Large strain mechanical behavior of 1018 cold-rolled steel over a wide range of strain rates
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11/7/03
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Large Strain Mechanical Behavior of 1018 Cold-Rolled Steel over a Wide Range of Strain Rates M. VURAL, D. RITTEL and G. RAVICHANDRAN The large-strain constitutive behavior of cold-rolled 1018 steel has been characterized at strain rates # ranging from 103 to 5 104 s1 using a newly developed shear compression specimen (SCS). The SCS technique allows for a seamless characterization of the constitutive behavior of materials over a large range of strain rates. The comparison of results with those obtained by cylindrical specimens shows an excellent correlation up to strain rates of 104 s1. The study also shows a marked strain rate sensitivity of the steel at rates exceeding 100 s1. With increasing strain rate, the apparent average strain hardening of the material decreases and becomes negative at rates exceeding 5000 s1. This observation corroborates recent results obtained in torsion tests, while the strain softening was not clearly observed during dynamic compression of cylindrical specimens. A possible evolution scheme for shear localization is discussed, based on the detailed characterization of deformed microstructures. The Johnson–Cook constitutive model has been modified to represent the experimental data over a wide range of strain rates as well as to include heat-transfer effects, and model parameters have been determined for 1018 cold-rolled steel.
I. INTRODUCTION
THE determination of large strain constitutive behavior of materials is a key step toward accurate modeling of numerous processes such as plastic forming, plastic fracture, and high-speed penetration. Moreover, the behavior of the material should be determined over a large range of strain rates, as these are well known to influence the overall mechanical response.[1] While a variety of techniques are available for this purpose, the constitutive behavior of a given material is often studied through the use of various specimens and experimental techniques. Here, one should mention the Kolsky apparatus (split Hopkinson pressure bar, Kolsky[2]) as the main experimental technique for the dynamic characterization of cylindrical specimens in the range of strain rates from 102 to 103 s1. At strain rates of 105 s1 and above, the key technique is that of plate impact experiments, for uniaxial strain and pressure shear experiments.[3] Shear testing at high strain rates has been carried out by means of a torsional Kolsky apparatus.[4] Using this technique, Marchand and Duffy[5] studied adiabatic shear band formation in HY100 steel (also Duffy and Chi,[6] on cold-rolled 1018 and martensitic steels). Gilat and Wu[7] investigated 1020 hot-rolled steel over a wide range of temperatures and strain rates, with pure shear tests. Gilat and Cheng[8] characterized the high rate shear behavior of 1100 aluminum and modeled the experimental setup using finite element analysis. To achieve large shear strains and strain rates, various specimen geometries were devised in which the linear displacement applied at the specimen boundary
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