Hauv cov txheej txheem ntawm kev ua cov khoom siv thiab kev tsim khoom, kev ntxhov siab seem yog ib qho tshwm sim, uas muaj feem cuam tshuam rau kev ua haujlwm thiab kev pabcuam lub neej ntawm cov ntaub ntawv. Kev nkag siab txog qhov ua rau muaj kev ntxhov siab nyob hauv qhov chaw, cov yam ntxwv ntawm kev faib tawm thiab nws qhov cuam tshuam rau cov khoom siv, txhawm rau txhim kho cov khoom zoo, kev tiv thaiv kev nyab xeeb yog qhov tseem ceeb heev.
I. Ua rau muaj kev ntxhov siab nyob
Residual stress hais txog qhov kawg ntawm kev ua cov khoom, lub workpiece tseem khaws cov kev ntxhov siab sab hauv. Qhov kev ntxhov siab no feem ntau tshwm sim los ntawm cov hauv qab no:
1. Cov yas deformation tsis sib xws
Thaum lub workpiece raug rau cov loads nyuaj (xws li txias dov, kos duab, extrusion thiab nto txhaj tshuaj peening, dov, thiab lwm yam), vim lub zog tsis sib xws ntawm tus ntoo khaub lig-section, qhov chaw ntawm lub zog loj tuaj yeem tsim cov yas deformation, thaum qhov chaw ntawm lub zog me me kuj tseem tuaj yeem deformation elasticity. Thaum unloaded, cov yas deformations tsis sib xws tuaj yeem ua rau muaj kev ntxhov siab nyob hauv qhov chaw ua haujlwm. Tshwj xeeb tshaj yog, cov cheeb tsam stretched yog raug compressive stresses tom qab unloading, thaum nyob ib ncig ntawm cov cheeb tsam yog raug rau tensile stresses. Qhov kev ntxhov siab seem no vim qhov tsis sib xws ntawm cov yas deformation yog ib hom kev ntxhov siab hauv cov txheej txheem machining.
2. Thermal cuam tshuam ntawm inhomogeneous kub teb
Hauv kev ua haujlwm thermal, cov txheej txheem cua sov thiab cua txias feem ntau yog qhov nyuaj heev, nrog rau cov cua kub ceev thiab cua txias, nrog rau cov cua sov thiab cua txias. Txij li thaum tshav kub tsuas yog kis tau los ntawm qhov chaw, lub workpiece yuav muaj qhov sib txawv ntawm thermal expansion vim kub inhomogeneity thaum lub sij hawm cua sov thiab txias, uas nyob rau hauv lem generates transient thermal stresses. Thaum tus nqi ntawm cov thermal stresses tshaj qhov kub siab yield txwv ntawm cov khoom, yas deformation tshwm sim nyob rau hauv tej qhov chaw. Thaum cov txheej txheem cua sov dhau lawm, txawm hais tias lub tshuab ua haujlwm tau txias rau hauv chav tsev kub, qhov kev ntxhov siab seem raug tsim tawm hauv qhov chaw ua haujlwm vim qhov tsis sib xws ntawm cov yas deformation thaum lub sijhawm cua sov. Cov kev ntxhov siab zoo li no vim qhov kub tsis sib xws yog qhov tshwj xeeb hauv cov txheej txheem kho cua sov.
3. Cov kev hloov pauv theem
Thaum lub sij hawm ua cov khoom, cov kev hloov hauv lub koom haum metallurgical (xws li austenite rau martensite transformation thaum lub sij hawm quenching) ua rau cov kev hloov nyob rau hauv lub internal tshwj xeeb ntim ntawm cov khoom, uas nyob rau hauv lem generates theem hloov kev nyuaj siab. Qhov kev hloov pauv theem no tseem yuav nyob hauv qhov chaw ua haujlwm tom qab ua tiav, tsim kev ntxhov siab seem.
Thib ob, spatial faib ntawm residual stress yam ntxwv
Lub spatial faib ntawm residual kev ntxhov siab nyob ntawm nws qhov ua rau thiab cov xwm txheej tshwj xeeb ntawm kev ua. Feem ntau hais lus, qhov kev ntxhov siab seem tuaj yeem muab faib ua peb pawg: macro residual stress, micro residual stress thiab ultra-micro residual stress.
1. Macro residual stress
Macroscopic residual stress yog nyob rau hauv lub workpiece raws li ib tug tag nrho los yog lub macro ntau yam ntawm residual kev nyuaj siab mus cuag equilibrium. Kev faib tawm ntawm qhov kev ntxhov siab no feem ntau yog sib xws, tag nrho kev ua haujlwm ntawm workpiece muaj kev cuam tshuam ntau dua. Hauv cov txheej txheem, vim qhov tsis sib xws ntawm cov yas deformation lossis qhov kub tsis sib xws ntawm cov nyhuv thermal, lub workpiece yuav tsim macro tensile lossis compressive residual stress.
2. Micro residual stress
Microscopic residual stresses yog residual stresses uas ncav cuag equilibrium nyob rau hauv ob peb nplej nyob rau hauv lub workpiece. Kev faib tawm ntawm qhov kev ntxhov siab no feem ntau yog qhov nyuaj, thiab cov duab, qhov loj me thiab kev taw qhia ntawm cov nplej thiab lwm yam. Thaum lub sij hawm yas deformation, microscopic tensile los yog compressive residual stresses yog generated vim grain sib cuam tshuam thiab muaj nyob rau hauv grain ciam teb. Cov kev ntxhov siab no muaj qhov cuam tshuam tseem ceeb ntawm cov khoom hauv zos ntawm cov khoom siv, xws li qaug zog lub zog thiab tawg qhov txuas ntxiv.
3. Ultra-microscopic residual stress
Ultra-microscopic residual stress yog ib tug loj tus naj npawb ntawm atomic nto nyob rau hauv lub workpiece, atomic kab nyob ze ntawm qhov sib npaug ntawm cov residual stress. Kev faib tawm ntawm qhov kev ntxhov siab no yog qhov nyuaj dua, thiab muaj feem cuam tshuam nrog microstructure ntawm cov khoom siv thiab qhov tsis xws luag thiab lwm yam. Thaum lub sij hawm hloov pauv, ultramicroscopic tensile los yog compressive residual stresses yog generated vim lattice distortions thiab tsis xws luag. Cov kev ntxhov siab no muaj kev cuam tshuam rau lub cev thiab tshuaj lom neeg ntawm cov khoom.
Lub spatial faib cov yam ntxwv ntawm cov residual stresses tsis tau tsuas yog nyob ntawm seb lawv ua, tab sis kuj yog ze ze rau cov tej yam kev mob ntawm tus txheej txheem. Piv txwv li, thaum lub sij hawm welding txheej txheem, weld seam thiab nws cov cheeb tsam nyob sib ze tau ceev cua sov thiab txias, uas ua rau ib tug complex faib ntawm residual stresses nyob rau hauv cov cheeb tsam no. Qhov tsis sib xws ntawm cov kev ntxhov siab no tuaj yeem muaj qhov cuam tshuam tseem ceeb ntawm lub zog thiab toughness ntawm cov vuam.
Thib peb, qhov cuam tshuam ntawm residual stress ntawm cov khoom siv
Residual stress muaj qhov cuam tshuam loj rau cov khoom siv kho tshuab ntawm cov khoom. Nyob rau hauv cov nqe lus ntawm yield zog, thaum muaj residual tensile stresses nyob rau hauv cov khoom, nws yuav txo tau lub yield zog ntawm cov khoom, ua rau cov ntaub ntawv ntau prone rau yas deformation. Conversely, residual compressive stresses nce yield zog ntawm cov khoom rau qee yam. Rau lub zog tensile, lub xub ntiag ntawm residual kev nyuaj siab yuav hloov qhov kev nyuaj siab faib khoom nyob rau hauv cov txheej txheem tensile, yog li cuam tshuam nws lub zog tensile. Tsis tas li ntawd, cov kev ntxhov siab uas seem yuav cuam tshuam rau lub plasticity, toughness thiab hardness ntawm cov khoom thiab lwm yam ntsuas. Piv txwv li, residual tensile kev nyuaj siab tsub kom lub elongation ntawm cov khoom, thaum residual compressive kev nyuaj siab txo lub elongation ntawm cov khoom. Nyob rau hauv cov nqe lus ntawm hardness, residual tensile kev nyuaj siab txo qhov hardness ntsuas, thaum residual compressive kev nyuaj siab nce hardness ntsuas.
Qhov cuam tshuam ntawm kev ntxhov siab nyob rau hauv lub neej qaug zog ntawm cov khoom siv tseem ceeb dua. Nyob rau hauv cov nyhuv ntawm alternating load, residual tensile kev nyuaj siab yuav superimposed nrog cov ntaub ntawv load, accelerating qhov tshwm sim thiab nthuav ntawm cov kab nrib pleb, txo cov qaug zog lub neej ntawm cov khoom. Yog li ntawd, hauv kev tsim thiab tsim khoom ntawm cov khoom siv tshuab, qhov cuam tshuam ntawm qhov seem ntawm qhov kev ntxhov siab yuav tsum tau txiav txim siab tag nrho txhawm rau kom tsis txhob qaug zog tsis ua haujlwm los ntawm kev ntxhov siab ntau dhau.
2. Kev cuam tshuam rau lub cev
Cov kev ntxhov siab uas seem tseem yuav cuam tshuam rau lub cev ntawm cov khoom. Piv txwv li, nyob rau hauv cov nqe lus ntawm lub coefficient ntawm thermal expansion, residual kev nyuaj siab yuav hloov lub sab hauv lattice qauv ntawm cov khoom, uas nyob rau hauv lem cuam tshuam nws thermal expansion yam ntxwv. Thaum muaj kev ntxhov siab nyob hauv cov khoom siv, cov coefficient ntawm thermal expansion yuav hloov, uas nyob rau hauv qee qhov kev siv kub rhiab heev (xws li, thermal tswj systems hauv aerospace) tuaj yeem ua rau muaj teeb meem nrog cov khoom haum. Tsis tas li ntawd, residual stress muaj qhov cuam tshuam rau thermal thiab hluav taws xob conductivity ntawm cov khoom. Cov kev tshawb fawb pom tau hais tias cov kev ntxhov siab nyob hauv yuav cuam tshuam cov atomic kev teeb tsa hauv cov khoom, ua rau muaj qhov tshwm sim ntawm tawg ntawm phonons thiab electrons, yog li txo cov thermal thiab hluav taws xob conductivity ntawm cov khoom. Nyob rau hauv cov khoom siv hluav taws xob, qhov twg cov cua kub dissipation thiab hluav taws xob conductivity yog ib qho tseem ceeb, qhov cuam tshuam los ntawm qhov kev ntxhov siab yuav ua rau txo qis hauv thermal efficiency thiab nce hauv qhov tsis kam ntawm cov cuab yeej, uas cuam tshuam rau kev ua haujlwm thiab kev ruaj ntseg ntawm lub cuab yeej.
