CAMCO Ute Deck Mounting Analysis
Client: Camco
Category: Mechanical Analysis
Background
Any product can and will fail, and the challenge is to eliminate or mitigate failures early before the cost of repair tips the balance the wrong way. CAMCO Industries were looking to increase the fatigue life of their deck mounting system and wanted to make design changes to reduce the chance of fatigue crack initiation. To avoid costly ad-hoc repair and warranty claims, CAMCO was looking for assurance that the changes implemented would achieve the desired life. In this case, that meant a minimum ten-fold increase in the fatigue strength was required.
Solution
A designer is fortunate if the precise level of fatigue loading and number of cycles is known! In this case, on the original design, we had a known point of failure (see figure 1 & 2) and an approximate number of kilometres to failure. We applied an ‘arbitrary’ fatigue load to give a resultant stress range in FEA at the point of failure and read off the number of cycles to failure from the material’s fatigue curve (S-N curve). From this we could then extrapolate the maximum permissible stress range for a desired (and much greater) number of cycles for the improved design, given the same ‘arbitrary’ loading.
From here, changes were made and assessed against the permissible stress range.
The ability to make changes to geometry was severely limited spatially, but despite this, CAMCO were able to turn around recommended design changes in short order. Increasing the joint stiffness to prevent local bending and torsion, changing materials of critical components, and increasing bolt torques, all led to a significant increase in the fatigue strength of the design.
Results
An important point with fatigue is that a small change in stress can have a dramatic impact on the fatigue life. By making the changes described above, the fatigue life in critical areas was able to be increased by at least a factor of 100x.
This result gave CAMCO the confidence to move to the next stage of manufacture, knowing that a significant improvement in design life had been achieved.
Motovated was handed a scope of work and with this supported CAMCO in understanding the mechanics of our deck and body mounting systems through the use of Finite Element Analysis and reports.
The result of this partnership with Motovated gave CAMCO a much better understanding of our design and how it would perform in the field. Motovated delivered the scope of work on time and within budget. Communication through-out the project was first class and we would recommend Motovated to anyone wanting to make use of their specialised skill sets.”
Pierre Bantjes, Operations Manager – CAMCO Industries
Figure 1: Original design of the ute mount
Figure 2: Initial fatigue cracking
Figure 3: Revised design of the ute mount with the same stress scale