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[QUOTE=knothead;536407
Lastly, I would strongly recommend that square holes be avoided at any cost. Choosing carriage bolts because of how pretty they are is really silly when you consider how much of a propensity there is for cracking to occur at the corners of square holes.[/QUOTE]
Absolutely NO square holes i n any cyclically loaded structure .... a square hole forms in material engineering and stress analysis/design what known as a 'stress-riser'. A stress-riser will severely reduced the ability to carry stress and WILL be the site of where fatigue cracking starts to propagate. With cyclically loaded components like chainplates you want NO sharp edges, all 'smooth', the LEAST amount of holes ... and those 'holes' having 'rounded' chamfers, etc. With a square hole stress riser and without actually dynamically testing one to failer, I'd probably reduce the fatigue endurance limit (30000psi) for 304/316 Stainless down to 20Ksi or even lower .... thats how BAD 'square holes' are.
Square holes (window shapes) were the cause of the early British Comet Jet passenger aircraft to catastrophically fail and break apart in flight .... NO square holes if you want a cyclically loaded part to 'last'.
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