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Archive for February 5th, 2008

While going through my old books,  I found a copy of a test I took on February 15^th, 1993.  The subject was Mechanics, and although it had only 4 problems, I remember it was a tedious one to solve.  For this particular test, we were required to determine the mass and moments of inertia of several solid bodies. This would usually mean having to solve a triple or at least a double integral, but luckily for us most of them were made up of the combination of different familiar solid bodies, like spheres, prisms and cones, and so determining their moments of inertia simply meant adding or subtracting those of the known shapes. This was still tedious and time consuming, no matter what. Without mentioning that, it real life, it’s rare for that to be the case. More often than not, what we will find is objects with capricious shapes, that are not that easy to break apart in smaller, familiar, easier solid bodies. That’s why I was flabbergasted when I learned that SolidWorks has a tool that does it all for you!

This makes it all look so easy! It certainly saves a lot of time and effort! All I have to do is use the Mass Properties tool  and I can instantly obtain a whole amount of information about my model, like in the following example.

As you can see, this tool gives you a report on volume, mass, surface area, center of mass (by default relative to the part or assembly default coordinate location), and moments of inertia. Something similar is available for planar faces and is called Section Properties tool.

These tools can be also be used to evaluate components and solid bodies in multi-body parts and assembly documents, but we have to be careful and select from the feature manager the component, body or part that we wish to evaluate; otherwise, the report will determine the properties of the whole multi-body part or assembly, as if it was one single body. There’s even an option that allows you to include in the evaluation any hidden bodies or components, so watch out for that one too!

We also need to be careful to specify the correct material before we use the Mass Properties tool.  You’ll notice, however, that even when no material has been specified for a part, you can still obtain a report on its mass and properties. How come? Well, that is simply because SolidWorks applies default material properties to every single new part, and so, unless you specify a material, those are the properties that it will use to produce the report. You can always change the material or even create your own.

There! So simple, isn’t it? Makes me wish I had had SolidWorks back then!