微合金低碳钢高温拉伸实验过程的有限元模拟

FINITE ELEMENT MODELLING OF TENSILE TEST FOR MICRO-ALLOYED LOW CARBON STEEL AT HIGH TEMPERATURE

开发了电势-热-力耦合有限元计算模型,该模型考虑了微合金低碳钢高温条件下的奥氏体γ和高温铁素体δ相变,建立了多相混合力学模型,描述了(δ+γ)两相混合区的力学行为.应用多场耦合计算模型对拉伸实验过程进行了数值模拟.实验及数值模拟结果表明,拉伸试样内存在较大径向及轴向温度梯度,该温度梯度导致试样内产生相体积分数的梯度分布,如高温铁素体相分数和液相分数的梯度分布,试样内产生非均匀变形,并且应力分布极不均匀.在进行实验钢高温力学本构方程的参数标定时,采用名义应力—应变的方法会导致较大误差,而基于数值模拟的方法则是十分有效及准确的,如本文所建立的数值模型.

In view of the numerical inverse identification of constitutive models,a forward numerical modelling of Gleeble tension tests is conducted.A coupled electrical-thermal-mechanical model is proposed for the resolution of electrical,energy and momentum conservation equations by means of finite element method.In momentum equation,the mixed rheological model in multi-phase region （e.g.δ-ferrite and 7 austenite（δ＋7 mixture）） is developed to consider theδ/γphase transformation phenomenon for micro-alloyed low carbon steel at high temperature.Experimental and numerical results reveal that significant thermal gradients exist in specimen along longitudinal and radial directions. Such thermal gradients will lead to phase fraction gradient in specimen at high temperature, such as 6 fraction gradient or liquid fraction gradient.All these gradients will contribute to the heterogeneous deformation of specimen and severe stress non-uniform distribution,which is the major difficulty for the identification of constitutive models,especially for the simple identification method based on nominal stress-strain.The proposed model can be viewed as an important achievement for further inverse identification methods,which should be used to identify constitutive parameters for steel at high temperature in the presence of thermal gradients.