Those were the days! When we had 3 TV channels, the remote control was a broom handle and no one had a mobile phone. Kids rode their BMX bikes on the pavement, all wearing their Parka coats with hoods over their heads and the coat flapping behind them like a Batman cape.
Times have changed and things have moved on in the world and in engineering design. The days of over designing components are long gone, engineers are using tools like CAD, CAE, FEA and CFD to make lighter, stronger and more durable products.
Here are my favourite top ten tips for designing durable components.
1. Compare older proven designs with new designs
Use tools such as FEA to make direct comparisons by modelling both old and new. Sure the older designs may not be optimised and have too much safety factor but on the other hand, it’s that extra margin of safety that may be the reason it’s a proven design and not just a prototype.
2. People design components not software
Too much reliance on software can be a Trojan horse. Engineering first principles haven’t changed, only the tools have. Learning how to operate software doesn't make people engineers.
3. Leave some margin of safety
Optimisation software is great for reducing component weight but it does tend to put in lots of holes and other shapes that increase stress concentration. In addition to that, components that have been stripped of safety margins may not fare well for the harder to define load cases such as impact.
4. Consider how the manufacturing process affects material properties
3D printing can really speed up the design process. Be aware that the material used for the 3D print is unlikely to be the same as the production material. Also quality control is not as well developed for 3D printing compared to other more traditional manufacturing processes.
5. Design by analysis to achieve targets
Use FEA to drive the design but apply it to achieve targets. Designing to increase stiffness is a different ball game to designing for durability or for overall strength.
6. Avoid features that are stress raisers
Avoid sudden changes of wall thickness or cross sections, increase fillet radii, avoid sharp corners and undercuts if possible. Don’t put identification marking in high stress areas, I once witnessed a fatigue failure originating from a marking.
7. Know your material
Brittle materials require a different design approach to ductile materials in some cases. Materials with more than 15% elongation fare better for high loading and impact than brittle materials. Harder materials fare better for wear.
8. Add design features to remove the risk
Eliminate the problem rather than try to manage it. For example shear stops eliminate the risk of shear failure in bolts. Moving a hole from a high stress region to a low stress area greatly reduces the risk of fatigue failure.
9. Use ‘off the shelf’ components where possible
Commercial off the shelf (COTS) parts are usually proven designs and save time and money, better than designing from scratch in most cases. Novel solutions come with a risk!
10. I got 99 problems and welds are most of them
Welds are often the source of durability failures. Use them sparingly and preferably nowhere near high stress areas.
Do you have any other tips for designing durable components?