caracterizarea bazata pe cunoastere a capacitatii de amortizare
caracterizarea bazata pe cunoastere a capacitatii de amortizare
caracterizarea bazata pe cunoastere a capacitatii de amortizare
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36<br />
( x, y, z)<br />
energie repulsiva ion-core (Born-Mayer) ;<br />
l parametru a energiei repulsive;<br />
2α volumul celulei elementare.<br />
. Ecuatiile constitutive <strong>pe</strong>ntru un material isotrop centrosimetric <strong>de</strong> tip Cosserat sunt (Lakes<br />
1982, Chiroiu, Munteanu si Dumitriu 2008)<br />
σ<br />
kl<br />
=λerrδ kl<br />
+ (2 µ +κ ) ekl +κεklm( rm −ϕ<br />
m)<br />
, m<br />
kl<br />
=αϕr, rδ kl<br />
+βϕ<br />
k, l<br />
+ γϕ<br />
l,<br />
k<br />
, (1.2.1)<br />
In (1.2.1) sase constante elastice ind<strong>pe</strong>n<strong>de</strong>nte <strong>de</strong>scriu comportarea solidului isotrop<br />
centrosimetric Coserat. Pentru un corp isotrop non-centrosymmetric <strong>de</strong> tip Cosserat, energia <strong>de</strong><br />
<strong>de</strong>formatie si tensorul <strong>de</strong>formatie se scriu sub forma<br />
si<br />
= ε ε + ϕ ϕ + ε ϕ , (1.2.2)<br />
2V Cklmn kl mn<br />
Bklmn k , l m, n<br />
Aklmn kl m,<br />
n<br />
ε = e +ε ( r −ϕ ). (1.2.3)<br />
kl kl klm m m<br />
Tensiunile si cuplele <strong>de</strong> tensiuni se obtin din<br />
∂V<br />
σ = , ∂ε<br />
kl<br />
kl<br />
m<br />
kl<br />
∂V<br />
= . (1.2.4)<br />
∂ϕ<br />
Din (1.2.3) si (1.2.4) obtinem ecuatiile constitutive <strong>pe</strong>ntru un corp isotropic noncentrosimetric<br />
<strong>de</strong> tip Cosserat<br />
sau<br />
σ<br />
kl<br />
= Cklmnε mn<br />
+ Aklmnϕ m,<br />
n<br />
, mkl Bklmn m,<br />
n<br />
Aklmn mn<br />
l,<br />
k<br />
= ϕ + ε . (1.2.5)<br />
σ = ε δ + ε + ε + ϕ δ + ϕ + ϕ (1.2.6)<br />
kl<br />
C1 rr kl<br />
C2 kl<br />
C3 lk<br />
A1 r, r kl<br />
A2 k, l<br />
A3 l, k,<br />
un<strong>de</strong><br />
m = Bϕ δ + B ϕ + B ϕ + Aε δ + A ε + Aε , (1.2.7)<br />
kl 1 r, r kl 2 l, k 3 k, l 1 rr kl 2 lk 3 kl<br />
C<br />
1<br />
=λ, C<br />
2<br />
= µ , C<br />
3<br />
=κ, B<br />
1<br />
=α, B<br />
2<br />
= β , B<br />
3<br />
= γ , A1 = C1, A2 = C2, A3 = C3,<br />
Ecuatiile constitutive (1.2.6) si (1.2.7) conduc la<br />
σ =λe δ + (2 µ +κ ) e +κε ( r −ϕ ) + Cϕ δ + C ϕ + C ϕ , (1.2.8)<br />
kl rr kl kl klm m m 1 r, r kl 2 k, l 3 l,<br />
k<br />
m =αϕ δ +βϕ + γϕ + C e δ + ( C + C ) e + ( C −C ) ε ( r −ϕ ). (1.2.9)<br />
kl r, r kl k , l l, k 1 rr kl 2 3 kl 3 2 klm m m<br />
Ecuatiile (1.2.9) reprezinta ecuatiile constitutive <strong>pe</strong>ntru un corp <strong>de</strong> tip Cosserat care se<br />
comporta isotropic in raport cu o rotatie a sistemului <strong>de</strong> referinta dar nu in raport cu o inversie.<br />
Constantele chirale Ci<br />
, i= 1, 2,3 caracterizeaza noncentrosimetria. Pentru C<br />
i<br />
= 0 se reobtin<br />
ecuatiile elasticitatii isotro<strong>pe</strong> micropolare. Pentru α=β = γ =κ= 0 , ecuatiile (1.2.8) and (1.2.9)<br />
se reduc la ecuatiile constitutive ale teoriei elasticitatiii liniare isotro<strong>pe</strong>.<br />
Conditiile <strong>pe</strong> frontiera sunt date <strong>de</strong><br />
σ<br />
lknl = t( n)<br />
k<br />
, mn<br />
lk l<br />
m( n)<br />
k<br />
Legea <strong>de</strong> miscare este in<strong>de</strong><strong>pe</strong>n<strong>de</strong>nta <strong>de</strong> simetria materiala. Avem<br />
= . (1.2.10)