2D Analysis

The 2D Analysis provides sectional properties for the selected geometry, a feature that is useful for many calculations related to design and drafting. Architects use the perimeter and area values for calculating material requirements; engineers use the moments of inertia for stress analysis; manufacturers use the centroid for balancing parts for turning. The following topics are covered in this section:

•     2D Analysis Command

•     Calculations

2D Analysis Command

The 2D Analysis command in the Layout menu displays the statistics on the selection, including the length of the perimeter, the enclosed area, the center of gravity (centroid), and moments of inertia. The selection must be a closed figure.

Tech Note: The closed figure is an area that could be crosshatched. If in doubt about the area, simply crosshatch the geometry to see if it represents the area that needs to be analyzed.

Performing 2D Analysis

1.     Select the geometry that defines a closed boundary. Use the Tracer tool to select the perimeter.

2.     Choose Layout>2D Analysis.

The analysis is performed and the values appear in the dialog box.

3.     If necessary, enter changes for the tolerance and weight per area values.

Tech Note: Once the area is crosshatched and the selection is correct, choose Undo to remove the crosshatching and still maintain the selection.

4.     Click CALCULATE.

The analysis recalculates and the new values appear in the dialog box.

The following items are included in the dialog box:

Tech Note: This tolerance value has no effect on the precision of the resultant values. The precision of the result is set by choosing Layout>Preferences>Units.

Tolerance Determines the accuracy of calculations for curved objects. The smaller the tolerance, the higher the accuracy. The default value is 0.01. Change the value by entering a new number.   The 2D analysis mechanism analyzes arcs, circles, ellipses and splines as straight line segments that deviate from the true curve by no more than the stated tolerance value. The smaller the number, the greater the accuracy, however, the greater the accuracy, the longer the calculation time. Weight Per Area A multiplier used to determine the actual weight of a part of constant thickness defined by a selected boundary. The weight of the part is the product of the Area multiplied by the Weight Per Area.   The default entry is 1. Change the value by entering a new number. Find the proper number for this entry in a handbook published by most material vendors, particularly for sheet steel and aluminum. Enter the weight for the thickness of the proposed material and click CALCULATE.   For example, to analyze a square as if it were a cube three inches thick, enter 3 *  the material's density in the weight per area box. Perimeter The length of all segments which define the selected boundary. This is the only value that appears if the boundary is not closed.   For circles, arcs and other curves, the accuracy depends on the tolerance setting. Area The surface area enclosed by the selected boundary.   For circles, arcs and other curves, the accuracy depends on the tolerance setting. Weight The product of the Area multiplied by the Weight Per Area.     Centroid X The X coordinate of the center of mass defined by the selected boundary. Centroid Y The Y coordinate of the center of mass defined by the selected boundary. Inertia IXX The moment of inertia about the central X-X axis which is parallel to the X-axis.   IXX = ½(y-Yc)2dA Inertia IYY The moment of inertia about the central Y-Y axis which is parallel to the Y-axis.   IYY = ½(x-Xc)2dA Inertia IXY The product of inertia about the centroid.   IXY = ½(x-Xc)(y-Yc)dA

Calculations

Graphite calculates the values for 2D Analysis before the dialog box appears. To make a change in the Tolerance or the Weight Per Area, click CALCULATE to recalculate the statistics.

The 2D Analysis mechanism evaluates the boundary in the same way the crosshatching mechanism does. For example, Graphite considers a circle inside a bounded area to be a hole. Crosshatching does not fill the hole and 2D Analysis does not include the area of the circle in the area calculation.

Displaying the Centroid

1.     Select the geometry defining the part.

2.     Choose Layout>2D Analysis.

The 2D Analysis dialog box appears.

3.     Choose Layout>Construction.

The Construction dialog box appears.

4.     In the Angle field in the Construction dialog box, enter 0;90. (Be certain to separate the numbers with a semicolon.)

5.     Enter the value for Centroid X in the X field of the Construction dialog box.

6.     Enter the value for Centroid Y in the Y field of the Construction dialog box.

7.     Press ENTER (Windows) or RETURN (Macintosh).

Construction lines display, intersecting at the centroid of the selected part.