DENT-Specimen

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DENT-specimen

General information

The Anglo-Saxon abbreviation DENT stands for ‘Double-edged Notched Tension’ and the DENT-specimen is referred to in German as a double-sided notched tensile test specimen (or a tensile test specimen notched on both sides).

Test specimen shape

Fig. 1:

Schematic representation of the DENT-specimen (B = thickness, W = width, a = initial crack length and H = length)

Dimensions (according to [1]):
${\frac {H}{W}}\geq 3$

Typical dimensions for plastics [2]:
H = 75 $\pm$ 1 mm
W = 10 $\pm$ 0.5 mm
B = 3 bzw. 4 mm
a = 1 $\pm$ 0.2 mm

Equation for determining the stress intensity factor [3]

$K_{I}={\frac {F_{max}}{B\cdot W}}\cdot f_{1}(a/W)$

$K_{I}={\frac {F_{max}}{B\cdot W}}\cdot f_{2}(a/W)$

$f_{1}(a/W)={\sqrt {\pi a}}\cdot {\frac {1}{1-{\frac {2a}{W}}}}\cdot {\sqrt {\frac {1.26+2.18{\frac {a}{W\left({\frac {1}{2}}-a\right)}}}{1+3.63{\frac {a}{W\left({\frac {1}{2}}-a\right)}}+5.31\left[{\frac {a}{W\left({\frac {1}{2}}-a\right)}}\right]^{2}}}}\!\$

$f_{2}(a/W)={\sqrt {\pi a}}\cdot {\sqrt {{\frac {W}{\pi a}}\left(tan{\frac {\pi a}{W}}+0.1sin{\frac {\pi a}{W\cdot {\frac {1}{2}}}}\right)}}$

Application

The DENT-specimen is used in quasi-static tensile tests, primarily for plastics with high matrix toughness, but in recent years also in elastomer and film testing [2, 4]. Due to problems with clamping, an additional hole is drilled in the DENT-specimens to improve the holder.

Fig. 2:

Schematic representation of a DENT-specimen for fracture mechanics experiments on elastomeric materials using the instrumented tensile impact test

Evaluation

The following Eqs. (1) and (2) are used to evaluate instrumented tensile impact tests on elastomer materials, i.e. to calculate J_d-values as resistance to unstable crack initiation and propagation.

$J_{d}={\frac {\eta \cdot A_{max}}{B\cdot \left(W-a\right)}}$

mit

Amax		deformation energy and
$\eta$		according [5] in the form

$\eta =-0.06+5.99(a/W)-7.42(a/W)^{2}+3.29(a/W)^{3}\!\$

An extensive overview of suitable test specimens for fracture mechanics investigations on plastics and composite materials can be found in fracture mechanics test specimens.

See also

• Essential Work of Fracture (EWF)-concept
• Instrumented tensile impact test (ITIT)
• Film testing
• Fracture mechanical testing
• Specimen for fracture mechanics tests

References

[1]	Sähn, S., Göldner, H.: Bruch- und Beurteilungskriterien in der Festigkeitslehre. Fachbuchverlag, Leipzig Köln (1993) p. 36, (ISBN 3-343-00854-0; see AMK-Library under E 26)
[2]	Reincke, K., Grellmann, W.: Instrumentierte Schlagzugprüfung von Elastomeren. In: Frenz, H. und Wehrstedt, A. (Eds.): Kennwertermittlung für die Praxis – Proceedings Werkstoffprüfung 2002. Wiley-VCH, Weinheim (2003) pp. 340–344, (ISBN 3-527-30674-9; see AMK-Library under M 10)
[3]	Richard, H.-A.: Interpolationsformel für Spannungsintensitätsfaktoren VDI-Zeitschrift 121 (1979) 22 - Nov. II 1138–1143
[4]	Reincke, K.: Bruchmechanische Bewertung von ungefüllten und gefüllten Elastomerwerkstoffen. Mensch und Buch (2005), (ISBN 978-3-86664-021-4; see AMK-Library under B 1-13)
[5]	Anderson, T. L.: Fracture Mechanics. Fundamentals and Applications, 3rd Ed., CRC Press Boca Raton (2005), (ISBN 978-08493-4260-8; see AMK-Library under E 8), DOI: https://doi.org/10.11201/9781420058215