改进Logistic蠕变应变预测模型及其有限元实现

Modified Logistic Creep Strain Prediction Model and Its Finite Element Implementation

提出一种针对蠕变全过程的改进Logistic蠕变应变预测(Logistic creep strain prediction,LCSP)模型,减少模型参数数量并解决初始蠕变应变复数值问题,结合加钒改进型2.25Cr1Mo钢的蠕变变形与断裂寿命数据,利用基于最小二乘法原理的模型参数识别方法,实现对材料的蠕变应变及应变速率的准确预测。综合分析Larson-Miller主曲线方程的寿命预测精度及寿命随应力的变化趋势,确定用于预测蠕变断裂寿命的模型多项式阶数。根据改进LCSP模型的蠕变应变解析公式,推导蠕变应变增量及其对等效应力以及蠕变应变的导数的计算表达式,确保计算收敛性,利用Fortran语言开发了针对改进LCSP模型的usercreep蠕变子程序,通过光滑圆棒试样蠕变有限元分析验证该蠕变子程序的准确性。

A modified logistic creep strain prediction(LCSP)model for the whole creep process is proposed to reduce the number of model parameters and to solve the complex value problem of initial creep strain.Combined with the data of creep deformation and rupture life of the vanadium-modified 2.25Cr1Mo steel,the model parameter identification method based on the principle of least square method is used to accurately predict the creep strain and its strain rate of materials.The life prediction accuracy of the Larson-Miller master curve equation and the variation trend of rupture life with stress are comprehensively analysed,and hence the order of the polynomial in the model that is used to predict the creep rupture life is determined.According to the analytical formula of the creep strain in the modified LCSP model,the calculation expressions of the creep strain increment and its derivatives to the equivalent stress and to the creep strain are derived,in order to ensure the calculation convergence.The usercreep subroutine for the modified LCSP model is developed by using Fortran language.The accuracy of the creep subroutine is verified through the finite element analysis of creep for the smooth round bar specimen.