Instrumented Tensile Impact Test (ITIT), Examples

Sprachauswahl/Language selection

Dieser Artikel ist auch auf Deutsch verfügbar

Instrumentierter Kerbschlagzugversuch, Beispiele

A service provided by

Polymer Service GmbH Merseburg
Tel.: +49 3461 30889-50 E-Mail: info@psm-merseburg.de Web: https://www.psm-merseburg.de
Our further education offers: https://www.psm-merseburg.de/weiterbildung
PSM on Wikipedia: https://de.wikipedia.org/wiki/Polymer Service Merseburg

Instrumented tensile impact test (ITIT), examples

General

The instrumented tensile-impact test (ITIT) is used for plastics and elastomers to determine or optimise their toughness [1, 2]. However, this method of polymer testing and diagnostics, which is relatively rarely described in the literature, can be advantageously applied to test specimens of small thickness, e.g. those cut from thin-walled plastic components, but particularly to plastic films. The validity of the method and the experimental procedure [3] have been explained in detail under “Instrumented tensile-impact test”.

The following examples demonstrate the suitability of the ITIT for investigating the influence of technological manufacturing parameters (e.g. rolling time) and formulation optimisation (e.g. sulphur and carbon black content in elastomers).

Example 1: Influence of manufacturing conditions on the optimisation of the toughness of polyvinyl chloride

As part of investigations into the optimisation of the toughness of impact-resistant PVC materials produced using roll-press technology, Hoffmann and Leps [4] evaluated the dependence on the technological parameter ‘rolling time’ using the ITIT (Fig. 1). To assess toughness, fracture toughness (see: fracture mechanics) was used as a characteristic value in the fracture mechanical tests (Eqs. (1) and (2)):

Dynamic stress intensity factor K_Id

Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle K_{Id}={\frac {F_{max}}{B\cdot W^{\frac {1}{2}}}}\cdot f\left({\frac {a}{W}}\right)}

(1)

with:

Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle f\left({\frac {a}{W}}\right)={\frac {\sqrt {\frac {\pi a}{2W}}}{\sqrt {1-{\frac {a}{W}}}}}\left[1.122-0.561\left({\frac {a}{W}}\right)-0.205\left({\frac {a}{W}}\right)^{2}+0.471\left({\frac {a}{W}}\right)^{3}+0.190\left({\frac {a}{W}}\right)^{4}\right]}

(2)

according to [5].

The two impact-resistant PVC materials each consist of 92 parts PVC and 8 parts modifier (EVA copolymer with 14 wt.-% VAC), with the PVC in composition 1 (K = 63) having the higher K-value (a measure of viscosity) compared with composition 2 (K = 60). The rolling temperature T_W was 170 °C.

Fig. 1:

Toughness optimisation of two tough PVC materials – influence of the rolling time t_W in the roll-press process on the stress intensity factor K_Id at a rolling temperature of T_W = 170 °C

For the dynamic stress intensity factor K_Id, a maximum toughness was determined for both compositions of the impact-resistant PVC materials at rolling times of 15 to 20 minutes; this is based on a parallel increase and decrease in both the maximum fracture load F_max and the fracture time t_B, which also allows for an evaluation using the concept of linear-elastic fracture mechanics.

The higher toughness values of composition 1 at longer rolling times are attributed, in the morphological analyses in [4], to the partial preservation of the network structure typical of good toughness behaviour (a PVC globular framework permeated by the rubber network), as illustrated by an example in Fig. 2.

Fig. 2:

Transmission electron microscopy (TEM) micrograph (stained ultra-thin section) of PVC-P, composition 1 roll time t_W = 15 min

Example 2: Formulation optimisation of styrene-butadiene rubber (SBR) vulcanisates with regard to toughness properties

Reincke [6‒10] significantly expanded the scope of application of the ITIT as part of investigations into the relationship between compounding formulations, structure and fracture mechanical properties of elastomeric materials. To evaluate toughness, the J_Id value — determined according to the J-integral concept — was used as a characteristic value in fracture mechanics testing (Eq. (3) and Eq. (4)).

J-value J_Id

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle J_{Id}=\frac{\eta \cdot A_{max}}{B(W-a)}}

(3)

respectively for occurring crack propagation energy A_p:

Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle J_{Id}=\frac{\eta \cdot \left (A_{max}+A_{p} \right )}{B(W-a)}}

(4)

Studies on unfilled and filled styrene-butadiene rubber (SBR) vulcanisates are presented as examples [6, 9, 10].

Cross-linking was carried out using sulphur. By varying the sulphur content as the cross-linking agent, it is possible to alter the chain density of the network formed during vulcanization and thus influence the properties of the elastomer. The filled SBR vulcanisates are vulcanisates with the same sulphur content but different proportions of the filler carbon black. Figure 3 shows the J-values as a measure of resistance to unstable crack propagation.

Fig. 3:

Effect of carbon black and sulphur content on the J-values of elastomeric materials, determined in an instrumented tensile-impact test

For the unfilled vulcanisates, the J-values determined show a steady decrease in toughness. For the filled vulcanisates, a maximum is observed. This maximum [11‒13] indicates that the addition of filler only improves the toughness properties of the material system under consideration up to 40 phr of carbon black under the given test conditions.

References

[1]	Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 272–275 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see AMK-Library under A 22)
[2]	Reincke, K.: Bruchmechanische Bewertung von gefüllten und ungefüllten Elastomerwerkstoffe. Mensch & Buch Publishing, Berlin (2005), (ISBN 978-3-86664-021-4; see AMK-Library under B 1-13)
[3]	MPK-Procedure MPK-ITIT (2012-06): Testing of Plastics – Instrumented Tensile-Impact Test (ITIT): Procedure for Determining the Crack Resistance Behaviour Using the Instrumented Tensile-Impact Test
[4]	Hoffmann, H., Leps, G., Grellmann, W., Stephan, R., Hanisch, H.: Beurteilung der Zähigkeitseigenschaften von schlagzähem PVC. Plaste und Kautschuk 32 (1985) 379‒381
[5]	Anderson, T. L.: Fracture Mechanics. Fundamentals and Applications. 3rd Ed, CRC Press Boca, Raton (2005) (ISBN 978-0849342608; see AMK-Library under E 8-2); https://doi.org/10.1201/9781420058215
[6]	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)
[7]	Reincke, K., Grellmann, W.: Elastomers. Impact loading. In: Grellmann, W., Seidler, S.: Mechanical and Thermomechanical Properties of polymers. Landolt-Börnstein. Volume VIII/6A3, Springer, Berlin (2014) pp. 502‒509, (ISBN 978-3-642-55165-9; see AMK-Library under A 16)
[8]	Reincke, K., Grellmann, W.: Approaches to characterise the mechanical properties of films and elastomers. In: Grellmann, W., Langer, B.: Deformation and Fracture Behaviour of Polymer Materials. Springer Series in Materials Science 247, Springer, Berlin Heidelberg (2017) 225‒336 (ISBN 978-3-319-41877-3; e-Book: ISBN 978-3-319-41879-7; see AMK-Library under A 19)
[9]	Grellmann, W., Reincke, K., Lach, R., Heinrich, G.: Characterization of crack toughness behaviour of unfilled and filled elastomers. Kautschuk, Gummi, Kunststoffe 54 (2001) 397‒402 Download as pdf; DOI: https://doi.org/10.3139/120.100575
[10]	Grellmann, W., Reincke, K.: Quality improvement of elastomers. Use of instrumented notched tensile-impact testing for assessment of toughness. Materialprüfung 46 (2004) 168‒175; https://doi.org/10.3139/120.100575
[11]	Reincke, K., Grellmann, W., Heinrich, G.: Investigation of mechanical and fracture mechanical properties of elastomers filled with precipitated silica and nanofillers based upon layered silicates. Rubber Chemistry and Technology 77 (2004) 662‒677 DOI: https://doi.org/10.5254/1.3547843
[12]	Reincke, K., Klüppel, M., Grellmann, W.: Investigation of fracture mechanical properties of filler-reinforced styrene-butadiene elastomers. Kautschuk Gummi Kunststoffe 62 (2009) 246‒251 Download as pdf
[13]	Grellmann, W., Reincke, K.: Technical material diagnostics – Fracture mechanics of filled elastomer blends. In: Grellmann, W., Heinrich, G., Kaliske, M. Klüppel, M., Schneider, K., Vilgis, T. (Eds.): Fracture Mechanics and Statistical Mechanics of Reinforced Elastomeric Blends. Springer, Berlin (2013) 227‒268

General

Example 1: Influence of manufacturing conditions on the optimisation of the toughness of polyvinyl chloride

Example 2: Formulation optimisation of styrene-butadiene rubber (SBR) vulcanisates with regard to toughness properties

See also

References