4 End-Notched Flexure Specimen

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4 ENF-specimen or also Four End-Notched Flexure (4 ENF) specimen

Diagram of the experimental setup

A modification of the ENF-test is the ‘4 End-Notched Flexure’ (4 ENF) test, which uses the test setup of the four-point bending test [1] (see Figure).

Fig.:

Schematic presentation of the test setup for the 4 ENF bending test [3]

The delamination front lies within the range of constant bending moment where no shear stresses occur; this reduces friction effects between the upper and lower crack surface. To determine the energy release rate, the compliance (see also: bend test compliance) is plotted as a function of the delamination length (crack length) and the increase in this curve is determined [2].

Equation of determination

If the deflection is too great, correction functions must be determined. The energy release rate G_IIc is calculated using the equation

$G_{IIc}={\frac {F^{2}\cdot \Delta C}{2\cdot W\cdot \Delta a}}$

with:

F		force
W		specimen width
$\Delta$C/$\Delta$a		increase in the dependence of compliance on crack length

An extensive summary of suitable test specimens for fracture mechanics investigations on plastics and composite materials is included in fracture mechanics test specimens.

See also

• Specimen for fracture mechanics tests
• ENF-specimen
• Fracture modes
• Composite materials testing
• CLS-specimen

References

[1]	Bierögel, C.: Quasi-static Test Methods. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 133–143 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see AMK-Library under A 22)
[2]	Altstädt, V.: Testing of Composite Materials. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 550/551 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see AMK-Library under A 22)
[3]	Robinson, P., Hodgkinson, J. M.: Interlaminar Fracture Toughness. In: Hodgkinson, J. M (Ed.): Mechanical Testing in Advanced Fibre Composites. Woodhead Publishing, Cambridge (2000) (ISBN 1-85573-312-9) https://doi.org/10.1533/9781855738911.170