Properties Of Composite Solid Propellants Research Articles

Review of multi‐scale mechanical behavior research on composite solid propellants based on data‐driven approach

AbstractComposite solid propellant is a kind of viscoelastic composite with high filling ratio and multi‐scale composition characteristics, and its macroscopic mechanical properties strongly depend on the microstructure of the propellant materia. However, with the increasing complexity of composition, structure and properties of composite solid propellants, the traditional research paradigm based on experimental observation, theoretical modeling and numerical simulation has encountered new scientific challenges and technical bottlenecks in the mechanical behavior analysis, charge design and manufacturing of composite solid propellants. Among them, the problems such as insufficient experimental observation, lack of theoretical model, limited numerical analysis and difficult verification of results restrict the development of composite solid propellants in future‐oriented engineering applications to a certain extent. The data‐driven computational mechanics method can directly establish complex relationships between variables from high‐dimensional and high‐throughput data, which can capture trends that are difficult to be found by traditional mechanics research methods, and has inherent advantages in the analysis, prediction and optimization of complex systems. This paper mainly reviews and evaluates the research of neural network based modeling, model‐free data‐driven calculation and data‐driven multi‐scale calculation, which provides the correct direction for the subsequent research of multi‐scale mechanical behavior of composite solid propellants based on data‐driven.

Effect of Accelerated Cyclic Aging on the Ballistic Properties of Composite Solid Propellant

Burn rate is a vital parameter of a propellant that highly influences the internal ballistics of a rocket motor. In the case of military applications of solid rocket motors, they are stored for a long duration, during which their performance deteriorates considerably due to aging. Conventionally, the accelerated isothermal technique is used for studying the effects of aging. However, in actual storage conditions, the temperature experienced by the propellant varies over time. In the present work, experimental investigations were carried out using accelerated cyclic and isothermal aging schemes. Here, the burn rates and temperature sensitivity of the propellant were recorded after the accelerated aging. A reduction in burn rates was observed in all aging techniques. There was a strong influence of the frequency of the aging cycle on burn rates. Theoretical analysis of motor performance indicates a reduction in chamber pressure to the tune of 18%, leading to deterioration of thrust by 20% and specific impulse by 2.5%. Remedies to recover the performance of the motor with aged propellant were explored, and throat inserts and thermal conditioning of aged motors were suggested as possible ways to overcome the aging effects.

A Step-by-Step Equivalent Microprediction Method for the Mechanical Properties of Composite Solid Propellants considering Dewetting Damage

Reliable prediction of the macromechanical properties of composite solid propellants in the microscale can accelerate the development of propellants with high mechanical properties. According to the characteristics of the composition ratio of a four-component hydroxyl-terminated polybutadiene (HTPB) propellant with the component ammonium perchlorate (AP), hydroxyl-terminated polybutadiene, aluminum powder (AL), and cyclotrimethylenetrinitramine (or RDX for short), an improved random delivery algorithm was developed to separately model filler particles with the different sizes. A step-by-step equivalent representative volume element (RVE) model was generated to reflect the microstructures of the propellant. The isotropy and uniformity of the RVE model were also tested using a two-point probability function. The Park-Paulino-Roesler (PPR) cohesive model was introduced to simulate the particle debonding (or dewetting) in solid propellant. The stress-strain curves of the propellant were obtained by the macroscopic test with the extension rate 200 mm/min at different temperatures. Based on these experimental data, the 8 characteristic parameters suitable for the microinterface of the propellant were obtained by using an inversion optimization method. A microscale finite element prediction model of the propellant considering dewetting damage was constructed to study the evolution process of the microdamage of the propellant. The predicted stress-strain curves of the propellant under different loading conditions were in good agreement with the test results.

Synthesis of two novel neutral polymeric bonding agents to enhance the mechanical properties of composite solid propellants.

Currently, only a few bonding agents can be utilized efficiently in nitramine filler material-based solid rocket energetic binder systems. Herein, we demonstrate the synthesis and specific characterization of two kinds of neutral polymeric bonding agents (NPBA-1 and NPBA-2) and their application in composite propellants consisting of the nitramine octogen (HMX) and glycidyl azide polymer (GAP). The as-obtained NPBAs were well-coated on the surface of HMX and RDX due to their functionalized groups, and they significantly affected the viscosity of the uncured propellant mixtures and possessed obviously enhanced mechanical properties in the cured AP/HMX/GAP propellant mixtures, even at low concentrations (down to 0.001 wt% of the whole propellant). In addition, because of the existence of an epoxy group and no hydroxyl functionalities, NPBA-2 exhibited improved mechanical strength and glass transition temperature as compared to NPBA-1, which has plenty of reactive hydroxyl groups. The as-synthesized epoxy-modified NPBAs are essential for obtaining NEPE propellants with high bonding and mechanical properties.

Effect of Microstructure on Micro-Mechanical Properties of Composite Solid Propellant.

This study was aimed at determining the effect of microstructure on the macro-mechanical behavior of a composite solid propellant. The microstructure model of a composite solid propellant was generated using molecular dynamics algorithm. The correlation of how microstructural mechanical properties and the effect of initial interface defects in propellant act on the macro-mechanics were studied. Results of this study showed that the mechanical properties of propellant rely heavily on its mesoscopic structure. The grain filling volume fraction mainly influences the propellant initial modulus, the higher the volume fraction, the higher initial modulus. Additionally, it was found that the ratio of particles influences the tensile strength and breaking elongation rate of the propellant. The big particles could also improve the initial modulus of a propellant, but decrease its tensile strength and breaking elongation rate. Furthermore, the initial defects lowered the uniaxial tensile modulus, tensile strength, and the relaxation modulus of propellant, but did not affect the relaxation behavior of the propellant.

Evaluation of Mechanical Properties of Composite Solid Propellant by Genetic Engineering of Materials: Part B: Modeling of Minimum Representative Unit for Multi‐Modal Particle Packing Structure Based on Formulation of Composite Solid Propellant

AbstractTo show the actual particle packing structure of AP/Al/HTPB propellant with multi‐modal fillers, a minimum representative unit of particle packing structure is established. In the minimum representative unit, the particle size of fillers in each mode is identical to the value in the propellant formulation. Meanwhile, on the basis of the amount series of fillers in the per unit propellant, the amount of fillers in each mode is respectively divided by that of the fewest filler, thus the amount series of fillers in the minimum representative unit is obtained. Further, with the condition that the average density of the unit is the same as that of the propellant, the side length of the minimum representative unit could be uniquely determined. In order to generate the particle packing structure with particles evenly distributed in the unit, a two‐step algorithm is put forward. In the first step, the genetic algorithm is adopted to search for an evenly and non‐overlapping distribution for the few and coarser particles. In the second step, the residual finer particles are randomly placed in the voids among the coarser particles by a modified L−S algorithm. Results showed that the particles are distributed more evenly in the packs generated by the two‐step algorithm than in packs generated by the classic L−S algorithm.

Storage Lifetime Prediction of Composite Solid Propellant based on Šesták‐Berggren Model

AbstractThe physical and chemical properties of composite solid propellant during storage period are greatly affected by environmental factors, and the aging mechanism is complicated. In view of the insufficient utilization of test data in the current research and the low accuracy of storage lifetime evaluation model, this paper takes composite solid propellant as the object and makes use of the destructive accelerated storage test data at different temperature levels to carry out storage lifetime prediction research from the perspective of thermal analysis kinetics. Taking the key mechanical performance parameter‐tensile strength as an example, a performance degradation model based on Šesták‐Berggren model (SB(m,n)) is established, and the optimal mechanism index (m,n) is determined according to the Akaike Information Criterion (AIC). Furthermore, the evaluation methods of storage reliability, storage reliable lifetimes and their lower confidence limits are given. Finally, take a certain type of composite solid propellant as an example to verify the model and method of the paper. The results show that the storage lifetime prediction method based on the SB(m,n) model is more accurate and the prediction results are more reliable. A good idea is provided to assess the storage lifetime of composite solid propellant, and it also provides reference for other propellant and explosive storage lifetime prediction.

Research on Creep Constitutive and Numerical Simulation of Composite Solid Propellant

Through the composite creep solid propellant creep experiment, the composite solid propellant curve is obtained. The power rate constitutive model, linear viscoelastic model and Schapery nonlinear constitutive model are used to describe the creep process. The study shows that Schapery modified nonlinear constitutive model can better describe the creep properties of composite solid propellants. Through the ABAQUS user subroutine, the finite element application of Schapery’s creep-type nonlinear constitutive model is studied. The research results in this paper can provide a reference for the analysis of the creep effect of the grain during the vertical storage of the solid rocket motor.

Synthesis of a Series of Dual-Functional Chelated Titanate Bonding Agents and Their Application Performances in Composite Solid Propellants.

Titanate-based bonding agents are a class of efficient bonding agents for improving the mechanical properties of composite solid propellants, a kind of special composite material. However, high solid contents often deteriorate the rheological properties of propellant slurry, which limits the application of bonding agents. To solve this problem, a series of long-chain alkyl chelated titanate binders, N-n-octyl-N, N-dihydroxyethyl-lactic acid-titanate (DLT-8), N-n-dodecyl-N, N-dihydroxyethyl-lactic acid-titanate (DLT-12), N-n-hexadecyl-N, N-Dihydroxyethyl-lactic acid-titanate (DLT-16), were designed and synthesized in the present work. The infrared absorption spectral changes of solid propellants caused by binder coating and adhesion degrees of the bonding agents on the oxidant surface were determined by micro-infrared microscopy (MIR) and X-ray photoelectron spectroscopy (XPS), respectively, to characterize the interaction properties of the bonding agents with oxidants, ammonium perchlorate (AP) and hexogen (RDX), in solid propellants. The further application tests suggest that the bonding agents can effectively interact with the oxidants and effectively improve the mechanical and rheological properties of the four-component hydroxyl-terminated polybutadiene (HTPB) composite solid propellants containing AP and RDX. The agent with longer bond chain length can improve the rheological properties of the propellant slurry more significantly, and the propellant of the best mechanical properties was obtained with DLT-12, consistent with the conclusion obtained in the interfacial interaction study. Our work has provided a new method for simultaneously improving the processing performance and rheological properties of propellants and offered an important guidance for the bonding agent design.

Numerical Study of Mechanical Properties of Composite Solid Propellant with Initial Defects

In order to study the effect of initial interface defects and initial void defects on the macro tensile mechanical properties of composite solid propellant, based on the Python script, the particle filling model of composite solid propellant with meso pores and interface defects was established in ABAQUS. Firstly, zero thickness cohesive elements were embedded at the adjacent elements of the matrix and the particle/matrix interface, and the traction separate law was used to simulate the fracture failure of composite solid propellant. Then, the influence of different shapes, porosity and interface defect ratio on the elastic modulus and tensile strength of composite solid propellant was studied. Accordingly, the relationship between the initial damage of the composite solid propellant and the porosity and interface defects was established. Morever, the initial damage surface of the composite solid propellant was depicted. Results showed that the initial damage of polygon filling model is larger than that of circular particle filling model under the same initial defect condition; The elastic modulus of composite solid propellant decreases linearly with the increase of porosity and interface defect ratio; The tensile strength of composite solid propellant decreases linearly with the increase of interface defect ratio, and decreases logarithmically with the increase of porosity.

Effect of Pre‐Strain Aging on the Microdamage Properties of Composite Solid Propellant

AbstractAccelerated aging tests under pre‐strain were conducted on HTPB‐based composite solid propellant with the goal of investigating the effect of pre‐strain aging on its microdamage properties. The tensile fracture morphologies, stress‐strain curve and dissipative energy density of propellant samples were analyzed. Results showed that there was no obvious dewetting macroscopically when the pre‐strain was less than 9 %, but the pre‐strain can still cause microdamage of propellant interface. The microdamage of propellant interface can be characterized by the critical dewetting strain, corresponded to pre‐strain by a linear law. The bonding performance between HTPB propellant matrix and solid filler was mainly affected by aging temperature. There was a critical temperature TC, For the HTPB propellant investigated in this study, the TC is between 65 °C and 70 °C. When aging temperature is below TC, there was no significant decrease in the overall levels of dissipated energy density, but decrease began significantly when the aging temperature is above TC.

Evaluation of Mechanical Properties of Composite Solid Propellant by Genetic Engineering of Materials: Part A.

AbstractThe uniaxial tensile constitutive models of a crosslinked polymer and plasticizer were established based on the characteristics of the network and plasticization by genetic engineering of materials. The key factors affecting the mechanical properties of the polymer matrix were chosen as the genomes of materials. The constitutive model for the crosslinked polymer network with no plasticizer was related to the molecular characteristics of the ingredients, such as the flexibility of the binder prepolymer, functionalities of the ingredients, as well as the curing parameters. On the basis of the constitutive relation of the crosslinked polymer, the constitutive model for the crosslinked polymer and plasticizer was also related to the volumetric fraction of the plasticizer and the interaction of the binder prepolymer and plasticizer molecules. Within the range of viscoelastic deformation in the tensile test, the viscoelastic characteristics of the network were considered in the model. Numeric results showed that the predicted and experimentally measured stress‐strain curves were consistent under uniaxial tensile loading, indicating that the model satisfactorily predicted the stress and strain response.

Influence of HTPB prepolymer on achieved properties of composite solid propellant

Changes/variations during manufacturing and storage of free radical-polymerized hydroxyl-terminated polybutadiene resin/prepolymer (widely used binder for the composite solid propellants) are not reflected in terms of appreciable change in the hydroxyl value. As a result, cured properties of the propellant mixed using the given formulation finalized by keeping R ratio (NCO/OH ratio) within 0.7–0.9 did not yield predicted mechanical properties. Investigations carried out subsequently, by the authors, identified the root cause to be variations in molecular weight and its distribution, which were not indicated in terms of change in hydroxyl value. Authors confirmed their findings by 1H1NMR studies whereby the variation in molecular weight distribution could be explained in terms of variation in spin–spin relaxation time ( T 2) values.

Dynamic Mechanical Characterization of Composite Solid Propellant for Propellant Grain Structural Integrity Assessment

The objective of this work was to characterize mechanical properties of composite solid propellant in order to conduct the structural integrity assessment of propellant grain. Data required for analyses regarding loads experienced during rocket motor transportation and flight were obtained. Based on time and temperature superposition, master curves were constructed from propellant mechanical properties determined by dynamic mechanical analysis. These curves can be used as input in finite elements analysis software, demonstrating the applicability of the proposed methodology.

Damage and Dilatometry for Solid Propellants with Digital Image Correlation

AbstractThe mechanical failure properties of composite solid propellants are determined largely by the strength of the particle matrix interfaces. Under applied loading, separation of the particulate matter from the surrounding matrix takes place, a phenomenon called dewetting. Vacuole formation and growth result in volume changes in the bulk material, so that, during tensile testing, in situ measurement of volume change correlates with this type of microstructural damage. Dewetting and dilatation have long been an important consideration, but characterization has been difficult. Fluid based dilatometry has been the dominant measurement technique but has some inadequacies. In this work, an alternative approach is shown that needs no contact with the specimen, that requires no gas or liquid, and that can accommodate various specimen geometries. Damage was induced in two common solid propellant types using either formulation considerations or strain induced damage. The volume changes during tensile testing were measured using this optical dilatometry method and show the ability of the approach to detect damage in solid propellants. Various parameters derived from the dilatation curves are compared. Verification of the approach with results from a conventional dilatometer are also included.

Mechanical Properties of Composite Solid Propellant with Initial Defects

Mechanical Properties of Composite Solid Propellant with Initial Defects

A Voronoi cell finite element method for estimating effective mechanical properties of composite solid propellants

The mechanical properties of Composite solid propellant (CSP) are the critical material parameters to analyze the structural integrity of propellant grains, and have a significant influence on the life and reliability of solid rocket motors. A Voronoi cell finite element method using an adaptive algorithm in the time domain is proposed for investigating the linear viscoelasticity of CSP in the present paper. A process is brought forward to produce a Representative volume element (RVE) model, which reflects the microstructural features of CSP. Numerical viscoelastic examples are used for varying the accuracy of this method. In addition, finite element simulations are conducted to understand the effect of microstructural morphology and material properties of inclusion on the effective mechanical properties of CSP using the new method. When this method is applied to the design process of CSP, it can reduce the design cost and shorten the design cycle effectively. The current microscopic numerical analysis method can be used to provide guidance for designing and analyzing the mechanical properties of composite viscoelastic materials.

Effect of Pre‐strain Aging on the Damage Properties of Composite Solid Propellants based on a Constitutive Equation

AbstractAccelerated aging tests under pre‐strain were conducted on HTPB‐based composite solid propellant with the goal of investigating the effect of pre‐strain aging on its damage properties. A statistical damage constitutive model based on continuum damage theory and statistical strength theory was established. The aging damage coefficient, making aging process of propellant equivalent to a form of damage, was introduced to correct the damage variable. Experimental results show that theoretical model has good agreement with experimental results and can accurately describe the mechanical behavior of propellant during pre‐strain aging. Further analysis indicated that the damage effects caused by pre‐strain can be identified from the equation of the aging damage coefficient. Aging time influences both tensile strength and shape characteristics of the stress‐strain curve of propellant in the damage stage, while pre‐strain only decreased the tensile strength. The strain damage threshold value decreased linearly over the aging period and with increasing pre‐strain level during the aging process.

고체 추진제 장시간 물성거동 반응 연구

고체 추진기관이 노즐마개에 의해 외기와의 교환이 완벽히 차단된다면, 구조적 안정성은 제작초기 조건인 내부조성간의 잔류반응(Post Cure, Migration etc.), 그리고 자유공간 내의 산소(또는 산화방지제)와 습기(제습제)와의 반응에 종속된다. 이로부터 발생하는 혼합형 고체추진제의 기계적 특성은 매우 복잡하며, 추진기관은 발사직전까지 일교차/년교차의 끊임없는 열하중을 받게 된다. 본 연구에서는 고체 추진기관의 제조공정인 성형오븐에서 출고 후 저장안정화까지의 거동을 고체추진제의 열유변학적 단순특성을 적용하여 신속하게 산출할 수 있는 방법을 제시하였다. 이를 위해 온도제어 가능한 Endurance Test 장치를 고안 제작하였으며, 추가적으로 점진적 응력과 변형율 증가에 따른 비선형 특성도 검토한다. Structural integrity of solid rocket depends on the residual reactions between constituents of its composition(post cure, migration etc.), the oxygen(or anti-oxydent) in the free volume and humidity (desiccant) under the perfect sealed condition. Mechanical Properties of composite solid propellant arising from those factors are very complex. Moreover the propulsion are faced with thermal loads from diurnal & seasonal cycle till firing. In this study, the fast evaluation method of long term mechanical properties is suggested based on Thermo-Rheological Simplicity from curing oven to cool-down stage in view point of thermal stabilization. For this subject, endurance tester having temperature control capability are devised. From the results from incremental load and strain, non-linear characteristics are discussed.

Effects of Different Nano-Sized Metal Oxide Catalysts on the Properties of Composite Solid Propellants

ABSTRACTSeveral industrial- and research-type composite solid propellants containing different nano metric metal oxide catalysts (Fe2O3, Co3O4, CuO, and PbO) with similar nominal composition, were prepared and experimentally analyzed. The effects of different nano-sized metal oxide catalysts on the rheological properties and hazardous properties were investigated. The strand burning rate and the associated combustion flame structure of composite propellants were determined. The results show that the nano-sized metal oxide powders can be sufficiently dispersed in hydroxyl terminated polybutadiene binder. The propellant formulations containing nano metal oxide particles are sensitive to impact and friction except for the base propellant without nano-sized powders, which is less sensitive to friction as compared to the other compositions. The nano-sized metal oxide additives can affect the combustion behavior and increase the burning rate of propellants compared with the reference propellant composition.