基于热力学理论的固体推进剂粘弹-粘损伤本构模型

Thermodynamics-Based Viscoelastic-Viscodamage Constitutive Model for Solid Propellant

关键词:  固体推进剂  粘弹性  力学特性  损伤  本构模型

Key words:  Solid propellant  Viscoelasticity  Mechanical performance  Damage  Constitutive model

摘要:

为了描述固体推进剂在不同应变率和围压环境下的非线性力学特性，首先假设推进剂非线性力学特性由损伤导致，基于不可逆热力学框架，推导出粘弹-粘损伤本构模型。在构建粘损伤模型时，以线性粘弹性应变能密度为损伤驱动力，引入了损伤历史、应变率和围压效应对损伤增长的影响。然后利用文献中HTPB推进剂的围压实验数据对一维形式下的本构模型进行了参数获取、验证和预测误差分析。在获取损伤萌发参数S₀时，基于时间-压强等效原理，构建了损伤萌发参数S₀主曲线。最后采用NEPE推进剂单轴拉伸实验验证了本构模型对于当前固体推进剂大变形非线性力学性能的适用性。结果表明，损伤萌发参数S₀随着围压和应变率的增加而增加。在应变率和围压的双重作用下，在相对压强5.516MPa、应变率0.24s^-1条件下的S₀值是相对压强0MPa、应变率6×10^-4s^-1条件下S₀值的10.7倍。另外，模型对于HTPB推进剂抗拉强度的最大预测误差为6.15%，模型预测结果与两种实验数据重合较好，表明建立的粘弹-粘损伤本构模型可以很好地预测HTPB推进剂在不同应变率及围压环境下的力学响应和当前NEPE推进剂的大变形非线性力学行为，可为点火增压载荷下固体推进剂药柱结构完整性数值分析提供理论基础。

Abstract:

To describe the nonlinear mechanical properties of solid propellant under various strain rates and confining pressure conditions， through assumping that nonlinear mechanical properties were induced by the damage， and based on the framework of irreversible thermodynamic， a new viscoelastic-viscodamage constitutive model was firstly developed. In the proposed viscodamage model， the linear viscoelasticity strain energy density was used as the damage driving force， and the effects of damage history， strain rate and confining pressure on the growth of damage were considered. Then， through the experimental data of the literature， the model parameters identification， validation and the relative errors analysis of one-dimensional version of the constitutive model were carried out. Based on the time-pressure superposition principle， the master curve of damage initiation parameter S₀ was constructed. Finally， the uniaxial tension tests of NEPE propellant were conducted to verify the applicability of the developed constitutive model to the large-deformation nonlinear mechanical properties of current solid propellant. The results show that the damage initiation parameter S₀ increases with the increasing of confining pressure and strain rate. With the coupled effects of confining pressure and strain rate， the value of S₀ at relative atmospheric pressure 5.516MPa and 0.24s^-1 is 10.7 times of its value at relative atmospheric pressure 0MPa and 6×10^-4s^-1. In addition， the maximum relative error of maximum strength of the model predictions is 6.15% for HTPB propellant. The model predictions are in good agreement with the two kinds of experimental results， indicating that the established constitutive model can well predict the mechanical responses of HTPB propellant under different strain rates and confining pressure conditions， as well as the large-deformation nonlinear mechanical behaviors of current NEPE propellant. It can provide a theoretical basis for the numerical analysis of the structural integrity of solid propellant grains under ignition pressurization loading.