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Thermal Effects on the Enhanced Ductility in Non-Monotonic Uniaxial Tension of DP780 Steel Sheet
Omid Majidi,Frederic Barlat,Yannis P. Korkolis,Jiawei Fu,Myoung-Gyu Lee 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.6
To understand the material behavior during non-monotonic loading, uniaxial tension tests were conducted inthree modes, namely, the monotonic loading, loading with periodic relaxation and periodic loading-unloadingreloading,at different strain rates (0.001/s to 0.01/s). In this study, the temperature gradient developing duringeach test and its contribution to increasing the apparent ductility of DP780 steel sheets were considered. In order toassess the influence of temperature, isothermal uniaxial tension tests were also performed at three temperatures(298 K, 313 K and 328 K (25 °C, 40 °C and 55 °C)). A digital image correlation system coupled with an infraredthermography was used in the experiments. The results show that the non-monotonic loading modes increasedthe apparent ductility of the specimens. It was observed that compared with the monotonic loading, the temperaturegradient became more uniform when a non-monotonic loading was applied.
Stress Relaxation for Formability Improvement
Hariharan, Krishnaswamy,Majidi, Omid,Kim, Chong Min,Lee, Myoung Gyu,Barlat, Fré,dé,ric Trans Tech Publications, Ltd. 2013 Key Engineering Materials Vol.554 No.-
<P>Improved formability has been reported due to stress relaxation when the continuous forming cycle is interrupted with steps by adjusting the punch motion. The contribution of stress relaxation and its parameters on the ductility of materials has not been established so far. In the present work, the stress relaxation behavior of three materials, low carbon steel, DP and TRIP steels are studied. The influence of strain rate and strain on the ductility enhancement due to stress relaxation is analyzed. It is observed that stress relaxation improved the ductility of materials in all the cases and therefore can be used as a potential method to improve formability in sheet metal forming.</P>