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{{Language_sel|LANG=ger|ARTIKEL=Risswiderstandskurve – Beispiele}}
{{PSM_Infobox}}
<span style="font-size:1.2em;font-weight:bold;">Crack resistance curve – Examples</span>
__FORCETOC__

==General information==

The [[Toughness|toughness]] of [[Plastics|plastics]] is characterised on the basis of the [[Crack Resistance (R) Curve|crack resistance (R) curve]] concept; where the [[Material & Werkstoff|material]] exhibits elastic-plastic behaviour, the stages of the entire fracture process—crack blunting, stable [[Crack Initiation|crack initiation]], stable [[Crack Propagation|crack propagation]], and, following this, often unstable crack propagation and [[Fracture|fracture]] — can be described.

==R-curve for isotactic polypropylene (PP)==

Using isotactic polypropylene ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: PP) as an example, this paper demonstrates the possibility of characterising structural modifications (see also: [[Microscopic Structure|microscopic structure]]) caused by nucleation in PP materials [1].

To experimentally determine the [[Crack Resistance (R) Curve|crack resistance curves]] as a basis for establishing the [[Fracture Mechanical Testing|fracture mechanics parameters]] of [[Crack Initiation|crack initiation]] and [[Crack Propagation|crack propagation]], the [[Quasi-static Test Methods|quasistatic tensile test]] was employed using [[SENT-Specimen|SENT]] (Single-Edge-Notched Tension) specimens [2–6].

The addition of nucleating agents influences the structure of PP. Semi-crystalline PP is polymorphic, i.e. it can crystallise into the α, β or γ modification depending on the cooling conditions and the nucleation process. The α-modification is characterised by a helical structure in a monoclinic unit cell, which is the thermodynamically most stable form and thus the most common modification. In comparison, the β modification is less ordered and hexagonal, featuring non-parallel, crossed lamellae. The orthorhombic γ modification can be induced under high pressure or by the use of a nucleating agent [7–9]. The crystal modification influences the fundamental mechanical properties due to its different physical and mechanical properties [8, 9]. PP with a predominant β-modification has a lower [[Elastic Modulus|modulus of elasticity]] and [[Yield Stress|yield stress]] at a comparable [[Strain Rate Basics|strain rate]], but increased [[Impact Test|impact strength]], tensile strain at break [7] and higher [[Crack Toughness|crack toughness]] [10] compared with PP with an α-modification. The crystal structure can be influenced, amongst other things, by the addition of nucleating agents or by the cooling rate.

The isotactic PP was blended with an α-nucleating agent (αPP) or a β-nucleating agent (βPP). The plastics were cooled at a rate of 1 K/min (abbreviated as -1) and moulded into sheets (see also [11, 12]). The [[Crack Resistance (R) Curve|crack resistance curves]] (R-curves) of the various [[Plastics|plastics]] were evaluated in accordance with the procedure set out in ESIS TC4 [13].

{|
|<div style="display: block; text-align: center;" width="600" height="500">[[File:Crack_Resistance_Curve_-_Examples_Fig1-1.jpg|400px]]</div>
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|<div style="display: block; text-align: center;" width="600" height="500">[[File:Crack_Resistance_Curve_-_Examples_Fig1-2.jpg|550px]]</div>
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{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px"|(a) R-curves for the plastics PP-1 and αPP-1, and (b) a typical [[Fracture Surface|fracture surface]] of a test specimen showing a metal-blade notch (1), stable crack propagation (2), the damaged zone (3) and the brittle fracture surface (4)
|}

==Effect of nucleation on polypropylene (PP)==

The R-curves for the three PP materials with different nucleation types are shown in '''Fig. 1a'''. At small stable crack extensions, the differences are relatively minor. At higher stable crack extensions, clear differences emerge between the non-nucleated PP-1 and the two nucleated types. For a comparable stable crack extension Δa, the J-values of αPP-1 and βPP-1 are significantly higher, although there is no significant difference between the two nucleated PP types.

This shows that, at a cooling rate of 1 K/min, the resistance of nucleated PP materials to stable [[Crack Propagation|crack propagation]] is higher than that of non-nucleated PP. A typical [[Fracture Surface|fracture surface]] of a PP material is shown in '''Fig. 1b'''. The metal blade notch, the zone of stable crack growth—characterised by a very [[Fracture Mirror|smooth surface]] and a clear boundary with the damage zone—and the residual fracture surface can be seen.

==See also==

* [[Fracture Mechanics|Fracture mechanics]]
* [[Crack Resistance (R) Curve|Crack resistance (R) curve]]
* [[Crack Resistance Curve – Experimental Methods|Crack resistance curve – Experimental methods]]
* [[Crack Resistance Curve – Elastomers Quasistatic|Crack resistance curve – Elastomers quasistatic]]
* [[Tearing Modulus|Tearing modulus]]

==References==

{|
|-valign="top"
|[1]
|Monami, A., Langer, B., [[Grellmann,_Wolfgang|Grellmann, W.]]: Moderne Methoden der Kunststoffprüfung zur Werkstoffentwicklung und Bauteilprüfung. Werkstoffprüfung. Fortschritte in der Werkstoffprüfung für Forschung und Praxis (2016), December 1 and 2, 2016, Neu-Ulm, Proceedings pp. 233–238 (ISBN 978-3-514-00830-4)
|-valign="top"
|[2]
|[https://www.researchgate.net/profile/Wolfgang-Grellmann Grellmann, W.], [[Reincke,_Katrin|Reincke, K.]], Monami, A., Kretzschmar, B.: Bruchmechanische Zähigkeitscharakterisierung von schichtsilikatverstärktem Polypropylen. In: [https://de.wikipedia.org/wiki/Michael_Pohl_(Metallurg) Pohl, M.] (Eds.): Konstruktion, Qualitätssicherung und Schadensanalyse. Stahleisen, Düsseldorf (2007), pp. 115−120 (ISBN 978-3-514-00753-6)
|-valign="top"
|[3]
|[https://de.wikipedia.org/wiki/Wolfgang_Grellmann Grellmann, W.], Langer, B., [[Bierögel,_Christian|Bierögel, C.]], Schoßig, M., Mecklenburg, T.: Bruchmechanische Zähigkeitsbewertung nukleierter glasfaserverstärkter Polyolefinwerkstoffe. In: Pohl, M. (Eds.): Konstruktion, Qualitätssicherung und Schadensanalyse, Publishing House Werkstoff-Informationsgesellschaft mbH, Frankfurt (2004) pp. 321−326 (ISBN 3-88355-337-9)
|-valign="top"
|[4]
|Kroll, M., Langer, B., Grellmann, W.: Toughness optimization of elastomer-modified glass-fiber reinforced PA6 materials. Journal of Applied Polymer Science 127 (2013) 57−66 DOI: [https://doi.org/10.1002/app.36853 https://doi.org/10.1002/app.36853]
|-valign="top"
|[5]
|Kroll, M., Langer, B., Schumacher, W., Grellmann, W.: The influence of carbon black batches on the fracture behavior of glass fiber reinforced PA6/PA66 blends. Journal of Applied Polymer Science 116 (2010) 610−618 DOI: [https://doi.org/10.1002/app.31611 https://doi.org/10.1002/app.31611]
|-valign="top"
|[6]
|Langer, B., Bierögel, C., Grellmann, W., Fiebig, J., Aumayr, G.: Material optimization of PP-short glass fibre compounds. In: Grellmann, W., [[Seidler,_Sabine|Seidler, S.]] (Eds.): Deformation and Fracture Behaviour of Polymers. Springer, Berlin, Heidelberg (2001) (ISBN 978-3540412472; see [[AMK-Library]] under A 7)
|-valign="top"
|[7]
|Maier, C., Calafut, T.: Polypropylene – The Definitive User’s Guide and Databook, William Andrew Publishing/Plastics Design Library (1998) (ISBN 978-0-0809-5041-9)
|-valign="top"
|[8]
|Marigo, A., Causin, V., Marega, C., Ferrari, P.: Crystallization of the gamma form in random propylene-ethylene copolymers. Polymer International 53 (2004) 2001−2008; DOI: [https://doi.org/10.1002/pi.1613 https://doi.org/10.1002/pi.1613]
|-valign="top"
|[9]
|Marigo, A., Marega, C., Causin, V., Ferrari, P.: Influence of thermal treatments, molecular weight, and molecular weight distribution on the crystallization of beta-isotactic polypropylene. Journal of Applied Polymer Science 91 (2004) 1008−1012; DOI: [https://doi.org/10.1002/app.13260 https://doi.org/10.1002/app.13260]
|-valign="top"
|[10]
|Raab, M., Kotek, J., Baldrian, J., Grellmann, W.: Übermolekulare Struktur und mechanische Eigenschaften von isotaktischem Polypropylen. In: Grellmann, W., Seidler, S. (Eds.): Deformation und Bruchverhalten von Kunststoffen. Springer Berlin Heidelberg (1998) (ISBN 3-540-63671-4; e-Book: ISBN 978-3-642-58766-5; see [[AMK-Library under A 6]])
|-valign="top"
|[11]
|Monami, A., Langer, B., Sadlik, J., Kucera, J., Grellmann, W.: Fracture mechanics properties of polymorphic molypropylene. Procedia Materials Science 3 (2014) 276−281; DOI: [https://doi.org/10.1016/j.mspro.2014.06.048 https://doi.org/10.1016/j.mspro.2014.06.048]
|-valign="top"
|[12]
|Androsch, R., Monami, A., Kucera, J.: Effect of an alpha-phase nucleating agent on the crystallization kinetics of a propylene/ethylene random copolymer at largely different supercooling. Journal of Crystal Growth 408 (2014) 91−96; DOI: https://doi.org/10.1016/j.jcrysgro.2014.09.028
|-valign="top"
|[13]
|Hale, G. E., Ramsteiner, F.: A Testing protocol for conducting J-crack growth resistance curve on plastics. In: Moore, D. R., Pavan, A., Williams, J. G. (Eds.): Fracture Mechanics Testing Methods for Polymers Adhesives and Composites, Elsevier, Amsterdam, London, New York, Oxford, Paris, Shannon, Tokyo (2001) 123–157 (ISBN 0-0804-3689-7)
|}

[[Category:Fracture Mechanics]]

Crack Resistance Curve – Examples - Revision history