8.2.11 Conversion of 8mm flat bar to 2” X 1” rhs

Fig. 51

Table 21

The upper triangulation on the rear firewall frame is of 8mm thick mild steel solid bar. This is approximately three times the mass of an equivalent section of 1” x 1” 16-gauge mild steel RHS and displays less torsional stiffness. Changing this to 2” x 1” 16-gauge mild steel RHS will not only reduce the mass but will also increase the torsional stiffness. This drop in mass and increase in torsional stiffness will inevitably lead to an increase in efficiency.

With an overall increase in torsional stiffness of 213% and an overall increase in efficiency of 197%, it is clear that the inclusion of all these modifications is viable.

8.3 Stage 3-Identical Modifications to Fully Panelled Chassis

The modifications as performed in 8.2 were performed on the fully panelled chassis to show the contribution to torsional stiffness provided by the shear panels. This also allowed an optimisation for mass as the panels could be changed from mild steel to aluminium and the effect on the stiffness of the modified chassis noted.

Fig. 52

Due to the panels partially obscuring the modifications (Fig.52) and their presence in 8.2, these results will be in a tabular form with no pictures of the chassis. The modifications were performed in the same order and are denoted by the notation 8.3.*.

Table 22

As can be seen in Table 22 when the modifications are performed on the fully panelled chassis from 8.1.9 the increase in torsional stiffness is almost 1000Nm/deg more than the sum of the individual improvements. This is due to the stiffening of the most flexible spring allowing a much greater improvement in the effectiveness of the stiffening of the passenger compartment. With an overall increase in torsional stiffness of 377% over the original chassis, these modifications show major improvement in the performance of the chassis. With an overall increase in efficiency of 286% over the original chassis, it can be assumed that more of the chassis is being used effectively to resist torsional loading

8.4 Stage 4-Optimisation Study

Now that a significant increase in torsional stiffness has been achieved, an optimisation study can be performed. This involves keeping the stiffness as high as possible but removing as much mass as possible. This can be achieved by conversion of mild steel panels to aluminium, by reduction in section size of beams that are not highly stressed or conversely increasing the section size of highly stressed beams. The optimisation has been aimed at achieving a minimum of 6000Nm/deg torsional stiffness with the minimum mass. It should be remembered at this stage that the baseline validation model was measured by the software as being 8Kg heavier than the original chassis. This means that the efficiency of the chassis will be even higher than the results suggest if a physical chassis with these modifications were to be constructed and it matched the predicted stiffness values. This is unlikely however and the efficiency is more likely to be as predicted due to the drop in mass and torsional stiffness that a physical chassis would have.