POSTER REFERENCE: ICF100346PR DYNAMIC FRACTURE TESTING USING CHARPY INSTRUMENTED PENDULUM Z. Radakovic 1, Gy. B. Lenkey 2, V. Grabulov 3, A. Sedmak 1, D. Radakovic 4 1 Department of Mechanical Engineering, University of Belgrade, 27. marta 80, 11220 Belgrade, Yugoslavia 2 Bay Zoltán Institute for Logistics and Production Systems, Department for Structural Integrity Iglói u. 2, 3519 Miskolc, Hungary 3 Military Technical Institute, Niska bb, 11132 Belgrade, Yugoslavia 4 Methode Electronics Malta Ltd., Mriehel Industrial Estate, Mriehel QMR09, MALTA ABSTRACT Charpy impact testing of a high strength low-alloyed (HSLA) steel has been performed by simultaneously recording two independent signals. The magnetic emission (ME) and potential drop (PD) techniques were used to determine critical crack initiation properties on standard V-notched and pre-cracked three-point bending specimens at room temperature. Both signals (ME and PD) were recorded and compared, with the purpose of more precise identification of critical fracture mechanics parameters determining the onset of ductile crack growth. Standard Charpy specimens made of HSLA steel, oriented perpendicular to rolling direction were tested by a modified instrumentation of the Charpy machine, which included the original magnetic emission, and the potential drop techniques. The strain gauges and emission probes, located on the hammer tup, measured the force, thus both the magnetic and electric potential drop signals were monitored and recorded as a function of time. The obtained results indicate good agreement between ME and PD techniques on evaluation of ductile crack growth initiation point. KEYWORDS Dynamic fracture, crack initiation, impact tests, fracture toughness, magnetic emission, potential drop INTRODUCTION The instrumentation of the Charpy testing machine by two independent techniques has been successful for dynamic fracture testing of the high strength micro-alloyed steel. The magnetic emission (ME) technique has been used for dynamic fracture testing by depicting the stable and unstable crack initiation [1], and has been applied for impact testing of certain types of steels, including railroad and reactor pressure vessel steels [2,3,4], as well as the HSLA steel [5]. In the case of ductile, or ductile/cleavage fracture, at temperatures well above nil-ductile, or at lower impact energies, it is sometimes difficult to distinguish the crack initiation event directly from the ME signal, and even the integrated ME signal sometimes has a slower rate of change, resulting in a plateau-like region without clear discontinuity. Alternatively, the potential drop method (PD) was also applied for the same purpose by recording the change in electrical resistance by drop in electric potential (PD) in the vicinity of the crack tip [6,7]. Results have also been obtained by applying this
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