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Case Study: Selecting a Material for an Aircraft Wing

Introducing the case study

This case study demonstrates a typical student exercise or component of a lecture in which the CES EduPack software is used to explore the world of materials in the context of a real engineering application. The application is choosing a material for use in an aircraft wing. The case study shows how the materials selection process can be explained to students, and how this process can be used to introduce students to underlying materials science and to other aspects of real engineering projects.

The materials selection problem

The starting point for any materials selection is the identification and specification of design requirements. In this case, we keep the example fairly simple – at the level that might be used in an introductory materials engineering course.

The requirements for the aircraft wing (illustrated, right) are:

A. High stiffness
B. High strength
C. High toughness
D. Low weight

The case study explores the selection problem but also discuss what we can learn about the world of materials, and their practical application in engineering, as we go along.

Exploring the world of materials

The first step in using the CES EduPack software to tackle our selection problem would be to open the software and browse its database of materials. At level 1 of the software (the appropriate level for an introductory course) the software contains 64 generic materials classes. Each material has a record that provides, first, a general description of the material and images of typical applications (helping students on introductory courses to get to grips with the real-world use of the material) and, second, detailed quantitative property data.

Using the CES EduPack software, the student can make plots of any combination of properties in the database. The following shows Yield Strength versus Young's Modulus for all of the materials in the database...

This materials selection (or 'Ashby') chart is interactive. We can highlight materials and label them to find out what they are and choose materials from the list to find them on the graph. Clicking on a material name takes us to the material record with its information about the material. These and other features make the graph a tremendous tool to help students think about materials and their properties. You could, for example, show how families of materials tend to cluster on the graph, leading to a discussion of bonding mechanisms.

For more on this topic, and to see some of these features, view the case study recording...

Performing a selection

To choose a material for our hypothetical aircraft wing, we begin with all 64 materials in the level 1 database. At the outset, we identified high stiffness and strength as requirements for our aircraft wing. We can select on the graph those materials with high values of both properties. The software can then be used to progressively apply our other requirements.

For more detail, and to see all of the selection stages, view the case study recording...

Trade-offs, costs, and conclusions

Of course, any real selection in industry must consider not just technical properties, but economics. In the case study, we explore this issue by plotting density against price for the 14 materials that remain once other selection criteria have been applied.

This plot helps us to reach a conclusion in our exercise. Carbon fiber composites are the lighter material but are currently about an order of magnitude more expensive that aluminum alloys, so these alloys are the material of choice for most commercial aircraft. The graph could be used as a tool to discuss trade-offs in design - e.g., how composite materials may be used in less cost-sensitive applications.

The charts above use level one of the CES EduPack database. Switching to level three shows many more materials on the plot, including spcecific types of the generic materials classes shown above. Such detail is useful for higher level courses - for example, final year projects.

For more detail on trade-offs and level three data, view the case study recording...

Benefits of the case study

This simple aircraft wing case shows how the CES EduPack can be used by teachers and students to explore:

• Materials, materials classes, their properties, and the science behind them
• Applications for these materials
• The technical factors to consider in materials selection and the selection process itself
• Real-life considerations in engineering decisions – such as cost and the need to trade off properties

It also shows how CES EduPack can support different levels of teaching.