Granta Material News, Feb 2012



Tip 1: How to find equivalent alloy grades using GRANTA MI:Substitute and the MI-21 database

In this excerpt from a recent web seminar, Granta's Dan Williams provides a five-minute case study on the identification of equivalent alloy grades using a combination of software (the newly released GRANTA MI:Substitute tool) and data (in this case, the MI-21 database, a collaboration between Granta, NAMTEC, the World Metal Index and TWI.)

The case study shows how this powerful combination of expert tools and specialist data can be applied to the common problem of identifying an equivalent substitute for  unrecognized grade on a legacy drawing – including an analysis of any potential issues which might arise as a result of such a substitution.

Launch video 

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Tip 2: Using the reference material and 'relative values' features in CES Selector to determine the change in free variable for a design

When you use the 'Performance index finder' to find optimal materials, you are asked to specify the fixed and free variables for the design. For example, for a lightweight stiff panel loaded in bending, you can specify that the length and width are fixed and the thickness is free. This means that you have the freedom to change, or optimize, the thickness to suit the material selected. For example, when you specify a lower stiffness material, you will need to recover the 'loss' in stiffness by specifying a larger panel thickness. This tip shows you how you can identify this change in free variable for different material options.

The chart below shows a typical mass vs cost trade-off plot for a panel loaded in bending. This is a classic trade-off: steels are cheap but heavy, composites are light but expensive, aluminium and magnesium alloys are somewhere in between. In considering this chart a designer also needs to understand how the free variable (i.e., panel thickness) varies with material choice as this may have implications on the design. For example if the current design is utilizing a low alloy steel (AISI 4130, air melted, quench & tempered'), how will the thickness change if it is switched to a high performance composite.

We can identify the existing material by setting it as the reference material in CES Selector. This will then be marked with a red pin throughout the software. To identify the reference material more clearly, toggle the "Show Reference Record" button on the graph tool bar: all other materials will be greyed out. To show the relative performance of the other materials to the reference, change the Y-Axis and X-Axis scales to 'Relative values' (double click on the axis titles to access the axis settings). The reference material now appears at 1:1.

Now, when you hover over the label for the Epoxy/HS carbon fiber the average values in the tooltip show the change in mass and cost relative to the reference material. In this example, the mass is roughly one quarter (0.254) and cost is roughly fifteen times higher (15.1).

But what is the change in the free variable thickness? This is connected to the part volume. As the panel length & width are fixed by the design, any change in free variable (thickness) will be represented by the change in volume.

This can be seen by creating a second chart of the mass vs volume trade-off . Again, setting the axes to 'Relative values' and hovering over the 'Epoxy/HS carbon fiber' label gives the value relative to the reference material. Here, the X-axis average (volume) is 1.27. This means that the composite part needs to 1.27 thicker than the existing steel part to achieve the identified weight savings.