Often, material selection is the most difficult thing to be done during a design process. Sometimes designers would choose based on its looks and alleged properties, without knowing the real properties of such materials. Luckily, we lived in the era where Prof Ashby have developed and refined an easy step by step method for material selection. But who is Prof Ashby?
Prof. Michael Farries Ashby CBE, FRS, FREng (born 20 November 1935) is a British metallurgical expert. He is a Royal Society Research Professor, and a Principal Investigator at the Engineering Design Centre at Cambridge University. He is known for his contributions in Materials Science in the field of material selection.
His contribution has revolutionized how scholars, engineers, and fellow researchers in looking how materials are selected. He created a system of graphics to for easy understanding of material properties as well as the approach to be used in choosing one material.
The Ashby Methodology
1. Translation
In this stage we discover the required properties of the product you are thinking of, most importantly:
- Functions: what does the component do
- Constrains: what are the essential properties, and what are the limitations
- Objectives: what do you want to achieve
- And Free Variables of your idea: what are the properties that does not have a strict restriction.
In this stage you should also brainstorm as many material selection that you can think of.
eg. Main frame of a skyscraper
- Function: Main backbone of the building
- Objective: Strong yet flexible
- Constraints: Carry load, Width, Heft
- Free Variables: Cost, Material, Positioning
2. Screening
In this stage you will select the materials that have properties close to what you needed. You should eliminate the materials that will not work.
Eg, Ceramics and Glass are not flexible and will shatter.
Here The Ashby Diagram would come to play.
3. Ranking
In this stage you will rank the materials that you did not eliminate from most suitable property to the least. You must not be surprised when there are no material that is 100% suitable.
Eg. Steel is very heavy but it is strong and flexible
4. Supporting Information
In this stage you will explore and understand the properties of the material that you ranked that is able to support the material that you choose.
Eg. The flexibility of steel equation
The Ashby Diagram
Ashby Diagram is the graphical diagram that Prof Ashby developed. These diagrams usually have 2 axes that represent a quantifiable properties of the materials.
For example:
- Strength vs Density
- Flexibility vs Strength
- Cost vs Density
In more advance analysis 3 axes or more would be used, taking account the 3D space of a graph. For example: Strength vs Density vs Cost.
With this Ashby Diagram, Engineers would be able to choose which material suits your product the best, and it will highly help you in choosing the most suitable material.
Conclusion
Prof Ashby research and methods is a highly dependable and robust method in choosing materials. With his method, choosing materials is not a game of trial and error, but it is a scientific approach that requires rigorous research and understanding, So what are you waiting for? Ashby Diagrams and Methodology is there for you to use! Now go and have a great Material Selecting Journey!
Thank you MIT MSL Laboratory, US for a concise summary of Ashby Method and Fudan University, China for the open e-book for the Prof Michael F. Ashby publication.
Also Prof Paul Mignone, for the great introduction to material selection process.
