keep reading-35

Designing architected materials, M Ashby, Scripta Materialia, 2013

Novelty/impact/significance:

The idea of seeking unknow higher-performance materials from known materials, the novel route by making hybrid or architectured materials, the corresponding methodology with concise fundamentals for optimized properties from constituents and configurations are described. The entire presentation is clear, coherent, and complete, a classical, lasting work in this field.

Scientific questions:

What are the reality-based hints for finding materials with better properties, what are hybrid/architectured materials, and how to design architectured materials effectively and efficiently?

Key of how:

Recognizing the ‘holes’ in material-property charts;

combinations of two or more constituent materials OR combinations of materials and space assembled in specially designed ways to have properties not possibly achieved by the constituents;

a rational design strategy including setting the criteria of excellence and analytical modelling for defined configurations and known properties of constituent materials, illustrated through an example and a typical tool (The CES Hybrids Synthesizer 2010).

Major points:

1. Goal.  From material-property charts, sparse or no material-occupied areas (holes) are regions where high-performance materials locate, if specific criteria of excellence (material property indices) are met. This is illustrated by, on a Young’s modulus-density (E-ρ) map, briefing the areas and the grid lines of E^1/3/ρ.

2. Hybrid or architectured materials.  They are combinations of two or more constituent materials OR combinations of materials and space assembled in specially designed ways to have properties not possibly achieved by the constituents. Engineering fiber-reinforced composites belong to these, but more possible interior structures such as sandwich structures are possible to expand the design space thus allowing materials with wider range of properties.

From this, a new, alternative approach to filling the holes is developing new hybrid, architectured materials (dense and/or porous), focusing on the diverse interior structures.

The structural variables of the architectured materials include components (constituent materials), relative volumes, configuration, connectivity, and length scale. Typical structural configurations include: fiber-matrix structure, cellular structure, strand (fibrous) structure, segmented structure, sandwich structure, multilayered structure.

Also, such a methodology needs a prerequisite: the architectured material is considered as one equivalent material; it has equivalent properties that can be judged with monolithic materials using the same criteria of excellence.

3. Analytical models.  To screening the best design after constituent materials and configuration (interior structure) are chosen, standard methods by optimization routines and finite-element analyses usually are time-consuming and inefficient. Thus approximate methods using analytical/simplified models on well-defined structural configurations are superior in providing equivalent properties effectively and efficiently. The models and theories are well documented in cited references, and one example analyzing an architectured material of sandwich panel (its equivalent flexural modulus and equivalent density trajectory are calculated from the properties of the constituent materials, and analyzing this trajectory versus the grid line of E^1/3/ρ) provides the position where the optimization lies on.

Such optimized position also passes through a ‘hole’ region, extending the conventional material property space.

4. Computer aided design.  A typical tool (The CES Hybrids Synthesizer) is introduced and how to use it is briefly described. The user selects the constituent materials with known properties and the selects the configurations, then make an architectured material with structural variables assigned (e.g., volume fraction and thicknesses). The tool will generate, for the architectured material, equivalent properties that can be compared with monolithic materials (or on material-property charts). This enables rapid exploration of a wide breadth of configurations and constituent materials for promising combinations and superior properties.

This paper is clear, coherent, and complete, with great brevity and beauty. Further separation of mechanical properties from constituent and architecture might contribute to wider application/impact. Here is the link of the fulltext:

https://www.sciencedirect.com/science/article/pii/S1359646212002965