰-镓系统，已经发现在昂贵的单晶中表现出“巨大的”场致应变，但在较便宜的多晶中只有最小的磁致伸缩。在这种情况下，多孔性的存在下，可以帮助放松内部的运动学约束的多晶由于强取向的磁致伸缩的晶粒，往往会阻止对方？s菌株。主要的挑战是要正确地考虑到这些材料在一般加载条件下的响应的本构模型中的孔隙度的压缩和松弛效应。这将通过最近开发的“迭代”非线性均匀化技术来实现，该技术利用适当选择的“线性比较”介质来产生对这些材料的多孔单晶和多晶样品的耦合非线性响应的高度准确和有效的估计。这项研究的好处将包括提高对高性能金属合金机械性能的理解和先进的建模，以用于汽车中的节能应用，这些材料用于航空航天和核工业，以及用于致动器、传感器和能量收集装置等应用的磁性形状记忆合金的磁弹性响应。该研究还有望改善净形金属成形操作的表征，以及通过空隙生长和聚结在多晶材料中的延性失效。此外，这些结果对于冰、岩盐和橄榄石等地质材料的建模也很有意义。 这项工作也可能与其他活性材料系统的开发有关，例如某些类型的多晶铁电体。

The research objective of this award is to investigate the effect of porosity and to develop constitutive models accounting for this effect in two different types of kinematically constrained material systems. Examples of the first type include low-symmetry metals, such as magnesium and zirconium alloys, which are nominally incompressible polycrystalline aggregates, but which can undergo significant volumetric strains when porosity is present. Examples of the second type include magnetic shape-memory alloys, such as nickel-manganese-gallium systems, which have been found to exhibit "giant" field-induced strains in costly single crystals, but only minimal magnetostriction in cheaper polycrystals. In this case, the presence of porosity can help relax the internal kinematic constraints in the polycrystal due to the strong orientational character of the magnetostriction in the grains that tend to block each other?s strains. The main challenge is to properly account for the dilatational and relaxational effects of the porosity in constitutive models for the response of these materials under general loading conditions. This will be accomplished by means of a recently developed "iterated" nonlinear homogenization technique, which makes use of suitably chosen "linear comparison" media to generate highly accurate and efficient estimates for the coupled, nonlinear response of porous single-crystal and polycrystalline samples of these materials.If successful, the benefits of this research will include improved understanding and advanced modeling of the mechanical properties of high-performance metal alloys for energy-efficient applications in the automotive, aerospace and nuclear industries, as well as of the magneto-elastic response of magnetic shape-memory alloys for applications such as actuators, sensors and energy-harvesting devices. The research is also expected to lead to improved characterization of net-shape metal-forming operations, as well as of ductile failure in polycrystalline materials via void growth and coalescence. In addition, the results will be of interest for modeling of geomaterials, such as ice, halite and olivine. The work may also be relevant for the development of other active material systems, such as certain types of polycrystalline ferroelectrics.