SimSolid by Altair is comprehensive, fast, accurate and easy-to-use software that can perform advanced structural analyses on complex, fully featured CAD assemblies within minutes. SimSolid eliminates geometry preparation and meshing: the two most time-consuming, expertise-extensive and error-prone tasks performed in a conventional structural simulation.
A great example of this functionality is how fasteners are handled in SimSolid. As part of the preprocessing phase, most other FEA programs require simplification of the CAD model before the study can be solved. Regarding fasteners, many FEA packages recommend the removal of nuts, bolts, pins and rivets from the assembly, and the replacement of these components with “virtual connectors.” A “virtual connector” will typically replace the shank of the bolt with a 1-dimensional beam element that mimics its stiffness, and rigid elements between the beam element and the CAD model to represent the bolt head and nut connections. SimSolid completely eliminates these steps and simplifications. The software has a built-in geometry detection algorithm that automatically finds bolts and nuts.
Let’s examine an ATV ramp assembly. The 138 part assembly consists of numerous beams, gussets and grates. Bolts and nuts are used to connect the gusset plates to other elements of the structure.
Upon importing this geometry into SimSolid, the geometry engine uses its smart algorithm to automatically recognize every nut and bolt in the assembly. All bolts and nuts are identified and assigned an appropriate symbol in the project tree.
Having correctly identified the fasteners, SimSolid can automatically assign the correct connections between the fasteners and the surrounding structure.
Clicking the “Automatic Connections” icon opens a dialogue box for creating all the connections in the assembly.
If we toggle the option to “Create local connections at bolts”, SimSolid will apply a bonded connection (depicted by the red crosshairs in the image below) between the nut and the bolt shank and between the underside of the bolt/nut head and the plate it is bolting. SimSolid will also apply a sliding connection (depicted by yellow crosshairs in the image below) between the shank of the bolt and the internal cylindrical face of the holes.
We can easily apply pre-tension to nuts and bolts by clicking either the “Bolt tightening” or “Nut tightening” buttons on the workbench toolbar.
In this case we don’t have any blind threaded bolts (all of our bolts have nuts), so we will use the “Nut tightening” option. We then select one or multiple nuts and apply a pretension by either specifying the number of nut turns, a torque or an axial pretension.
After clicking the “OK” button, the graphics window displays a counterclockwise rotation arrow around each nut that has been tightened.
Once the rest of our pre-processing is complete (assigning fixtures, loads etc) and the solution is complete there are some cool options available in SimSolid for postprocessing of nuts and bolts.
We postprocess bolts and nuts by clicking “Bolt/Nut resultant forces” on the workbench toolbar.
The window displays tabulated results of forces and moments for each fastener in our model. We can check that our pretension has been applied correctly by comparing the input pretension value with the value of “Axial force at head.”
While post processing stress results in our model, if we click on the magnifying glass button in the lower left corner, the result window will zoom to an isolated close-up view of the selected bolt, where we can get an accurate depiction of local bolt stresses.
SimSolid’s geometry detection algorithm, meshless technology, automatic connection functionality and post processing capabilities make running complicated, fully-featured FEA assemblies a breeze.
Alon Finkelstein
Simulation Product Specialist
