Ductility Plastics

Sprachauswahl/Language selection

Dieser Artikel ist auch auf Deutsch verfügbar Duktilität

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

Ductility plastics

General

In the field of solids, the terms strength, toughness, viscosity, as well as brittleness and ductility are used for property evaluation [1]. In the literature, ductile and toughness material behaviour are often used synonymously without a more differentiated consideration.

In practical use, plastics and composites with a polymer matrix exhibit very different deformation behaviour under different loading conditions. Many amorphous plastics (e.g. polystyrene ( abbreviation: PS) or poly(methyl methacrylate) ( abbreviation: PMMA) are brittle under tensile stress, but deform plastically under compressive stress or pure shear stress (see: Shear Modulus). Similarly, epoxy resins ( abbreviation: EP) show a high degree of deformability under compressive stress. Typical representatives of plastics with pronounced deformation behaviour are, for example, polypropylene ( abbreviation: PP), polyethylene ( abbreviation: PE) or also polyamide ( abbreviation: PA [2]).

Definition of ductility

The ductility of a material is understood to be its ability to undergo permanent plastic deformation under shear stress before ultimate failure through fracture occurs. Ductility represents an elongation-determined material parameter, with tensile stress and break (see tensile strength) used as a measure of the degree of ductility [6]. In contrast, toughness is an energy-determined material parameter that can be traced back to the measured parameters force and extension (displacement rsp. deflection). A higher ductility is always based on an increased deformability. The metal gold, for example, which can be applied to surfaces in the form of gold leaf with an extremely low layer thickness, has a particularly high ductility.

The ductile material behaviour of plastics is usually represented in the stress–strain diagram for tensile loading, which is technically simple to produce [2]. These diagrams allow an informative statement on the brittle or ductile behaviour on the basis of the habit (see: tensile strength). A typical representative of a ductile plastic is polyamide 6 ( abbreviation: PA6) under standard stress (see: tensile test elongation Figure 2). The deformation behaviour is characterized by the occurrence of linear-elastic (see elasticity) and nonlinear-viscoelastic deformation regions, as well as a typical yield point formation. This yield point (see: Yield stress) marks the onset of plastic deformation. Macroscopically, this deformation process is accompanied by the formation of necking fronts, which cause a reduction in cross-section. In addition to the change in internal energy, the deformation process in tensile tests on plastics is also associated with heat tinting.

Requirements profile

The use and application limits of plastics and composites are also determined by the demand for the most precise possible prediction of the expected composite properties. The variety of influencing factors, on the other hand, means that comprehensive theoretical predictions of the properties of individual parameters cannot be expected in the future. It therefore seems most appropriate to use empirically determined material values depending on the type of requirement profile. While tensile stress at break is not a suitable parameter due to the one-sided property characterization of the material behaviour, the possibilities of modelling the toughness behaviour of, for example, short-fibre-reinforced composites and particle-filled thermoplastics is reported in the publication fracture behaviour. Since the tensile stress at break (see: tensile strength) has a limited informative content, an approach using the work of fracture decomposed into different fractions is followed when modelling the toughness. Such models have been successfully used for property prediction of short-fibre reinforced thermoplastics [3] and particle composites [4, 5].

When selecting suitable plastics and composites for complicated components or complex structures, the basic ductility requirements must be taken into account. Special consideration must be given to how the requirement profile changes as a result of thermal, medial, corrosive or erosive influence as well as ageing. In addition to singular stress, particular attention must be paid to superpositions of different load collectives, such as static and oscillatory stress (see: fatigue). A comprehensive literature analysis on the experimental data of a wide range of stress types is given in [1].

Applications of ductility

Ductility is not only important for material selection, but also plays an important role in manufacturing technology in machining processes, such as turning and milling of thermoplastics and thermosets, where it decisively influences the choice of machining tool or the cutting or feed rate [7].

In the automotive industry, elastomer-modified PP materials or special foams have been used for many years for classic bumpers or bumper systems integrated into the body, which are characterized by particularly high energy absorption even at low temperatures in the frost range. In modern bumper systems, crash elements (impact elements) are specifically installed that enable reversible deformation at low impact speeds (< 7 km/h) and represent crumple zones at high impact speeds that can absorb a high proportion of the impact energy [8]. In addition, high-end vehicles incorporate crash elements in fender linings (front and rear), wheel covers, longitudinal and transverse, as well as in frames and battery covers, which are often made of fibre-reinforced composites but also of highly ductile metallic materials. Such crash elements are tested in crash tests on the component and in vehicle installations and are subject to extensive testing.

See also

• Fracture behaviour
• Fracture parables
• Hybrid methods of plastic diagnostics
• Thermosets
• Vibration-induced creep fracture
• Fibre–Matrix adhesion

References

[1]	Grellmann, W., Seidler, S. (Eds.): Mechanical and Thermomechanical Properties of Polymers. Landoldt Börnstein. Volume VIII/6A2, Springer Berlin (2014) (ISBN 978-3-642-55166-6; see AMK-Library under A 16)
[2]	Bierögel, C.: Tensile Test on Polymers. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser Munich (2022) 3rd edition, pp. 106–123 (ISBN 978-1-56990-806-8; see AMK-Library under A 22)
[3]	Lauke, B., Friedrich, K.: Fracture Toughness Modelling of Fibre Reinforced Composites by Crack Resistance Curves. Adv. Compos. Mater. 26 (1991) 261–275
[4]	Grellmann, W., Bohse, J., Seidler, S.: Fracture mechanical analysis of the toughness behavior of particle-filled thermoplastics. Materialw. und Werkstofftechn. 21 (1990) 9, pp. 359–364
[5]	Bohse, J., Grellmann, W., Seidler, S.: Micromechanical Interpretation of Fracture Toughness of Particulate-filled Thermoplastics. J. Material Science 26 (1991) 24, 6715–6721

Weblinks

[6]	Wikipedia – The Free Encyclopedia: https://en.wikipedia.org/wiki/Ductility
[7]	https://www.beutter.de/de/glossar/duktilitaet
[8]	https://de.wikipedia.org/wiki/Stoßstange_(Karosserie)