Only a daft idiot would design to the UYS or UTS of a material ... unless he/she WANTED the part to break at a certain value.
You are mistaken on several account. First the values given are for *Cruicible Steel's* own produced stainless steel
and only if the metal is accompanied by the usuall mill certifications. These values wouild not apply to metal produced by "Nan Fujngs Art Foundry and Delicatessen". Each mill's values will be different, and different from lot to lot. Without certifications based on actual testing values you MUST 'de-rate' those value to be prudent/safe.
Hardness is only a correlation to the strengths and if you are designing for other than hardness, then you need to apply de-rating 'safety factors' that lower the apparent ultimate values. And, one must KNOW that these values are for slowly applied direct tension/compression; and, thats NOT how a chainplate works !!!!!!!!!!!!!!!!!!!!!!!! The portion of the chainplate (as normally ill-designed by boat 'architects') that attaches to the bost is usally WRONG or EXTREMLY WEAK with respect to 'proper' / normal stress transmission
. These are cantilever/shear connections that usually require that the attachment materials (bolts) be used at ONE FOURTH of their tensile values .... and then further 'derated' by the 'normal' safety
factors for such service
As for 'elongation' .... sorry but 30ksi is 1/3 the fiber stress of 90ksi ... and if the bolting holes elongate it means that the metal has yielded (ductile failure) and the designer
didnt know what he/she was doing and probably simply 'hung' the bolting in simple shear (w/cantilever) instead of making a 'compression/friction joint' wherein the compressional force of the torqued bolting was used to force the plate and its base together and that 'friction' is what transmits the stress. 99% of most chainplates are improperly designed as flat plates and are unsymmetrically loaded where the plate meets the base attachment .... this puts the bolting into 'cantilever stress' which automatically decreases the load bearing ability of the bolt by 1/4th !!!!!! If boat designers actually knew what they were doing, they would design the plates so that the terminal bottom end would be a CLEVIS connection (and free of 'stress risers' of bolt threads touching chainplates) .... just like how the other rigging
components are designed. If properly designed, chainplates would hardly every fail !!!!!!!
Those 'book' values of metals (yield and UTS) are ONLY for straight slowly applied tensile loads. Applying impact, cyclical, cantilever loads, etc. and then use a material that is long term incompatibble with sea water
(crevice corrosion) .... you better KNOW what you are doing and KNOW what 'safety factors' are normaly applied (historical scantlings). If you think that one can read a straight tensile value from a book and apply those values to non-straight line tension compression
.... then you risk having the mast
come down into your cockpit
. I state again those book values for metals are for DUCTILE failure mode, not FATIGUE modes and those values are WITHOUT the safety
factors that MUST BE additionally applied by the designer
. If you dont know what safety factors by which you DE-RATE the material strengths, you risk catastrophic failure when the material eventually 'work hardens' becaues it was a BAD design in the first place. A minimum *safety factor* of 3 (4 or 5 is better) to derate 300 series to usage at less than 30ksi is VERY prudent for usage versus cyclical loads in a halide corrosion atmosphere.