Composite Modified Double-base Propellants Research Articles

Correlation between microstructural evolution and mechanical properties of CMDB propellant during uniaxial tension

AbstractNumerical simulation of the deformation and damage evolution process of composite modified double base (CMDB) propellant based on the microstructure is of great significance for improving its macro‐mechanical properties. The macro‐mechanical properties and damage evolution of CMDB propellant were studied experimentally and numerically in current work. To establish the correlation between microstructural evolution and the macro‐mechanical response of the propellant, a three‐dimensional microstructure model of the CMDB propellant was constructed utilizing the molecular dynamics particle filling approach. At the interface between RDX particles and the nitrocellulose‐nitroglycerine (NC‐NG) matrix, the conventional cohesive element was replaced by cohesive contact, and the parameters of the cohesive zone model (CZM) at the interface between the particles and the matrix were obtained by parameter inversion based on the Hooke‐Jeeves parameter optimization algorithm. The processes of damage initiation, propagation, convergence, and failure at the cohesive interface were simulated using the bilinear cohesive zone model (BCZM). The results revealed that the fracture strength of NC‐NG propellant with added RDX particles was significantly increased and the fracture elongation was reduced. The three‐dimensional microstructure model can accurately describe the microstructure of CMDB, and dewetting at the interface is the primary cause of propellant degradation when subjected to an external load, which compromises the mechanical properties of the propellant.

Investigation of the Effect of Axial Gap on the Mechanical Response of a Cartridge-Loaded CMDB Propellant Grain under Vibration Loads

In this study, the effect of the axial gap on the mechanical response of a cartridge-loaded propellant grain under vibration loads is investigated. The wide strain rate range of uniaxial compression tests ( 1.7 × 10 − 3 ~ 4 × 10 3 s − 1 ) on the composite modified double base (CMDB) propellant was carried out by using a universal testing machine, a hydraulic testing machine, and a split Hopkinson pressure bar system, respectively. A linear viscoelastic constitutive model of the CMDB propellant was developed by using the experimental measurements. The results show the studied CMDB propellant has a strong strain rate dependence, exhibiting an initial linear elasticity followed by a strain hardening region. The dynamic process of collision between the propellant grain and the motor case in the axial direction induced by vibration loads was simulated with the developed constitutive model by using the finite element method. The effects of the gap size between the propellant grain and the case and the vibration frequency on the mechanical response of the grain were studied. This shows that with a constant vibration frequency, the stress of the grain increases first and then decreases with increasing gap size. Moreover, the stress increases with increasing vibration loads.

Mechanical behaviors and failure mechanisms of CMDB propellant under wide strain rate tension loading

Composite modified double-base (CMDB) is a sort of mature propellant with a stable structure and high performance. Its tensile mechanical properties should be considered in the structural integrity design of solid propellant charges. The tensile tests were performed on the CMDB by a quasi-static measurement machine. The Hopkinson tension bar (SHTB) under strain rates from 0.0001s−1 to 2500s−1 was modified for structural integrity evaluation, and the stress-strain curves were accurately obtained. After comparing under different strain rates, the results show that the initial modulus of elasticity and stress level are significantly affected by the level of strain rate. Furthermore, the strain hardening becomes more distinct with increasing strain rates. Failure specimens were observed by scanning electron microscopy (SEM). It is indicated that the failure under a low strain rate is mainly debonding of filled particles from the matrix. However, it is mainly caused by their embrittlement under dynamic loading.

ReaxFF molecular dynamics simulations on thermal decomposition of RDX-based CMDB propellants.

ReaxFF molecular dynamics (ReaxFF MD) simulations were performed to study the thermal decomposition property of cyclotrimethylenetrinitramine (RDX)-based composite modified double base (CMDB) propellants. The intermediate products and final products of the decomposition of RDX-based CMDB propellants at 2000K, 2500K, and 3000K are obtained. The simulation results show that the decomposition of RDX and RDX/HTPB/Al is primary triggered by N-NO2 rupture, and then, the intermedia products undergo a series of complex interactions to form final products. The final products of RDX/HTPB/Al are H2 and N2, while the final products of pure RDX are H2, N2, and H2O. In addition, the abundance of the main intermediate products generated by RDX/HTPB/Al is lower than that of RDX, in that the reaction between intermediate products is more complex for RDX/HTPB/Al. Moreover, the decomposition rate of RDX/HTPB/Al increases with the increasing temperature.

Quickly determination of resorcinol in composite modified double-base propellants based on near-infrared reflectance spectroscopy

Resorcinol, as a stabilizer component, plays an important role in maintaining the stability of composite modified double-base (CMDB) propellants. Near-infrared reflectance spectroscopy (NIRS) was used to quickly detect the resorcinol content of CMDB propellant. The optimal spectral interval was determined to be 4126.92–6927.05 cm−1 by analyzing the useful characteristic peaks in sample spectra. The partial least squares (PLS) algorithm was used to establish the resorcinol prediction models. By comparing the performance of the developed models with different preprocessing, the best method of spectral preprocessing was determined as standard normal variate transformation (SNV) + first-order derivative (1ST). The optimal number of factors was 7 for resorcinol model. For the developed model, the determination coefficients of calibration and cross-validation (Rc2, Rcv2) were 0.997 and 0.987, respectively. The root mean square errors of calibration and cross-validation (RMSEC, RMSECV) were 0.013 %, 0.024 %, respectively. The determination coefficients (Rp2) and the root mean square errors of prediction (RMSEP) of prediction were 0.991 and 0.018 %. The average relative error of the proposed and reference methods was only 0.253 %. The developed method can be used for quickly determining the content of resorcinol in CMDB propellants. In addition, methyl violet test showed that the stability of CMDB propellant became worse with the decrease of resorcinol content. In terms of stability, qualified CMDB propellant should contain resorcinol content not less than 1.285 %. Thus, the prediction model of resorcinol is available for judging the stability of CMDB propellants qualified or unqualified.

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.

Simulation of the plasticizing behavior of composite modified double-base (CMDB) propellant in grooved calendar based on adaptive grid technology

The frequent occurrence of safety accidents during the calendering process is caused by the flammable and explosive properties of composite modified double-base (CMDB) propellant. Optimization of process parameters with the aid of fluid simulation technology could effectively ensure the safety of the calendering process. To improve the accuracy of the simulation results, material parameters and model structure were corrected based on actual conditions, and adaptive grid technology was applied in the local mesh refinement. In addition, the rheological behavior, motion trajectories and heat transfer mechanisms of CMDB propellant slurry were studied with different gaps, rotational rates and temperatures of two rollers. The results indicated that the refined mesh could significantly improve the contour clarity of boundaries and simulate the characteristics of CMDB propellant slurry reflux movement caused by the convergent flow near the outlet. Compared with the gap, the increased rotational rate of roller could promote the reflux movement and intensify the shear flow of slurry inside the flow region by viscous shear dragging. Meanwhile, under the synergistic effect of contact heat transfer as well as convective heat exchange, heat accumulated near the outlet and diffused along the reflux movement, which led to the countercurrent heat dissipation behavior of CMDB propellant slurry. The plasticizing mechanism of slurry and the safety of calendering under different conditions were explored, which provided theoretical guidance and reference data for the optimization of calendering process conditions. Based on the simulation results, the safety of the CMDB propellant calendering process could be significantly improved with a few tests conducted during a short research and development cycle.

The effect of strain rate on compressive behavior and failure mechanism of CMDB propellant

The compressive mechanical behavior of composite modified double base (CMDB) propellant was investigated across a wide scope of strain rates ranging from 10−3 s−1 to 4210 s−1 at room temperature, by applying a conventional universal testing machine and a split Hopkinson tension bar (SHPB), respectively. The derived stress-strain curves at different strain rates show a strong rate dependence, indicated that yield stress, ultimate stress and strain energy density of CMDB propellant all increase with strain rate by following a power law function, while the amplification of increase are different. The deformation and damage modes of CMDB propellant has changed from a typical ductile manner (cracking along the axial direction) to a brittle manner (maximum shear failure) with increasing of strain rate. Scanning electron microscopy (SEM) was employed to explore the microscopic failure characteristics of CMDB propellant. Under quasi-static loading, the nearly parallel micro-cracks propagating along the axial direction and the debonding of RDX particle without particle crushing can be observed. While under dynamic loading, the micro-crack is 45° angle to the axial direction, and multiple cracking modes of RDX particles appeared. Finally, the correlation between strain energy density and failure mechanisms of CMDB propellant was revealed by developing four characteristic failure modes. The findings of this study is very important to evaluate the structural integrity of CMDB propellant.

Preparation and Properties of a Flake Aluminum Powder in an Ammonium-Perchlorate-Based Composite Modified Double-Base Propellant

A flake aluminum powder (f-Al) is prepared by a bi-directional rotation mill method using a spherical aluminum powder (s-Al) as a raw material. Then, these two kinds of aluminum powders are used to prepare ammonium perchlorate-based composite modified double-base (AP-based CMDB) propellants. The properties of two kinds of AP-based CMDB propellants, such as the thermal decomposition performance, mechanical sensitivity, and combustion performance, are comprehensively researched. The results show that the exothermic peak temperature of the f-Al/AP-based CMDB propellant is lower than that of the s-Al/AP-based CMDB propellant. The impact and friction sensitivities of the propellant decrease by 12% and 187% after using f-Al to replace s-Al. In addition, the burning rate of the f-Al/AP-based CMDB propellant is 5.5% higher.

Preparation and Properties of a Flake Aluminum Powder in an Ammonium-Perchlorate-Based Composite Modified Double-Base Propellant

Preparation and Properties of a Flake Aluminum Powder in an Ammonium-Perchlorate-Based Composite Modified Double-Base Propellant

Application and Properties of CL‐20/HMX Cocrystal in Composite Modified Double Base Propellants

AbstractThe composite modified double base (CMDB) propellants containing 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazatetracyclo[5.5.0.05,9.03,11] dodecane (CL‐20), 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX) or CL‐20/HMX cocrystal were prepared by the solventless extrusion formation technique. The performances of CMDB propellants were evaluated by means of stability, sensitivity, combustion and mechanical experiments. Raman spectra analysis indicated the stability of CL‐20/HMX cocrystal is partially destroyed in the rolling process under 90 °C, 10 MPa. Methyl violet tests revealed that the colored time of CMDB propellants containing CL‐20/HMX cocrystal, CL‐20 or HMX are 77, 60, and 75 min, respectively. Burning rate tests shown that the burning rates of CMDB propellants containing CL‐20/HMX cocrystal, CL‐20 or HMX in the pressure range of 8 to 18 MPa, increased 1.82, 4.67, and 4.67 mm/s, with the pressure exponents 0.095, 0.306, and 0.346, respectively. Mechanical property tests revealed that the mechanical properties of CMDB propellant containing CL‐20/HMX cocrystal are inconsistent, but the tensile strength has improved compare with CMDB propellant containing CL‐20. These results suggest that CL‐20/HMX cocrystal is a potential material to solve the application problem of the safety performance and stability of the propellants containing CL‐20.

Study on Comparative Performance of CL‐20/RDX‐based CMDB Propellants

AbstractThe energy, combustion and combustion residues properties of composite modified double‐base (CMDB)propellants with CL‐20 were compared to those propellants with RDX. The energy characteristic of CL‐20/RDX‐CMDB propellants had also been calculated theoretically based on the principle of minimum free energy. The energy property of propellants with CL‐20 was found to be evidently enhanced in comparison to those propellants containing RDX. The findings on combustion properties revealed that the combustion properties of CL‐20‐CMDB propellants were contrary to the of RDX‐CMDB propellants. With the mass fraction of CL‐20 increasing in the propellants, the burning rates of propellants can be enhanced significantly, but the burning rates of propellants containing RDX decreased. Analysis of the combustion residues for CL‐20/RDX‐CMDB propellants revealed that the C, Cu and Pb elements aggregated on combustion surface, which may be useful for guiding the regulation of combustion performance of high‐performance CMDB propellants containing CL‐20.

Thermal Safety of a Gun‐Launched Missile's Solid Rocket Motor Under Conditions of High Environm. Temp. and Overloaded Forces

AbstractTo verify a hypothetical failure cause of a gun‐launched missile's solid rocket motor (SRM) under conditions of high environmental temperatures and overloaded forces of up to 6000∼12000 g, experiments and simulations were conducted and a new criterion variable was proposed. Uniaxial compression tests of the composite modified double base (CMDB) propellant used in the gun‐launched missile were carried out at low and intermediate strain rates at 50 °C to characterize the CMDB propellant's dynamic properties. The Schapery nonlinear viscoelastic constitutive model was employed and applied in finite element analyses. Contact and an oscillating frictional direction between the grain and the case were observed when the overload curve oscillated with time. Three key variables of the process were researched: the contact pressure, the relative velocity, and the total contact time. Based on these, a new criterion variable q is proposed for judgements regarding the SRM's thermal safety. By comparing the results with those from friction sensitivity tests, it was discovered that the grain had a possibility of self‐ignition that cannot be ignored. Meanwhile, the gap width between the case and the grain was determined to be a key influencing factor.

Applying Mechanically Activated Al/PTFE in CMDB Propellant

AbstractA novel reactive powder (aluminum/polytetrafluoroethylene, Al/PTFE 75/25 mass %) containing two kinds of PTFE (pre‐sintering PTFE and fresh PTFE, P‐PTFE and F‐PTFE) was prepared by a two‐step mechanical activation (MA) method. By introducing it into composite modified double base (CMDB) propellant, an attempt to improve the propellant performance of this mechanically activated Al/PTFE was made. Scanning electron microscopy (SEM) characterization indicated that F‐PTFE in activated powders deformed to abundant fibers under uniform shear forces. These fibers significantly enhanced propellant tensile properties and show improved safety performance. Compared to blank CMDB propellant (without PTFE), the elongation at maximum strength for propellant with activated Al/PTFE inclusions was increased to 3.7 times at −40 °C and to 3.9 times at −70 °C, the friction sensitivity and impact sensitivity were reduced by 88.9 % and 20.4 %, respectively. P‐PTFE in activated powders promoted the Al reaction activity, thereby reducing the propellant combustion agglomeration. The average diameter (D50) of coarse products for propellant with activated Al/PTFE 75/25 mass‐% was reduced by 82 % compared to that of blank CMDB propellant with spherical aluminum. This novel activated Al/PTFE shows increased propellant mechanical performance, decreased sensitivity and improved combustion efficiency of Al, which might expand the application field of CMDB propellants.

Experimental and theoretical studies on stability of new stabilizers for N-methyl-P-nitroaniline derivative in CMDB propellants

Although N-methyl-P-nitroaniline (MNA) was a quite effective stabilizer in composite modified double base (CMDB) propellants, it undergoes crystallization easily from nitroglycerin (NG) during storage. In order to improve its solubility in nitroglycerin (NG) and the stability in propellants, several new stabilizers including N-ethyl-p-nitroaniline (ENA), N-n-propyl-p-nitroaniline (n-PNA), N-i-propyl-p-nitroaniline (i-PNA), N-n-butyl-p-nitroaniline (n-BNA) and N-t-butyl-p-nitroaniline (t-BNA) were designed and synthesized to replace MNA by increasing the carbon chain length. The interaction between NG and different stabilizers was simulation by Materials Studio 5.5 and the stability and the high temperature stability performance of those new stabilizers in propellants were calculated by Gaussian 09. It was found that both the solubility of new stabilizers in NG and the stability and the high temperature stability performance of those in propellants were improved when the carbon chain length of substitution groups on nitrogen atom was increased. Thus, the n-BNA was a most potential stabilizer. Then all properties of the stabilizers were studied experimentally, which was agreement well with the theoretical analysis.

Influence of strain rate on the compressive yield stress of CMDB propellant at low, intermediate and high strain rates

The mechanical properties of composite modified double base (CMDB) propellant significantly depend on the strain rate. In particular, the yield stress increases dramatically at higher strain rates. To study this behaviour, low, intermediate and high strain rate compression testing (1.7 × 10−4 to 4 × 103 s−1) of CMDB propellant at room temperature was conducted by using a universal testing machine, a hydraulic testing machine and a split Hopkinson pressure bar (SHPB) system, respectively. The yield stress was observed to increase bilinearly with the logarithm of strain rate, with a sharp increase in slope at a strain rate of 5 × 101 s−1, which was supported by dynamic mechanical analysis (DMA) testing. The Ree-Eyring model, involving two rate-activated processes, was employed to predict the yield behaviour of CMDB propellant over a wide range of strain rates. The predictions are in excellent agreement with the experimental data.

Strain rate and temperature dependence of the compressive behavior of a composite modified double-base propellant

The quasi-static and dynamic compressive properties of a composite modified double-base (CMDB) propellant were studied over a wide range of strain rates from 10−4s−1 to 103s−1 at low temperatures of −40°C to 0°C, using a conventional universal testing machine and a split Hopkinson pressure bar apparatus. The experimental results show that the mechanical properties of the CMDB propellant, in terms of yield stress, initial compressive modulus, and ultimate strain, were greatly affected by the applied strain rate and the temperature, and the stress–strain responses exhibited an initial viscoelastic phase, followed by yielding, and then a subsequent strain hardening or softening stage, which was strongly dependent on the strain rate and temperature. It was found that the yield stress increased with both increasing strain rate and decreasing temperature. According to the experimental results, the strain rate effect, but not the temperature effect, was accentuated at higher rates. Moreover, the Eyring cooperative model was employed to predict the yielding behavior, and a master curve of reduced yield stress versus strain rate was built. The results show that the Eyring cooperative model provides reasonable prediction over a wide range of strain rates under low temperatures.

Synthesis, thermal behavior, and application of 4-amino-3,5-dinitropyrazole lead salt

Lead salt of 4-amino-3,5-dinitropyrazole (PDNAP) was synthesized from 4-amino-3,5-dinitropyrazole by the process of metathesis reaction, and its structure was characterized by IR, element analysis, TG, and DSC. The thermal decomposition kinetics and mechanism were studied by means of different heating rate differential scanning calorimetry (DSC) and thermolysis in situ rapid-scan FTIR simultaneous. The effects of PDNAP as an energetic combustion catalyst on the combustion performance of the solid propellant were studied. The results show that the peak temperature is 319.2 °C on DSC curve. The kinetic equation of major exothermic decomposition reaction is $$ \frac{{\text{d}}\alpha}{{\text{d}}T} = \frac{{10^{15.45} }}{\beta }4(1 - \alpha )[ - \ln \left( {1 - \alpha } \right)]^{{{3 \mathord{\left/ {\vphantom {3 4}} \right. \kern-0pt} 4}}} \exp ({{ - 1.972 \times 10^{5} } \mathord{\left/ {\vphantom {{ - 1.972 \times 10^{5} } {RT}}} \right. \kern-0pt} {RT}}). $$ The PDNAP is shown by IR spectroscopy to convert to PbO during the decomposition process. Combustion experiments show PDNAP can reduce the burning rate pressure exponent of the double-base or composite-modified double-base propellant.

BTATz–HNIW–CMDB propellants

The high nitrogen compound 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine and the high energy density material hexanitrohexaazaisowurtzitane (HNIW), were used as substitute of hexogen (RDX) in the composite modified double base (CMDB) propellant formulations, the propellant samples were prepared, the thermal behaviors, nonisothermal reaction kinetics, and thermal safety were carried out, and the eight important parameters were calculated and obtained as the self-accelerating decomposition temperature (T SADT), thermal ignition temperature (T TIT), critical temperatures of thermal explosion (T b), critical temperature of hot-spot initiation (T cr,hot-spot), characteristic drop height of impact sensitivity (H 50), critical thermal explosion ambient temperature (T acr), safety degree (S d), and thermal explosion probability (P TE). It shows that the content of HNIW has a large effect on the decomposition reaction mechanism of the CMDB propellant, when the content of HNIW is 10 %, the decomposition reaction are controlled by the random nucleation and subsequent growth (n = l), and the reaction mechanism obeys Mampel law; but when the content of HNIW is 20 %, the decomposition reaction are controlled by the chemical reaction (n = 1/4). The mechanism can not be changed by the catalysts, and they just make the apparent activation energy change slightly. For the sample, from BC01 to BC04, the values of T SADT and T TIT making an upward tendency, show the resistivity to heat: BC04 > BC03 > BC02 > BC01; the values of T acr and S d, BC01 are the maximum and BC02 are the minimum, show the heat sensitivity: BC01 > BC03 > BC04 > BC02. For the same radius, the thermal safety of the sphere sample is greater than that of the infinite cylinder one.

Study on the Notch Strength and Notch Sensitivity of Composite Modified Double-Base Propellants

To obtain the notch strength of the composite modified double base (CMDB) propellant, three-point bending tests on the single-edge U-notched thin plate specimens and uniaxial tensile tests on standard tensile specimens were carried out at 20°C. Experimental data include three parts in different range of the stress concentration factor Kt of specimens. The stress concentration factor Kt of the specimens have a distinct effect on the notch strength in a specific range. When Kt is less than the notch sensitivity factor KbN which is approximately equal to 1.35, the notch strength of CMDB propellant is approximately equal to its fracture strength and independent of the stress concentration factor of test specimens. When Kt is upper than 2.41, the notch strength change to be steady to a proper value which associate with the fracture toughness of the propellant . This shows that the CMDB propellant is insensitive to notch. The tensile test data is used to predict the value of the notch strength and notch sensitivity factor,and the prediction fit well with the test results of the notched specimens in a specific range.