huangyhg

fatigue life enhancement with hi-lite
dear all,
maybe somebody can explain what is the advantage of hi-lite over hi-lok regarding fatigue ? i have visited hi-shear site already, but not so much of an explaination that i can get from there regarding the above subject. what i am looking for is actually why can we install hi-lite with higher interference compared to hi-lok and how much. but i have recieved an answer from hi-shear already and according to them the higher interference that can be achieved with hi-lite is due to the different lead-in radius design. the remaining question would then be how much interference and fatigue life enhancement that can be achieved of joints using hi-lite compared to hi-lok. thanks sparweb, for your suggestion to start a new thread.
regards,
hi-lok's have the feature of limiting the torque that can be applied to the collar when they are installed. by not over-torquing, they are not significantly stretched, so the diameter of the fastener does not decrease, either. there is some torque, though, so the hi-lok is okay for shearing loads.
hi-lites are a little different. they have the features of the hi-lok that i described above, but the threading is changed. there is an improvement in how the collar threads onto the pin that increases fatigue life of the fastener, meaning the collars for hi-lok and hi-lite are not interchangeable. the different threading also reduces the size of the collars, cutting down their weight (hence the name).
there are also hi-tigue bolts, that have a slight bulb in their shank. apparently, as you tap them into an undersize hole, the bulb cold-works the hole surface. by burnishing it, a residual stress remains that improves fatigue life. from reading about it, i expect that hi-tigues are much more expensive, too.
if sealing the joint is important, note that the sealed collars may not be available for all types of fastener.
steven fahey, cet
thanks sparweb,
but can we also obtain some slight cold work effect on the hole wall with hi-lite and hence increase the fatigue life of the joint ?
regards,
fatstress
i'm afraid i don't know the answer to that one. i can't see how a hi-lite would be any different than a hi-lok in that regard... where's mr. w.k. taylor when you need him?
steven fahey, cet
fatstress... and you-too sparweb...
in a nutshell鈥?br>
hi-loks [hl] were the first generation fastener of it's type. designed for installation in close-tolerance clearance and transition-fit holes [i favor the term 鈥渘et-fit鈥濃�?where hole diameter ~= pin diameter ~+/-0.0010%]. although precision made, hl pins have a relatively sharp transition edge between threads and shank鈥?and have threads that are only slightly smaller than the pin shank鈥?which hinders installation in true interference-fit holes. hls can only be pressed-into light interference fit holes [-0.0010% to -0.0020%] in aluminum by carefully pressing-in wet with primer or sealant (which act as a 鈥渓ubricant鈥?to prevent damaging the hole walls). hls can only be installed in medium interference-fit holes [-0.0020% to 0.0030% if shrunk to minimum diameter in ln2鈥?and are installed rapidly but carefully into holes pre-coated with primer of sealant (and god-help-you are slow to drive the pins into position and allow the fasteners to re-expand before fully installed!!!!). hl collars reflect the first generation nature of these fasteners (match the hl pins and are moderately weight conscious). essentially hl pins and collars are permanent light-weight bolt/nut installations!!!
hi-tigues [hlt] were designed explicitly for installation in interference-fit holes [fatigue reduction]. the transition between the shank and threads is a polished-smooth radius with a very slight bulge. although the radius was advertised as a feature for 鈥渂urnishing鈥?holes during fastener installation, it doesn鈥檛 seem to be of value for that purpose. however, what is important is that hlts have relatively low drive-in force and can be installed in heavy interference in aluminum structure鈥?and light/medium interference [frozen] in titanium structure, without damaging the holes. hlt threads are recessed substantially below the shank diameters to minimize potential for thread-scoring the holes in high-interference-fit conditions. hlts collars accommodate the thread profile changes and the radiused/bulged transition between the shank/threads and are moderately weight conscious.
hi-lites [hst] are a 鈥渘ext generation hi-tigue鈥?style fasteners. they retained the 鈥渂enefits鈥?of hlts but were re-designed with slightly reduced features such as shank diameters, lowered head profiles, reduced thread diameters and lengths, reduced size collars, etc鈥?for absolute minimum installed weight vs performance (trying to approach the minimum installation weight-to-performance of interference-fit swaged-collar lock-bolts鈥?and the good interference characteristics of hlts).
note: all three fastener types benefit from hole cold working... although benefits of heavy interference are as apparent in cx'd holes
the esteemed [late] dr lincoln [fatigue guru for the usaf] cautioned me about the "benefits" of high performance fastener installations: they are only as good as the worst possible random combination of hole quality, fastener fit and installation abuse... and the chance that these "worst-case" discrepancies will occur [undetected] at the worst possible structural locations.
regards, wil taylor
hello wktaylor,
thanks a lot...quite a thorough explaination..
i appreciate it..
just a simple question. which is then better in term of fatigue ? hi-lite or hi-tigue ?
regards,
hi-lites are titanium hi-loks, and more expensive.
hi-tigues (i think) have a slightly different thread form, and so would be slightly better in a tension loading situation.
i would have thought that they (hi-loks, hi-lites, hi-tigues) were reasonably equivalent for shear loads; tho' ,cynically, i expect that the hi-shear salemen can show that the more expensive one is "better". <watch out, in-coming>
i would prefer to use an an bolt (or something like it) for tension loading so i can control the pre-load better ... by that i mean hi-lok collars shear off at a predetermined value which is probably very good at quality control on the preload, but doesn't allow me to specify a high preload for a particular tension loading situation.
fatstress...
i suspect that hi-tigue and hi-lite [pin/collar] fasteners would perform about the same in a one-on-one testing [assuming properly set with similar hole fit].
the advantage to hi-lites would be a weight savings of ~4%-to-8% per fastener installation... depending on whether grip-length was properly sized for the stack-up. individually this is a very small savings鈥?but multiplied by several thousand [hundred thousand] fasteners this savings eliminates several hundred pounds [kilos] of dead weight.
regards, wil taylor
quote:
there is an improvement in how the collar threads onto the pin that increases fatigue life of the fastener.
wil鈥檚 correct. take a look at the fastener minimum lot acceptance tension-tension fatigue lives (and loads) in the respective hi-lok/hi-tigue (
obviously kenneth is well informed about hi-shear fasteners ... there's actually a neat table in the collar spec (table iv in spec 345 in the hi-shear catalogue) that defines minimum preload. this comes out to be about 50% of the 95ksi steel fastener tension allowable ... higher than i'd have thought.
still if you've a cyclic tension loading, possibly an an bolt would allow higher preloads (which would be better).
kenneth good catches... you earned a (*) from me. thanks for setting this reply "straight".
guys, this was an obvious "aw-shoot" (**) on my part for sloppy work on "details". teaches me to refer to old data ... and just a "quick-pass review" of data.... before responding.
note: in my experience, i only used interference fit hi-tigues with ~0.0010+ larger shank diameters such as hlt10, etc..
(**) a red star = atta-boy. however, a thousand atta-boys, can easily be canceled by one "aw-shoot".
regards, wil taylor

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