Instrumented Charpy Impact Test

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Instrumented Charpy impact test (ICIT)

General

The instrumented Charpy impact test (ICIT) is a method of mechanical materials testing or experimental fracture mechanics testing (see: fracture mechanical testing) that is increasingly used in materials development and optimisation.

Informativeness of the ICIT

Figure 1 shows the importance of instrumented testing (see: electronic instrumentation) when performing the notched impact test. While the notch impact energy A, which is identical for both materials in conventional toughness assessment due to its integral character (A₁ = A₂ and a_cN1 = a_cN2), the result of the instrumented test shows clear differences in terms of force (F_max1 > F_max2) and deformation component (f_max1 < f_max2). In addition, the instrumented Charpy impact test enables the determination of fracture mechanics toughness parameters K_Id, δ_Id and J_Id, which differ significantly for the two materials compared and thus enable differentiation (see also: levels of knowledge in fracture mechanics).

Fig. 1:

Schematic representation of a load–deflection diagram for two materials with different deformation behaviour

Another case where problems can arise when assessing the toughness of materials using conventional notched impact tests is shown in Fig. 2. Here, in the notch impact test on identical materials 1 and 2 (A₁ = A₂), a not insignificant amount of crack propagation energy A_R occurs in material 1, which, however, is only visible and quantifiable when the test is performed with instruments. Since this part is not taken into account in a fracture mechanical evaluation, both materials have an identical toughness level for all fracture mechanical characteristics as a result of A₁ = A₂. If conventional notch impact tests are carried out on these materials, the crack propagation energy, if present, will be included in the evaluation. As a result, material 1 is overrated in terms of its toughness level due to A₁+A_R > A₂, even though A₁ = A₂.

Fig. 2:

Schematic representation of load–deflection diagrams for materials with and without crack propagation energy

Application

The instrumented Charpy impact test can therefore be used either to determine the impact strength or Charpy impact strength a_cU or a_cN, or to evaluate the load–deflection behaviour (see: conventional impact test). In this case, the ISO 179-2 standard is applied, or the instrumented Charpy impact test is performed as an experimental basis for a fracture mechanical toughness characterisation of materials.

See also

• Fracture mechanical testing
• Electronic instrumentation
• MPK-Procedure MPK-ICIT
• Instrumented Tensile Impact Test (ITIT)
• Impact Loading Pendulum Impact Tester
• Impact Loading Plastics
• Toughness

References

• Blumenauer, H., Schröder, H.: Anwendung des registrierenden Schlagbiegeversuches zur Prüfung von Polymerwerkstoffen. Plaste und Kautschuk 20 (1973) 11, 832–833
• Grellmann, W.: Beurteilung der Zähigkeitseigenschaften von Polymerwerkstoffen durch bruchmechanische Kennwerte. Habilitation (1986), Technische Hochschule Merseburg, Wiss. Zeitschrift TH Merseburg 28 (1986), No. 6, pp. 787–788 (Content, Summary)
• Grellmann, W.: Probleme und Ergebnisse der instrumentierten Kerbschlagbiegeprüfung von Polymerwerkstoffen. In: Henning, K., Michel, B. (Eds.): Fracture Mechanics, Micromechanics and Coupled Fields (FMC). Series (1982) No. 3, pp. 102–111 (see AMK-Library under E 43)
• Grellmann, W.: Probleme der Ermittlung von Bruch- und Trägheitskräften bei der Bestimmung dynamischer Bruchzähigkeiten von Polymerwerkstoffen. In: Henning, K., Michel, B. (Eds.): Fracture Mechanics, Micromechanics and Coupled Fields (FMC). Series (1982) No. 3, pp. 142–151 (see AMK-Library under E 43)
• ISO 179-2 (2020-05): Plastics – Determination of Charpy Impact Properties – Part 2: Instrumented Impact Test
• ESIS P2-92 (1992): Procedure for Determining the Fracture Behaviour of Materials
• ESIS TC 4 (2001): A Testing Protocol for Conducting J-Crack Growth Resistance Curve Test on Plastics
• MPK-Procedure_MPK-ICIT (2016-08): Testing of Plastics – Instrumented Charpy Impact Test (ICIT): Procedure for Determination the Crack Resistance Behaviour using the Instrumented Impact Test
• Grellmann, W., Langer, B.: Methods for Polymer Diagnostics for the Automotive Industry. Materialprüfung 55 (2013) 17–22 Download als pdf

Further literature references, see Electronic Instrumentation