Dynamic effects on fracture toughness for ferritic steel in the ductile-to-brittle transition
Résumé
Dynamic loading effects on ferritic steel toughness have
been evaluated in the brittle-to-ductile transition, considering
loading rates representative of object drops. To verify that the
brittle-to-ductile transition curve, initially defined from static
tests, tends to shift to higher temperatures due to dynamic
effects even in the case of object drops, experiments on
16MND5 steel have been performed.
A three-point bending set-up and a thermal chamber have
been designed in order to perform dynamic fracture tests on
large Single Edge-notched Bending SE(B) specimen, at very
low temperature using a drop-shock machine. In a first step,
considering that the reference temperature of the material
(according to the master curve concept) is -122 °C, dynamic
tests at -120 °C have been performed. These tests have
confirmed that the fracture mode is still brittle at this
temperature, when an impact speed of 4.85 m/s is used.
Elastic-plastic or viscoplastic dynamic simulations of the
tests, compared to classical static analysis, have demonstrated
that the effects of inertia and viscosity on fracture toughness are
negligible considering the very low values obtained on these
tests at -120 °C. These results also confirm the decrease of
fracture toughness due to dynamic loading compared to
experimental data from static tests. A further step will be to
complete this demonstration with dynamic tests at higher
temperatures in the brittle-to-ductile transition.
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