Naked Science Forum

Non Life Sciences => Technology => Topic started by: Yahya on 10/05/2018 08:20:26

Title: What determines when a steel spring develops metal fatigue?
Post by: Yahya on 10/05/2018 08:20:26
how many cycles can steel spring stores before it reaches fatigue ? giving steel spring energy density 300 J/Kg , what if I stored 300 Joules in say 10 Kg instead of 1 Kg how many times will the number of cycles increase ?
Title: Re: What determines when a steel spring develops metal fatigue?
Post by: chris on 13/05/2018 23:10:41
This article on the mechanism of metal fatigue (https://www.thenakedscientists.com/articles/features/metal-fatigue) might help to get the ball rolling.
Title: Re: What determines when a steel spring develops metal fatigue?
Post by: Colin2B on 15/05/2018 10:22:55
The best place to start is by finding the Stress Life Cycle curve for the particular steel you are working with.
These usually show the the applied stress S as a proportion of the steelís ultimate tensile stress Su, against the number of stress cycles to failure. The scale is usually log.
Obviously the applied stresses are in Pa so are dependant on csa rather than mass, but you could easily do the conversions. Also bear in mind that these curves assume no stress concentration points or stress raisers, nor any surface treatments. Although you are probably not too worried about it at the moment, remember that compressive surface stresses increase fatigue load carrying capacity, so compression is better than tension.
Title: Re: What determines when a steel spring develops metal fatigue?
Post by: Yahya on 10/06/2018 17:41:52
typical springs have 10 million cycles until they reach fatigue so a traditional clock would work hundreds of years before its spring lose efficiency
Title: Re: What determines when a steel spring develops metal fatigue?
Post by: Colin2B on 10/06/2018 17:47:04
Depends on the quality of the spring. Many postwar alarm clocks failed after <20yrs and hairspring failure was even more common, although that might have been through people throwing them across the room!