Behavioral modeling is powerful functionality that measures and tracks engineering information related to the geometry or mass properties of your Pro/ENGINEER model. This information—such as volume, distance between two entities, surface area, or the center of gravity—automatically updates as the model changes. The information is represented as parameters (as in the case of mass) and datum features (as in the case of the center of gravity).

Taking the concept of behavioral modeling a step further, you can now optimize your models according to engineering goals. For example, if you want the mass of the model to be a certain value, minimized or maximized, Pro/ENGINEER will change the geometry to reach that goal. Similarly, if you have to locate the center of gravity on an axis of rotation to avoid an imbalance in a rotating machine element such as a shaft, Pro/ENGINEER will change the geometry to locate the proper center of gravity. This optimization capability eliminates many of the time-consuming iterations required in the past. In fact, behavioral modeling not only speeds the optimization process, but often aids in finding a better solution than manual iteration.

The following example explains how to use behavioral modeling to determine cross sectional properties of a beam and optimize the beam to have constant sectional properties along its length.

Step-by-Step Process

The section modulus is a property that determines how much stress is applied to a beam’s cross section in pure bending. Stress due to bending defined across a section is Û=Mc/I, where M is the bending moment, c is the distance from the neutral axis to a location in the cross section, and I is the area cross sectional moment of inertia. The section modulus is defined as I/c. A constant section modulus along the length of a beam means that the stress and curvature due to deflection is constant and more importantly, that the beam has no unnecessary material.

Take a beam with a rectangular cross section of 2.5 x 1.0 and a length of 10, with a pattern of holes (Fig. 1). In this case, you cannot measure the section modulus directly using a datum analysis feature, even though it can be measured using a section analysis. The cross sectional area moment of inertia can, however, be measured in a datum analysis feature. The greatest distance to the upper and lower section boundary can also be measured and a relation can be used to divide the inertia by the distance (I/c).

To measure the modulus about the Y axis, follow these steps.

Figure 1 (click to enlarge).

1. To use behavioral modeling, you need to create some construction features. First create a datum curve representing the length of the part. A field point is placed on the curve and datum plane, SEC_DTM, is created through the point and normal to the datum curve (Fig. 2).

Given that a field point represents the entire domain of its reference, this point represents the entire curve. Any information gathered from a cross section through the datum plane is therefore represented across the length of the part.

Figure 2 (click to enlarge).