镍基单晶高温合金的屈服准则研究

STUDY OF YIELD CRITERION FOR SINGLE CRYSTAL NICKEL-BASED SUPERALLOYS

将Hill屈服准则用于DD3单晶合金屈服应力的预测 ,通过与试验结果比较发现 ,在 760℃时的误差较大。根据单晶材料的屈服特点 ,考虑单晶合金偏轴受载时存在拉、剪应力耦合作用的情况 ,提出一个考虑拉、剪应力耦合能量分量 ,在工程上实用的单晶合金屈服准则 ,给出确定该屈服准则参数的方法 ,并重新定义适合新屈服准则的等效应力和等效应变。对各向同性材料 ,新屈服准则退化为vonMises屈服准则 ,新定义的等效应力和等效应变退化为vonMises等效应力和等效应变。在新屈服准则中出现的参数可以通过单向拉伸试验确定。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屈服准则相比 。

Hill's(1948) yield criterion for plastically orthotropic solids is used to predict the yield stresses of single crystal Nickel-based superalloys DD3, but the correlation to experiments at 760℃ is poor. Taking into account the effects that the components of tension and torsion stresses are coupled with each other, a new yield criterion for single crystal Nickel-based superalloys is put forward in term of the characteristics of single crystal Nickel-based superalloys. This new criterion can be applied to engineering conveniently. The method of figuring out coefficients of the new criterion is given in the paper. Equivalent stress and equivalent strain that adapt to the new criterion are defined. The new criterion, new equivalent stress and equivalent strain will degenerate to the von Mises's for isotropic material, and the coefficients that in the new criterion can be determined from uniaxial tension tests. Using the new criterion to predict the yield stresses of single crystal Nickel-based superalloys, the correlation to experiments is very good and more accurate than that of Hill's.