Mechanical Properties Of Propellants Research Articles

Microencapsulation of ADN with HTPB‐based membrane in the presence of the bonding agents Tepan or Tepanol**

AbstractAmmonium dinitramide (ADN) has appeared as a promising oxidizer for green propellants and thereby a potential substitute for ammonium perchlorate, largely in use in composite propellants for tactical and strategic long‐range missiles. The novelty lies in replacing ammonium perchlorate with a chlorine‐free oxidizer less harmful to the health and environment. However, ADN is hygroscopic and can potentially react with other chemical components, which could be overcome by microencapsulating the particles. The simple coacervation method was tested herein to microencapsulate ADN with a membrane made of hydroxyl‐terminated polybutadiene as pre‐polymer and methylene diphenyl diisocyanate as the curing agent. The effect of polyamine bonding agents on the capsule formation was tested by adding 0.5 or 2 % of Tepan or Tepanol, whose efficacy to bond to ADN was confirmed by detecting ammonia release through infrared spectroscopy. The capsule membrane was examined by optical and scanning electron microscopy. The dissolution time and rate were the parameters adopted to quantify permeability in a straight dissolution test in water, which demonstrated that 0.5 % Tepanol can provide the most effective protection. The infrared spectroscopy indicated that 60 °C temperature for prolonged periods, normally experienced by propellants, does not chemically affect the capsules’ membrane but can turn it lumpy. In conclusion, these polyamine bonding agents can assist the capsule formation over ADN particles using the simple coacervation method, however, their functionality on mechanical properties of propellants needs to be substantiated in forthcoming works as well as the effect of the concentration of bonding agents on propellant formulations.

Numerical Conversion Method for the Dynamic Storage Modulus and Relaxation Modulus of Hydroxy-Terminated Polybutadiene (HTPB) Propellants.

As a typical viscoelastic material, solid propellants have a large difference in mechanical properties under static and dynamic loading. This variability is manifested in the difference in values of the relaxation modulus and dynamic modulus, which serve as the entry point for studying the dynamic and static mechanical properties of propellants. The relaxation modulus and dynamic modulus have a clear integral relationship in theory, but their consistency in engineering practice has never been verified. In this paper, by introducing the "catch-up factor λ" and "waiting factor γ", a method for the inter-conversion of the dynamic storage modulus and relaxation modulus of HTPB propellant is established, and the consistency between them is verified. The results show that the time region of the calculated conversion values of the relaxation modulus obtained by this method covers 10-8-104 s, spanning twelve orders of magnitude. Compared to that of the relaxation modulus (10-4-104 s, spanning eight orders of magnitude), an expansion of four orders of magnitude is achieved. This enhances the expression ability of the relaxation modulus on the mechanical properties of the propellant. Furthermore, when the conversion method is applied to the dynamic-static modulus conversion of the other two HTPB propellants, the results show that the correlation coefficient between the calculated and measured conversion values is R2 > 0.933. This proves the applicability of this method to the dynamic-static modulus conversion of other types of HTPB propellants. It was also found that λ and γ have the same universal optimal value for different HTPB propellants. As a bridge for static and dynamic modulus conversion, this method greatly expands the expression ability of the relaxation modulus and dynamic storage modulus on the mechanical properties of the HTPB propellant, which is of great significance in the research into the mechanical properties of the propellant.

Biaxial tensile test and meso damage numerical simulation of HTPB propellant

Aiming at the shortcomings of the current research on the mechanical properties of solid propellants under complex stress conditions, an effective cross-shaped test piece configuration and variable-scale biaxial tensile test method are designed in this paper, and the meso-simulation model of propellant is constructed by Micro-CT test and random filling algorithm. Then, based on the Hook-Jeeves method and the cohesive force model, the mechanical performance parameters of each mesoscopic component were obtained, and finally the damage evolution process of the propellant was numerically simulated. The results show that the stress–strain curve of the propellant under biaxial loading is similar to that of uniaxial stretching, and has obvious rate dependence and stress state dependence. The mechanical properties of the propellant under biaxial tensile loading are significantly lower than those in uniaxial stretching, and the maximum elongation is only 45–85% of that in uniaxial stretching. The fracture process of propellant can be divided into initial linear stage, damage evolution stage and fracture stage. The dewetting phenomenon generally occurs at the interface between the large-sized AP particles and the matrix. With the loading of the load, the pores formed by the dewetting and matrix tearing continue to converge into cracks and expand in the direction perpendicular to the resultant force, and finally fracture. The propellant dehumidifies more easily under high strain rate loading, but the degree of dewetting is lower when the same strain is reached.

Research on Constant Speed Tension and Compression Mechanical Properties of Azide Polyether Propellant

AbstractAzide polyether propellant is a new type of high‐energy solid propellant with broad application prospects. In order to measure the mechanical properties of azide propellant, tensile tests of propellant under different loading conditions were carried out, and compression test pieces of azide propellant of different sizes were designed and tested, and the tensile and compressive stress‐strain curves of azide propellant were obtained. Through qualitative and quantitative analysis, the influence law of loading rate and temperature on the mechanical properties of propellant was obtained, the linear variation law of mechanical properties parameters with logarithmic strain rate was analyzed, and the mathematical relationship between propellant stiffness and strength was found. The master curve of the compressive initial modulus and maximum strength of the azide propellant was drawn. The test results can provide theoretical basis for the performance research of azide propellant and the nondestructive testing of this type of engine.

Study of the Mechanical Properties of a CMDB Propellant Over a Wide Range of Strain Rates Using a Group Interaction Model

Composite modified double base (CMDB) propellants are heterogeneous propellants in which properties are significantly improved by adding solid particles into the polymer matrix. A molecular group interaction model that can predict the mechanical properties of polymers through a molecular structure is used to predict the viscoelastic behavior of the CMDB propellant. Considering that the addition of solid particles will improve the crosslinking degree between polymer molecules and reduce its secondary loss peak, the input parameters of the model are modified through dynamic mechanical analysis (DMA) experimental data. By introducing the strain rate into the expression of model glass transition temperature, the mechanical properties of propellant over a wide strain range ( 1.7 × 10 − 4 s-1 ~ 3000 s-1) are obtained. The reliability of the model is verified by comparison with uniaxial compression test data. By modifying the input parameters of the model, the effects of different mass ratios of nitrocellulose (NC)/nitroglycerin (NG) on the mechanical properties of the CMDB propellant were analyzed. The results show that the glass transition loss increases with increasing mass ratio of NC/NG, while Young’s modulus and yield stress decrease.

Energy characteristics and mechanical properties of cyclotrimethylenetrinitramine (RDX)-based insensitive high-energy propellant

In order to improve the energy performance and mechanical properties of insensitive high-energy propellants, cyclotrimethylenetrinitramine (RDX)-based insensitive high-energy propellant with nitrocellulose (NC) and glycidyl azide polymer-energetic thermoplastic elastomer (GAP-ETPE) blends as the binder was prepared by solvent method. The effects of GAP-ETPE/NC ratio and RDX content on the energy properties of propellants were analyzed by numerical calculations. The effects of GAP-ETPE/NC ratio, RDX particle size and RDX content on the mechanical properties of propellants were studied by compression test, impact test and solid surface properties test. The impact sensitivity and friction sensitivity of all the propellant compositions were tested. The theoretical calculation results showed that the introduction of GAP-ETPE into propellant significantly decreased the explosion temperature and increased the specific volume. The density, compression strength, and surface energy of the propellant were gradually decreased with increasing the GAP-ETPE/NC ratio, and the impact strength was increased gradually as well. The mechanical properties and surface energy of the propellant were improved greatly when the RDX particles were smaller. The studied propellants showed a linear increase in the propellant force and explosion temperature with increasing the RDX content. However, increasing the RDX content significantly reduced the impact strength and surface energy. Mechanical reinforcement with solid fillers increased the compression strength and propellant density to a certain degree. Compared with the standard propellants SF-3, the prepared propellant composition is insensitive to the impact and friction.

An alternative approach to improve burning rate characteristics and processing parameters of composite propellant

Modification in burn rate of composite solid propellant has become a necessity of a mission. Burn rate can be modified by various mean viz. (i) tailoring the ammonium perchlorate (AP) particle size, (ii) use of nano-sized particles and (iii) incorporating burn rate modifiers. Literature discusses about various burn rate modifiers. Out of these, Iron oxide (Fe2O3)/IO is the well known burn rate enhancer. Here a systematic study was carried out by undertaking experiments at varying levels of IO in composite propellant compositions. This paper attempts to understand the effect of IO content and its specific surface area on burn rate characteristics of composite propellant. This study also attempts to find out alternative to ultrafine AP and nano burn rate enhancer to account for high burning rate of composite propellant along with reduced slurry viscosity and longer pot life for easy processing. As ultrafine AP and nano burn rate enhancers have their limitations in terms of (i) high end of mix (EOM) propellant slurry viscosity, (ii) difficulty in propellant processing, (iii) less reproducibility in attaining the similar particle size in each batch results in lesser repeatability in ballistic properties of propellant, (iv) hazards involved in size reduction, (v) limitations in handling, storage and shelf life and also (vi) the higher cost of nano particles. Therefore an extensive experimental study was performed to achieve this objective. In this study, we incorporated two different grades of IO(A) and IO (B) in composite propellant compositions. The average particle size of both grades of IO i.e., A and B are of ∼1 µm. But the specific surface area of IO (B) was about 15 times more than IO (A). The large difference in specific surface area of both IO was due to difference in the manufacturing process. During the manufacturing of IO, the calcination temperature plays very important role in deciding the specific surface area. High specific surface area is obtained if calcination is done at very high temperature (>1773 K). Burning rate measurements were carried out. It was observed that IO is a good burn rate enhancer. Initially, the burn rate increased with the increase in % of IO. But after that only a marginal enhancement in burn rate was observed. It was noticed that though both grades of IO are effective burn rate enhancer but IO(B) was 30% more effective than IO(A). Also it was found that IO(B) is an alternative to ultrafine AP and nano burn rate modifiers. This IO(B) was further used to develop the propellant compositions with high burn rate without incorporating ultrafine AP and nano particles. Viscosity measurement and mechanical properties determination revealed that both the IOs did not much adversely alter the processing characteristics and mechanical properties of propellant.

A Facile Way to Prolong Service Life of Double Base Propellant.

The safe storage time for double base propellant (DBP or DB propellant) with stabilizers could usually be calculated to be greater than 40 years. However, the actual service life is far below that, which is largely caused by the decline of propellant mechanical performance. In this work polytetrafluoroethylene (PTFE) was introduced into the double base propellant formula as an additive. The tensile properties of this propellant before and after artificial aging were determined. The evaporation and diffusion characteristics of nitroglycerin (NG) in propellant were evaluated by thermogravimetry analysis (TGA). The results showed that mechanical properties of propellant were improved due to PTFE, especially for elongation at −40 °C, which was greatly increased by 115%. Moreover, the results of TGA showed that NG migration was reduced due to PTFE, which delayed the decline of propellant mechanical performance during aging. The reduction in elongation at −40 °C caused by aging was decreased by 68.5% for PTFE modified DBP. Enhanced mechanical properties and reduced NG migration could potentially prolong propellant service life.

Research Progress of Bonding Agents for Nitramine Composite Solid Propellants

This review article summaries the method to improve mechanical properties of nitramine composite solid propellants. It concludes that the use of bonding agents is an economical, effective and convenient way to enhance the mechanical properties of propellants. The bonding mechanism and characteristics of bonding agents are analyzed. The review article presents the overview on the types and development of bonding agents for nitramine composite solid propellants. It is considered that the multi-functionalization of polymer bonding agents is a development direction of bonding agents. According to the surface characteristics of nitramine fillers and the structure characteristics of different binders, a universal bonding agent suitable for different binder-nitramine systems should be prepared through molecular design. Some suggestions are put forward for the design of universal bonding agents.

HTPB 바인더의 화학적 구조에 따른 추진제의 유변학적, 기계적 특성 연구

HTPB 바인더의 화학적 구조에 따른 추진제의 유변학적, 기계적 특성 연구

Probing the compatibility of energetic binder poly-glycidyl nitrate with energetic plasticizers: thermal, rheological and DFT studies

The essential idea of developing energetic binders and plasticizers is to enhance the thermal stability and energy content, reduce the glass transition temperature and improve other mechanical properties of propellant and explosives formulations.

Surface Coating of Nitroamine Explosives and Its Effects on the Performance of Composite Modified Double-Base Propellants

T HE traditional high-energy nitroamine explosives, cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX), have been widely used in many plasticbonded explosives, propellants, and powders due to their high energy performance, smokeless combustion products, and low price [1–4]. The content of nitroamine explosives exceeds 80% in some composite modified double-base (CMDB) and nitrate ester plasticized polyether propellants, respectively [5]. Nitroamine explosives can greatly enhance the specific impulse of propellants. It can, however, degrade the safety, mechanical properties, and processing properties of the propellants, which restricts the application of these highenergy propellants. More recently, much interest has been generated on how to improve the propellant’s overall properties. The main approaches include the following: 1) using advanced binders or plasticizers, such as glycidyl azide polymer [6,7] or 3,3diazidomethyloxetane [8,9]; 2) improving the particle properties of the solid fillers by reducing the particle size [10–13] or changing the particle morphology [14–16]; and 3) optimizing the propellant’s formulation and charge structure [17,18]. An acutely popularmethod to improve the propellant properties is to coat its sensitive fillers. Manning and Thelma [19] used graphite to surface-coat RDX fillers by solvent-evaporation and investigated the application in propellants. Their experimental results showed that, by such surface coating, the drop heightH50 of RDX andRDX-containing propellant increased by 40%and115%, respectively. In addition, some previous researchers have also indicated that the mechanical properties of propellants were improved via coating of the nitroamine fillers with polymer or bonding agent [20–23]. The properties of the coated particles depend on the kind of coating materials. For the nitroamine explosive used in some propellants, the best coating materials should be selected from the propellant ingredients [5]. Nitrocellulose (NC) is necessary for the energy and mechanical properties of double-based propellants. In our previous work, RDX particles coated with NC were prepared by solvent evaporation. These coated samples exhibited par dispersion [24]. Another coating technology, slurry solution distillation (SSD), has also been used to prepare themolding powders [25,26].However, there are two limitation to this method: 1) the energy of the explosive is greatly decreased because the addition of coating materials is higher than 5%; and 2) agglomerates composed of multiple particles can be formed easily, which leads to a change in particle size distribution. Herein, a new method, slurry emulsion distillation (SED), was exploited to coat NC and centralite-1 (C-1) onto the nitroamine particles by introducing a high-shear force in the SSDmethod. Also, the effects of such surface coating on properties of nitroamine explosives and CMDB propellants were investigated.

Study on the Relationship between Microscopic Structure and Mechanical Properties of HTPB Propellant

By means of a tensile instrument and SEM, the mechanical property parameters of HTPB propellant test samples with different formulas were tested, and their microscopic fracture cross section patterns were observed. Take advantage of these testing results, the relationship between microscopic structure and mechanical properties of HTPB propellant was studied. The results show that the mechanical properties of a propellant are closely related to its microscpic structure state. The structural integrity of propellant is mainly influenced by the bond effect of the interface between binder and solid particles, solid particle’s shape, size and its distribution, the content of binder matrix, etc. These factors have important effects on the mechanical properties of propellant.

Characterisation of mechanical and thermal properties of double base propellant

A double base propellant is a polymer which is used as an energetic material to propel rockets. Advances in computers are making it possible to simulate a rocket as a whole, i.e. structurally and thermally. Among the rocket elements, little literature exists regarding the thermal and mechanical properties of propellants at a specified environment. In this study, a double base propellant is produced and then characterised. Accordingly, tensile specimens of the propellant are prepared according to JANNAF specifications to determine its mechanical properties. The tests are carried out at a possible 74°C and also at varying crosshead speeds of 1·3, 6 and 30 mm min−1. As of the thermal properties, the heat conduction coefficient, the specific heat and the density have been determined. All these properties complete the basic data for a thermomechanical simulation of a rocket on computer.

Effect of ageing on ballistic and mechanical properties of propellants having various oxidiser loadings

Propellants having high performance and goodstorage stability are always desirable for space applications. It is well known that the burning rate (1:) of composite solid propellants generally increases with oxidiser loading [1]. Recently, we have published a paper [2] on the effect of oxidiser loading on burning rate and thermal stability of polystyrene (PS) and ammonium perchlorate (AP) propellant systems and it was shown that higher oxidiser-loaded propellant has better storage stability as judged by burning rate changes. In general, the ageing of the propellant leads to changes in ballistic and mechanical properties which characterize the performance of the propellant. The tolerance limit of changes in these parameters depends upon the applications of the rocket motor in a specified mission. However, mechanical properties are generally used to characterise the ageing characteristics. The object of this short note is to present some results on the effect of oxidiser loading on the mechanical property of the propellant during ageing. The experimental details have been presented in our recent papers [2, 3] . The ageing studies on mechanical-property changes were carried out for PS/AP propellants having different AP loading. The results on the ultimate-compression strength (uc) for different AP-loaded propellants (aged at 100°C for 20 days) are presented in Table 1. The data for ~: changes (obtained from our earlier work