Banerjee Dilip K, Iadicola Mark A, Creuziger Adam
National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
J Res Natl Inst Stand Technol. 2022 Feb 22;126:126050. doi: 10.6028/jres.126.050. eCollection 2021.
Uniaxial tensile tests are routinely conducted to obtain stress-strain data for forming applications. It is important to understand the deformation behavior of test specimens at plastic strains, temperatures, and strain rates typically encountered in metal forming processes. In this study, the Johnson-Cook (J-C) flow stress model was used to describe the constitutive behavior of ASTM International (ASTM) A 1008 steel specimens during uniaxial tensile tests at three different average strain rates (10-⁵ s-¹, 10-³ s-¹, and 10-¹ s-¹). The digital image correlation (DIC) technique was used for displacement and strain measurement, and two-dimensional (2D) infrared (IR) imaging was employed for temperature measurement. Separate optimization studies involving relevant finite element (FE) modeling with appropriate measured data yielded optimum values of convective heat transfer coefficients, J-C parameters, and inelastic heat fraction variables. FE modeling employing these optimum parameter values was then used to study the mechanical behavior. While FE predictions matched measured strain localization and thermal field very well in the intermediate- and low-rate experiments, the high-rate test showed narrower strain localization and a sharper temperature peak in the experiment. Possible use of a higher steel thermal conductivity value and/or exclusion of material inhomogeneities may have resulted in discrepancies between computed and measured temperature and strain fields. The study shows that an optimized set of parameters obtained with a controlled test could be reasonably applied for other tests conducted at very different strain rates.
常规进行单轴拉伸试验以获取用于成型应用的应力-应变数据。了解在金属成型过程中通常遇到的塑性应变、温度和应变速率下试样的变形行为非常重要。在本研究中，采用约翰逊-库克（J-C）流动应力模型来描述美国材料与试验协会（ASTM）A 1008钢试样在三种不同平均应变速率（10⁻⁵ s⁻¹、10⁻³ s⁻¹和10⁻¹ s⁻¹）下单轴拉伸试验期间的本构行为。使用数字图像相关（DIC）技术进行位移和应变测量，并采用二维（2D）红外（IR）成像进行温度测量。涉及相关有限元（FE）建模与适当测量数据的单独优化研究得出了对流换热系数、J-C参数和非弹性热分数变量的最佳值。然后使用采用这些最佳参数值的有限元建模来研究力学行为。虽然在中低速试验中有限元预测与测量的应变局部化和热场非常吻合，但高速试验显示试验中的应变局部化更窄且温度峰值更尖锐。可能使用更高的钢热导率值和/或排除材料不均匀性可能导致计算和测量的温度及应变场之间存在差异。该研究表明，通过控制试验获得的一组优化参数可以合理地应用于在非常不同应变速率下进行的其他试验。
