Tbuelna... good general description of shear VS tension bolts, typical hex-head.
Sorry folks... another long-winded/winding 'Taylor' discussion follows...
To emphasize: head, shank, head-shank-radius, thread style, thread-length, alloy/HT, fabrication methods, etc delineate the male [externally threaded] 1/2 of the threaded fastener equation. The mating female [internally threaded] fastener element [nut, threaded insert, etc] is as critical an element to the equation: Nut depth, thread engagement length, thread style [locking, NOT-Locking, Class, etc], alloy/HT, etc. define the nut capabilities.
NOTE.
Washers are an over-looked/under-appreciated factor in these joints that have multiple functions and their own significant issues.
Here is how I generally try to describe it to engineers.
o A tension-rated hex/flush-Hd/thread-bolt threaded into a tension rated nut/insert, meeting aircraft quality installation standards [not bottomed on thread runout and threads showing past top of nut], produces fastened joint capable of reliable tension-shear [tension and/or shear intended].
NOTE.
One characteristic of a well-designed tension joint [bolt-nut combination] is the presence of a strong washer under the nut [and-sometimes under the bolt head] to mitigate higher torque-tension installation forces and prevent friction-related structural damage; then withstand in-service tension [crushing] loads. SEE CAUTION.
CAUTION.
Bolt and/or nut MUST be torqued to a preload-value consistent with a tension rated joint [high preload].
Added washers MUST be capable of withstanding applied crushing loads from tension forces to be a true tension rated joint. IF the washer fails [deforms] under crushing tensile pre-loads-or-service loads, or torque-tension forces] the joint will fail.
o A tension-rated hex/flush-Hd/thread-bolt threaded into a shear-rated nut/insert [and tension or shear rated washers if needed], meeting aircraft quality installation standards [not bottomed on thread runout and threads showing past top of nut], produces fastened joint capable of reliable shear in with very low-tension capacity [not intended for significant tension other than to stabilize the bolt].
CAUTION.
Bolt and/or nut MUST be torqued to a preload-value consistent with a shear rated joint [low preload].
Added washers MUST be capable of withstanding applied crushing loads from nut torque-tension forces only [usually the only significant tension load on the joint]. Also 'soft' washers [aluminum or low-strength steel, etc] 'by default' de-rate the joint to "shear-only" by being unable to withstand significant tension crushing loads [without deforming].
o A shear-rated hex/flush-Hd/thread-bolt threaded into a shear-rated nut/insert [and thin shear rated washers if needed], meeting aircraft quality installation standards [not bottomed on thread runout and threads showing past top of nut], produces fastened joint capable of reliable shear in with very low-tension capacity [not intended for significant tension other than to stabilize the bolt].
NOTE.
Shear rated male fasteners with short threads are rarely capable of accepting a tension rated nut + washer within normal quality requirements, IE: the nut + washer stack-up is generally too deep for short/shear male threads. At best, a thin shear rated nut, with a thin [0.016, 0.032] washer [low strength OK], stack-up is possible. NOTE in some cases the low torque-tension pre-load on a nut may eliminate the need for any washer: and the joint integrity will rely only on the low-installation shear-nut-torque to prevent structural surface damage.
COMMENTS.
In general lock-bolts [crush-collars] and Hi-Loks [threaded collars] follow-these rules... except washers are generally optional and not necessarily desireable.
Evolution/history of threaded, and collared, solid-shank fasteners adds complexity to simple-strawman picture presented here. I haven’t the time to explain… back-to-work!
I have not even scratched the surface for bolts/nuts intended primarily for high-tension service [limited/no significant shear].
Regards, Wil Taylor
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