Frequency Response Control

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Frequency response control

Control of frequency response in the instrumented Charpy impact test (ICIT)

Criteria for the fracture time

A necessary requirement for accurately determining the relationship between impact load and fracture time, or deflection, is the control of the frequency response. An exact metrological measurement of the impact load (F) –time (t) signal is only possible if the experimental conditions governing the relationship between fracture time and the rise time of the electronic measurement chain are adhered to.

$t_{B}\,>\,1{.}1\,t_{R}$

with

tR

rise time of electronic measuring chain (amplifier and frequency filter)

Criteria for frequency filtering

The condition for frequency filtering to occur is:

$t_{R}\,=\,{\frac {0{.}35}{f_{0{.}915}}}\;;\qquad t_{R}\,=\,{\frac {0{.}27}{f_{0{.}707}}}$

where

f0.915dB		frequency at which the amplitude is 90 %
f0.707dB		frequency at which the amplitude is 70 %

$t_{R}\,=\,1{.}4\,\tau$

τ

period of the characteristic inertial oscillation

Mechanical and electronic frequency filtering

Mechanical damping elements or electronic filters are used to improve the interpretability of the F–t signals; filter frequencies of 3 to 10 kHz are appropriate in relation to the fracture time.

For impact-modified, filled and reinforced plastics, filtering is unsuitable in cases where the change in crack propagation energy A_R is to be considered for deriving toughness parameters. Filtering results in a quantitative distortion of A_R and thus of the parameters derived from it, such as the ductility index.

See also

• Instrumented Charpy impact test
• ICIT – Experimental conditions
• ICIT – Types of impact load–deflection diagrams

References

• Grellmann, W.: Zähigkeitsbewertung mit bruchmechanischen Methoden. In: Grellmann, W., Seidler, S. (Eds.): Kunststoffprüfung. Carl Hanser, Munich (2024) 4th Edition, pp. 258/259 (ISBN 978-3-446-44718-9; E-Book: ISBN 978-3-446-48105-3; see AMK-Library under A 23)
• Jungbluth, H.: Untersuchungen zum Verformungs- und Bruchverhalten von PVCC-Werkstoffen. Technische Hochschule Leuna-Merseburg (1987) (see AMK-Library unter B 1-1) (Bibliographic summary/Table of contents)