## Fatigue strength and fracture mechanics

- If fracture mechanics shall be applied to the total lifetime respectively the fatigue limit of components (within the meaning of the S-N curve approach) it has to address four challenges: (a) It has to adequately describe so-called short crack propagation, which cannot be based on the common long crack concepts for principle reasons. Since the crack size is in the order of the plastic zone size, the modelling of short crack propagation cannot be based on the common linear elastic Delta K concept. Instead, an elastic-plastic parameter such as the cyclic J integral has to be applied. A second point is that the crack closure concept has to be modified in that the crack opening stress is not a constant, crack size- independent parameter but shows a transient behaviour with increasing short crack size. (b) It has to provide a meaningful definition of the initial crack dimensions as the starting point for an S-N curve relevant (residual) lifetime analysis. This can be based either on theIf fracture mechanics shall be applied to the total lifetime respectively the fatigue limit of components (within the meaning of the S-N curve approach) it has to address four challenges: (a) It has to adequately describe so-called short crack propagation, which cannot be based on the common long crack concepts for principle reasons. Since the crack size is in the order of the plastic zone size, the modelling of short crack propagation cannot be based on the common linear elastic Delta K concept. Instead, an elastic-plastic parameter such as the cyclic J integral has to be applied. A second point is that the crack closure concept has to be modified in that the crack opening stress is not a constant, crack size- independent parameter but shows a transient behaviour with increasing short crack size. (b) It has to provide a meaningful definition of the initial crack dimensions as the starting point for an S-N curve relevant (residual) lifetime analysis. This can be based either on the (statistical) size of material defects which can be treated as cracks or by the size of the crack which would arrest subsequent to early crack propagation, whatever is larger. (c) It has to cope with the problem of multiple cracks for load levels higher than the fatigue limit such as it occurs in many applications in the absence of very large initial defects. (d) This requires consequent statistical treatment taking into account variations in the local geometry of the area where crack initiation has to be expected as well as the scatter in the initial crack size and in the material data used for the analyses.…

Autoren/innen: | Uwe Zerbst, Mauro Madia, M. Vormwald |
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Dokumenttyp: | Vortrag |

Veröffentlichungsform: | Präsentation |

Sprache: | Englisch |

Jahr der Erstveröffentlichung: | 2017 |

Organisationseinheit der BAM: | 9 Komponentensicherheit |

9 Komponentensicherheit / 9.1 Betriebsfestigkeit und Bauteilsicherheit | |

DDC-Klassifikation: | Technik, Medizin, angewandte Wissenschaften / Ingenieurwissenschaften / Ingenieurwissenschaften und zugeordnete Tätigkeiten |

Freie Schlagwörter: | Fatigue strength; Fracture mechanics; Initial crack size; Multiple crack propagation; Short crack propagation |

Themenfelder/Aktivitätsfelder der BAM: | Material |

Veranstaltung: | 2nd International Conference on Structural Integrity |

Veranstaltungsort: | Funchal, Madeira, Portugal |

Beginndatum der Veranstaltung: | 04.09.2017 |

Enddatum der Veranstaltung: | 07.09.2017 |

Verfügbarkeit des Dokuments: | Datei im Netzwerk der BAM verfügbar ("Closed Access") |

Datum der Freischaltung: | 17.10.2017 |

Referierte Publikation: | Nein |