Toughness

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Toughness

General information

When plastic components are used in various branches of industry such as the automotive industry, in building construction, chemical apparatus engineering, microelectronics, medical technology or the household appliance sector, toughness is a material parameter that is relevant to the application and must be verified using various test methods.

In addition to static and oscillating (dynamic) stresses, impact or shock-type stresses also occur very frequently (see also: Impact loading plastics).

Methods of toughness testing

Due to the comparatively simple realisation of conventional toughness test methods

the impact and notched impact test
- in Charpy arrangement according to ISO 179-1 [1], parameters: impact strength a_cU, notched impact strength a_cN
- in Izod arrangement according to ISO 180 [2], parameters: impact strength a_iU, notched impact strength a_iN
- in Dynstat arrangement according to DIN 53435 [3], parameters: impact strength a_dU, notched impact strength a_dA or a_dD

the uniaxial impact tensile and notched impact test according to ISO 8256 [4]
- Characteristic values: impact tensile strength a_tU, notched impact tensile strength a_tN and
- the biaxial puncture or drop bolt test according to ISO 6603-1 [5].

Parameter: 50 % damage work E₅₀

are frequently used, whereby their use in quality assurance is undisputed. Additional information on these parameters is obtained with the instrumented test methods in accordance with ISO 179-2 [6] and ISO 6603-2 [7], as force–deformation diagrams with increased informative values are recorded here.

Importance of fracture mechanics testing

A new generation of material parameters with significantly increased information content are geometry-independent fracture mechanics parameters (see: geometry criterion), which serve as target variables in material development and in the dimensioning of components [8], whereby the basic prerequisite here is also the application of instrumented test methods, but with varied test conditions.

The most important methods of fracture mechanics testing are subdivided into quasi-static, cyclic and impact testing according to the type of stress. The parameters used are

Fracture toughness K_Ic or K_Id (see: fracture mechanics)
Critical crack opening displacement δ_Ic or δ_Id (see: crack tip opening displacement concept) and the
J-integral values (see J-Integral evaluation methods (overview))

which make it possible to specifically take into account a number of factors influencing the toughness behaviour, such as design-related notches, production-related defects, multi-axial stress states, medial stresses, low temperatures and high speeds in their effect.

Blumenauer [9] refers to the combined effect of these factors, particularly at low temperatures, the presence of cracks and notches, residual stresses and impact loading. The fracture stress can be considerably lower than the yield strength of the material, which is referred to as a low stress fracture. For plastics, a change in the deformation and fracture mechanism from ductile fracture to brittle fracture is often observed with decreasing temperature, e.g. at application temperatures below the glass temperature (see: types of fracture). In this case, it is necessary to analyse the entire temperature dependence of the characteristic values in order to be able to verify the toughness with the aid of transition temperatures (see: brittle-tough transition) or limit temperatures.

A comprehensive compilation of fracture mechanics parameters for plastics, elastomers and composite materials is compiled in [10–12].

[1]	ISO/DIS 179-1 (2025-05): Plastics – Determination of Charpy Impact Properties – Part 1: Non-instrumented Impact Test (Draft)
[2]	ISO 180 (2023-09): Plastics – Determination of Izod Impact Strength
[3]	DIN 53435 (2024-10): Testing of Plastics – Bending Test and Impact Test on Dynstat Test Specimen
[4]	ISO 8256 (2023-11): Plastics – Determination of Tensile-impact Strength
[5]	ISO 6603-1 (2000-03): Plastics – Determination of Puncture Impact Behaviour of Rigid Plastics – Part 1: Non-instrumented Impact Testing
[6]	ISO 179-2 (2020-09): Plastics – Determination of Charpy Impact Properties – Part 2: Instrumented Impact Test
[7]	ISO 6603-2 (2023-06): Plastics – Determination of Puncture Impact Behaviour of Rigid Plastics – Part 2: Instrumented Impact Testing
[8]	Grellmann, W., Seidler, S. (Eds.): Kunststoffprüfung. Carl Hanser, Munich (2025) 4th Edition, pp. 237–291 (ISBN 978-3-446-44718-9; E-Book: ISBN 978-3-446-48105-3; see AMK-Library under A 23)
[9]	Blumenauer, H., Pusch, G.: Technische Bruchmechanik. Deutscher Verlag für Grundstoffindustrie, Leipzig (1993) 3rd Edition, pp. 42‒49 (ISBN 3-342-00659-5; see AMK-Library under E 29-3)
[10]	Grellmann, W., Seidler, S.: Mechanical and Thermomechanical Properties of Polymers, Landolt-Börnstein. Volume VIII/6A3, Springer Verlag, Berlin (2014), (ISBN 978-3-642-55165-9; e-Book ISBN 978-3-642-55166-6; DOI 10.1007/978-3-642-55166-6; see AMK-Library under A 16)
[11]	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 Heidelberg (2013), (ISBN 978-3-642-37909-3; see AMK-Library under A 14)
[12]	Grellmann, W., Langer, B. (Eds.): Deformation and Fracture Behaviour of Polymer Materials. Springer Series in Materials Science 247, Springer Berlin Heidelberg (2017), (ISBN 978-3-319-41877-3; e-Book: ISBN 978-3-319-41879-7; see AMK-Library under A 19)

General information

Methods of toughness testing

Importance of fracture mechanics testing

See also