Blank GCD
The Blank GCD is specific to the Sheet Metal process groups. It represents the flattened part. Its properties (such as Perimeter, Thickness, SER Length, and SER Width) are listed in the Geometric Cost Drivers pane.
aPriori determines the outline of the flattened part based on a forming simulation which uses a finite element analysis derived from the part’s CAD model and the properties of the selected material.
When you select the Blank GCD in the Geometric Cost Drivers pane, the Viewer displays the following:
• Blank outline in pink
• Blank SER in yellow: this is the smallest-area rectangle that encloses the blank.
You can display the flat pattern head on, in a separate window, together with its associated SER, by selecting Flat Outline from the Analysis menu in the Viewer toolbar.
As mentioned above, determination of the flattened outline takes into account material properties, including the following:
• Density
• Young's Modulus
• Poisson's Ratio, K (strain-hardening coefficient)
• N (strain-hardening exponent)
• R (Lankford parameter, average). 
Materials in starting point VPEs specify these properties. If your VPE includes a material that doesn’t specify these properties, aPriori uses the following default values based on material type:
Material Type
Young's Modulus (MPa)
Poisson Ratio
K (strain-hardening coefficient, MPa)
N (strain-hardening exponent, MPa)
R (Lankford parameter, average)
Aluminum
69000
0.33
341.1
0.21
0.7
Copper
115000
0.33
317
0.54
0.99
Galvanized Steel
207000
0.28
543
0.21
0.99
Stainless Steel
207000
0.28
1426
0.502
1
Steel
207000
0.28
0.28
479.3
1.345
 If the material type is not one listed in the table above, the entries for Steel are used.
Note that if you change the material selection for a given part and re-cost, you must be CAD-connected so that the part’s flat outline can be recalculated and geometry re-extracted.