CES EduPack Bulletin, May 2012

Hints and Tips

In this edition:

  1. Accessing level 2 property information—using subsets to access eco and durability options
  2. Using subsets with more advanced datasets—galvanic potentials for stainless alloys
  3. Graphing penalty functions—plotting curved selection lines in CES EduPack

Tip 1. Accessing level 2 property information—including eco and durability options

This tip provides a quick tour of the material property information available within the level 2 MaterialUniverse, using Age-hardening wrought Al Alloys as an example.

Opening CES EduPack with a Level 2 database, use the browse tree to find the material in question. At Level 2, the datasheet opens with a picture of the material (often showing potential applications), together with a description and compositional information.

Scrolling down, you can see General, Mechanical, Thermal, Electrical, and Optical Properties. Hyperlinks open textbook-style descriptions of each property, as shown here for the 'Date first used' attribute, new in CES EduPack 2012

Level 2 datasheets also contain processibility and limited Eco properties, in addition to Supporting information, including design guidelines and technical notes. In this case, these include a phase diagram—further details on phase diagrams are available in the hyperlinked science note.

When teaching on durability, the Level 2 database contains many further material attributes which can be helpful. To access the full range of durability properties, change the Subset to "Edu Level 2 with durability properties"

This then provides access to durability properties for 55 different environments, including aqueous solutions, acids, alkalis, gases, and more. Again, each material property is linked to science notes which help the student drill deeper.

In the same way, additional eco properties can be accessed by changing to the "Edu Level 2 with Eco properties":

Tip 2: Using subsets with more advanced datasets—galvanic potentials for stainless alloys

Level 3 provides more detailed material property information: in this tip we show how to access the new galvanic potentials available for stainless alloys. Open a Level 3 database, and choose the Stainless alloys subset:

There is considerably more information available in Level 3 than the Level 2 datasheets shown in tip 1: this provides support for advanced teaching and research. For example, more detailed compositional information is accompanied by international designations:

Further down the datasheet, properties include the new Galvanic potential that supports the teaching of corrosion, highlighting the relative position of material and the likelihood of galvanic corrosion. You also have access to further corrosion information, such as pitting resistance. These properties are not just available within the datasheets, of course, but can be visualized in materials property charts and used when constructing performance indicators.

Tip3: Graphing penalty functions in CES EduPack

Material selection is always a compromise between conflicting objectives. Bubble charts make it relatively straightforward to visualize a trade-off between two possible objectives, plotted on the x- and y-axes.  This will provide a compromise between the objectives. One way to select a single solution on such a surface is to aggregate the various options into a single objective function. By defining an appropriate penalty function, a linear relationship can be constructed around an exchange constant, α. The question that is often asked is how these linear relationships can be plotted using CES EduPack.

Consider a standard bubble chart, such as this comparison of price and tensile strength:

As with all material selection charts, the axis are displayed on a logarithmic scale. However, the penalty function is based on a linear relationship, with a slope of -1/α. To draw the correct contours, therefore, the axis settings in CES EduPack should be changed to linear for both x and y, as shown:

The Line Selection tool can then be used to draw the penalty function with appropriate slope:

This puts the expected straight line on the bubble chart. Click  above or below the line to indicate the group of materials you wish to include within the selection. As you drag the line down the chart, the number of materials which 'pass' the selection stage will decrease, as expected. However, by plotting the chart with linear axes you lose the ability to clearly visualize the trade-off surface:

When the axes are converted back to the log scale, the familiar pattern of the trade-off surface will be restored, and the line from the penalty function is also converted. Plotted on logarithmic scales, the linear relation now appears as a curved line that can, as with any selection line, be dragged across the chart.

When combined with an appropriate trade-off surface, the best candidate material would be the one nearest the point at which one of these curves touches just touches the trade-off surface.

Read more about penalty functions in Chapter 7 of Ashby's 'Materials Selection in Mechanical Design' (fourth edition).