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{{Language_sel|LANG=ger|ARTIKEL=Rissöffnungsmoden}}
{{PSM_Infobox}}
<span style="font-size:1.2em;font-weight:bold;">Crack opening modes</span>
__FORCETOC__

==General information==

The terms ‘crack opening modes’ and ‘crack opening types’ are used interchangeably in the literature on [[Fracture Mechanics|fracture mechanics]]. Fracture mechanics assumes that the [[Fracture|fracture]] of a [[Fracture Behaviour of Plastics Components|component]] and thus of the [[Material & Werkstoff|material]] occurs as a result of the propagation of initial cracks. It examines the conditions for [[Crack Propagation|crack propagation]] and allows quantitative relationships to be established between the external [[Stress|stress]], i.e. the nominal stress acting on the [[Plastic Component|component]] or [[Specimen|test specimen]], the size and shape of the cracks, and the resistance of the material to [[Crack Propagation|crack propagation]] [1].

==Types of crack opening==

In practice, a [[Crack|crack]] in a workpiece is usually subject to quite complex stress fields, which can be represented by the superposition of three simple characteristic types of stress (modes) (see also: [[Fracture Modes|fracture modes]]).

Depending on the possible relative movement of the crack surfaces, a distinction is made between the following modes, depending on the external [[Stress|stress]]

* Mode I: simple crack opening; symmetrical lifting of the crack edges,
* Mode II: longitudinal shear; sliding of the crack surfaces in the crack plane

and

* Mode III: longitudinal shear; sliding of the crack surfaces in the crack plane

whereby these types of crack opening can be represented schematically using the example of an edge crack in a pane:

[[file:rissoeffnungsmoden.jpg|600px]]
{|
|- valign="top"
|width="50px"|'''Figure''':
|width="600px" |Schematic illustration of the three types of crack opening that are possible in principle
|}

==Practical significances==

Crack opening mode I is the most important in practice [2]. It is effective, among other things, in [[Component Testing|components]] with internal or surface cracks that are subjected to [[Tensile Test|tensile]] or [[Bend Test|bending]] stresses, as well as in cracks in components under internal pressure (see: [[Component Failure|component failure]]). Modes II and III occur, for example, under shear or torsional stress. Mode II and mixed stress (mixed mode) have become more important in practice for fibre-reinforced composites (FRCs). Mode III tests are of lesser importance in practice.

Based on the description of the [[Fracture Modes|fracture modes]] shown in the figure, special [[Specimen for Fracture Mechanics Tests|fracture mechanics test specimens]] have been developed which are used to determine geometry-independent [[Material Value|characteristic values]] (see: [[Geometry Criterion|geometry criterion]]).

The application of [[Fracture Mechanics|fracture mechanics]] to the evaluation of fibre-reinforced composite components requires the availability of these [[Material Value|characteristic values]], which can be determined using the procedure described by [[Altstädt, Volker|Altstädt]] in [3] (see: [[Composite Materials Testing|testing of composite materials]]).

==See also==

* [[Fracture Modes|Fracture modes]]
* [[Fracture Mechanics|Fracture mechanics]]
* [[Crack]]
* [[Specimen for Fracture Mechanics Tests|Specimen for fracture mechanics tests]]

'''References'''

{|
|-valign="top"
|[1]
|[[Grellmann, Wolfgang|Grellmann, W.]], [[Seidler, Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 231/232 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see [[AMK-Büchersammlung|AMK-Library]] under A 22)
|-valign="top"
|[2]
|[[Blumenauer, Horst|Blumenauer, H.]], Pusch, G.: Technische Bruchmechanik. Deutscher Verlag für Grundstoffindustrie, Leipzig Stuttgart (1993) 3rd Edition, (ISBN 3-342-00659-5; see [[AMK-Büchersammlung|AMK-Library]] under E 29-3)
|-valign="top"
|[3]
|[[Altstädt,_Volker|Altstädt, V.]]: Testing of Composite Materials. In: [https://www.researchgate.net/profile/Wolfgang-Grellmann Grellmann, W.], [https://de.wikipedia.org/wiki/Sabine_Seidler Seidler, S.] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 515–568 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see [[AMK-Büchersammlung|AMK-Library]] under A 22)
|}

[[Category:Fracture Mechanics]]

Crack Opening Modes - Revision history