Rubber Joint
Background
Figure 1 – Elastic Joint Concept
Two plastic tubes needed to be connected in a flexible way, i.e. allowing them to rotate one to each other (Figure 1), while still being capable to withstand the internal pressure of the fluid.
The Challenge
Because of the high internal pressure and the big rotation angle required, it was clear to our Customer that some simulations were necessary in order not to enter into an endless trial & error process and CG CAE was chosen as the partner to perform those simulations because of our experience in dealing with high tech and/or particular materials, like rubber is, and because of our strong knowledge in highly non linear models.
For this case, the nonlinearities are coming from the material (hyperelasticity) and from the contacts between the pins (used to realize the pivot axis) and the two flanges.
The FE Model
Because of the kind of structure, only half a model has been built and the proper symmetry boundary conditions were applied at the section plane (see Figure 2).
Tetrahedral second-order elements (10 nodes) were used in a rather coarse mesh for the two flanges, for whom there was no interest at all, while 8 nodes hexahedral elements (bricks) were used to model the rubber part with a finer mesh.
Internal pressure, imposed rotation and a pulling force (axial) were applied as load step to the model.
Figure 2
AHyperelastic Material Properties
Each kind of rubber has its own properties and the Shore hardness will only tell a little portion of the whole story. Such materials require at least a uniaxial test, in both compression and tension in order to find out the hyperelastic material model that better suites the test data. This has been done and the results are shown in Figure 3.
Figure 3 – Material model and experimental data
Figure 4 – Displacement magnitude and Maximum Principal Strain
Figure 5 – Maximum Principal Strain
Some results
Finally, Figure 6 illustrates a section taken along the pivot axis when the design pullout force is applied (Von Mises stress)
Figure 6 – Von Mises stress
Conclusions
The simulation results were compared with the hyperelastic material properties and our Customer decided to produce some parts to be tested and the test were successful, so that series production could start.
