Elemente de Tribologie - Catedra de Organe de Masini si Tribologie
Elemente de Tribologie - Catedra de Organe de Masini si Tribologie
Elemente de Tribologie - Catedra de Organe de Masini si Tribologie
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4. Ecuatia <strong>de</strong> echilibru are forma<br />
+ z x<br />
e<br />
( x,z) dx dz = 0<br />
N − p<br />
(4.21)<br />
−z<br />
x<br />
e<br />
i<br />
∫ ∫<br />
e<br />
Pentru cel mai <strong>si</strong>mplu caz <strong>de</strong> lubrificatie EHD trebuie rezolvat <strong>si</strong>stemul (4.12), (4.16),<br />
(4.19) <strong>si</strong> (4.21).<br />
4.5.3 Meto<strong>de</strong> <strong>de</strong> rezolvare a ecuatiilor regimului EHD<br />
Grubin <strong>si</strong> Vinogradova, folo<strong>si</strong>nd o metoda <strong>si</strong>mplificata, au reu<strong>si</strong>t sa rezolve pentru<br />
prima data ecuatiile EHD în conditii izoterme, pornind <strong>de</strong> la ecuatia<br />
dΠ<br />
dx<br />
= 6 ⋅ η<br />
0<br />
⋅ u<br />
0<br />
h − h<br />
⋅<br />
h<br />
m<br />
3<br />
(4.22)<br />
un<strong>de</strong><br />
−α⋅p<br />
1 − e<br />
Π = <strong>si</strong> u 0 = 2⋅u este viteza redusa <strong>de</strong> rostogolire.<br />
α<br />
Pentru rezolvarea acestei ecuatii, Grubin a facut mai multe ipoteze:<br />
a) Într-un contact hertzian lubrifiat, geometria este data <strong>de</strong> teoria lui Hertz, cu o<br />
translatare pe directia Oy a celor doua soli<strong>de</strong>.<br />
b) Filmul separator este continuu <strong>si</strong> nu modifica distributia <strong>de</strong> pre<strong>si</strong>uni.<br />
c) Pre<strong>si</strong>unea redusa Π atinge valoarea 1/α <strong>si</strong> are distributia din figura 4.16.<br />
Π<br />
1<br />
α<br />
0<br />
1<br />
Figura 4.16<br />
2<br />
p<br />
Din teoria hertziana au rezultat urmatoarele caracteristici:<br />
2 N<br />
- pre<strong>si</strong>unea maxima hertziana este data <strong>de</strong> σ H max = ⋅ ;<br />
π b ⋅ L<br />
- semilatimea contactului este<br />
- raza redusa (echivalenta) este<br />
- modulul <strong>de</strong> elasticitate redus<br />
b<br />
H<br />
R<br />
1<br />
2<br />
⎛ 4 ⋅ N ⋅ R ⎞<br />
= ⎜ ⎟ ;<br />
⎝ L ⋅ E′<br />
⎠<br />
e<br />
−1<br />
⎛ R1<br />
⋅R<br />
2<br />
⎞<br />
= ⎜<br />
R1<br />
R<br />
⎟ ;<br />
⎝ + 2 ⎠<br />
H<br />
−1<br />
⎡ 2 2<br />
1 ⎛1<br />
1 1 ⎞⎤<br />
2<br />
E ⎢ ⎜<br />
−ν − ν<br />
′ = ⋅<br />
⎟⎥<br />
⎢<br />
+<br />
⎣<br />
E1<br />
E<br />
.<br />
π<br />
⎝<br />
2 ⎠⎥⎦<br />
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