.. _R7.04.01:

**r7.04.01** Estimation of lifespan in fatigue with a large number of cycles and in oligocyclic fatigue
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**Summary:**

Most industrial structures are subjected to forces that vary over time which, repeated a large number of times, can lead to their breakage due to fatigue. In this note, we present the main functionalities of the POST_FATIGUE [:external:ref:`U4.83.01 <U4.83.01>`] and/or CALC_FATIGUE [:external:ref:`U4.83.02 <U4.83.02>`] and/or CALC_CHAMP [:external:ref:`U4.81.04 <U4.81.04>`] commands that make it possible to estimate the endurance limit and the accumulation of damage of a part.

The various methods available are:


* linear accumulation: methods based on uniaxial tests (Wöhler, Manson-Coffin methods

and Taheri).

What these methods have in common is that they determine a damage value from the evolution over time of a **scalar** component characterizing, for the calculation of damage, the magnitude of stresses or deformations of the structure.

To do this, it is necessary to extract, by a cycle counting method, the elementary loading cycles undergone by the structure, determine the elementary damage associated with each cycle and determine the total damage by a linear accumulation rule;


* nonlinear accumulation: Lemaître method and Lemaître-Sermage method

These methods make it possible to calculate the damage :math:`D` at each instant :math:`t`, from the data of the stress tensor :math:`\sigma (t)` and the cumulative plastic deformation :math:`p(t)`;


* endurance limit: Crossland and Dang Van Papadopoulos criteria

These criteria apply to uniaxial or multiaxial loads under **period** stresses. They provide a criterion value that indicates whether or not there is fatigue. The equivalent constraints defined for these criteria can also be used to calculate the accumulation of damage.

 **Table of Contents**




.. toctree::
    :hidden:

    self

.. toctree::
    :maxdepth: 2
    :numbered:

    Introduction
    M_thodes_de_W_hler__Manson-Coffin_et_Taheri
    Calcul_du_dommage_de_Lema_tre_g_n_ralis_
    Crit_res_de_Crossland_et_Dang_Van_Papadopoulos
    Conclusion
    Bibliographie
    Description_des_versions_du_document