A Computational Investigation on Bending Deformation Behavior at Various Deflection Rates for Enhancement of Absorbable
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INTRODUCTION
OVER the last few decades, transformation-induced plasticity (TRIP) steel has attracted the interest of the scientific community.[1–9] Past studies[2,10,11] have proven that TRIP steel possesses promising mechanical properties such as high strength, excellent formability, and toughness because of strain-induced martensitic transformation (SIMT). In addition, during the inelastic deformation process of TRIP steel, energy supplied from an external field can be consumed by not only plastic deformation but also transformation to a martensitic phase. At the same time, it is possible that a process of instantaneous deformation such as volume expansion and shape change related to the transformation can dissipate a large amount of energy. As a result, TRIP steel might have an excellent energy-absorption characteristic. Therefore, TRIP steel may be suitable for
HANG THI PHAM, Doctoral Student, is with the Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8527 Japan, and Lecturer with the Faculty of Engineering, Vietnam National University of Agriculture, Ngoxuanquang street, Trauquy, Gialam, Hanoi, 131004 Vietnam. TAKESHI IWAMOTO, Associate Professor, is with the Institute of Engineering, Hiroshima University, 1-4-1 Kagamiyama, HigashiHiroshima, Hiroshima, 739-8527 Japan Contact e-mail: iwamoto@ mec.hiroshima-u.ac.jp Manuscript submitted January 20, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
automotive structures such as crash boxes, front side members, bumpers, and side panels from the viewpoint of safety.[12] A dominant mechanism that ensures safety upon collision in automobiles, manufactured using such structures, is buckling. Bending deformation due to buckling is one of the major collapse modes of the automotive structures. In addition, compared with the axial deformation, an experiment for the bending deformation provides more stable results at a structural level. Thus, an investigation on the bending deformation behavior and energy-absorption characteristic of TRIP steel is indispensable to clarify the mechanism that produces better performance. For understanding the mechanism governing the energy-absorption characteristic during deformation in TRIP steel, it is presumed that SIMT plays a major role in improving the characteristic. However, the SIMT may be suppressed under dynamic loading conditions because of temperature rise in the material due to adiabatic heating by inelastic irreversible work.[8] At the same time, this heating phenomenon introduces thermal softening of the material. The effect of the amount of transformed martensite on the energy-absorption characteristic in TRIP steel at a high deformation rate seems to be studied insufficiently and the mechanism governing the energy-absorption characteristic is still unclear. The energy absorption of materials can be evaluated from the stress-strain curve obtained by a tensile test. However, at high deformation rate, an interaction between a
plastic wave and unstable deformation during te
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