IV. CON CLUSION
H. 5 Suphu thuoc cua VQ vdo irng sudt do tren mdu CO Ta 250 "C tai cdc tdn so khdc nhau
Co the nhan thay rang cac ket qua do theo chieu tang va giam cua irng suat la kha triing nhaụ Dd thi
VQ((5} bao gom hai phan: a phan tuong irng vdi irng
suat nho dudi 45 MPạ t'u tang gan nhu tuyen tinh
theo a: khi irng suat tac dung ion hon, V(^ tang cham
d^n vdi cac tan so f < 50 kHz hoac lien den trang thai bao hda doi vdi tan so f > 50 kHz. Nguyen nhan cua hien tugng nay cd the dupe giai thich nhu sau: ban d^u cac momen tir trong mau dugc sap xep hon loan, dudi tac dung mot irng suat dpc theo chieu dai cua mau, cac momen tir se dugc dinh hudng theo chieu
cua irng suat tac dung va lam tang dp tií tham ỵ cua vat lieụ Ket qua la the hieu V„ cung tang len (xem
phuang trinh 3), Khi ta tiep tuc tang iing suat thi se cd nhi6u momen tir dupe dinh hudng lai va den mot liic nao do, g^n nhu tat ca cac momen tir da dupe dinh
hudng song song, do đ dp tir tham \i va V,i se tang rat
cham va ti6n den gia trj bao h6ạ Ben canh do, o cac
t^n s6 khac nhau thi dp Idn cua V,, do tai cimg mot
gia tri irng su^t la khac nhaụ Nhin chung khi tang tan
sd din 120 kHz thi Vn tang theo va dudng cong V(^((5)
HQI N G H I V A T L Y C H A T R A N T O A N Q U O C L A N THLT 5 - V u n g T a u 12-14/11/2007
cung sdm dat trang thai bao hda han. Nguyen nhan cd the do viec day nhanh qua trinh dinh hudng eiia cac momen tir theo phuong irng suat dudi tac dung ciia tan sd caọ
Ket qua khao sat su phu thuoc ciia VQ vao irng suat
tai tan sd 120 kHz tren cac senso che tao tir cac mlu khac nhau dupe trinh bay tren hinh 6. Ngoai trir mau ii nhiet d r^ - 250 °C, cac mau khac deu kem nhay vdi irng suat tac dung va de bao hdạ Vdi mau u nhiet d
250 °C, VQ chi bao hoa khi gia tri CT > 80 MPạ Ngoai
ra tin hieu do dugc thay doi rat manh theo irng suat,
AKo = 235 mV tuong irng vdi dai do Aa = 85 MPa
(Af^o/f'(a = 0)=100%). 500 450 400 % 350 > 300 250 200 W o o - •^"^ nnanoacagaÁ^ĐĐaanDn ,Đ^ • , o " - , o O O ^ <^ : o c c>cOOC'OcX)Cx.->Ooo(r;r chua u ; T^= 160°C I " T ; " = 2 5 0 X I T ' = 3 5 0 X I 20 40 60 a (MPa) 80 100