Chng 1 Nhng kin thc c s v bin dng doB mn Gia cng p lc VIN C Kh - HBK H ni 11.1.1 Khi qut v qu trnh bin dngS dch chuyn tng i gia cc cht im, cc phn t ca vt th rndi tc dng ca ngoi lc, nhit hoc ca mt nguyn nhn no dnn s thay i v hnh dng, kch thc vt th, lin kt vt liu c boton, c gi l bin dng do. Chng 1. Nhng kin thc c s v bin dng do1.1 c s vt l ca qu trnh bin dng (C s kim loi hc)B mn Gia cng p lc VIN C Kh - HBK H ni 2 Tt c mi phng php GCAL u da trn mt tin chung l thchin mt qu trnh bin dng do. Vt liu di tc dng ca ngoi lc s thay i hnh dng v kch thcm khng mt i s lin kt bn cht ca n. Kh nng bin dng do c coi l mt c tnh quan trng ca kim loi. lm sng t qu trnh bin dngtheo di th nghim ko gin n. Di tcdng ca lc ko, mu ko lin tc b ko di cho n khi b ko t. Trong thnghim ko vi cc thit b ph hp ta c th o c lc ko v dn ditng ng, t xc nh ng sut v bin dng theo cc mi quan h sau:- Vng bin dng n hiBin dng mu khi th koB mn Gia cng p lc VIN C Kh - HBK H ni 3ng cong ng sut - bin dng- Vng bin dng n hi do(trong bin dng n hi rt nh so vi bin dng do- Vng ph huCho SV xem Video th ko mu.Bin dng n hi v bin dng do trong tinh thBin dng ca vt th l tng hp ca cc qu trnh bin dng trong tng httinh th v trn bin gii htmun tm hiu c ch ca qu trnh bindng trong a tinh th trc ht hy nghin cu s bin dng trong n tinhth l tng (khng c khuyt tt).Bin dng n hiB mn Gia cng p lc VIN C Kh - HBK H ni 4Bin dng do trong tinh thBin dng trong n tinh th c hai c ch ch yu: trt v i tinh.TrtKhi mu n tinh th b koxut hin cc bc trn b mt ca mu. iu chng t c s trt ln nhau gia cc phn ca tinh th. S trt xy ra ch yutrn nhng mt nht nh v dc theo nhng phng nht nh gi l mt trt vphng trt. Mc trt thng l bng mt s nguyn ln khong cch giacc nguyn t trn phng trt.B mn Gia cng p lc VIN C Kh - HBK H ni 5Mt trt v phng trt l nhng mt v phng c mt nguyn t lnnht. iu ny cng d hiu bi l lc lin kt gia cc nguyn t trn mt vphng l ln nht so vi nhng mt v phng khc.S lng h trt cng ln th kh nng xy ra trt cng nhiu c ngha l cngd bin dng do.Bi vy kh nng bin dng do ca kim loi c th cnh gi thng qua s lng h trt.c im ca trt:-Trt ch xy ra di tc dng ca ng sut tip.B mn Gia cng p lc VIN C Kh - HBK H ni 6Trt ch xy ra di tc dng ca ng sut tip.- Phng mng khng thay i trc v sau khi trt.- Mc trt bng mt s nguyn ln khong cch gia cc nguyn t- ng sut tip cn thit gy ra trt khng ln.Song tinh (i tinh)Khi ng sut tip t ti mt gi tr ti hn no th mt phn ca mng tinh ths x dch n mt v tr mi i xng vi phn cn li qua mt mt phng gi l mtsong tinh. Song tinh cng ch xy ra trn cc mt v cc phng xc nh.Mt song tinhB mn Gia cng p lc VIN C Kh - HBK H ni 7Song tinh c nhng c im sau:- Ging nh trt s to thnh song tinh ch xy ra di tc dng ca ng sut tip- Khc vi trt l song tinh km theo s thay i phng mng ca phn tinh th b x dch.- Khong x dch ca cc nguyn t t l thun vi khong cch gia chng ti mt songtinh v c tr s nh hn so vi khong cch nguyn t.- ng sut cn thit to thnh i tinh c hc thng ln hn ng sut cn thit gy ratrt. Bi vy ni chung trt s xy ra trc v ch khi cc qu trnh trt gp kh khn thsong tinh mi to thnh.V x dch ca cc nguyn t khi to thnh song tinh nh nn song tinhkhng dn n mt mc bin dng do ng k trong tinh th (chvi %).Nu cng vi song tinh cn xy ra trt th trt s ng vai tr chnhtrong qu trnh bin dng do.Trong cc tinh th lin kt ng ho tr nh Bi , Sb ... ton b bin dngdo cho n lc ph hy ch yu do song tinh to nn, v th mc bin dng do trong cc tinh th rt nh, chng c coi l nhngvt liu rnSong tinh (i tinh)B mn Gia cng p lc VIN C Kh - HBK H ni 8vt liu rn.i vi nhng kim loi mng lc phng xp cht nh Zn , Mg , Cd dos lng h trt t nn thng to thnh song tinh, song ngha casong tinh i vi bin dng do khng ln m quan trng hn l dosong tinh lm thay i phng mng nn c th lm xut hin mt vinh hng mi c li cho trt. Trong trng hp ny bin dng doxy ra thng tng ln so vi trng hp ch c trt n thun. Tuynhin s thay i ny khng ln nn cc kim loi mng lc phng xpcht vn l nhng vt liu c tnh do km.Khuyt tt trong mng tinh thCc dng khuyt tt mngCu trc tinh th ca vt liu kim loi b ri lon do s xut hin ca cc khuyt tt mng.Cn c vo kch thc ca cc khuyt tt c th chia chng thnh ba dng:- Khuyt tt im: cc nt trng, cc nguyn t xen k- Khuyt tt ng: v d cc loi lch- Khuyt tt mt: bin gii ht, bin gii pha, khuyt tt xpCc khuyt tt im1- Nt trng2- Nguyn t xen kB mn Gia cng p lc VIN C Kh - HBK H ni 93- Nguyn t thay th 4- Nguyn t ngoi lai xen kKhuyt tt ng (lch)Lch binLch xonB mn Gia cng p lc VIN C Kh - HBK H ni 10Khuyt tt mtBin gii ht Khuyt tt xpB mn Gia cng p lc VIN C Kh - HBK H ni 11Bin gii pha1.1.2 Ho bn bin dngHin tng ng sut chy tng ln theo mc bin dng trong qu trnh bin dng.Mt hin tng rt quan trng xy ra trong qu trnh bin dng.nh hng nh n tnh cht ca sn phm.Xy ra khi bin dng nhit cn tng i thp.Ho bn bin dng lm tng ti trng i vi dng c bin dng, i hi tiu hao v lc vcng bin dng ngy cng tng. V vy, c th t c mt mc bin dng mongmun no trong nhiu trng hp phi tin hnh cc bc nhit luyn trung gian nhmgim bt ng sut chy v khi phc tnh do. trnh hin tng ho bn bin dng --> thc hin bin dng nhit cao, song chnh xc v cht lng b mt ca sn phm li km hn nhiu so vi bin dng ngui.B mn Gia cng p lc VIN C Kh - HBK H ni 12Nguyn nhn ca hin tng ha bn:Lch khng ngng c sinh ra,Khi chuyn ng, lch hoc gp phi chngngi vt hoc ct nhau --> dn li --> rng lchMun tip tc chuyn ng --> phi tng ngsut.tt c nhng nhn t no gy cn tr cho s snsinh v chuyn ng ca lch u l nguyn nhndn n ho bn bin dng.1.1.3 Cc qu trnh kch hot nhitKhi tng nhit :--> Tinh cht kim loi thay i, tr nn mm v do hn.--> Lc v cng bin dng nh, mc bin dng ln.Tuy nhin:--> D b xy ho b mt dn n cht lng b mt km--> chnh xc ca sn phm khng caoB mn Gia cng p lc VIN C Kh - HBK H ni 13(1) hi phc (2) kt tinh li(3) ln ln ca ht(1)(2) (3)Hi phcB mn Gia cng p lc VIN C Kh - HBK H ni 14a din ho trong tinh th b un(a) sp xp ca lch trong tinh th b un(b) sp xp ca lch sau khi a din hoKt tinh liT chc ca thp Cc bon thp sau khi bin dng ngui v sau khi mt gi nhng nhit khc nhau(a) cha (b) 5250CB mn Gia cng p lc VIN C Kh - HBK H ni 15(a) cha (b) 5250C(c) 5500C (d) 6500CBin dng nguiBin dng na nngBin dng nng Thng thc hin nhit phng Nhit bin dng nh hn nhit kt tinh liL bi d l Nung nng khi bin dng Nhit bin dng cao hn nhit kt tinh li Nung nng khi bin dng Nhit bin dng khong xung quanh nhit kt tinh li Gim lc bin dng, kh biNhit bin dngB mn Gia cng p lc VIN C Kh - HBK H ni 16 Lc bin dng ln, vt liu b ha bn, kh nng bin dng do thp V d vi Thp C: Bin dng Nhit phng l bin dng ngui Gim ng k lc bin dng, tnh do ca vt liu cao, ng sut chy gim nhiu do kt tinh li V d vi Thp C: Bin dng nng nhit t 1150-1250oCnng cao kh nng bin dng do, ng sut chy gim do c s phc hi, mt phn kt tinh li V d vi Thp C: Bin dng na nng nhit t 650-800oCVt liuNhit kt tinh liVt liuNhit kt tinh liC-Thp 550-730oC Sn 0-40oCAl (99,9%) 290-300oC Zn 50-100oCV d nhit kt tinh li ca mt s loi vt liuB mn Gia cng p lc VIN C Kh - HBK H ni 17Al hp kim 360-400oC Mo 870oCCu 200oCW 900-1000oCPb -50-50oC Ni 400-600oC1.1.4 ng sut chy v ng cong chyng sut cn thit (xc nh trong trng thi ng sut n) lm cho vt liut c trng thi do hoc duy tr trng thi do gi l ng sut chy (cngi l bn bin dng- k hu l kfhoc f). ng sut chy l mt thng sc bn ca vt liu, n ph thuc trc ht vo bn thn vt liu (thnh phn,t chc, cu trc, ... ) v cc iu kin bin dng (nhit , mc bin dng,tc bin dng, trng thi ng sut).ng sut chykf = f(vt liu, nhit , mc bin dng, tc bin dng, trng thi ng sut) B mn Gia cng p lc VIN C Kh - HBK H ni 18ng cong sut chyng cong biu din s phthuc ca ng sut chy vo mc bin dng (hoc tc bindng) gi l ng cong chyhoc ng cong ho bn.Thp C15 Thp C15ng cong chyB mn Gia cng p lc VIN C Kh - HBK H ni 19Bin dng nguiBin dng nngng chy ngui ca cc vt liu khc nhaung chy nng thp C25 ph thuc vo tc bin dngB mn Gia cng p lc VIN C Kh - HBK H ni 20S ph thuc ca ng sut chy vo nhit , tc bin dng ca thp C15B mn Gia cng p lc VIN C Kh - HBK H ni 21Cc phng php xc nh ng chy bng thc nghimTh nghim koTh nghim nnTh nghim xonB mn Gia cng p lc VIN C Kh - HBK H ni 22M hnh ton hc ca ng cong chyTure StressRuptureExtrapolatedmumnfC =( )nC = +NG CHY NGUIC: h s ph thuc vo tng vt liun: s m ha bn ph thuc vo vt liu B mn Gia cng p lc VIN C Kh - HBK H ni 23True StrainUniform StrainingNeckingUniform maximstrain0( )fC = +nfA B = +20 1 2 fA A A = + + +KVt liu f0 (MPa) C (MPa) n Vt liu f0 (MPa) C(MPa) nSt38*730 0.100 42CrMo4 420 1100 0.149St42*850 0.230 16MnCr5*810 0.090St60*890 0.150 20MnCr5*950 0.150C10*800 0.240 100Cr6*1160 0.180Ck10*,**260 730 0.216 Al99.5*110 0.240Bng thng s NG CHY NGUIB mn Gia cng p lc VIN C Kh - HBK H ni 24Ck15**280 760 0.165 Al99.5**60 150 0.222Ck22**320 760 0.157 Al99.8**60 150 0.222Ck35*960 0.150 AlMgSi1**130 260 0.197Ck35**340 950 0.178 AlMg3*390 0.190Ck45**390 1000 0.167 CuZn10**250 600 0.331Cf53**430 1140 0.170 CuZn30**250 880 0.43315Cr3*850 0.090 CuZn37**280 880 0.43334Cr4**410 970 0.118 CuZn40*800 0.330M hnh ton hc ca ng cong chyNG CHY nngn mfK =&ng chy na nng:n: s m ha bnB mn Gia cng p lc VIN C Kh - HBK H ni 25mfK =&ng chy nng:n: s m ha bnm: s m tc ha bnBng thng s NG CHY NngVt liu m K (MPa) T(oC) Vt liu m K (MPa) T(oC)C15** 0.154 99/84 1100/1200 CuAl5** 0.163 102 800C35** 0.144 89/72 1100/1200 Al99.5** 0.159 24 450C45** 0.163 90/70 1100/1200 AlMn** 0.135 36 480C60** 0.167 85/68 1100/1200 AlCuMg1** 0.122 72 450X10Cr13** 0.091 105/88 1100/1250 AlCuMg2** 0.131 77 450X5CrNi189** 0.094 137/116 1100/1250 AlMgSi1** 0.108 48 450B mn Gia cng p lc VIN C Kh - HBK H ni 26X5CrNiTi189**0.176 100/74 1100/1250 AlMgMn** 0.194 70 480E-Cu** 0.127 56 800 AlMg3** 0.091 80 450CuZn28** 0.212 51 800 AlMg5** 0.110 102 450CuZn37** 0.201 44 750 AlZnMgCu1,5**0.134 81 450CuZn40Pb2** 0.218 35 650CuZn20Al** 0.180 70 800CuZn28Sn** 0.162 68 800Chng 1. Nhng kin thc c s v bin dng do1.2 C hc qu trnh bin dng1.2.1 ng sutNi lc v ng sut trong vt thnh ngha ng sut ti mt im ng sut ti php v tipP1P2P3P4P5PnB mn Gia cng p lc VIN C Kh - HBK H ni 27ng sut theo cc phngTrn mt mt phng c 3 thnh phn: mt ng sut php v hai ng sut tip.1.2.1 ng sutl0FFdlA0Ang sut k thut v ng sut thc t thB mn Gia cng p lc VIN C Kh - HBK H ni 2800FA =FA =Ch : trong bin dng do ta s dng ng sut thc!ng sut k thutng sut thc x xy xzy yzz 1.2.1 ng sutB mn Gia cng p lc VIN C Kh - HBK H ni 29H to cc1230 00 00 0ij = H to chnhKhi kho st bi ton bin dng do ta thng s dng h ta chnh.Ten x ng sut c 3 bt bin:- Bt bin I1l bt bin bc nhtI constx y z 1 = + + = - Bt bin I2l bt bin bc hai( )1.2.1 ng sutChuyn t h ta cc sang h ta chnh da vo cc bt bin ca ten x ng sutB mn Gia cng p lc VIN C Kh - HBK H ni 30( )I constx y y z z x xy yz zx 22 2 2= + + + + + = - Bt bin I3la bt bin bc baI constx y z xy yz zx x yz y zx z xy 32 2 22 = + = 3122 30 = I I I1; 2; 3 l nghim ca phng trnh:1.2.2 bin dngMt im c to ban u l x, y, z,sau khi bin dng nhc to l x, y, z.Chuyn v ca im tng ng theophng x, y, z:x - x = uxB mn Gia cng p lc VIN C Kh - HBK H ni 31y - y = uyz - z = uzBin dng di v bin dng gc trn mt phng z1.2.2 bin dngxxyyzuxuyu===Bin dng di v bin dng gc : += += += u uyuzuxuyux zzyyzyxxyB mn Gia cng p lc VIN C Kh - HBK H ni 32zz +z xzxTen x bin dng: ijxx xy xzyx yy yzzx zy zz= && & && & && & & ijxx xy xzyx yy yzzx zy zz= Ten x tc bin dng: 1.2.2 bin dngBin dng k thut v bin dng thcl0Trng thiBan uFFTrng thi B mn Gia cng p lc VIN C Kh - HBK H ni 33ll1dl gang bin dngTrng thi sau bin dng1.2.2 bin dng00 1l l l = Bin dng k thut (bin dng dn di):Bin dng thc (bin dng logarit):1lldldB mn Gia cng p lc VIN C Kh - HBK H ni 3401lllnldld = = ( ) + = 1 lnTa c:Ch : Bin dng do trong CN GCAL l bin dng ln nn ta s dng bin dng thc1.2.3 Quan h gia ng sut v bin dngTrong bin dng n hi, quan h gia ng sut v bin dng tun theoinh lut Hooke :( )( )( )EEEx x y zy y z xz z x y = += += +E - m un n hi dc - h s PoissonB mn Gia cng p lc VIN C Kh - HBK H ni 35( )GGGyxy xyyz yzzx zx ===222( )E G = + 2 1 h s PoissonG - m un n hi trt( )( )+ =+ =1 3 2 23 2 1 121 121 1 DDTrong bin dng do, ta cquan h gia ng sut v bindng nh sau:1.2.3 Quan h gia ng sut v bin dngB mn Gia cng p lc VIN C Kh - HBK H ni 36( ) + = 2 1 3 321 12 DDS khc nhau c bn gia cc m un E v G trong bin dng n hi vi m un D trong bin dng do l ch E v G l hng s i vi mt vt liu nht nh cn D th thay i trong sut qu trnh bin dng.Trong bin dng n hi E = tg = const, cn trong bin dng do D = tg m th lun lun thay i trong qu trnh bin dng.1.2.4 iu kin doL iu kin kim loi qu t trng thi n hi sang trng thi do. Xt trng hp ko mt thanh trn theo hng trc. Thanh s b bin dng do nu no ng sut ko trn tit din ca n t ti gii hn chy.Trng hp tng qut: khi vt th chi tc dng ca tI trng bn ngoi, bn trong vt th xut hin ng sut tng ng t ti ng sut chy ca vt liu th vt th ny b bin dng do.L iu kin kim loi qu t trng thi n hi sang trng thi do. k 2 kf min max= = iu kin do Tresca-Saint Venant:Ten x ng sut trong vt th:B mn Gia cng p lc VIN C Kh - HBK H ni 371230 00 00 0ij = ( ) ( ) ( ) 1 222 323 122 22 6 + + = = k kfiu kin do Huber-Mises:Trong cc biu thc trn k gi l ng sut tip chy, c xc nh trong trng hp ct thun tu. Theo iu kin do ca Tresca th max= k = kf/2, theo iu kin do ca Mises th:k k kf f= 130 575 ,1.2.4 iu kin doNhng biu thc ring ca iu kin do- Trng thi ng sut phng: y xy yz= = = 02f2xz z x2z2xk 3 = + + 12321 32+ = kf- Trng thi bin dng phng:z xy + = ( ) x z xz fk k + = =22 24 4*22B mn Gia cng p lc VIN C Kh - HBK H ni 382y xy yz= = 0k 2 k k32*f f 3 1 = = = 131312= = = k k kf f*- Trng thi ng sut i xng trc: = =z0( )( )( ) + + + =2222 26 2z z z fk1.2.5 Nhng nguyn tc, nh lut trong bin dng doQuan h gia ng sut chy v bin dng thc xc nh theo ng cong chy ca vt liuVt th bin dng tun theo nh lut do, nh lut th tch khng i, nguyn tc tr lc bin dng nh nht.nh lut th tch khng iTh tch vt th khng thay i trc v sau khi bin dng. Tng cc thnh phn bin dng trn ng cho chnh bng khngB mn Gia cng p lc VIN C Kh - HBK H ni 39V = X0.Y0.Z0= Xn.Yn.ZnNguyn tc tr lc bin dng nh nhtS chy hng knh ca kim loi khi chnNu cc cht im trong vt th bin dngs dch chuyn trn phng no c tr lcnh nht.B mn Gia cng p lc VIN C Kh - HBK H ni 40kim loi khi chnLy v d chn c st v khng ma st; dp khi trn khun h c vnh bin.