Multi‐Criteria Material Selection of Monolithic and Multi‐Materials in Engineering Design

Abstract

The benefits of combining different homogeneous materials to give heterogeneous materials have been recognized since our early history; straw-reinforced brick and goat hairreinforced pottery are examples. [1] Such combinations are known as multi-materials [2] or hybrid materials. [3] A useful working definition [4] is "a combination of two or more materials in a pre-determined configuration and scale, optimally serving a specific engineering purpose". Established examples are particular and fiber-reinforced composites, [1,5] like CFRP and GFRP, and sandwich structures. Barbero classifies multi-materials -composites as he terms them -into three classes: reinforced composites, laminated composites and hybrid composites. [6] Ashby includes lattice materials and segment materials in addition to reinforced composites and sandwich structures. [7] Four classes of multi-materials, following Ashby, [7] are presented in Figure 1. This article describes a tool to support designers in comparing the performances of multi-materials with those of other materials and to guide their selection for a given application. One particular type, sandwich panels, is chosen as a focus to implement and illustrate the methodology.Approaches to multi-material selection: Designers should ideally explore the widest possible range of conceptual solutions before selecting one. Thus, the material search space should be as broad as possible at the conceptual design stage, as shown in Figure 2. As the design proceeds this space is narrowed, culminating in a single choice.Multi-material selection is more complicated than that of monolithic materials for two reasons: first, because the configuration in which the constituents are to be combined must be chosen, and, second, because, in optimizing the combination, the number of free variables is greater -it now includes the relative volumes of the two constituents, their configuration and their scale. What is needed is a way of exploring and optimizing these. Designers can then bring multi-materials into consideration in either of two broad approaches, as mentioned by Phillips [8] and Quinn. [9] Catalogue approach: Particulate and fibrous compositesthe best known hybrids -can be included in a materials database in the same way as monolithic materials, allowing direct comparison and selection by established material-selection methodologies. [7] An example is the Cambridge Engineering Selector (CES) database, [10] which includes some 200 composites and foams. Work on developing a knowledge-based system to assist composites selection has also been undertaken. [11] This allows selection from among existing, commercially available composites, but it does not allow for optimization; to do that requires ways of exploring all feasible combinations of material, configuration, and, where relevant, scale.The proposed approach: The alternative is to think of multimaterials as the combination of several constituents. This approach might well lead to a better solution since the multimaterials can be tailored to meet t...

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