Crack Resistance Curve – Experimental Methods

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Crack resistance curve – Experimental methods

Crack resistance curve – Experimental methods

For the experimental recording of crack resistance (R) curves under dynamic (impact) loading, e.g. in the Instrumented Charpy impact test (ICIT), four different possibilities are known in principle from the literature:

1. ICIT energy method (ICIT low-blow technique)
2. ICIT support span method
3. ICIT specimen length method
4. ICIT stop block method

The objective of all experimental methods is to vary the stable crack growth Δa (distance between original crack size and crack front after loading) as a basis for determining the fracture mechanics parameters of crack initiation and propagation using the R-concept.

The algorithm for recording R-curves in the instrumented notched impact test (ICIT), for example, is comparable for all the methods listed above [1 – 4]:

• Generation of stable crack initiations (multi-specimen technique / single-specimen technique) (stop-block, low-blow, energy method ...)
• Recording of load (F)–deflection (f) diagrams
• Generation of cryogenic fractures (brittle fracture surfaces)
• Determination of the amount of stable crack growth (light microscopic)
• Determination of load parameters from the F–f diagrams (in case of determination of J-values including the amount of stable crack growth)
• Graphical representation of the R-curves
• Evaluation of the R-curve (validity check, curve fitting ...)
• Determination of Material values (physical or technical crack initiation values J_i; δ_i; J_0.2; δ_0.2 and JT_J; δT_δ;T_J; T_δ)

See also

• Fracture mechanics
• Crack resistance (R) curve
• Crack resistance curve – examples
• Crack resistance curve – elastomers quasistatic
• Bend test and light microscopy
• Stretch zone

References

[1]	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; siehe AMK-Library under A 16)
[2]	Grellmann, W., Seidler, S. (Eds.): Deformation and Fracture Behaviour of Polymers. Springer Berlin Heidelberg 2001, 626 Pages, 447 Illustrations and 51 Tables, ISBN 3-540-41247-6, ISBN 978-3-450-41247-2; see AMK-Library under A 7) https://link.springer.com/book/10.1007/978-3-319-41879-7
[3]	Seidler, S.: Anwendung des Risswiderstandskonzeptes zur Ermittlung strukturbezogener bruchmechanischer Werkstoffkenngrößen bei dynamischer Beanspruchung. VDI-Verlag Düsseldorf, 1998, ISBN 3-318-323118-2; see AMK-Library under B 2-1
[4]	Grellmann, W., Seidler, S.: Risszähigkeit von Kunststoff-Messungen bei dynamischer Beanspruchung. Materialprüfung 33 (1991) 7-8, pp. 213−218