Lightweight Materials and Structures
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Lightweight Materials and Structures A.G. Evans The following article was contributed by Anthony G. Evans (Princeton Materials Institute), recipient of the MRS David Turnbull Lecturer Award at the 2000 MRS Fall Meeting in Boston on November 29, 2000. Evans was cited for “outstanding contributions and leadership in bringing fundamental insights in mechanical behavior to materials engineering through research, teaching, mentoring, writing, and lecturing.”
Introduction Many technologies require load-sustaining components that are as lightweight and compact as possible. This requirement is especially true in the transportation area, where lightness equates with fuel efficiency and range. Concept implementation is dictated by the tradeoff between
performance and manufacturing cost, which is manifest in a value factor.1–4 The attainment of the minimum weight has a long history.5–14 Four technical factors are involved: materials selection,1,2 utilization of shape,2,15–17 topology optimization,2,18–21 and multifunctionality.2,22 The new developments to be addressed in this article arise in topology optimization. Multifunctionality has been elaborated elsewhere.2,22 The ability to sustain loads has as much to do with component shape as with the material of construction.2,15–17 Shortcomings in material density can be circumvented by designing shaped components that optimize load capacity. Well-known examples include I-beams, box beams, and panels with “hat-shaped” stiffeners, used in aerospace design. Other topologies can be
used to achieve load capacity at yet lighter weights, as exemplified by truss structures and honeycomb panels.18–21 The truss topology has the further benefit that its open spaces can be used to impart functionalities in addition to load-bearing, such as cooling,2,22 whereupon the extra weight of an additional component normally needed to provide that function can be saved. Novel categories of topologically designed metallic alloys are addressed in this article,18–21,23–25 along with the performance attributes that underlie their implementation. The metals are configured in trusslike arrangements with open domains that occupy most (90%) of the volume. The choice of the topology is crucial: it must be designed such that when sheared, the trusses are in either tension or compression, with no bending. A procedure has been established for selecting the materials most applicable to aerospace structures, which are limited by their ability to support bending and compressive loads.1,2 The associated metrics are encapsulated as diagonals superposed on maps of Young’s modulus E, as a function of density (Figure 1a), and the yield strength Y against (Figure 1b). One metric is for beams (E/, Y2/3/) and another is for panels (E1/3/, Y/).2 The materials that best combine high strength with low density are those that reside at
Figure 1. Property diagrams used for materials selection: (a) stiffness and (b) strength. The diagonal dotted lines indicate equivalent performance for lightweight beams and pan
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