Introduction to Shape Factor

In the lecture on the application of Ashby process to obtain the Property Index, we have focused only on the Material Property. If you recall, the objective function was shown to be the product of three functions – the loading function, geometry function and material property function or the material property index. Now, we will talk about a modified material property function augmenting some of the geometrical parameters. The loading function of course is non-compromisable since this comes directly from the functional requirement of the client. No body would possibly want to purchase a refrigerator and use it as a closet for storing dresses!

While some of the dimensions of a mechanical element is fixed to begin with, one can still have lot of freedom in choosing the shape of the element. For example, consider a frame which is designed to carry the bending load. While the length and the over-all dimension of the frame is specified – there’s still freedom in choosing the cross-section profile of the frame – should we go for an I-section or a T-section or a circular section? All the materials are not equally workable – hence, same section is not available for all the materials – this tells us that the material property index should be farther modified to include the shape factor in it. In this lecture we will farther elaborate the process.