摘要
对原有Johnson−Cook本构模型中的项进行修正,提出一种新的现象学的、基于经验的本构模型。该模型可用于描述和预测具有不同初始晶粒尺寸的AA1070铝在热加工过程中的流变应力。该模型考虑热软化、应变速率硬化、应变硬化、初始晶粒尺寸及其相互影响,能够正确模拟具有不同应变、应变速率和初始晶粒尺寸AA1070铝的高温行为。通过压缩试验测试的AA1070铝的热流变行为,温度范围为623~773 K,应变速率为0.005~0.5 s−1,初始晶粒尺寸为50~450μm。结果表明,初始晶粒尺寸对AA1070铝的流变行为有显著影响。通过相关系数(R)、平均绝对相对误差(AARE)、相对误差评估模型的可预测性。结果表明,新模型预测的具有不同初始晶粒尺寸材料的流变应力与实验值完全一致,平均相对误差为1.19%,证实新修正的Johnson−Cook关系能准确估计考虑初始晶粒尺寸时AA1070铝的热流变应力。
A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson−Cook constitutive model.The new model can be used to describe and predict the flow stress of AA1070 aluminum with different initial grain sizes in the hot working process.This developed model considers thermal softening,strain-rate hardening,strain hardening,initial grain size,and interactions with each other and can correctly model the behavior of AA1070 at elevated temperature with different strains,strain rates,and initial grain sizes.The hot flow behavior of AA1070 was investigated through compression tests over wide ranges of temperature from 623 to 773 K,strain rate from 0.005 to 0.5 s−1 and initial grain size from 50 to 450μm.Results show that the initial grain size has a significant effect on the flow behavior of AA1070.Then,correlation coefficient(R),average absolute relative error(AARE),and relative error were examined for comparative predictability of the model.Results show that flow stresses for different initial grain sizes calculated by the new proposed model perfectly correlate with experimental ones,with a mean relative error of 1.19%,which confirms that the new modified Johnson−Cook relation can give a precise estimation of the hot flow stress of AA1070 aluminum by considering the initial grain size.
