镍基单晶合金弹塑性本构模型

Hill模型用于面心立方单晶的弹塑性变形,在描述屈服特性的晶向相关性时精度不高。考虑正交各向异性材料在偏轴受载时存在拉、剪应力耦合效应的影响,通过增加一项由应力偏张量分量的二次项乘积构成的应力不变量,对Hill屈服模型进行修正,并根据单晶合金的屈服特点提出了新的单晶合金屈服准则。用该屈服准则对DD3单晶合金的屈服应力进行预测,760℃时能很好地符合试验结果;与Hill屈服准则比较,预测精度显著提高。在此基础上,重新定义了适合新屈服准则的等效应力,并由联合流动法则,以屈服函数作为塑性势函数,采用等向硬化模型,建立了单晶合金的弹塑性本构模型,推导出相应的弹塑性矩阵。对于各向同性材料,新屈服准及其等效应力则退化为VonMises屈服准则和其相应的等效应力。 

Study of Elastic-Plastic Constitutive Model for Single Crystal Nickel-Based Superalloy

The correlation of crystal orientation to yield characteristic of FCC single crystal is not good when Hill's (1948) yield criterion is used to describe the elastic-plastic deformation of FCC single crystal.Taking into account the effects that the components of tension stress are coupled with components of torsion stress when off-axis loads are applied to orthotropic material,Hill's yield criterion for plastically orthotropic solids is modified by adding an invariant which is composed of quadratic product item of components of deviatoric stress tensor,as a results,a new yield criterion for single crystal Nickel-based superalloy is put forward in the present paper in terms of the characteristics of single crystal Nickel-based superalloy.Using the new criterion to predict the yield stresses of single crystal Nickel-based superalloy DD3,the correlation to experiments is very good and more accurate than that of Hill's at 760℃.Equivalent stress adapted to the new criterion is defined.Thinking of the yield function as a plastic potential function from the associated flow rule and with reference to the isotropic hardening model,the elastic-plastic constitutive model for single crystal Nickel-based superalloy is constructed and the corresponding elastic-plastic matrix is educed.New yield criterion and its equivalent stress will be reduced to Von Mises yield criterion and corresponding equivalent stress for isotropic material.