Fracture Mechanical Testing

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Fracture mechanical testing

General information

Different experimental methods can be used to determine fracture mechanics parameters for plastics and elastomers. The loading speed or the type of loading ( stress) is of great importance here, which is why a distinction is made between impact, quasi-static and cyclic test methods.

Impact testing

• Instrumented Charpy Impact Test (ICIT)
• Instrumented tensile impact test (ITIT)
• Instrumented puncture impact test (Instrumented free-falling dart test (IFT))

Carrying out such experiments allows the determination of geometry-independent material parameters (see geometry criterion), which react sensitively to structural changes in the material. For this reason, fracture mechanics parameters are often used in questions of material development and optimisation.

The instrumented notched Charpy impact test and the instrumented puncture test can also be carried out under temperature stress, which is of great practical importance, e.g. with regard to the determination of material application limits via the determination of brittle-tough transition temperatures.

Static fracture mechanics test

Additional equipment such as laser double scanners, crack opening displacement (COD) technology, mixed mode, optical strain field measurement enable quasi-static fracture mechanics tests to be carried out with standard universal testing machines.

Testing the fatigue fracture behaviour

To quantitatively describe the relationship between the crack propagation velocity da/dN and the change in the fracture mechanical parameters ΔJ, ΔK or ΔT, methods are used in which metal blade notched test specimens are subjected to cyclic loading. The form of this stress (harmonic, stochastic...) depends, for example, on the use of the material. In order to characterise a tyre material in a practical manner, for example, high-frequency stresses are applied to which a pulse is additionally superimposed after a defined time interval.

A comprehensive literature analysis of fracture mechanics values for plastics and fibre-reinforced composites under impact, quasi-static and cyclic loading is contained in Landolt-Börnstein Volume VIII/6A3 (see References).

See also

• Fracture mechanics
• Crack tip opening displacement concept (CTOD)
• J-integral concept
• Instrumented Charpy impact test (ICIT)
• MPK-Procedure MPK-ITIT
• Material testing machine

References

• Grellmann, W., Seidler, S. (Eds.): Mechanical and Thermomechanical Properties of Polymers. Landolt-Börnstein, Volume VIII/6A3, Springer Berlin (2014) (ISBN 978-3-642-55165-9; see AMK-Library under A 16)
• Anderson, T. L.: Fracture Mechanics; Fundamentals and Applications. CRC Press, Boca Raton (2005) 3rd Edition, (ISBN 978-0849342608; see AMK-Library under E 8-2) https://doi.org/10.1201/9781315370293
• Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 236–239, (ISBN 978-1-56990-806-8; e-book ISBN 978-1-56990-807-5; see AMK-Library under A 22)