改性双基推进剂非线性本构模型及其数值实现

Nonlinear constitutive model and numerical implementation of modified double⁃base propellant

为分析改性双基(CMDB)推进剂在复杂载荷下的力学响应,建立了一种含损伤变量的CMDB推进剂非线性粘弹性本构模型。鉴于CMDB推进剂的拉压不对称性,通过单轴拉伸、单轴压缩以及对应的松弛试验获得本构模型中的关键参数。当使用含应变和应变率的双指数形式表征与应变率呈“负相关”的损伤变量时,CMDB推进剂的非线性力学行为能被准确地描述。同时,引入体积应变作为拉伸和压缩条件的判定变量,发展出基于User-Material Subroutine(UMAT)子程序的非线性本构模型数值实现方式。将该考虑拉压不对称性的本构模型及数值实现方式应用于燃气发生器药柱在点火冲击载荷作用下的力学响应分析,并与单一拉伸参数分析结果进行对比。结果表明,考虑拉压不对称性时,结构的等效应变和损伤变量与使用单一拉伸参数时的分析结果存在显著差异。因此,判断结构的拉压状态并选用正确参数具有重要意义。

In order to analyze the mechanical response of modified double⁃base(CMDB)propellant under complex loads,a nonlinear viscoelastic constitutive model of CMDB propellant with damage variables was established.In view of the tensile⁃compres⁃sion asymmetry of CMDB propellant,the key parameters in the constitutive model were obtained by uniaxial tensile,uniaxial com⁃pression and corresponding relaxation tests.The nonlinear mechanical behavior of CMDB propellants can be accurately described when the damage variable negatively correlated with strain rates was characterized by means of a double exponential form with strain and strain rate.At the same time,volume strain was introduced as the determinant variable of tensile and compression conditions,and a numerical implementation method of nonlinear constitutive model based on UMAT subroutine was developed.The constitutive model considering tensile⁃compression asymmetry and its numerical implementation method were applied to the mechanical response analysis of the gas⁃generator grain under ignition impact load,and the analysis results were compared with those of single tensile pa⁃rameters.The results show that when tensile⁃compression asymmetry is considered,the equivalent strain and damage variable of the structure are significantly different from the analysis results using single tensile parameters.Therefore,it is of great significance to judge the tensile and compressive state of the structure and select the correct parameters.