What are shells, beams, and trusses? - SOLIDWORKS Tutorial

- This course focuses on the use of shell, beam and truss elements used in SOLIDWORKS simulation. So the question is, what are these elements? To answer that question, this introductory video describes the difference between the conventional FEA solid elements and these alternative shell, beam and truss elements. These elements are special purpose elements which will allow for more sophisticated idealization methods in Finite Element Analysis. They're an alternative to using the traditional 3D solid elements. While that might seem curious because 3D elements seem to match 3D geometry and so why would we bother to do anything else? Well these alternatives can provide much faster, more efficient analysis solutions. Now in the conventional approach to FEA meshing, we would take a typical SOLIDWORKS 3D model made up of 3D geometric bodies and we would mesh that with 3D solid elements. And why would we want ever to do anything other than that. Meshing with solid elements tends to give us a very high element count which means we're using lots of memory and the run times can potentially pretty long. Now there are lots of stress results which means that if we want to investigate detailed stress concentrations or understand load powers we've got to work pretty hard in the post processor. Now if we want to redesign and reanalyze, how quickly can we reconfigure the mesh, control the mesh and rerun again. It can get complicated with 3D meshing. In particular this can slow down the turn around of concept designs and it might well be that a simpler approach to idealization can help here. So here's an alternative approach. We start with full 3D geometry but then we simplify it in preparation for a simpler form of idealization. So we're going to mesh the geometry with simpler 1D beam elements and this is what they look like. In fact if we take away the 3D visualization, the pre-processor, it just comes down to a simple line element. Using beam elements we can look at traditional engineering diagrams which include bending moment, shear force and torque diagrams. Using simple hand calculation techniques, this allows us to carry out a very fast visual assessment of the strength of our components. This means that we can investigate design changes pretty quickly. However, when we're thinking about using beam elements, we've got to make sure we're targeting beam-like structures. So for example, the bridge here is an ideal candidate but on the other hand it wouldn't be much use looking at something like the solid object here and then trying to represent that in anyway with a beam-like element. So as the old saying goes, if it looks like a beam, feels like a beam, then let's analyze it as a beam. We've seen that beams are great simplification over using 3D solid elements. But is there anything can be simpler than a beam and the answer is yes, we've got truss elements. Now these can only carry end load, no torsion, bending moment or shear. And here is some typical trusses used in the construction industry. A truss is making up a crane jib. I'm sure you've guessed the punch line by now. If it looks like a truss, feels like a truss, then we're going to analyze it like a truss. As a contrast, there are many examples of thin walled structures. So for example, part of an aircraft fuselage and part of the hull of a ship being built. Using solid elements in this kind of situation is incredibly expensive, way way too many elements. These industries and the automotive industry, for example, rely almost exclusively on using shell elements. And here's a simple piece of solid geometry which has been meshed using shell elements. Shell elements restrict to the carrying membrane and the bending loads only. And here comes the punch line again. If the structure looks like a shell, feels like a shell, then lets model it and analyze it as a shell. So let's summarize all that. There are three classes of elements. 3D solids which are very traditional and they mash the geometry directly. We're not gonna cover those on this course. We're going to look at 2D shells which mesh surfaces or sheet metal bodies. Then we'll look at 1D beams and trusses which can mesh weldments or lofted or similar 3D geometry.