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NGHIEN ciiu-TRAO DOI Thiet |ie clii tiet mav theo phticing phap iac suat (*) NGUYEN DINH MAN TOM TAT Tii trade tdi nay, van de thie't iBj) TAP CHI c a KHI VIET NAM V So 09-Thang nam2010 NGHIEN cuu-TRAO001 va tri chirc nang, nhiem vu dd sudt thdi han da dinh nhiing dieu kien dat trudc Do ben va ring suat la cac dai lugng ngau nhien, dugc ky hieu tuong irng la B va U Khi biet dugc ban chat ngau nhien ciia ben va irng suat va neu nhu luat phan phdi cira ben g(b) va luat phan phdi ciia irng suat f(u) dugc xac dinh thi ta cd the giai quyet dugc bai toan sau day: 1- Xac dinh dugc cac chi tieu ve DTC cua chi tiet may Hinh 1: Mien irng suat U va mien ben B Thiet ke chi tiet may theo phuong phap xac suat ddi hdi phai cd thdng tin ve phan phdi ben va phan phdi irng suat Mudn vay, ngudi thiet ke can dua tren kinh nghiem hieu biet day dii ve dieu kien lam viec ciing nhu ve tinh chat vat lieu ciia chi tiet dang xet Khi tinh toan irng suat, can cd sd lieu thdng ke ve tai trgng va ke tdi cac phan phdi xac suat ciia cac yen td anh hudng den iing suat, chang han nhu su tap trung irng suat, Khi tinh toan ben, can cd sd lieu thdng ke ve tinh chat cira vat lieu chgn dimg va ke tdi cac phan phdi xac suat ciia cac yeu td anh hudng tdi ben, chang ban, bdng be mat, 2- Neu DTC ciia chi tiet may dugc dat trudc theo yeu cau ciia ngudi sir dung, ta giai bai toan thiet ke ma nghiem ciia bai toan la kich thude cua chi tiet DTC la mgt ham ciia thdi gian t, vay cac chi tiet maj', may dugc xem xet sudt qua trinh khai thac sau cua chiing, do cac chi tieu DTC khdng can viet theo bien t va dugc hieu la DTC ca thdi ky khai thac danh dinh ciia chimg Gia thiet ham mat phan phdi ciia ben g(b) va irng suat f(u) dugc bieu dien tren hinh Xet virng giao thoa giiia ben va img suat if(u),g(b) Cac tham sd ve ket cau, ve kich thude hinh hgc va mdi trudng mdt mat anh hudng tdi irng suat, mdt mat anh hudng tdi ben Thiet ke chi tiet may theo phuang phap xac suat can tien hanh theo trinh tu chir yeu sau day: 1- Xay dung nhiem vu thiet ke Hmli2 2- Xac dinh dii lieu ve tap sd lieu ciia tai trgng 3- Tinh toan ung suit tai tiet dien nguy hiem 4- Xac dinh luat phan phdi chinh xac ciia iing suat 5- Xac dinh du: lieu ve tap sd lieu cua ben (gidi han ben, gidi han chay, ) 6- Xac dinh luat phan phdi chinh xac ciia ben 7- Tinh toan kich thude ciia chi tiet theo tin cay dat tmdc 2.2 Do tin cay (DTC) ciia chi tiet may tren co sd ben va ung suat Theo dinh nghia, DTC ciia chi tiet may la xac suat de ben cd gia tri Idn hon irng suat hoac la xac suat de ling suat cd gia tri nhd hon ben: (1) R = P(B>U) hoac R = P(U0) = jf(y)dy=j Ta thiy (5) tuong duong (8) Sir dung cac cdng thirc tdng quit cd the giii quyet bai toan: Thiet ke chi tiet may theo yeu ciu DTC dat tmdc vdi gii thiet da biet cac quy luat ngiu nhien ciia ben va irng suit So 09-Thing nam2010 ' =exp | y~i^Y dy Neu ta dat dai lugng chuin hoa ^ y~l^Y , ta cd d2 = — ' suy dy=SYdz c;^ NGHIEN cuu-TRAO001 Biy gid ta xac dinh sai lech chuin ciia irng suit nen ciia chi tiet a-^ Tir cdng thirc (12), su dung quy tic phin chia tirng phin ta cd: Khi dd (11) dugc viet lai thanh: (12)R = J =exp Z, a^ " Y V2jr Oydz r do, cin dudi Z, duoc tinh nhu sau: (20) o ' / dll ] ^ Op [UP.1 ' (13) z,=z! ^ + v d "] ' ddiy: Nhu viy, tri sd ciia Z, la ket qui tinh toin tir tri sd ky vgng toin va sai lech chuin ciia ben va irng suit Cdn cin tren Z = Zl = oo ^•)i|H nd' Op = ^ O p = U p- •4906 —T- p' iy=co Do dd, xac suit khdng hdng (12) dugc viet lai dudi dang: au (22) R= ^ j e x p ( - ^ U ^ = U ^ ^ = 4U=y^ ad \ (14) ( dii ] ^ dz JJ- he sd sai lech cua d, Y^= 0,1 Thay cac gia tri ciia (22), (21) vao (20) ta dugc: /' hay: (15) R = i-(i) \ HB-IIU 1-0(Z,) (23) Trong dd: 0(Zj) l i ham Laplace da cho d phu luc II [ ] Diy chinh l i cdng thirc cira DTC ben va irng suit cd phin phdi chuin Sir dung (15) ta giii bii toan nhu sau: Ung suit nen cua chi tiet dugc xac dinh bdi cdng thirc: F U'.0,0409 Thay cac gii tri ciia: Schay = N/mmo = N/ mm" Schay U tinh theo (19), vao cdng thirc (24) sau: Trong dd F la dien tich chiu nen ciia chi tiet dugc tinh nhu sau: nd ^ ^ , l ^ 70032 J CT^2tinhtheo(23) (16) U (17) F = a-„=U- jtd (24) Z, ^chay U Schay ^ + R6ranh U Ta duoc: d day: + d^ = 30mm 170032 7id' -4906 80 — + Fg^_^ dien tich cua ranh d i u , Iiy g i n dimg Fg_ = F, / = X 700mm2 Iranh (25 Vay:(18)p^Z^Z^,4200 [ Kd" -4906(mm') 5'+0,0409 Thay gia tri cua F vao (16) ta cd irng suat nen cira chi tiet: (19) !^_4906 r (26) z, \ 170032 Ttd -4906 V 277964-17,27d' Vl,386d' -17730d' -h 1499,7.10* TAP CHica KHi VIET NAM •> So 09-Thing nam 2010 ^^ NGHIEN ciiu-TRAO001 Giii phuong trinh (26) irng vdi cac DTC dat tmdc: 0,5; 0,9; 0,99; 0,999 va 0,9999: Bang 1: Dudng kinh cua "Dia tmgt" tuong ring vdi tin ciy dat tmdc Do tin cay 0,5 0,9 0,99 0,999 Duong kinh (mm) 127 139 147 160 Khi DTC dat truoc = 0,5; tinh d: Khi tin ciy = 0,5, tir (15) ta cd (D(Z,)=0,5, tra bang II [ ] cdZj = Thay vio (26) tacd: - (277964-17,27^') ^}l,3Ud* -m30d- +1499,7 x 10' Giii v i loai nghiem khdng dim bao yeu ciu ta dugc: d = 127mm Khi DTC dat trudc =0,9; tinh d: Khi tin cay =0,9 thi Z = -1,282 Thay vao (26) duac: •1,282: -(277964-17,27c/-) Vl,386J'* - 17730J' +1499,7 x 10" Giai v i loai nghiem khdng dim bio yeu ciu ta dugc d = 139mm III- K E T LUAN: Tir tmdc tdi nay, vin de thiet ke chi tiet miy mdi chi dugc xem xet theo ben, gia tri ciia tai trgng va ben thudng dugc Iiy theo gia tri tmng binh v i sir dung them mgt he sd an toan Thiet ke chi tiet may theo phuong phip xie suit da ke den tinh ngiu nhien ciia cic tham sd thiet ke Theo phuang phip ta cd the xac dinh dugc kich thude ciia chi tiet theo yeu ciu DTC dat trade Diy la mdt vin de rit cd y nghia ddi vdi cic nha nghien ciiu, cac nha thiet ke Bai bio da dua dugc cdng thirc tdng quit DTC cua chi tiet miy theo ben va irng suit Tren ca sd dd ta cd the giii quyet bai toin sau: - Xie dinh DTC ciia chi tiet may biet ham mit phin phdi ben v i iing suit Khi DTC dat trudc =0,99; tinh d: - Xac dinh cic gia tri thiet ke ciia irng suit v i ben de dat dugc DTC cho trade Khi tin cay =0,99 thi Zj =-2,326 Thay vio (26) duac: - Thiet ke chi tiet miy biet ham mit phin phdi ben va iing suit va DTC theo yeu ciu -2,326: •(277966-17,27^') Vl,386c/''-17730c/'+1499,7x10' Ket qui nghien ciru ciia bii bio cd the ap dung vio cdng tic thiet ke chi tiet miy tai cac nhi miy, xi nghiep; ddng thdi cd the sir dung de giing day cho sinh vien, hgc vien cao hgc v i nghien ciru sinh **' Giai va loai nghiem khdng dam bio yeu ciu, ta dugc d =147inm Tai lieu t h a m k h a o : Khi DTC dat trudc =0,999; tinh d: Khi tin ciy =0,999 thi Z = -3,72 Thay vao (26) duac: -3,72 = -(277964-17,27^/') Vl,386c-/' - 17730J' +1499,7 x lO' Giii va loai nghiem khdng dim bio yen ciu dugc d = 160mm Ket qua thiet ke chi tiet "Dia t r u o t " theo yeu cau DTC dat trudc duoc tong hop d bang [1] Phan Van Khoi (2001), Ca sa ddnh gid tin cdy, NXB Khoa hoc va Ki thuat Ha Noi [2] Birolini Alessandro (1999), Reliability Engineering Theory and Practice, Springer, Berlin [3] Birolini Alessandro (2003), Reliability Engineering, Springer-Verlag, Berlin Heidelbeg ['^.Doty'L.k{l9%5,\9%9),Reliability to theTechnologies, Industrial Press, New York [5] Kapur K.C, (1977), Reliability in Engineering Design, John Wiley, New York [6] Singiresu S Rao (1992), Reliability based design, School Technology Engineering Universit>' Purdure University, Mc.Graw, Hill USA TAP CHica KHi VIET NAM V Sd 09-Thing nam 2010 ... de thiet ke chi tiet miy mdi chi dugc xem xet theo ben, gia tri ciia tai trgng va ben thudng dugc Iiy theo gia tri tmng binh v i sir dung them mgt he sd an toan Thiet ke chi tiet may theo phuong... miy Gach chiu lira Cdng ty Gang thep Thai Nguyen "Dia tmgt" la chi tiet chiu nen nhu hinh 4, vat lieulad6ngEPOL(C6-6-3 Cac so lieu qua khao sat thong ke: - Luc nen len chi tiet tudn theo ludt... xem xet sudt qua trinh khai thac sau cua chiing, do cac chi tieu DTC khdng can viet theo bien t va dugc hieu la DTC ca thdi ky khai thac danh dinh ciia chimg Gia thiet ham mat phan phdi ciia ben