Coffin-Manson model

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In materials engineering, the Coffin-Manson relationship describes the course of the strain Wöhler curve in the low-cycle fatigue range (LCF), i.e. in the range from 1 to 10 ⁵ cycles . In this area, components are so heavily stressed that plastic deformations occur in the cycle . According to Coffin and Manson, in the LCF area i. W. determining the plastic strain amplitude :

${\displaystyle {\frac {\Delta \epsilon _{\mathrm {pl} }}{2}}=\epsilon _{\mathrm {f} }'\cdot (N_{\mathrm {B} })^{c}}$.

• ${\displaystyle \epsilon _{\mathrm {f} }'}$= Coefficient of fatigue ductility , corresponds roughly to the true elongation at break (in the quasi-static tensile test).
• ${\displaystyle c}$= Fatigue ductility; for ductile materials applies: . ${\displaystyle -0{,}7\leq c\leq -0{,}5}$
• ${\displaystyle N_{\mathrm {B} }}$= Number of cycles until break .

A double logarithmic plot results in a falling straight line, with the ordinate now plotting on the ordinate compared to the normal Wöhler diagram. ${\displaystyle \log \left({\frac {\Delta \epsilon _{\mathrm {pl} }}{2}}\right)}$

See also

• Basquin equation

literature

• Ralf Bürgel, Hans Jürgen Maier, Thomas Niendorf: Handbook high temperature materials technology: Fundamentals, material stresses , high temperature alloys and coatings , Springer Fachmedien Wiesbaden, Wiesbaden 2015, ISBN 978-3-658-10591-4 , pp. 196-200