低应变率下NEPE推进剂“双屈服”特性及其粘-弹-塑性屈服模型

‘Double yield’characteristics and visco-elastic-plastic yield model of NEPE propellant at low strain rate

固体发动机全寿命周期中,推进剂药柱长期处于低应变率状态。为了分析硝酸酯增塑聚醚(NEPE)推进剂在低应变率下的屈服与损伤特性,开展了NEPE推进剂在低应变率(1.190×10^(-5)~2.381×10^(-2)s^(-1))下的单轴拉伸试验。研究表明,NEPE推进剂的应力-应变曲线呈“双屈服”态,最大抗拉强度、断裂强度随拉伸速率的下降而明显下降,但初始屈服点(“脱湿点”)与后继屈服点不受应变率的影响,两级屈服点应变近似保持一个稳定值,分别为13.5%和55.4%。因此,可将“脱湿点”应力视为推进剂的屈服强度。在此基础上,构建了NEPE推进剂粘-弹-塑性屈服模型,通过引入动屈服函数,建立了动屈服强度、粘塑性应变率与静屈服强度之间的关系。结合试验数据,NEPE推进剂静屈服强度为0.22 MPa。

Throughout the operational lifespan of a solid rocket motor,the propellant grain endures pro⁃longed exposure to low strain rates.To investigate the yield and damage characteristics of nitrate ester plasticized polyether(NEPE)propellant under such conditions,a series of uniaxial tensile tests were conducted within the low strain rate regime(ranging from 1.190×10^(-5)s^(-1)to 2.381×10^(-2)s^(-1)).The findings reveal a‘double yield’phe⁃nomenon in the stress-strain curve of NEPE propellant.Notably,the maximum tensile strength and fracture strength exhibit a conspicuous decline with decreasing tensile rates.However,the initial yield point(referred to as the‘dewetting point’)and the subsequent yield point remain unaffected by changes in the strain rate.More⁃over,the strain values at these two-stage yield points(13.5%and 55.4%)exhibit relative stability over varying strain rates.Consequently,the stress at the‘dewetting point’can be deemed representative of the propellant's yield strength.Built upon this foundation,the visco-elastic-plastic yield model of NEPE propellant was developed.Through the introduction of the dynamic yield function,a relationship between dynamic yield strength,vis⁃coplastic strain rate,and static yield strength was established.The static yield strength of NEPE propellant,de⁃termined through integration with experimental data,is 0.22 MPa.