Now that we know what internal forces are and the different types, how do we analyze said forces?
The Exploratory Section
To analyze internal forces, we have to expose these components. We can do that by placing an exploratory section on the object.
Imagine having a magical knife that would slice the object in one plane. But rather than cutting the object into two, it reveals the internal forces inside for both segments (axial, shear, moment, and torsion).
Orienting the Exploratory Section
It's essential to note that internal forces heavily depend on how we place the exploratory section - its position and orientation along the object. Say we have a rectangular prism like a piece of French Fry, and we've applied a pulling force at its ends. Let's put an exploratory section in the middle and orient it in different ways:
- If the plane is perpendicular to the resultant pulling force, only the axial force resists the pull.
- If the plane is neither perpendicular nor parallel to the resultant pulling force, axial and shear forces provide resistance to the pull.
- If the plane is parallel to the resultant pulling force, only the shear force resists the pull.
You can see that the type of internal force changes depending on the plane's orientation.
How Should We Orient the Section?
How should we place the section? That depends on what we're investigating.
Most of the time, we need to find out the maximum internal force developed on the object. These computed values give us a reasonable basis for how strong our object should be to resist all loads.
Later on, we'll discuss how to orient the plane properly so that it will give said results.
Summary
To analyze internal forces, we have to expose these components. We can do that by placing an exploratory section on the object.
Internal forces will depend on the position and orientation of exploratory sections.
