Notched Tensile Impact Test

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Notched tensile impact test, conventional

General

The aim of the conventional notched tensile-impact test in accordance with DIN EN ISO 8256 ‘Plastics – Determination of tensile-impact strength’ is to investigate the behaviour of test specimens at relatively high impact speeds and to evaluate the toughness or brittleness of plastics and elastomers [1].

In principle, the notched tensile-impact test (using notched test specimens) is particularly suitable for investigating materials for which the performance of impact tests and notched impact tests according to Charpy (three-point bending configuration) is unsuitable due to the nature of the test specimens (thickness, flexibility). Very thin test specimens, e.g. those made from films, or very flexible test specimens (elastomeric materials), can therefore be subjected to impact loading, thereby allowing their toughness properties to be assessed under sudden loading conditions.

Carrying out the method

The test is carried out using the notched tensile- impact test at a relatively high deformation velocity. The method is suitable for test specimens produced from moulding compounds or taken from semi-finished products and moulded parts, and is used for production and quality control. The conventional notched tensile-impact test also makes it possible to determine the mechanical anisotropic behaviour by taking test specimens from test plates or components (see: component testing) in different directions and testing them.

Pendulum impact testers are used to carry out such experiments; these are equipped with the additional equipment required for tensile impact tests, such as special pendulum hammers and clamping devices (e.g. the Resil Impactor from Ceast).

Fig. 1:

Resil Impactor pendulum impact tester manufactured by Ceast (Italy) for carrying out impact and notched tensile-impact tests

The dimensions of the test specimens used to determine the notched tensile-impact strength are as follows:

Length L = 80 mm

Width W = 10 mm

Notch depth a: 2 mm for each of the notches on both sides

To carry out the notched tensile-impact tests, the test specimens are secured within the test rig using a fixed clamping device on one side and a crosshead clamp on the other. After the pendulum hammer is released from its initial position, the test specimens are loaded in the longitudinal direction until fracture occurs.

Parameters

The results of the experiment are used to determine the impact energy E_c, and subsequently the conventional notched impact- tensile strength a_tN is calculated:

$a_{tN}\,=\,{\frac {E_{c}}{b_{N}\cdot h}}$

A comprehensive literature review on the conventional tensile-impact strength a_tN for numerous plastics is provided in [2].

To determine fracture mechanics parameters for films and elastomers, the conventional notched tensile-impact test must be instrumented with force and displacement sensors. The method of the instrumented tensile impact test enhances the informative value of the results obtained and enables the optimisation of material properties as well as an improved assessment of the service behaviour of components [3].

See also

• Tensile impact test
• Impact loading pendulum impact tester
• Multipurpose test specimen
• Tensile test

References

[1]	ISO 8256 (2023-11): Plastics – Determination of Tensile-impact Strength
[2]	Reincke, K., Grellmann, W.: Tensile-impact toughness. In: Grellmann, W., Seidler, S.: Mechanical and Thermomechanical Properties of Polymers. Landolt-Börnstein. Volume VIII/6A3, Springer, Berlin (2014) pp. 236–240 (ISBN 978-3-642-55165-9; see AMK-Library under A 16)
[3]	Reincke, K.: Elastomere Werkstoffe – Zusammenhang zwischen Mischungsrezeptur, Struktur und mechanischen Eigenschaften sowie dem Deformations- und Bruchverhalten. Habilitation. Martin-Luther-Universität Halle-Wittenberg, Shaker Publishing (2016) (ISBN 978-3-8440-4637-3; see AMK-Library under B 2-2)