Structural Integrity Analysis Of Gun Launched Missile Engine Charge

With the index of weapons for a long range increasing in recent decades,a variety of technologies for extending the range of weapons are utilized by a range of weapons.As one of the most widely utilized technology for extending weapons’range,the gun launched rocket extended range technology has been studied deeply by several researchers around the world.Due to that the need for gun launched rocket to bear a huge launching load during the launching stage as well as the high pressure from the ignition,it is significant to pay attention to the effect of impact on the structural integrity of propellant.In current study,the machinal response curves of modified double base propellant under different temperatures in the range of high strain rate of 10³～10⁴s^-1 and low strain rate of 10^-4～10^-1s^-1 were obtained by quasi-static compression test and high-strain rate Hopkinson bar test.It was clearly that the propellant has obvious temperature and rate dependent phenomena,indicating that the material is typically viscoelastic.Furthermore,the results shown that the propellant has obvious strain rate hardening effect under all temperature conditions.The variation of temperature could make the material appear the phenomenon of stress softening.The maximum stress of the material decreases with the increase of temperature while the viscoelastic characteristics of the material at low temperature are not obvious,and its characteristics are more similar to brittle materials.Therefore,current study chose the ZWT nonlinear viscoelastic constitutive model which can describe the material’s low strain rate performance and high strain rate performance at the same time.Through fitting the experimental data attained,it was found that ZWT model could accurately indicate the mechanical behavior of materials under both high and low strain rates.Due to the lack of ZWT constitutive model in the commercial finite element software ABAQUS,and thus current study imported the constitutive model by writing VUMAT subroutine.Firstly,the one-dimensional ZWT nonlinear constitutive model was extended to three-dimensional form.Subsequently,the three-dimensional form was rewritten to the incremental form,and then the incremental form was written into VUMAT subroutine by using FORTRAN language and inserted into ABAQUS for subsequent calculation.After testifying that simulated results agree with the experimental results in the range of 10%,the constitutive model could be thought to be applied to the structural integrity analysis of an engine.By assigning the analysis of mechanical response of the charge under different temperatures,the stress and strain curves of the charge at low temperature,ambient temperature and high temperature were obtained,and the mechanical response of the charge under different temperatures was contrasted.The simulated results shown that for the same temperature charge,the stress and strain caused by firing overload was higher than that under ignition load,and the maximum point of stress and strain occurred at the contact position between the end face of the grain bottom and the cushion vent.Comparing the results under different temperatures,it could be found that the grain stress was higher and the strain was lower at low temperature.On the contrary,if the strain was taken as the criterion to check the structural integrity at high temperature,the grain at low temperature may be in a more dangerous situation,while the grain at normal temperature and high temperature is safer.The cushion with different elastic modulus and thickness was taken as variable to compare the effect of different cushion on the mechanical response of grain.The results shown that the cushion with low elastic modulus could improve the stress and strain of grain at the position of vent,while the cushion with high elastic modulus could cause less stress and strain at the center of grain.By changing the thickness of the cushion,it could be found that the cushion thickness had no obvious effect on reducing the stress concentration near the vent,but it had a better effect on reducing the stress and strain in the center of the grain and other areas with the same radius as the vent.In current study,the structural integrity of solid rocket motor charge was analyzed systematically,which provided a theoretical basis for the design of solid rocket motor in the future.