Evaluation of Mechanical Properties of Solid Propellants in Rocket Motors by Indentation Technique

It is essential to evaluate the mechanical properties of propellants in a solid propellant rocket motor (SPRM) for structural integrity and its performance evaluation before the flight test. Conventionally, uni‐axial tensile testing on an universal testing machine (UTM) is used to evaluate the mechanical properties of solid propellant carton which is cast along with SPRM. Propellants in rocket motors experience various types of loading during storage, transportation, and environmental conditions over the period of time before actual flight whereas the propellant carton doesn’t experience the same as it is stored in magazine. At present, the mechanical properties of propellant cast in a carton are considered to be the mechanical properties of propellant in a rocket motor, which is not truly representative. Therefore, a non‐destructive indentation technique has been used to establish a method for evaluating the mechanical properties of solid propellants in rocket motors based on hydroxyl terminated polybutadiene. The test results obtained using the penetrometer indentation technique was analyzed comprehensively and compared with UTM results. The mathematical correlations were also developed using least square method and established by conducting the penetrometer indentation test on similar propellant composition. Further, the developed correlation was used to evaluate the mechanical properties of propellant in flight SPRM by penetrometer indentation technique.     

Ultrasonic Investigation of Mechanical Properties of Double Base Rocket Propellants

For a series of double base rocket propellants and for poly- methylmethacrylate (PMMA) the longitudinal and transverse sound wave velocities are measured at a frequency of 0.351 MHz in t h e temperature range of −40°C to +60°C. The relations between these acoustic properties and mechanical properties are given and the principal independent elastic constants are calculated. With increasing temperature these constants of the propellants decrease gradually, which points to a softening of the material. This is important for the functioning of the propellant grains in the rocket motors.     

Sensitivity of Solid Rocket Propellants for Card Gap Test

Card gap test, which is standardized in Japan Explosives Society, was modified in order to apply it to solid rocket propellants and carried out to evaluate sensitivities against shock stimuli. Solid propellants tested here were mainly azide polymer composite propellants, which contained ammonium nitrate (AN) as a main oxidizer. Double base propellant, composed nitroglycerin and nitrocellulose (NC), and ammonium perchlorate (AP)-based composite propellants were also evaluated in order to compare with the azide polymer propellants. It is found that the sensitivity was dominated by the oxidizer characteristics. AP-and AN-based propellant had less sensitivity and HMX-based propellant showed higher sensitivity, and the adding of NC and TMETN were contributed to worse sensitive for the card gap test. Good relationship was obtained between the card gap sensitivity and the oxygen balance of propellants tested here.     

固体推进剂高过载冲击动态力学性能研究

综述了近年来固体推进剂受过载冲击时动态学响应研究的各种方法，分析对比了各种研究方法的优劣，讨论了未来固体推进剂受冲击载荷时动态力学性能研究的方向。     

Mechanical Properties of Smokeless Composite Rocket Propellants Based on Prilled Ammonium Dinitramide

Ammonium dinitramide (ADN) is a high performance solid oxidizer of interest for use in high impulse and smokeless composite rocket propellant formulations. While rocket propellants based on ADN may be both efficient, clean burning, and environmentally benign, ADN suffers from several notable disadvantages such as pronounced hygroscopicity, significant impact and friction sensitivity, moderate thermal instability, and numerous compatibility issues. Prilled ADN is now a commercially available and convenient product that addresses some of these disadvantages by lowering the specific surface area and thereby improving handling, processing, and stability. In this work, we report the preparation, friction and impact sensitivity and mechanical properties of several smokeless propellant formulations based on prilled ADN and isocyanate cured and plasticized glycidyl azide polymer (GAP) or polycaprolactone‐polyether. We found such propellants to have very poor mechanical properties in unmodified form and to display somewhat unreliable curing. However, by incorporation of octogen (HMX) and a neutral polymeric bonding agent (NPBA), the mechanical properties of such smokeless formulations were significantly improved. Impact and friction sensitivities of these propellants compare satisfactorily with conventional propellants based on ammonium perchlorate (AP) and inert binder systems.     

评估固体推进剂压强温度系数的方法

提出了目前评价压强温度系数所存在的问题,较系统地分析了压强温度系数的变化规律,建立了参比压强温度系数的计算方法。     

固体火箭推进剂用燃烧催化剂研究新进展

从纳米燃烧催化剂、含能催化剂和双金属燃烧催化剂三方面综述燃烧催化剂的研究新进展。总结了各类催化剂的特点和发展过程中的技术难题,指出燃烧催化剂的发展方向,如纳米催化剂的团聚抑制和催化机理、含能催化剂能量与感度的统一以及双金属催化剂的结构表征和含能化等。附参考文献55篇。     

固体推进剂燃烧波结构研究

设计了一套分析燃烧波结构的数值计算方法,可以利用热偶数据有效地分析均质推进剂固相反应的细节,为了解固体推进剂机理提拱了一种重要的手段;提出了均质推进剂也没有明显的固气界面的观点,因而也无表面温度可言;设计了固相反应热计算模型,提出了固相反应机理的观点,并指出压力不同固相反应机理基本相同,但固相放热程度不同;提出Π型热偶不宜测量非均质推进剂燃烧波结构的观点。     

Burning Mechanism of Aluminized Solid Rocket Propellants Based on Energetic Binders

This paper reports results obtained from an experimental study of the combustion mechanism of aluminized propellants based on an energetic binder. The techniques used in this investigation include:     

A New Method for Determining the Vapor Pressure of Nitroglycerine Above Solid Rocket Propellants

Measuring the vapor pressure of compounds such as nitroglycerine (NG) which have a low volatility has not been a straightforward task in the past. There are a wide range of values in the literature for the vapor pressure of NG and furthermore, there is little information regarding the vapor pressure of this compound above solid rocket propellant formulations. We have devised a new method for determining the vapor pressure of NG both above the pure material and solids containing this nitrate ester. The values obtained for pure liquid NG are in good agreement with some previously published values. It was also found that the vapor pressure of this compound is slightly lowered when it is incorporated into solid rocket propellant formulations.     

时温叠加法在轮胎混炼胶流变性能快检中的应用

研究高剪切速率条件下混炼胶加工性能的测试。针对混炼胶流变性能测试中存在的不能反应实际加工剪切速率区间流变性质的问题,基于时温叠加的原理,使用较低温度条件下三点相位角的高频动态扫描数据来预测混炼胶在高剪切速率下的加工性能。     

Thermomechanical Properties of Rocket Propellants and Correlation with cookoff behaviour

The cookoff behaviour of several plasticized HTPB/AP and HTPB/RDX propellants has been evaluated using the standard Small-Scale Cookoff Bomb (based on the NWC design) and a modified version of the standard equipment (whereby the reaction violence can be measured quantitatively) to investigate the effects of (1) plasticizer level on the thermomechanical properties and its role in moderating the cookoff response, and (2) heating rate. A change from slow to fast cookoff behaviour was observed for the plasticized HTPB/RDX propellants; the measured pressures/energy output at the slow heating rate were much lower than those at the fast heating rate for the same propellants. The thermal distribution/gradient at various positions and depths in the cylindrical propellant specimen, during fast and slow cookoff, were measured in order to understand the reversal in the severity of the response shown by the plasticized RDX propellants when the heating rate was changed. Thermomechanical properties of the propellants were measured and correlated with cookoff behaviour, to provide further insight into the cookoff mechanisms.     

A Nonlinear Viscoelastic Theory for Solid Rocket Propellants Based on a Cumulative Damage Approach

A uniaxial nonlinear viscoelastic constitutive equation incorporating cumulative damage was developed and used to successfully model three highly filled composite solid propellants, two based on hydroxy-terminated polybutadiene with an ammonium perchlorate oxidizer and the third on a glycidyl azide polymer with a phase stabilized ammonium nitrate oxidizer. The nonlinear component of the model consists of a strain rate term, a damage term and a nonlinear exponent. The cumulative damage function itself is calibrated using data from two constant strain rate tests at opposing extreme values of strain rate. Four parameters in the nonlinear viscoelastic model are calibrated at a reference strain rate(low rate of strain) for various conditions of cumulative damage and two parameters are calibrated at the opposing extreme rate of strain for the condition of total damage(i.e., when cumulative damage equals unity). The theoretical predictions at intermediate strain rates are very encouraging, providing a good correlation with the experimental stress--strain data measured under uniaxial constant strain rate loading conditions. The incorporation of cumulative damage theory into the nonlinear viscoelastic constitutive equation enables the strength and failure time to be quantitatively defined in terms of the damage history. Predicted values of strength versus failure time and strength versus constant strain rate at the condition when the cumulative damage equals unity, agree reasonably well with the observed experimental results.     

Mechanical Properties of Plateau Burn Azide Composite Propellants

The effects of cure ratio, crosslinking density, ammonium perchlorate (AP) particle size, and other additives on the mechanical properties of azide polymer composite propellants were characterized. The equivalence ratio of 1.0 and IPDI/TPA=7/3 were effective on low temperature mechanical properties. Relatively high amount of plasticizer was required in BAMO/NMMO binder and preferred the equivalence ratio of 1.0 to retain itself in the three-dimensional binder matrix. Excellent elasticity was obtained at a temperature range between −20°C and 2°C and normal strain rate dependency was obtained at from 54°C to −20°C. Glass transition occurred at −30°C to −35°C in Sample 17. The increase in contact area between AP particle and binder and in bonding strength played an important role on the prevention of the propagation of crack around a boundary and, therefore, ϵ_m was increased with decrease of particle size. Almost exactly the same σ_m, however, was observed in whole temperature range with increment of 5% to 10% in ϵ_m.     

Combustion Behavior and Thermochemical Properties of RDX-Based Solid Propellants

The combustion behavior and thermochemical properties of two types of RDX-based composite propellants, XM39 and M43, are studied and compared in order to investigate the effect introduced by an energetic ingredient in the M43 propellant formulation. Due to the enhanced rate of heat release on the burning surface caused by the energetic material of M43 propellants, the burning rate of M43 propellants is found to be higher than that of XM39 propellants. The presence of the energetic material in the M43 propellant formulation also increases the burning surface temperature and thermal diffusivity of M43 propellants; it does not, however, introduce any observed changes in the flame structure and the heat feedback from the gas phase to the condensed phase. Based upon SEM pictures, burning-surface structures of the recovered XM39 and M43 propellant samples are found to be significantly different, indicating the strong effect of the energetic material on the surface reaction. A set of important thermochemical properties of XM39 and M43 propellants is deduced from the experimental data.     

发射药抗冲击力学性能研究进展

综述了利用落锤法、摆锤法、数值仿真等方法研究发射药抗冲击力学性能的研究状况,并介绍了从发射药微观结构研究其力学性能的研究进展。     

Maxwell Fluid Model for Generation of Stress–Strain Curves of Viscoelastic Solid Rocket Propellants

Solid rocket propellants are modeled as Maxwell Fluid with single spring and single dashpot in series. Complete stress–strain curve is generated for case‐bonded composite propellant formulations by taking suitable values of spring constant and damping coefficient. Propellants from same lot are tested at different strain rate. It is observed that change in spring constant, representing elastic part is very small with strain rate but damping constant varies significantly with variation in strain rate. For a typical propellant formulation, when strain rate is varied from 0.00037 to 0.185 per second, spring constant (K) changed from 5.5 to 7.9 MPa, but damping coefficient (D) varied from 1400 to 4 MPas. For all strain rates, stress–strain curve is generated using developed Maxwell model and close matching with actual test curve is observed. This indicates validity of Maxwell fluid model for case‐bonded solid propellant formulations. It is observed that with increases in strain rate, spring constant increases but damping coefficient decreases representing solid rocket propellant as a true viscoelastic material. It is also established that at higher strain rate, damping coefficient becomes negligible as compared to spring constant. It is also observed that variation of spring constant is logarithmic with strain rate and that of damping coefficient follows a power law. The correlation coefficients are introduced to ascertain spring constants and damping coefficients at any strain rate from that at a reference strain rate. Correlation for spring constant needs a coefficient “H,” which is function of propellant formulation alone and not of test conditions and the equation developed is K₂=(K₁‐H)×{ln(dε₂/dt)/ln(dε₁/dt)}+H. Similarly for damping coefficient (D) also another constant “S” is introduced and prediction formula is given by D₂=D₁×{(dε₂/dt)/(dε₁/dt)}^S. Evaluating constants “H” and “S” at different strain rates validate this mathematical formulation for different propellant formulations. Close matching of test and predicted stress–strain curve indicates propellant behavior as viscoelastic Maxwell Fluid. Uniqueness of approach is to predict complete stress–strain curves, which are not attempted by any other researchers.     

Prediction and Comparison of Shelf Life of Solid Rocket Propellants Using Arrhenius and Berthelot Equations

The Arrhenius equation and the Berthelot equation for the prediction of shelf life of composite propellant formulations are compared. The elongation has a measurable variation with time and is taken as the fastest degrading parameter for HTPB/AP/Al based composite solid rocket propellants. An HTPB based aluminized composite propellant with 85 % solid loading and an initial elongation of 63.24 % is prepared. It is kept at an elevated temperature of 60 °C to achieve a higher rate of degradation for a prolonged time period (1 year). The elongation is monitored at regular intervals using JANNAF class C dog bone specimen in uni‐axial tensile mode. A reduction of the elongation to less than 50 % is taken as the end‐of‐shelf life of the propellant. The shelf life of the propellant is calculated to be 1.2 years at 60 °C. For the extrapolation of the shelf life at 60 °C to the shelf life at 27 °C, the results of both the Arrhenius equation and the Berthelot equation are compared. The activation energy (E) in the Arrhenius equation is obtained as 72.8 kJ mol⁻¹ and the 10 °C reaction rate rise factor (γ₁₀) is found to be 2.4. This comparison is independent of the propellant formulation and other researchers have reported a similar range of values for these parameters. The shelf life of this propellant formulation at 27 °C is conservatively predicted to be 20 years using both equations. In addition to estimation of shelf life by both equations using elongation as control parameter, this paper gives scaling curves, which are valid universally for predicting shelf life at 27 °C from data of shelf life at 60 °C. The use of scaling curves is independent of properties, propellant formulation and degradation mechanism considered for analysis.     

辅助增塑剂对AP-CMDB推进剂力学性能的影响

为解决高氯酸铵基复合改性双基(AP-CMDB)推进剂易出现高温过软、低温过脆的力学性能问题,研究了多种辅助增塑剂对AP-CMDB推进剂力学性能的影响。结果表明:固体辅助增塑剂吉纳(DINA)和1,3,3-三硝基氮杂环丁烷(TNAZ)可明显改善AP-CMDB推进剂高温条件下(50℃)的力学性能;液体辅助增塑剂聚缩水甘油醚硝酸酯(PGLYN)、双叠氮乙二醇二乙酸酯(EGBAA)及三羟甲基乙烷三硝酸酯(TMETN)可提高AP-CMDB推进剂-40℃的力学性能。所选择辅助增塑剂中TNAZ和TMETN的增塑效果最佳。