Sources/Lexikon/Spannungs-Dehnungs-Beziehung (Stress-Strain-Relation)

Allgemeines Werkstoffgesetzt (3D)

Der Zusammenhang zwischen Dehnung un Spannung für isotropes, linear-elastisches Werkstoffverhalten wird durch

${\underline {\sigma }}={\underline {\underline {E}}}\cdot {\underline {\varepsilon }}$

beschrieben. In Komponenten-Schreibweise ist dies

$\displaystyle {\begin{bmatrix}\sigma _{xx}\\\sigma _{yy}\\\sigma _{zz}\\\sigma _{yz}\\\sigma _{xz}\\\sigma _{xy}\end{bmatrix}}\,=\,{\begin{bmatrix}2\mu +\lambda &\lambda &\lambda &0&0&0\\\lambda &2\mu +\lambda &\lambda &0&0&0\\\lambda &\lambda &2\mu +\lambda &0&0&0\\0&0&0&2\mu &0&0\\0&0&0&0&2\mu &0\\0&0&0&0&0&2\mu \end{bmatrix}}{\begin{bmatrix}\varepsilon _{xx}\\\varepsilon _{yy}\\\varepsilon _{zz}\\\varepsilon _{yz}\\\varepsilon _{xz}\\\varepsilon _{xy}\end{bmatrix}}$,

wobei λ und μ die Lamé'schen Konstanten sind und zum Elastizitäts-Modul E und der Querkontraktion ν folgende Beziehung haben:

${\begin{array}{l}\displaystyle \lambda ={\frac {E\nu }{(1+\nu )(1-2\nu )}}\\\displaystyle \mu ={\frac {E}{2(1+\nu )}}\end{array}}$

/* Maxima */
/* version 5.38.1 */
/* general strain-displacement relation (sdr)*/
declare("σ", alphabetic);
declare("ε", alphabetic);

params: [%lambda=E*nu/((1+nu)*(1-2*nu)), mu=E/(2*(1+nu))];

sdr[3]: E = 2*mu*diagmatrix (6, 1) + 
            %lambda*matrix([1,1,1,0,0,0],
                           [1,1,1,0,0,0],
                           [1,1,1,0,0,0],
                           [0,0,0,0,0,0],
                           [0,0,0,0,0,0],
                           [0,0,0,0,0,0]);

σ : matrix([  sigma[xx]],[  sigma[yy]],[  sigma[zz]],[  sigma[yz]],[  sigma[xz]],[  sigma[xy]]);
ε : matrix([epsilon[xx]],[epsilon[yy]],[epsilon[zz]],[epsilon[yz]],[epsilon[xz]],[epsilon[xy]]);
print(σ," = ", subst(sdr[3],E),"∙",ε)$

Ebener Spannugnszustand

Alle anderen Werkstoff-Gesetze lassen sich daraus ableiten, z.B. für den ebenen Spannungszustand mit

$\sigma _{zz}=0,\sigma _{xz}=0,\sigma _{yz}=0$

erhalten wir

$\displaystyle {{\sigma }_{\mathit {xx}}}={\frac {2\lambda \mu {{\epsilon }_{\mathit {yy}}}+\left(4{{\mu }^{2}}+4\lambda \mu \right)\,{{\epsilon }_{\mathit {xx}}}}{2\mu +\lambda }},{{\sigma }_{\mathit {yy}}}={\frac {\left(4{{\mu }^{2}}+4\lambda \mu \right)\,{{\epsilon }_{\mathit {yy}}}+2\lambda \mu {{\epsilon }_{\mathit {xx}}}}{2\mu +\lambda }},{{\sigma }_{\mathit {xy}}}=2\mu {{\epsilon }_{\mathit {xy}}},{{\epsilon }_{\mathit {zz}}}=-{\frac {\lambda {{\epsilon }_{\mathit {yy}}}+\lambda {{\epsilon }_{\mathit {xx}}}}{2\mu +\lambda }},{{\epsilon }_{\mathit {yz}}}=0,{{\epsilon }_{\mathit {xz}}}=0$

In Matrixschreibweise erhalten wir

$\left({\begin{array}{c}\sigma _{xx}\\\sigma _{yy}\\\sigma _{xy}\end{array}}\right)=\left({\begin{array}{ccc}{\frac {4{{\mu }^{2}}+4\lambda \mu }{2\mu +\lambda }}&{\frac {2\lambda \mu }{2\mu +\lambda }}&0\\{\frac {2\lambda \mu }{2\mu +\lambda }}&{\frac {4{{\mu }^{2}}+4\lambda \mu }{2\mu +\lambda }}&0\\0&0&2\mu \end{array}}\right)\cdot \left({\begin{array}{c}\varepsilon _{xx}\\\varepsilon _{yy}\\\varepsilon _{xy}\end{array}}\right)$

bzw mit E und ν

$\left({\begin{array}{c}\sigma _{xx}\\\sigma _{yy}\\\sigma _{xy}\end{array}}\right)=\left({\begin{array}{ccc}{\frac {E}{1-{{\nu }^{2}}}}&{\frac {E\;\nu }{1-{{\nu }^{2}}}}&0\\{\frac {E\;\nu }{1-{{\nu }^{2}}}}&{\frac {E}{1-{{\nu }^{2}}}}&0\\0&0&{\frac {E}{\nu +1}}\end{array}}\right)\cdot \left({\begin{array}{c}\varepsilon _{xx}\\\varepsilon _{yy}\\\varepsilon _{xy}\end{array}}\right)$.

/* Maxima */
/* version 5.38.1 */
/*ebener Spannungszustand*/
assumption: [sigma[zz]=0, sigma[yz]=0, sigma[xz]=0];
/* general strain-displacement relation (sdr)*/

equs: subst(assumption,makelist(σ[i][1] = (subst(sdr[3],E).ε)[i][1],i,1,6));
Q: [  sigma[xx],  sigma[yy],  sigma[xy],
    epsilon[zz],epsilon[yz],epsilon[xz]];

sol: ratsimp(solve(equs,Q))[1];

ACM: augcoefmatrix([-sol[1],-sol[2],-sol[3]],[epsilon[xx],epsilon[yy],epsilon[xy]]);
sdr[2] : submatrix(ACM,4);

sdr[2]: [sdr[2],ratsimp(subst(params,sdr[2]))];

</math>

Eindimensionaler Spannungszustand

Ganz entsprechend erhalten wir für

$\sigma _{yy}=0,\sigma _{zz}=0,\sigma _{xz}=0,\sigma _{yz}=0,\sigma _{xy}=0$

die Ergebnisse

$\displaystyle {{\sigma }_{\mathit {xx}}}={\frac {\left(2{{\mu }^{2}}+3\lambda \mu \right)\,{{\epsilon }_{\mathit {xx}}}}{\mu +\lambda }},{{\epsilon }_{\mathit {yy}}}=-{\frac {\lambda {{\epsilon }_{\mathit {xx}}}}{2\mu +2\lambda }},{{\epsilon }_{\mathit {zz}}}=-{\frac {\lambda {{\epsilon }_{\mathit {xx}}}}{2\mu +2\lambda }},{{\epsilon }_{\mathit {yz}}}=0,{{\epsilon }_{\mathit {xz}}}=0,{{\epsilon }_{\mathit {xy}}}=0$

bzw.

<math>\displaystyle {{\sigma}_{\mathit{xx}}}=E\,{{\epsilon}_{\mathit{xx}}},{{\epsilon}_{\mathit{yy}}}=-\nu{{\epsilon}_{\mathit{xx}}},{{\epsilon}_{\mathit{zz}}}=-\nu{{\epsilon}_{\mathit{xx}}},{{\epsilon}_{\mathit{yz}}}=0,{{\epsilon}_{\mathit{xz}}}=0,{{\epsilon}_{\mathit{xy}}}=0

/* Maxima */
/* version 5.38.1 */
/*eindimensionaler Spannungszustand*/
assumption: [sigma[yy]=0, sigma[zz]=0, sigma[yz]=0, sigma[xz]=0, sigma[xy]=0];
/* general strain-displacement relation (sdr)*/

equs: subst(assumption,makelist(σ[i][1] = (subst(sdr[3],E).ε)[i][1],i,1,6));
Q: [  sigma[xx],
    epsilon[yy], epsilon[zz],epsilon[yz],epsilon[xz], epsilon[xy]];

sol: ratsimp(solve(equs,Q))[1];