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Licensed Unlicensed Requires Authentication Published by De Gruyter November 21, 2017

Method for determining the strain rate sensitivity factor for the Johnson-Cook model in Charpy tests

Verfahren zur Bestimmung des Dehnratensensitivitätsfaktors für das Johnson-Cook-Modell im Charpy-Versuch
Michał Stopel, Dariusz Skibicki and Wojciech Moćko
From the journal Materials Testing

Abstract

The basis for the study was the necessity to design a supporting structure of the road infrastructure subjected to high strain rates occurring during vehicle accidents. Mathematical models of hardening due to the high strain rates are reviewed. Commonly used methods for determining constants for one of the models, i. e., Johnson-Cook model are characterized. The main section of the study presents a proposed method for determining the strain rate sensitivity of the material. It is a hybrid method which requires Charpy tests using unnotched specimens and a series of calculations using the finite element method to simulate the tests. Several variants of strain measurement of specimen subjected to failure in Charpy tests, as required for the proposed method are analyzed. Using the suggested method, a strain rate sensitivity factor was obtained with a value similar to the value obtained using the split Hopkinson pressure bar technique. The advantages of the suggested method compared to the existing methods are the high availability of the instruments, simple and quick processing of the results and significantly lower costs.

Kurzfassung

Die Basis für die diesem Beitrag zugrunde liegende Studie bestand in der Notwendigkeit, eine Stützstruktur für die Fahrbahninfrastruktur auszulegen, die hohen Dehnraten infolge von Fahrzeugunfällen ausgesetzt ist. Mathematische Modelle der Verfestigung aufgrund der hohen Dehnraten werden überprüft. Die gewöhnlich angewandten Verfahren zur Bestimmung der Konstanten für eines der Modelle, dem Johnson-Cook-Modell, werden charakterisiert. Der Hauptteil der Studie stellt ein propagiertes Verfahren vor, um die Dehnratensensitivität des Werkstoffes zu bestimmen. Hierbei handelt es sich um ein Hybridverfahren, das Charpy-Tests mit einer ungekerbten Probe und eine Reihe von Berechnungen unter Verwendung der Finite Elemente Methode erfordert, um den Versuch zu simulieren. Verschiedene Varianten der Dehnungsmessung der Proben, die einem Versagen im Charpy-Test ausgesetzt waren und die für das propagierte Verfahren erforderlich waren, werden analysiert. Unter Anwendung des vorgeschlagenen Verfahrens wurde ein Faktor der Dehnratensensitivität ermittelt, der einen Wert ähnlich dem Wert hat, der mittels des Split-Hopkinson-Versuches erhalten wurde. Der Vorteil des vorgeschlagenen Verfahrens im Vergleich zu existierenden Verfahren besteht in der hohen Verfügbarkeit der Instrumente, einer einfachen und schnellen Verarbeitung der Ergebnisse und signifikant niedrigeren Kosten.


*Correspondence Address, Prof. Eng. Dariusz Skibicki, UTP University of Science and Technology in Bydgoszcz, Kaliskiego 785-796 Bydgoszcz, Poland, E-mail:

MSc Eng. Michał Stopel obtained his basic education in the area of Mechanical Engineering at the University of Science and Technology in Bydgoszcz, Poland in 2013. He started to work on his PhD thesis in the field of Machine Construction. He is interested in particular in dynamic loads and strain rate dependent materials. He is an assistant at the University of Bydgoszcz in Poland, where he deals mainly with CAD and FEM problems.

Prof. Eng. Dariusz Skibicki obtained his basic education in the area of Mechanical Engineering at the University of Science and Technology in Bydgoszcz, Poland in 1992. He started to work on multiaxial fatigue of materials in 2000 and defended his PhD. After receiving the doctorate degree, his scope of interest has been enlarged by encompassing the fatigue of materials with problems of defining nonproportionality measures. Now, he is Assistant Professor at the University of Bydgoszcz in Poland, where he deals mainly with FEM problems.

Prof. Eng. Wojciech Moćko obtained his basic education in the area of Electronics at Warsaw University of Technology, Poland in 2004. In 2008, he defended his PhD thesis with the title “Application of Image Sensors for Colorimetric Analysis”. He is an employee of the Institute of Motor Transport since 2003. Currently, he is working at ITS Material Research Center, Warsaw, Poland.


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Published Online: 2017-11-21
Published in Print: 2017-11-15

© 2017, Carl Hanser Verlag, München