Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=DCB-Prüfkörper}} {{PSM_Infobox}} DCB-specimen FORCETOC ==Test specimen shapes== Blumenauer [1, 2] requires that the size of the plastic zone (see also: effective crack length) must be small compared to the crack length and the test specimen dimensions. '''Test procedure F = const.''' {| border="0" |file:dcb1.jpg | {| border=0 |-va..."

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Created page with "{{Language_sel|LANG=ger|ARTIKEL=DCB-Prüfkörper}} {{PSM_Infobox}} DCB-specimen __FORCETOC__ ==Test specimen shapes== Blumenauer [1, 2] requires that the size of the plastic zone (see also: effective crack length) must be small compared to the crack length and the test specimen dimensions. '''Test procedure F = const.''' {| border="0" |file:dcb1.jpg | {| border=0 |-va..."

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{{Language_sel|LANG=ger|ARTIKEL=DCB-Prüfkörper}}
{{PSM_Infobox}}
DCB-specimen
__FORCETOC__

==Test specimen shapes==

Blumenauer [1, 2] requires that the size of the plastic zone (see also: [[Effective Crack Length | effective crack length]]) must be small compared to the crack length and the test [[Specimen|specimen]] dimensions.

'''Test procedure F = const.'''

{| border="0"
|[[file:dcb1.jpg]]
|
{| border=0
|-valign="top"
|width="20px"|2''H''
| –
|heigth
|-valign="top"
|''W''
| –
|width until load attack point shift
|-valign="top"
|''B''
| –
|thickness
|-valign="top"
|''a''
| –
|notch length
|-valign="top"
|''F''
| –
|force (load)
|}
|}
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px" |Scheme of the DCB-specimen at constant loading
|}

'''Determination equation [1, 2]'''

{|
|-
|width="20px"|
|width="500px" | <math>K_I = \frac{F \cdot a}{B \cdot H^{3/2}} \cdot \left ( 3.46+2.38\frac{H}{a}\right )</math>
|}

'''Test procedure ''v'' = const.'''

{| border="0"
|[[file:dcb2.jpg]]
|
{| border=0
|-valign="top"
|width="20px"|2''H''
| –
|heigth
|-valign="top"
|''W''
| –
|width until load point shift
|-valign="top"
|''B''
| –
|thickness
|-valign="top"
|''a''
| –
|notch depth
|-valign="top"
|''V''
| –
|deformation/notch displacement
|}
|}
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="650px" |Scheme of DCB-specimen at constant deformation; realized with a wedge (a) and with screws (b)
|}

'''Determination equation [1, 2]'''

{|
|-
|width="20px"|
|width="500px" | <math>K_I = \frac{E \cdot V \cdot H \left[3H\left (a+0.6H\right)^2+H^3\right ]^{1/2}}{4\left[\left(a+0.6H\right )^3+H^2a\right] }</math>
|}

with
{|
|-
|''K''I
|width="15px" |
|[[Fracture Mechanics|crack toughness]]
|-
|''E''
|
|[[Elastic Modulus | elastic modulus]]
|}

'''Other specimen shape: TDCB (Tapered-double-cantilever beam)-specimen'''

Different specimen shapes of the same basic type are described in the literature. Blumenauer gives such a specimen type in [1]:

{| border="0"
|[[file:dcb3.jpg]]
|
{| border=0
|-valign="top"
|width="25px"|''H''
|width="10px"|=
|50.8 mm
|-valign="top"
|''H''0
|=
|2 ''H''
|-valign="top"
|''L''
|=
|6 ''H''
|-valign="top"
|''L''1
|=
|1.04 ''H''
|-valign="top"
|''L''2
|=
|2.7 ''H''
|-valign="top"
|''a''0
|=
|0.8 ''H''
|-valign="top"
|''f''1
|=
|0.417 ''H''
|-valign="top"
|''f''2
|=
|0.5 ''H''
|-valign="top"
|''D''
|=
|0.5 ''H''
|-valign="top"
|''B''
|=
|''H''
|}
|}
{|
|- valign="top"
|width="50px"|'''Fig. 3''':
|width="600px" |Scheme of a TDCB-specimen [1]
|}

'''Determination equation'''

Load due to tensile force ''F'':

{|
|-
|width="20px"|
|width="500px" | <math>K_{I} = 4.22 \frac{F}{B \cdot H^{\frac{1}{2}}}</math>
|}

Load due to crack opening V:

{|
|-
|width="20px"|
|width="500px" | <math>K_{I}=0.13\ E\ H^{\frac{1}{2}}\ 2 V</math>
|}

for 0.8 < (''a''/''H'') < 2.4

Another form of [[TDCB-Specimen|TDCB-specimen]] is listed under test [[Specimen for Fracture Mechanics Tests | specimen for fracture mechanics tests]].

==Determination of fracture mechanical values under the influence of media for the evaluation of stress corrosion cracking==

The principle procedure for carrying out the test is shown in '''Figure 4'''. The [[Stress|loading]] on the DCB-specimen can be applied either by a constant load (''F'' = const.) or by a constant deformation (''v'' = const.) using wedges or bolts. In the case of ''F'' = const., the ''K''I value that triggers the start of stable [[Crack Propagation|crack propagation]] is determined over several differently loaded test [[Specimen|specimens]], whereby the corresponding values of ''F'' and ''a'' are to be used in the determination equation for ''K''I. At ''v'' = const. the ''K''I value decreases with increasing crack extension in the corrosive medium and causes the crack to stop. The ''K''Iscc value to be calculated belongs to this crack length ''a'' and the present [[Notch | notch]] displacement ''v'' according to the corresponding determination equation. Further detailed information on the dimensions of the test [[Specimen|specimen]] and the test procedure can be found in [3]. In analogy to linear elastic [[Fracture Mechanics|fracture mechanics]] (LEFM), the requirements for the geometry of the test specimens must also be controlled when determining fracture mechanical values under the influence of media for the evaluation of stress corrosion cracking in the plane strain state.

'''Geometry criterion for metals:'''

{|
|-
|width="20px"|
|width="500px" | <math>B, a, (W-a) \geq 2.5 \bigg(\frac {K_{Iscc}}{R_e}\bigg)^2</math>
|}

'''Geometry criterion for polymers:'''

{|
|-
|width="20px"|
|width="500px" | <math>B, a, (W-a) \geq \beta \bigg(\frac {K_{Iscc}}{\sigma_y}\bigg)^2</math>
|}

the following applies: ''R''e = ''σ''y = [[Yield Stress | yield stress]] (yield point)

The geometry constant ''β'' is material-dependent (see also [[Geometry Criterion | geometry size criterion]], [[Fracture Mechanics | fracture toughness]]).

[[file:DCB-Specimen - 4.jpg|400px]]
{|
|- valign="top"
|width="50px"|'''Fig. 4''':
|width="600px" |Crack-growth velocity in dependence on stress-intensity factor and kind of experimental condition at constant loading or deformation
|}

Further detailed information on the test methods mentioned with regard to test specimen dimensions and the test procedure can be found in [3] and [4].

==Determination of fracture mechanical values on DCB-specimens for fibre composites==

The DCB-specimen was originally developed for [[Fracture Mechanical Testing | fracture mechanics tests]] on bonded joints, but was then transferred to unidirectional (UD) laminates [5].

'''Standards'''

* ASTM D 5528/D5528M (2021): Standard Test Method for Mode I Interlaminar Fracture of Unidirectional Fiber-Reinforced Polymer Matrix Composites
* ISO 15024 (2023-02): Fibre-Reinforced Plastic Composites – Determination of Mode I Interlaminar Fracture Toughness, GIc, for Unidirectionally Reinforced Materials
* ISO 25217 (2009-05): Adhesives – Determination of the Mode I Adhesive Fracture Energy of Structural Adhesives Joints using Double Cantilever Beam and Tapered Cantilever Beam Specimens

'''Specimen'''

[[file:DCB-Specimen - 5.jpg|500px]]
{|
|- valign="top"
|width="50px"|'''Fig. 5''':
|width="600px" |DCB-Specimen with blocks (top) and hinges (bottom) for force initiation
|}

''L'' = 225 mm
 
''B'' = 20 mm
 
''a'' = 50 mm

'''Test method'''

To obtain a defined initial crack, a 50 mm long foil is inserted. Characteristic for this test method is a stable [[Crack Propagation|crack propagation]], i.e. the crack progress can be controlled during the test. Either aluminium blocks or hinges are used for force initiation. The DCB-specimen is continuously loaded in a [[Material Testing Machine|universal testing machine]] – the crack opening is recorded at intervals of approx. 10 mm and the crack length after unloading. There are several established methods for evaluation, of which the area method will be presented here (see '''Fig. 6'''). Other methods are described by Hodgkinson in [6]. The critical [[Energy Release Rate|energy release rate]] ''G''Ic is determined with the help of the load-unload curve according to '''Fig. 6''' using the following equation:

{|
|-
|width="20px"|
|width="500px" | <math>G_{Ic}=\frac{\Delta A}{B \left(a_2-a_1 \right)}</math>
|}

[[file:dcb6.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 6''':
|width="600px" |Determination of GIc in the DCB test with the area evaluation method
|}

==Test system for performing DCB tests==

The test set-up shown in '''Fig. 7''' was implemented at [https://de.wikipedia.org/wiki/Polymer_Service_Merseburg Polymer Service GmbH Merseburg] to carry out fracture mechanics tests under Mode I loading on DCB-specimens. The left partial image shows the installation of a DCB-specimen in a universal testing machine Z 050 from [https://www.zwick.de/ ZwickRoell GmbH & Co. KG] in the unloaded state. The right partial image shows a loaded condition with [[Crack Propagation | crack propagation]].

{|
|- valign="top"
|[[file:DCB-pruefanordnung_PSM1a.jpg|300px]] 
|[[file:DCB-pruefanordnung_PSM1b.jpg|348px]]
|-
|colspan="2"|
{|
|- valign="top"
|width="50px"|'''Fig. 7''':
|width="600px" |Test system to carry out fracture mechanical investigations on DCB-specimen ([[Polymer Service GmbH Merseburg|Polymer Service GmbH Merseburg]])
|}
|}

==Determination of fracture mechanical values on DCB-specimens for bonded joints==

In work by Schlimmer and co-workers [7], the DCB-specimen is used for [[Fracture Mechanical Testing|fracture mechanics evaluation]] of bonded joints.

==See also==

*[[Specimen for Fracture Mechanics Tests | Specimen for fracture mechanics tests]]
*[[TDCB-Specimen | TDCB-specimen]]
*[[Geometry Criterion | Geometry criterion]]
*[[Fracture Mechanics | Fracture mechanics]]
*[[Energy Release Rate | Energy release rate]]

'''References'''

{|
|-valign="top"
|[1]
|[[Blumenauer, Horst|Blumenauer, H.]], Pusch, G.: Technische Bruchmechanik. Deutscher Verlag für Grundstoffindustrie, Leipzig Stuttgart (1987) 2nd Edition, pp. 127–129 and p. 140 (ISBN 3-342-00096-1; see [[AMK-Büchersammlung|AMK-Library]] under E 29-2)
|-valign="top"
|[2]
|Blumenauer, H., Pusch, G.: Technische Bruchmechanik. Deutscher Verlag für Grundstoffindustrie, Leipzig Stuttgart (1993) 3rd Edition, pp. 122–124 (ISBN 3-342-00659-5; see [[AMK-Büchersammlung|AMK-Library]] under E 29-3)
|-valign="top"
|[3]
|Heady, R. B.: Evaluation of Sulfide Corrosion Cracking Resistance in Low Alloy Steels. Corrosion 33 (1977) 3, pp. 98–107
|-valign="top"
|[4]
|Dietzel, W, Schwalbe, K.-H.: GKSS-Bericht 87/E/46
|-valign="top"
|[5]
|[[Altstädt,_Volker|Altstädt, V.]]: Testing of composite materials. In: [[Grellmann, Wolfgang|Grellmann, W.]], [[Seidler, Sabine|Seidler, S.]] (Hrsg.): Polymer Testing. Carl Hanser Munich (2022) 3rd Edition, pp. 547–548 (ISBN 978-1-56990-806-8; e-book: ISBN 978-1-56690-807-5); see [[AMK-Büchersammlung|AMK-Library]] under A 23)
|-valign="top"
|[6]
|Hodgkinson, J. M. (Ed.): Mechanical Testing of Advanced Fibre Composites. Woodhead Publishing, Cambridge (2000)
|-valign="top"
|[7]
|Großkurth, L., Schlimmer, M.: Bruchmechanische Untersuchungen von Dickschichtklebungen. In: Grellmann, W.: Herausforderungen neuer Werkstoffe an die Forschung und Werkstoffprüfung. Deutscher Verband für Materialforschung und -prüfung. Tagungsband 2005, pp. 377–382 (ISSN 1861-8154; see [[AMK-Büchersammlung | AMK-Library]] under A 8)

[[category:Fracture Mechanics]]
[[category:Specimen]]

DCB-Specimen - Revision history