Hello,

My name is Peter and I am working on a project to model snap-through buckling behaviour in an arch.

I am wondering how I might be able to model a simple beam spring under a normal load as it is deflected and eventually buckles and undergoes snap-through buckling. I would like to have the spring (arch) fixtured on its outside edges so that there is no translation in the x, y or z directions, and the only motion allowed on the outside edges is rotation to allow the outer edges of the spring to rotate with the load. I would like to use a prescribed displacement on the uppermost part of the arch (-9mm) to cause the arch to buckle. This downward displacement should cause the spring to deflect and buckle, and eventually undergo snap-through behaviour as more load is applied. Since I have a fixture in the study which gives the prescribed displacement of the arch, I am using the force-length control method for solving the simulation. I tried using the arc-length control method to solve the simulation, but it ended in an error because it stated that solving for the prescribed displacement required that I use the force control method. I am wondering if this method is not the correct method to use since it cannot solve past the buckling point in the arch when the tangent to the force-displacement (equilibrium) curve is horizontal.

Force

I have completed the Solidworks tutorial problem on snap-through analysis, 'Snap-Through/Snap-back of a Cylindrical Sheet', and I am still in need of assistance. I have a result from the simulation as I currently have it set up, and I'm wondering if it's correct. I would also like to validate the snap-through behaviour of the arch using an equilibrium plot but I am unsure how to define the equilibrium plot after I have the results. I have included the model and results files of the example part which I would like to model.

Any help on these problems would be greatly appreciated.

Thank you,

Peter

Peter,

I'm afraid I can't be of much assistance when it comes to the details of the solvers for snap-through analyses. But once you get that part worked out, I wanted to share a story from many years ago when I was designing calculators. This was back in the days when analysis was always done by specialists and a snap-through analysis was something that only one or two programs could handle. We had a professor in the local university analyze the Mylar snap domes on our keyboards. A big question was what the boundary conditions should be. We started out assuming that the edges were fixed, but we got numbers about ten times higher than our measured values. We then assumed that the edges were free to rotate and got numbers much closer to what we expected. To help us understand what was going on, we had the model shop make a clamping fixture out of fairly stout steel plates with big screws. Now the measured values matched the analysis for fixed edges. So be careful when you assume fixed edges; it can take a lot more than you might expect to truly fix an edge.

Jerry S.