Notch
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Notch
Definition
The distinction between the fracture mechanics terms notch and crack is often somewhat blurred in the literature.
Notches and cracks differ in that the inner boundary surfaces of a crack are in contact in the unloaded state, whereas they are not in the case of a notch. From a mathematical point of view, a crack is a discontinuity surface limited by the crack contour for displacements in the undeformed body. In mathematical modelling, a cut across the largest surface expansion results in a line for the crack and an ellipse for the notch. This means that a crack has an infinitely large curvature at its ends, whereas a notch has a finite curvature at each point of the ellipse. In the direction of its largest surface extension, an internal crack is also assumed to be elliptical, while a surface crack is assumed to be semi-elliptical.
Geometry in the notch base
Both cracks and notches are characterised by discontinuities in which surfaces come very close to each other over large areas and which have a linear boundary (crack edge, crack front, notch base) with a very small radius of curvature at least at one point (see: notch geometry). The surfaces of notches and cracks are very large compared to the volumes they enclose. As cracks grow, the volume hardly changes, while the crack surfaces continue to increase.
Influence on the characteristic value level
In materials testing, notches of various geometries are specifically introduced into test specimens (see: notch geometry) in order to investigate their effect, e.g. on the toughness parameters.
Less common are side notches, which are used specifically in fracture mechanics to obtain flat crack fronts. (see: ICIT – Types of impact load–deflection diagrams).
See also
- Notch geometry
- Notch sensitivity
- Instrumented Charpy impact test (ICIT)
- ICIT–Types of impact load–deflection diagrams
References
- Morgner, W.: Wechselwirkungen zwischen ZfP und Bruchmechanik oder „Alles über den Riss“. In: Berichtsband 65 „ZfP und Bruchmechanik“. DGZfP Berlin (1998), (ISBN 3-931381-26-9)
- Blumenauer, H., Pusch, G.: Technische Bruchmechanik. Deutscher Verlag für Grundstoffindustrie, Leipzig Stuttgart (1987) 2. Auflage (siehe AMK-Library under E 29-2)
- Anderson, T. L.: Fracture Mechanics. Fundamentals and Applications. 2nd Ed., CRC Press, Boca Raton (1995) 2nd. Edition (ISBN 978-0849342608; see AMK-Library under E 8-1); https://doi.org/10.1201/9781315370293
- Sähn, S., Göldner, H.: Bruch- und Beurteilungskriterien in der Festigkeitslehre. Fachbuchverlag, Leipzig Köln (1993), (ISBN 3-343-00854-0; see AMK-Library under E 26)