Unlike the majority of FEA tools in industry today, SOLIDWORKS Simulation is fully integrated into the CAD environment. One of the major benefits to this is that those who are already familiar with SOLIDWORKS CAD can easily pick up and learn SOLIDWORKS Simulation; you in no way feel like you are learning a brand new software. The effect of this is that SOLIDWORKS Simulation is beginning to be used earlier in the design process by the everyday engineers and designers who may not have an in depth understanding of the underlying FEA theory. That isn't a problem because of how easy SOLIDWORKS Simulation is to use, but there are times when understanding the FEA theory and how it relates back to the software can come in handy.
Out of all the simulation packages that SOLIDWORKS offers, I would say the basic package, Simulation Standard, is by far the most readily used. Don't get me wrong, the Professional and Premium simulation packages are of great value but I think the questions that come to peoples' minds first when they think of FEA are: Is my design going fail? Am I above my required Factor of Safety? Do I have enough material? Or do I have too much material? All of these questions can be answered using the Linear Static portion of Simulation Standard. When it comes to other failure modes such as temperature, buckling, fatigue, or vibrations, Simulation Professional or Premium are needed.
So those of you that are using the Linear Static portion of SOLIDWORKS Simulation, this tip is directed toward you. Have any of you ever thought about what the "Linear" in Linear Static really means? Well in case you haven't, we are going to take a look at what it really means and how we can use that knowledge to help us practically save time when designing our products.
What the "Linear" in Linear Static means is that everything we do in this package is going to follow Hooke's Law
If you are having a hard time reaching back into all those Strengths of Materials memories that you have, maybe you will recognize this other form of Hooke's Law, F = kx. The "k" in this equation refers to the stiffness of the structure that we are analyzing. The stiffness is a function of both the geometry and the material it's made out of. One of the basic assumptions when running Linear Static analyses is that this stiffness value does not change. So if we assume that the stiffness is held constant in the above equation, then we end up with a proportional relationship between our force, F, and our resulting displacement, x. In other words, when the Force doubles, the displacement is going to double. We can use this idea to help us save time when running analysis on our designs. Let's take a look at an example and see how this is done! To illustrate how we can use this information to save us time, we are going to run a simple analysis on these pliers.
To start, we are going to apply a 225 N load to the end of each arm of the pliers and run an initial analysis. After running this analysis once, we see that each end of the handle has displaced about 0.4mm.
If our design only required us to test this at a 225 N load, then we would be done analyzing these pliers. But let’s say we wanted to find out how much of a force it would take to touch the ends of the handles. One way we could do this is to run a few more studies and gradually increment the load until the ends meet, but this could take a considerable amount of time depending on the size of the problem. So another way we can approach this is to use the fundamental principal of linear static to our advantage. We said previously that if we double the load we are doubling the displacements (or vice versa) based on the assumption of a constant stiffness. Well if we apply this thinking to our pliers example we can figure out the load needed to clamp the ends of the pliers. We know that with no load applied, the ends of the plier handles are 15.24mm apart. At 225N on each handle, each handle displaced 0.4mm. So in total the handles came together by 0.8mm. If we want the handles to touch they need to come together by 15.24mm. By dividing 0.8mm into the total 15.24mm we get a multiplication factor that we can then apply to the load. The factor that we get is 19.05. If we multiply 19.05 by 225N we get a load of 4,286N. To verify that this is the correct load needed to bring the ends together we can run one more study.
As you can see, with the load we calculated, the plier ends now touch and we saved ourselves the time of having to run multiple studies to figure this out! By forcing the handles to touch however, we caused the pliers to develop stresses that exceeded the yield strength of the material which is outside of the linear portion of the stress strain curve. In order for us to analyze this situation, we would need to use our Non-Linear package found in Simulation Premium.
By: Chris Olson, Simulation Applications Engineer