Blog Post 10: Preliminary FEA for Design Concept 1

Here are the results of the first round of Finite Element Analysis I carried out on Design Concept 1. Using these results I can begin optimising the design by reducing material where it isn't needed for structural integrity under working conditions.

Enclosure Assembly:

Shown above are the results attained from the first round of FEA on the enclosure assembly when 5Nm of torque was applied, with fixed points for the study being located at the traction pads as these will need to be static when they grip the top of the lid. Although there are clearly no points of failure on the assembly under working conditions, the corners of the traction pads as well as the edges of the enclosure wall did exhibit considerable amounts of stress compared to the rest of the geometry. The blue areas indicate the presence of excess material which will be addressed as the design progresses.

Rack (Gripper):

Above you can see the calculations I have made to determine the minimum gripper force. First the force from the gripping surface acting tangential to the lid (Ft) was calculated, using this value and the frictional coefficient between rubber and steel (gripping surface and jar lid respectively), the force acting on the gripper normal to the centre of the lid (Fn) was deduced. Since the outward force imposed on the gripping surface by the jar lid would have to be equal to the inward force of the gripper/rack: Fn = Fg. Therefore, the inward force acting on each gripper would be 95.28N.

The results from FEA carried out on the grippers seen above indicate that this component will fail at point A without modifications to its geometry when subjected to working forces. The results here were attained by applying 95.28N to the gripping surface with the same force being applied in the opposite direction at the two linear gear teeth that will be in contact with those on the pinion gear. Judging by the concentration of stress at point A, it is clear that any modifications to the component’s geometry will need to consist of adding support material to this point.

Handle:

Because the gripper force had already been calculated, a simple force/beam diagram could be drawn with the unknown handle force on one end and the sum of the two rack (gripper) forces on the other, with the pivot (centre of the pinion gear) in between. Seeing as the pinion gear’s radius as well as the approximate distance from the gear’s centre to the handle’s intended contact point were already known, it was just a case of calculating the moments at each point and deducing the missing force by rearranging the formulae.

The preliminary FEA results shown above indicate that there are no points of failure when the calculated working force (13.8N) is applied to the handle’s grip. The fixed point at the gear dowel hole acts to simulate the stresses endured before the jar lid gives way – this is when the strength of the handle will be truly tested under typical working conditions. It is clear from these results that significant amounts of excess material could be removed from both the inside of the handle and the area surrounding the gear dowel hole whilst maintaining the component's structural integrity.

To do:

• See if material can be eliminated from the enclosure's traction pads.

• Add support geometry to the gripper's corner, FEA results indicate that this area is prone to failure under working conditions (chamfer?).

• Remove obsolete material from handle.