考虑围压效应的NEPE推进剂药柱结构完整性分析

Structural Integrity Analysis of NEPE Propellant Grain Considering Confining Pressure

关键词:  NEPE推进剂  围压  结构完整性  双剪强度准则  安全系数

Key words:  NEPE propellant  Confining pressure  Structural integrity  Twin shear strength criterion  Safety factor

摘要:

为研究围压效应对NEPE推进剂药柱结构完整性的影响，对包含围压效应的含损伤非线性粘弹性本构模型进行了增量推导，编制本构模型的UMAT子程序对NEPE药柱在点火增压载荷下的力学响应及结构完整性进行了分析。结果显示：围压效应对NEPE推进剂药柱力学响应的影响与损伤应变阈值有关，当药柱的应变响应低于0围压下NEPE推进剂的损伤应变阈值时，围压效应对药柱的力学响应的影响可忽略；当药柱的应变响应高于0围压下NEPE推进剂的损伤应变阈值时，药柱应力响应增大、应变响应降低。5.4MPa围压作用使药柱最大等效应力增加约26%，等效应变降低约12%。围压的压实作用能够大幅降低药柱的损伤程度，5.4MPa的围压作用可降低损伤系数约40%左右。考虑围压效应时采用双剪强度准则和Von Mises应力准则计算得到药柱安全系数分别为3.06和2.11，未考虑围压效应时采用传统的Von Mises应力准则计算得到药柱安全系数为1.97，围压效应可明显提高药柱安全系数，传统的发动机药柱结构完整性评估方法趋于保守。

Abstract:

In order to investigate the effects of confining pressure on the structural integrity of NEPE propellant grain， the incremental derivation of the nonlinear viscoelastic constitutive model with damage and confining pressure was carried out， and the UMAT subroutine of the propellant material constitutive model was complied. The mechanical responses and structural integrity of NEPE propellant grain under ignition pressurization were evaluated. The results show that the effects of confining pressure on the mechanical response of NEPE propellant grain are associated with damage strain threshold， when the strain response of the grain is less than the damage strain threshold value of NEPE propellant without confining pressure， the confining pressure has little effect on the mechanical response of grain. The stress response of grain increased and the strain reduced compared without confining pressure when the strain response of the grain was higher than damage strain threshold value of NEPE propellant. The maximum equivalent stress increased 26% and maximum equivalent strain decreased 12% with the confining pressure of 5.4MPa. The compacting effect of confining pressure can significantly decrease the damage of propellant grain， the damage coefficient reduced about 40% with the confining pressure of 5.4MPa. When considering the confining pressure effect， the safety factor of the grain obtained by twin shear strength criterion and Von Mises stress criterion were 3.06 and 2.11， respectively. When the confining pressure effect was not considered， the safety factor obtained by the traditional Von Mises stress criterion was 1.97. The confining pressure effect can improve safety factor significantly， and the traditional method of structural integrity assessment is conservative.