Mysterious Failures?
Fatigue failure is not a new phenomenon - it has been observed for more than 150 years and yet fatigue failures still occur far too frequently. Why? There are a lot of possible reasons but one of the most common is that the stresses due to manufacture such as...bolt stress, pre-load, proof stressing, thermal distortion due to welding
and loads due to transportation i.e. loads incurred as the product is moved to its working position that are not normal operational loads are often ignored in the fatigue design of the product.
A cracking story!
A well known fatigue failure occurred in 1954 when the De Havilland Comet 1 aircraft suffered catastrophic fatigue failure in service. The fatigue test showed the life of the airframe should have been at least 19,000 pressure cycles. However, the fatigue failures in flight occurred after just 1,286 cabin pressurisation cycles. What is less well known is that the reason for this was finally proven based on modern fatigue simulation methods. The important information is that fatigue test airframe had been used for a proof test where 2 x normal cabin pressure had been applied prior to being used for long term fatigue testing. This pre-history in the loading meant that all the pre-existing cracks had been "blunted" and so the fatigue life was much longer than for the production airframes which had no proof test.
De Havilland lost the aeroplane business to Boeing due to this critical error!
So whether you are making paper clips or power stations, machines or motor cars, a correct understanding of stresses and fatigue is vital to the success of your product!
Why not contact us today for a free and confidential discussion about your product development and testing?