Micromechanics-Based Approach to the Design of Ceramic/Metal Functionally Graded Materials.

本研究涉及基于计算力学的陶瓷-金属梯度多层结构体系结构，称为“功能梯度材料（FGM）”，其主要应用目标是针对热结构部件的传统热障涂层的改进。这些多层结构最重要的特点是，通过控制最外层的全陶瓷和全金属复合层之间的单个复合层的成分和微观结构，具有热屏蔽和热应力缓解功能的可定制性。这种裁剪涉及在各种规定的热机械载荷条件下的热传导和应力分析，并且由于FGM结构固有的双尺度非均质性，这些分析需要“宏观力学”和“微观力学”方法。本工作中开发的计算程序具有非弹性分析的特点，允许金属相的屈服和塑性流动。这是通过经典层合板理论的直接扩展来制定的，其中包含约束塑性的微观力学模型，以导出弹塑性状态下的层本构方程。通过系统的计算研究，证明了热应力的分布是如何随着成分和微观结构的变化而变化的。用热压合成分级的多层粉末混合物绿色压块制备了片状样品，并对氧化锆-镍体系进行了相关实验。这包括(i)通过热成像仪测量稳态厚度温度分布，以便“现场”测定各层的导热系数；（ii）对各层对应的成分均匀样品进行“圆盘弯曲”试验，以确定其在等双轴载荷条件下的破坏强度；(3)准单向热流条件下分级多层试样的重复热加载试验。从这项调查中得出的一般结论是，女性生殖器切割的概念确实非常有吸引力，目前基于计算力学的方法可以为女性生殖器切割的体系结构提供许多有用的指导方针。少

This investigation is concerned with a computational mechanics-based architecture of ceramic-to-metal graded multilayr constructions, called "functionally graded materials (FGM) ", their prime application target being directed toward the improvement of conventional thermal barrier coatings in hot structural components. The most important feature of these multilayr constructions is a tailorability of heat-shielding and thermal stress-mitigating functions through compositional and microstructural control of individual composite layrs in between the outermost fully ceramic and fully metallic ones. The tailoring as such involves heat conduction and stress analyzes under various prescribed conditions of thermomechanical loading and, because of the dual-scale heterogeneity inherent to the FGM structure, these analyzes require both "macromechanical" and "micromechanical" approaches.The computational procedure developed in the present work features an inelastic analysis that permits yielding a … More nd plastic flow of the metal phase. This is formulated via a straightforward extension of the classical laminated plate theory, wherein a micromechanical model of constrained plasticity is incorporated to derive the lamina constitutive equation in the elastoplastic regime. A systematic computational study has been carried out to demonstrate how the distributions of thermal stresses change by changing the gradations in composition and microstructure.Some related experiments have also been done on the zirconia-nickel system using discshaped samples fabricated by hot pressing composition-graded multilayr green compacts of powder mixtures. These include (i) the measurement of steady state through-the thickness temperature distributions by means of thermography for "in situ" determination of the thermal conductivities of individual layrs, (ii) "disc-bending" tests of compositionally uniform samples corresponding to individual layrs in order to determine their failure strengths under equi-biaxial loading conditions, and(iii) repeated thermal loading tests of graded multilayr samples under quasi-unidirectional conditions of heat flow.A general conclusion drawn from this investigation is that the FGM concept is quite attractive indeed and the present computational mechanics-based approach can produce many useful guidelines to the FGM architecture. Less