Fastener Khoom Xaiv
Nyob ntawd yog tsis muaj ib fastener material uas yog rau txhua qhov chawment. Xaiv txoj cai fastenermaterial
los ntawm qhov loj array ntawmmaterials muaj tuaj yeem tshwm rau ua a txaus ntshai txoj hauj lwm. Ceev faj consideration may xav
to ua giua ven to strength, temperature, corrosintawm, vibration, qaug zog thiab mlwm yam sib txawv. Txawm li cas los xij, nrog li ntawdme pib kev paub thiab nkag siab, a weyuav xav txog kev ntsuam xyuas ua tau ua mua ade.
Mechanical Properties
Most ceev daim ntawv thov yog tsim rau txhawb los yog transmnws yog li ntawdme daim ntawm siv sab nraud load. Yog the zog ntawm the fastener yog the tsuas yog txhawj xeeb, thib ere feem ntau tsis muaj xav tau rau saib uayond carbon hlau. Tshaj
90 feem pua ntawm tag nrho cov fasteners yog mua ade ntawm carbon hlau. Hauv dav dav, considkev the tus nqi ntawm raw materials, tsis-ferrous yuav tsum ua considua ered tsuas yog thaum a daim ntawv thov tshwj xeeb yog yuav tsum tau.
Tensile zog
Covmost dav txuammechanical cuab yeej txuam nrog sawv ntsugard threaded fasteners yog tensile lub zog. Tensile zog yog the maxismum siv zog load the fastener ua tau pab prior rau los yog coinciding nrog nws tawg (saib daim duab 1).
Tensile load ib fastener tuaj yeem nrogtthiab yog determined los ntawm the raumua ula
P = St x As Example (saib daim ntawv ntxiv rauSt thiab As tus nqi)
qhov twg 3/4-10 x 7" SAE J429 Qib 5 HCS
P = tensiv load (lb., N) St = 120,000psi
St = tensile zog (psi, MPa) As = 0.3340 sq. hauv
As = tenSile stress area (sq. in, sq. mm) P = 120,000 psi x 0.3340 sq. hauv
P = 40,080 lb.
Rau thyog kev sib raug zoo, a tseem ceeb consideration must ua muab rau the txhais ntawm the tensile kev nyuaj siab cheeb tsam,As. When a txheem thnyeem fastener ua tsis tiav dawb huv tensintawm, it kojpically fractures thntxhib the thnyeemporti uaon (thyog characteristically nws yog smtag nrho cheeb tsam). For thyog reasntawm, the tensile stress area yog calculig
thntxhib ib empirical raumua ula koom nrog the tsis muajminua diameter ntawm the fastener thiab the thnyeem suab. Tables hais thyog cheeb tsam yog muab rau ykoj hauv the daim ntawv ntxiv.
Pov thawj Load
Daim duab 1 Tensile Stress-Txoj kev Daim duab
Cov pov thawj load sawv cev the siv tau zog ntau rau meej txheem fasteners. Los ntawm txhais, the pov thawj load yog ib siv zog load thntawm the fastener must txhawb yam tsis muaj permua deformkev ua. Hauv lwm yam
words, the ib bolt returns rau nwsori ibginal ib shape ntawmce the load yog removed.
Fiua guib re1 mobustrates ib typical stress-strain kev sib thamntawmshib ip of a ib bolt as tension load yog appdagd. The steel muaj qee yam amelasticity raws li nws yog stretched. Yog tus thauj khoom yog remua oved thiab tus fastener yog tseem txawj ntsehhauv thua elasticnge, the ceevner yuav ib txwm return kev rau nwsori ibginal ib shape. Yog tias,hopebvua, the load appdag ua rau the fastener rau ua coj dhau nwsyield taw tes, nws tam sim no nkag the yas ntau yam. Ntawm no, the steel tsis yog lawm muaj peev xwm rovurn kev rau nws original cev yog the load yog remua oved. Cov yield zog yog the point ntawm qhov twg raumanent elongation tshwm sim. Yog peb wua txuas ntxiv rau thov a thauj khoom, peb yuav ncav cuag a taw tes ntawm maxismum
kev ntxhov siab hu ua ultimnoj tensile zog. Dhau qhov point no, tus fastener continuj rau "caj dab" thiab elongate
1
fuua rthua cu ib reduction hauv kev ntxhov siab. Addnwsntawmib strhing yuavultimua cauyog the ceevnua to break ntawm thua tensile point.
