Crack Propagation
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Crack propagation
General terms
Crack propagation is a physical process that occurs under certain conditions in a moulded part or component after crack initiation and can lead to macroscopic separation and fracture. Crack propagation occurs in the material when material-dependent limit values, such as the critical stress intensity factor, are exceeded.
In principle, a distinction is made between different types of crack propagation:
- stable crack propagation and
- unstable crack propagation.
Stable crack propagation is characterised by a relatively low crack velocity. In addition, the crack requires further externally applied energy in order to continue to grow. This is the case, for example, with crack propagation as a result of fatigue.
In contrast, unstable crack propagation is characterised by crack velocities up to the ultrasound velocity in the material in question. Unstable crack propagation also involves the release of energy.
The fracture surfaces resulting from the different types of crack propagation often differ in terms of their structure and characteristics. This is an important aspect in the context of damage analysis, for example, where conclusions can be drawn about crack propagation using microfractographic analyses.
In the context of technical fracture mechanics, characteristic values can be determined on the basis of different concepts, which describe the material resistance to unstable or stable crack propagation separately and quantitatively.
If the microscopic (morphological) area is included in the considerations, it has been shown for plastics in the work of Seidler [1, 2] that structural changes in these materials are reflected much more strongly in the characteristic values that describe crack propagation, such as the tearing modulus. The physical crack initiation, on the other hand, is a continuum mechanical crack model is required to assess the stability of a body with a macroscopic crack. This did not include the deformation processes taking place in the microscopic range [3].
A continuum mechanical crack model is required to assess the stability of a body with a macroscopic crack. This did not include the deformation processes taking place in the microscopic range [3].
The best-known crack model was introduced by Griffith, Alan Arnold [4] in connection with his energetic fracture hypothesis. This GRIFFITH crack is a long and narrow crack of length 2a in a disc of infinite extension under tensile stress.
See also
- Fracture mechanics
- Notch
- Crack resistance curve – Experimental methods
- Crack models
- Crack model according to GRIFFITH
References
| [1] | Seidler, S., Grellmann, W.: Zähigkeit von teilchengefüllten und kurzfaserverstärkten Polymerwerkstoffen. Fortschr.-Berichte VDI-Reihe 18: Mechanik/ Bruchmechanik Nr. 92, VDI Verlag GmbH, Düsseldorf (1991), (ISBN 3-18-149218-3; see AMK-Library under A 4) |
| [2] | Seidler, S.: Anwendung des Risswiderstandskonzeptes zur Ermittlung strukturbezogener bruchmechanischer Werkstoffkenngrößen bei dynamischer Beanspruchung. Habilitation (1997). Martin-Luther-Universität Halle-Wittenberg. VDI Verlag GmbH, Düsseldorf (ISBN 3-18-323118-2; see AMK-Library under B 2-1) |
| [3] | Blumenauer, H., Pusch, G.: Technische Bruchmechanik. Deutscher Verlag für Grundstoffindustrie, Leipzig Stuttgart (1987) (see AMK-Library under E 29-2) |
| [4] | Griffith, A. A.: In: Proceedings of the first International Congress for Applied Mechanics, Delft (1924) |