Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Bruchspiegel}} {{PSM_Infobox}} Fracture mirror FORCETOC ==General information== Information about the cause of the fracture (see: fracture formation), the type of stress (static, dynamic or tensile, bending, torsion, etc.) and..."

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{{Language_sel|LANG=ger|ARTIKEL=Bruchspiegel}}
{{PSM_Infobox}}
Fracture mirror
__FORCETOC__

==General information==

Information about the cause of the fracture (see: [[Fracture Formation|fracture formation]]), the type of stress ([[Quasi-static Test Methods|static]], [[Fatigue|dynamic]] or [[Tensile Test|tensile]], [[Bend Test|bending]], [[Dynamic-Mechanical Analysis (DMA) – Torsional Stress|torsion]], etc.) and design and material (see: [[Errors|errors]]) (inhomogeneities, foreign inclusions) can be obtained from the [[Fracture Surface|fracture surface]].

==Consideration of the fracture mirror when specifying characteristic values==

The diagnosis of the [[Fracture|fracture]] is referred to as [[Fractography|fractography]] or microfractography. The [[Fracture Surface|fracture surfaces]] of standardised test [[Specimen|specimens]] for the fracture mechanical determination of parameters contain information on the appearance and [[Initial Crack Length|length of the initial crack]] and on the formation of the [[Plastic Zone|plastic zone]] in front of the [[Crack|crack tip]]. The length of the plastic zone is used in [[Fracture Mechanics#Linear-elastic fracture mechanics with small-scale yielding|LEFM with small-scale yielding]] to determine characteristic [[Material Value|values]]. Provided that this plastically deformed area is small in relation to the component dimensions and the ligament length (''W''–''a''), it can be approximated by assuming an [[Effective Crack Length|effective crack length]]

{|
|-
|width="20px"|
|width="500px" | <math>a_{eff}\,=\,a\,+\,r_{pl}</math>
|}

with
{|
|-
|''r''pl
|width="15px" |
|radius of the [[Plastic Zone|plastic zone]]
|-
|''a''
|
|[[Initial Crack Length|length of the initial crack]], notch depth (often also referred to as ''a''0)
|}

in the form of the effective [[Fracture Mechanics|stress intensity factor]]

{|
|-
|width="20px"|
|width="500px" | <math>K_{I}(a_{eff})\,=\,\sigma\left(\pi a _{eff}\right)^\frac{1}{2}\, f \left(\frac{a_{eff}} {W} \right)</math>
|}

Statements on the theoretical basis of this extension of [[Fracture Mechanics#Linear-elastic fracture mechanics with small-scale yielding|linear elastic fracture mechanics (LEFM) to small-scale yielding]] and the size of the circular [[Plastic Zone|plastic zone]] are presented in the fracture mechanics literature [1–3].

In fracture mechanics value determination, the radius of the plastic zone is observed as a fracture surface phenomenon in the form of the fracture mirror, whereby the [[Initial Crack Length|initial crack length]] ''a'' is extended by the length of stable crack growth, which is often measured microscopically, and with

{|
|-
|width="20px"|
|width="500px" | <math>a_{eff}\,=\,a\,+\,a_{BS}</math>
|}

with
{|
|-
|''a''BS
|width="15px" |
|fracture [[Fracture Surface|surface]], length of stable crack growth
|}

the transition from linear elastic fracture mechanics (LEFM) to [[Fracture Mechanics#Linear-elastic fracture mechanics with small-scale yielding|LEFM with small-scale yielding]] is formally completed [4]. In very brittle structures, at high [[Test Speed|test speed]] or low temperatures, the fracture surface is very small or negligible.

==Formation of the fracture mirror on broken glass surfaces==

The existence of a fracture mirror was first proven for glass and is described by Spauszus in [5]. Spauszus describes the fracture pattern and the appearance of the [[Fracture Surface|fracture surface]] in a glass rod under [[Tensile Strength|tensile stress]] ('''Figure 1''').

[[file:bruchspiegel1.jpg|600px]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="650px" |Fracture surface after tensile stress on a round glass rod (according to Leeuverik and Burgers) [5] 
a) Light microscopic; 
b) Schematic)
|-
|}
{|
|-
| ''S''p
| width="15px" |
| Mirror 
|-
| ''R''f
|
| Surface with fine roughness 
|-
| ''R''g
|
| Surface with coarse roughness; ''G'' must reach or exceed the critical value ''G''c required for fracture initiation.
|}

The fracture origin is followed by a circular, completely smooth area on the [[Fracture Surface|fracture surface]], which is referred to as a fracture mirror (''S''p) due to its appearance.

Both mirror surfaces of the rod half can be joined with optical precision. An area of fine roughness (''R''f) is followed by a zone of coarse roughness (''R''g). While the mirror surfaces are oriented perpendicular to the main stress direction, the rough zones form angled surfaces as a result of a fracture branch to the mirror, whereby a wedge-shaped piece of glass is often ejected during the fracture process ('''Figure 2''').

[[file: bruchspiegel2.jpg|600px]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px" |Fracture pattern in a glass rod under tensile stress [5] 
1 Mirror surface 
2 Fracture branching 
3 Rough fracture surface 
4 Wedge-shaped piece of glass
|}

==See also==

* [[Fracture Surface|Fracture surface]]
* [[Fracture Process Zone|Fracture process zone]]
* [[Fracture Formation|Fracture formation]]
* [[Effective Crack Length|Effective crack length]]

'''References'''

{|
|-valign="top"
|[1]
|[[Blumenauer, Horst|Blumenauer, H.]], Pusch, G.: Technische Bruchmechanik. Verlag für Grundstoffindustrie, Leipzig (1987) 2nd Edition, p. 66 (see [[AMK-Büchersammlung|AMK-Library]] under E 29-2)
|-valign="top"
|[2]
|Anderson, T. L.: Fracture Mechanics, Fundamentals and Application. 3rd Ed., CRC Press Boca Raton (2005) (ISBN 978-0849342608; siehe [[AMK-Büchersammlung|AMK-Library]] under E 8-2) DOI: [https://doi.org/10.1201/9781420058215 https://doi.org/10.1201/9781420058215]
|-valign="top"
|[3]
|Schwalbe, K.-H.: Bruchmechanik metallischer Werkstoffe. Carl Hanser, Munich Vienna (1980) (ISBN 3-446-12983-9; see [[AMK-Büchersammlung|AMK-Library]] under E 15)
|-valign="top"
|[4]
|[[Grellmann, Wolfgang|Grellmann, W.]], [[Seidler, Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 235–236 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5 [[AMK-Büchersammlung|AMK-Library]] under A 23)
|-valign="top"
|[5]
|Spauszus, S.: Werkstoffkunde Glas. Deutscher Verlag für Grundstoffindustrie, Leipzig (1974) (see [[AMK-Büchersammlung|AMK-Library]] under Q 2)
|}

[[category:Bend Test]]
[[category:Fracture Mechanics]]
[[category:Instrumented Impact Test]]

Fracture Mirror - Revision history

Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Bruchspiegel}} {{PSM_Infobox}} Fracture mirror __FORCETOC__ ==General information== Information about the cause of the fracture (see: fracture formation), the type of stress (static, dynamic or tensile, bending, torsion, etc.) and..."

Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Bruchspiegel}} {{PSM_Infobox}} Fracture mirror FORCETOC ==General information== Information about the cause of the fracture (see: fracture formation), the type of stress (static, dynamic or tensile, bending, torsion, etc.) and..."