### Abstract

Mathematical modelling of deformation of construction
steels at elevated
temperatures was in-
vestigated in the present work. Special attention was
paid to the derivation of
constitutive equations
using irreversible thermodynamics. As a practical example
the creep equation
proposed by Le Gac
and Duval was studied from the thermomechanical point of
view.
Physical and mathematical modelling of creep processes
were briefly considered.
Two different
physical interpretations found in literature, together
with their mathematical
formulations for the
constitutive equations proposed by Le Gac and Duval, were
examined in detail. A
detailed critique
on the interpretations and their mathematical
formulations was given, and some
improvements were
also suggested.
The meaning of a 'correct set' of state variables was
discussed. The
consequences of the second law
of thermodynamics found by studying 'constitutive
processes' were also
considered. The significant
role of the 'constitutive processes' in the derivation of
the Clausius-Duhem
inequality was pointed
out. The author suggested that scientists should examine
the reality of the
'constitutive processes', i.e.
that the material under consideration can actually follow
the 'constitutive
process'.
The explicit forms of the specific Helmholz free energy
and the specific
dissipation function (or their
Legendre transformations) were set out. Using the
above-mentioned functions,
the constitutive
equation proposed by Le Gac and Duval was derived.
The values of the material parameters for the power plant
material 10 CrMo 9 10
were given. The
material model was implemented into the ABAQUS finite
element method program.
The computed
examples showed that even a 27-year-long creep response
can be predicted.

Original language | English |
---|---|

Place of Publication | Espoo |

Publisher | VTT Technical Research Centre of Finland |

Number of pages | 150 |

ISBN (Print) | 951-38-4631-8 |

Publication status | Published - 1994 |

MoE publication type | Not Eligible |

### Publication series

Series | VTT Publications |
---|---|

Number | 193 |

ISSN | 1235-0621 |

### Keywords

- materials
- thermodynamics
- predictions
- models
- temperature
- rates (per time)
- simulation
- three dimensional systems
- creep
- constitutive equations
- steels

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## Cite this

Santaoja, K. (1994).

*Thermomechanics of creep equation proposed by le Gac and Duval*. VTT Technical Research Centre of Finland. VTT Publications, No. 193