Response Of Propellant Research Articles

Damage characteristics and failure mechanism analysis of NEPE propellant at high strain rates

The study of mechanical properties and failure mechanism of propellants under impact loads is crucial for analyzing structural integrity of propellant charges. An experimental investigation was conducted on NEPE propellant using a separated Hopkinson pressure bar to conduct high strain rate uniaxial impact tests. Deformation and failure processes of the propellant under impact conditions were recorded with a high-speed camera. The microscopic failure forms of the propellants were observed using a scanning electron microscope and an optical microscope. Stress-strain curves and high-speed images revealed that the damage behavior and failure mechanism of NEPE propellants are significantly influenced by strain rate. As the strain rate increases, there is a notable increase in the deformation degree of the propellant specimens, with a more pronounced shear effect. This leads to an earlier occurrence of failure and a more severe degree of failure. The predominant failure forms observed in NEPE propellants include transgranular failure, matrix tearing, and cavity merging. A nonlinear visco-hyperelastic constitutive model with damage at high strain rates was established to provide a precise account of the mechanical response of NEPE propellant under high strain rates.

Experimental investigation of solid propellants combustion response to pressure oscillations using advanced high-resolution diagnostics

The combustion response of solid propellants plays a crucial role in determining the combustion stability of solid rocket motors (SRMs). This study employs multiple advanced combustion diagnostic techniques, including high-speed photomicrography, two-color pyrometry, and laser shadowgraphy, to simultaneously capture mesoscale flame dynamics and burning surface regression characteristics of AP/HTPB composite propellants under pressure oscillations. This experimental configuration enables the simultaneous achievement of high temporal resolution (0.25 ms) and spatial resolution (4.9μm/pixel). Pressure oscillations are generated by loudspeakers, cover a range of frequencies (168.9 Hz to 506.7 Hz) and amplitudes up to approximately 0.44% of the equilibrium pressure. The investigated propellants exhibit varying oxidizer characteristics, including coarse (330μm) and fine (150μm) AP particle sizes, as well as different AP mass fractions (81% and 86%). Results reveal that finer oxidizer particles and higher oxidizer content both result in an increased mean steady burning rate, with the former exhibiting a more pronounced influence on the burning rate increment. Under pressure oscillations, the mean burning rate increases with increasing pressure oscillation amplitude, accompanied by a reduction in flame height, an expansion in mean flame swing angle, and an elevation in mean flame temperature. The observed frequency dependency indicates a stronger combustion response when the oscillation frequency aligns with the characteristic frequency of propellant, which is closely associated with the mean burning rate, irrespective of the amplitude of pressure oscillation. This frequency-dependent phenomenon results in the highest combustion response, characterized by a maximum mean burning rate increment exceeding 165%. The innovative experimental platform employed in this study demonstrates the capability to simultaneously capture various flame fluctuation characteristics, such as flame swinging, flame temperature, and burning rate fluctuation in a single test. This facilitates a more thorough and comprehensive analysis of combustion responses in solid propellants under pressure oscillations.

Damage analysis of solid propellants with default defects based on macro-microscopic approach

Solid Rocket Motors (SRMs) rely on solid propellants, directly impacting the energy capacity of launch vehicles. High energy density material (HEDM) propellant exhibits superior energy density owing to the incorporation of a substantial quantity of energetic particles. However, the elevated particle fill ratio makes the formation of pores more prevalent during the manufacturing process of propellants. These pores, representing default defects, are indispensable factors in the investigation of mechanical properties of propellants. This study investigated default defects effects on HEDM propellants, analyzing both microscopic and macroscopic perspectives. Utilizing micro-CT imaging, the microstructure and default defects were characterized. Subsequently, using the cohesive zone model (CZM), microscopic damage evolution was depicted with the representative volume element (RVE) model, allowing in-depth analysis. Furthermore, a damage constitutive model, based on microscopic damage, was developed, with its softening function calibrated using microscopic damage evolution characteristics. Implemented into ABAQUS via user-defined material subroutine (UMAT), this model enabled the prediction of the mechanical response of HEDM propellants with different defects. The results demonstrate that the developed model accurately predicts the mechanical responses of HEDM propellants with different defects, showcasing the potential of macro-microscopic approaches in analyzing propellants with default defects.

Dynamic mechanical response and failure behavior of solid propellant under shock wave impact

Solid rocket motor propellants are typically subjected to shock wave loads during ignition. To analyze the dynamic mechanical response and failure behavior of hydroxyl-terminated polybutadiene (HTPB) propellant under varying shock intensities, this study innovatively employed a shock tube apparatus in conjunction with schlieren imaging and 3D-DIC techniques. Shock loading experiments were conducted on propellant samples of three different thicknesses under pressures ranging from 0.3 to 0.7 MPa, capturing the dynamic deformation processes. Results revealed that deformation initiated at the clamped region, extending towards the center and forming a parabolic shape. The maximum deformation of the samples shows an approximately linear relationship with the launch pressure and decreases with increasing sample thickness. The 5 mm sample failed under a 0.6 MPa shock pressure, with electron microscopy images identifying matrix damage, particle debonding, and particle fracture as the principal failure mechanisms. Finite element simulations based on the generalized Maxwell linear viscoelastic constitutive model were conducted, demonstrating good agreement with experimental data. The critical stress for fracture was determined to be 4.12 MPa, and the ultimate shock wave pressures for 3, 6, 9, and 12 mm thicknesses were approximately 0.3 MPa, 0.65 MPa, 1.1 MPa, and 1.4 MPa, respectively. These findings provide valuable insights for assessing the structural integrity of solid rocket motors under ignition shock conditions.

Analysis of the mechanical response of solid rocket engine propellant under acceleration shock

The increased-range solid rocket engine of new ammunition often needs to withstand extremely high acceleration overload, leading to damage to the propellant’s structural integrity. To address this issue, this paper constructs a nonlinear viscoelastic constitutive model for the CMDB propellant by using low- and high-strain rate mechanical property tests. Combined with the secondary development of explicit dynamics and numerical simulation technology, the mechanical response of a certain type of solid rocket propellant under different acceleration impacts is analyzed. The results show that under acceleration impact loads, the propellant will compress, rebound, and recover over time, continuously cycling. Its axial displacement, maximum equivalent stress, and maximum equivalent strain exhibit irregular sinusoidal wave-like periodic cycles. Looking at the time when the peaks appear, the time when the maximum equivalent stress appears always lags behind the time when the maximum axial displacement peak appears. Due to the viscous effect of the viscoelastic material of the propellant, the time when the equivalent strain peak appears will lag behind the equivalent stress. Because of the material’s damping effect, both the peak values of the maximum equivalent stress and equivalent strain decrease over time. Under continuous high acceleration impact loads, this viscous damping phenomenon continuously diminishes, and the peak value of the propellant’s axial displacement gradually increases.

NEPE Propellant Mesoscopic Modeling and Damage Mechanism Study Based on Inversion Algorithm.

To accurately characterize the mesoscopic properties of NEPE (Nitrate Ester Plasticized Polyether) propellant, the mechanical contraction method was used to construct a representative volume element (RVE) model. Based on this model, the macroscopic mechanical response of NEPE propellant at a strain rate of 0.0047575 s-1 was simulated and calculated, and the parameters of the cohesive zone model (CZM) were inversely optimized using the Hooke-Jeeves algorithm by comparing the simulation results with the results of the uniaxial tensile test of NEPE propellants. Additionally, the macroscopic mechanical behavior of NEPE composite solid propellants at strain rates of 0.00023776 s-1 and 0.023776 s-1 was also predicted. The mesoscopic damage evolution process of NEPE propellants was investigated by the established model. The study results indicate that the predicted curves are relatively consistent with the basic features and change trends of the test curves. Therefore, the established model can effectively simulate the mesoscopic damage process of NEPE composite solid propellants and their macroscopic mechanical properties.

Ignition response of NEPE-based propellants under drop weight through experiments and numerical simulation

ABSTRACT Experimental and numerical studies were conducted to investigate the effects of drop height on the ignition mechanism of NEPE nitrate ester plasticized polyether-based propellants. A modified drop-weight system was equipped with a high-speed camera to capture the ignition response images during the whole impact process. A macro-mesoscopic thermomechanical model considering the microcrack and viscous shear flow hotspot formation mechanism was established. The experimental results showed that the ignition responses of the propellants heavily depended on drop height, and the main ignition mechanism was viscous shear flow. The whole loading process could be summarized into three stages: radial extension (viscous shear flow), macroscopic crack initiation and ultimate failure (multiple macroscopic cracks or ignition). The ignition threshold was 35 cm. The posttest scanning electron microscopy (SEM) images further revealed that viscous shear flow played an important role in the ignition of propellants. The numerical simulation results indicated that viscous shear flow was the dominant ignition mechanism compared with the microcrack hotspot mechanism. Point A (along L1) was the most dangerous location under the drop-weight experiment. The predicted features of ignition evolution were consistent with the experimental results and prove that the critical drop height of ignition was 35 cm.

Low/intermediate speed impact‐induced ignition and damage of a novel high‐energy solid propellant

AbstractThe damage and ignition response of a novel propellant is investigated using a modified split Hopkinson pressure bar (SHPB). The mechanical response of the propellant exhibits strong strain rate dependency following a power law. The whole process from mechanical damage to onset of ignition, deflagration and potential deflagration to detonation transition (DDT) under different strain rates (1000–5000 s−1) is captured via high‐speed photography and digital image correlation (DIC). To clarify the onset and extent of the resulting reaction in terms of the mechanical damage caused by impact, meso‐scale analysis is used to evaluate the propellant before and after dynamic impact loading. The ignition response under impact loading is mainly caused by shear flow, and ignition after multiple impacts due to the reflection of stress waves. Dense debris clouds produced by the first impact are observed in the case of a strain rate of 5000 s−1 leading to DDT when the second impact initiated ignition.

Method of Measurement of Admittance of Composite Solid Propellants Using Impedance Tube Technique

ABSTRACT Mitigation of combustion instability of solid propellant rocket motors is ever being attempted by several researchers as the problem is very complicated in nature. The acoustic admittance of composite solid propellants (AP/HTPB/RDX/Al) is experimentally investigated using Impedance tube technique. It is one of the indirect experimental techniques to determine the combustion response of the solid propellants besides T-burner. The governing equations based on the conservation of mass, momentum and energy (reactive flow is simplified to have only the axial temperature gradient) are linearized and solved to determine the acoustic admittance of the burning propellant. Different methods of analysis were explored to validate/compare the results obtained and are matching well. Some of the unreported details of the analysis are brought out. A novel way of utilizing the outer tube besides the inner tube as against the literature (wherein the inner tube is kept inside the outer tube) to maintain the chamber pressure is explored. A test conducted at fundamental acoustic mode (110 Hz) at 2 MPa at room temperature (303 K) is considered for the analysis. A rotary valve capable of operating up to a mean chamber pressure of 12 MPa is developed in this work to act as an acoustic driver for the experiments. The advantage of the impedance tube technique over T-burner is that the former is capable of measuring both the real and imaginary part of combustion response whereas the latter can only measure the real part. The imaginary part of the combustion response besides the real part is useful to predict the stability characteristics of the solid propellant rocket motor.

A viscoelastic constitutive model considering deformation and environmental-induced damages for solid propellants

Realistically representing the constitutive response of solid propellants is crucial for industrial use and service life assessment of solid rocket motors (SRMs), as they are generally stored for a long time and exposed to complex loadings and environmental conditions, resulting in the possible loss of the grain structural integrity of SRMs and consequently the failure in the motor. This contribution develops a three-dimensional viscoelastic constitutive model that considers the effects of damages caused by environmental factors and large deformation. Environmental-induced damages are represented by introducing normalized crosslinking density (CLD) and micropore evolution, which is assumed to be the coupled results of oxidation, hydrolysis, degradation, migration, etc. Deformation-induced damages are attributed to interface debonding or failure in the binder as well as cyclic loadings. An ABAQUS subroutine based on the current model is then applied for numerical analysis. The effects of strain rate, temperature, confining pressure, cyclic loadings, and environmental aging on the stress response are presented. The predicted results match reasonably well the experiments. As the model takes into account the microstructural changes both due to mechanical loadings and environmental effects, it applies to the stress analysis of solid rocket motors, whether new or stored for years.

AP/HTPB combustion response simulation with a new equivalent linear system method

In the study of solid rocket motor (SRM) combustion instability, modeling and analyzing the combustion response of the solid propellant is a laborious task. We propose a new idea, an equivalent linear system method, for modeling solid propellant combustion response with three steps: first, simulating the transient combustion process under pulse pressure excitation for only one CFD case; then, treating the combustion process as a black-box and obtaining the transfer function of the combustion process from the CFD result; finally, predicting and analyzing the combustion response based on the transfer functions. For the AP/HTPB sandwich propellant withp¯=3MPa, the amplitude, duration, and direction of excitation pulses are studied. The new method is also verified, with a maximum relative error of 4.3% for burning rate response under p˜≤1MPa (as high as one-third of the pressure DC). Applicability of this new method is demonstrated for another two AP/HTPB sandwich propellants with different configuration under p¯=8MPa and p¯=10MPa, showing that the system-simulated combustion responses of burning surface temperature and burning rate are consisted well with the CFD results and the maximum relative error of burning rate response is 2.1%. Asymmetric combustion response for positive and negative pressure perturbations is a new finding based on the CFD and simulation results. Besides, a new approach using dual transfer functions is proposed to ensure high accuracy for the simulation of solid propellant combustion. The pressure-coupled response function is predicted by this method for the sandwich propellant under p¯=5MPa and p˜=20kPa within a wide continuous frequency range (0–3000 Hz). The comparison with CFD results indicates that the relative bias of Rp is less than 2%. With the proposed method, the combustion response to arbitrary pressure excitations can be simulated with high accuracy, high time-resolution, and high speed. The method shows great advantage and potential in simulating and predicting combustion instability.

Experimental and numerical investigation on dynamic deformation and ignition response of NEPE-based propellants

An experimental and numerical study has been conducted to investigate the effects of strain rates on the mechanical responses and ignition mechanism of NEPE-based propellants (Nitrate Ester Plasticized Polyether). The modified split Hopkinson pressure bar (SHPB) equipped with a high-speed camera was used to capture the mechanical-chemical feature images during the whole impact process. The macro-mesoscopic thermomechanical model was employed to describe the viscous shear flow hotspot formation at the mesoscale. The results showed that the mechanical and ignition responses of the NEPE-based propellants are heavily dependent on strain rates. It is observed that the impact processes can be summarized into four stages: homogeneous deformation, shear flowing, initiation of local shear region and ultimate fracture (or ignition). Selected image sequence and SEM images indicate that viscous shear flow is important to the ignition of propellants. The calculated axial stress-strain curves indicate that propellant exhibits a remarkable rate-dependence and viscous effect. The predicted features of hot spot-ignition evolution are consistent with the experimental phenomenon and prove the critical strain rate of ignition is 4500 s−1.

Effect of Initial Grain Temperature on Combustion Response of Composite Solid Propellants in T-burner

ABSTRACT The effect of initial grain temperature on the combustion response of composite solid propellants (AP/HTPB/RDX/Al) is experimentally investigated using a T-burner. Tests were conducted at different frequencies ranging from 200–400 Hz and at different pressures of 1–8 MPa at different initial propellant temperatures using a novel method (303 K, 243 K and 343 K) for two industrial-grade propellants, propellant-A and propellant-B. The test results revealed that the hot and cold temperatures increase the response. The combustion responses of the propellant-B are lower than propellant-A. Pulsed tests are conducted when the propellant showed low or negative response. This work highlights that the initial grain temperature is a crucial factor in determining the stability of solid rocket motors. The negative response compels us to further investigate toward a better understanding about the unsteady combustion behavior since there is no model available which could predict negative responses as of today.

Mechanism of AP effect on slow cook-off response of HTPE propellant

Due to safety requirements, insensitive behaviour under slow cook-off conditions is the desirable behaviour for HTPE (Hydroxyl-terminated block copolyether) propellant. In this paper, in order to study the effect of AP (ammonium perchlorate) on slow cook-off response of HTPE propellants, the slow cook-off behaviour of AP and the effect of HTPE binder on AP were investigated firstly. The results showed that, the weightlessness rate of AP was only 2.2% in closed system till heated to 250°C, but the figure was 35.91 % in opened system. Then the slow cook-off behaviour of two groups of HTPE propellants with different AP content and diameter respectively were tested. The results indicated that, as the AP content increased from 52% to 67%, or the diameter of AP decrease from 400 μm to 5 μm, the violence of slow cook-off response all increased. The possible mechanism was proposed. It expressed that, thermal damage of propellant produced during the slow cook-off test, the combustion sensitivity to pressure of damaged propellant increased as the AP content rise and the AP diameter decrease, leading a more violent response to slow cook-off.

A Nonlinear Ultrasonic Method for Detection and Characterization of Dewetting Damage in Solid Propellant

AbstractThe dewetting damage of solid propellant under loading is a key factor affecting the constitutive properties of solid propellant, and it will weaken structural integrity of solid rocket motor charge. The quantitative characterization of its evolution process has always been a very active research field. In this study, a nonlinear ultrasonic (NLU) method is proposed to investigate and monitor in real‐time the nonlinear dynamic response of solid propellant. The NLU parameter, which can evolve dewetting damage, is expressed by some physical quantities such as the frequency peak, the propagation distance and so on, and is recorded at different strain in the tensile tests of the round rod solid propellant specimens. Then, the initial dewetting point, characteristic dewetting point and characteristic dewetting rate are defined to characterize the dewetting performance. The results show that NLU parameter changes continuously with the evolution of tensile process and increases sharply at the initial dewetting damage point. By analyzing the data, an empirical formula characterizing the variation law of NLU parameter with strain is proposed, which is well fitted to the experimental data under different strain rates. In addition, relevant numerical simulation is carried out, and the simulation results verify the feasibility of the NLU method.

A one-dimensional model for the aging and damage effects on the response of composite double-base propellants

A one-dimensional model for the aging and damage effects on the response of composite double-base propellants

Mechanism of PSAN effect on slow cook-off response of HTPE propellant

ABSTRACT Due to safety requirements, insensitive behavior under slow cook-off conditions is the desirable behavior for HTPE propellant. As a low sensitivity oxidant, PSAN is used to partially replace for AP in HTPE propellant formulation to improve the slow cook-off behavior further. But the effect of PSAN on the slow cook-off behavior of propellant is inconclusive. So, in this paper, two kinds of HTPE composite propellant contained either AP as oxidant or a mixture of AP and PSAN were manufactured, named HTPE/AP/Al propellant and HTPE/AP/PSAN/Al propellant respectively. Then the slow cook-off behavior of the two propellants were tested. The results indicated that the slow cook-off response of HTPE/AP/PSAN/Al propellant was much more violent than the response of HTPE/AP/Al propellant. Then the possible mechanism was proposed. It expressed that, during the slow cook-off test, the PSAN decomposed much more than AP, the crack and hole produced in propellant grain; meanwhile the decomposition of PSAN also accelerated the decomposition of HTPE binder, the the crack and hole or AP particles could not be covered effectively by the liquefied decomposition product of HTPE binder; if the ignition occurred, the combustion of thermal damaged propellant was sensitive to pressure, leading a violent response to slow cook-off.

Effect of Block Structure of Copolyether Binder on Slow Cook‐Off Response of Composite Propellant

AbstractAs the typical insensitive propellants, hydroxyl‐terminal block copolyether (HTPE) and hydroxyl‐terminal block copolyether (PET) propellant all belong to copolyether propellants. The two binders of propellants have different arrangements of copolyether structure. But, the effect of copolyether structure arrangement on the slow cook‐off behavior of propellants and its possible mechanism has been unknown. So, in this paper, the slow cook‐off behaviors of HTPE and PET propellants were tested. The result showed PET propellant responded more violently than HTPE propellant. Then, the changes of mass loss, explosion heat, and combustion performance of propellants during the cook‐off test were studied. Combined with the slow cook‐off behavior of AP and binders, the mechanism of block structure effect on slow cook‐off response of propellant was proposed. It expressed that, the binders of HTPE and PET propellant all degraded into liquid products due to the copolyether structure; but the block structure has a significant effect on the chain scission process of copolyether binder, which makes slight degradation and the mild response to slow cook‐off for HTPE propellant. While the binder of PET propellant with the random structure degraded seriously, making more mass loss, bigger explosion heat, and worse combustion performance, the PET propellant responds violently to slow cook‐off.

An experimental study on dynamic deformation and ignition response of a novel propellant under impact loading

Investigations on high-energy and low-vulnerability propellants can provide a guarantee for improving the power and safety of solid rocket motors. In the present study, mechanical-thermal coupled responses were recorded by a high-speed infrared thermal imaging systems. The dynamic compressive properties and damage-ignition response mechanism under high strain rates of a novel type of propellant were studied, using a split Hopkinson pressure bar apparatus. The experimental results suggested that the mechanical properties of the novel propellant, in terms of yield stress, initial compressive modulus, and ultimate stress, were greatly affected by the loaded strain rate. The stress-strain responses exhibited an initial linear elasticity region, followed by yielding, and then a subsequent strain hardening or softening stage (plateau region), which was strongly dependent on the strain rate. It was found that the yield stress and ultimate stress increased with the strain rates. Moreover, the ignition response was accentuated at higher strain rates, resulting in an earlier and more intense ignition. According to the high-speed images and the post-test SEM images, the critical strain rate for ignition is 4500 s−1. Finally, by calculating the bulk and local temperature rise (considering the friction mechanism), it is clear that the dominant ignition mechanism of the novel propellant is the friction which is macroscopically represented as viscous shear flow.

High-strain-rate mechanical response of HTPE propellant under SHPB impact loading

The high-strain-rate dynamic response of a hydroxyl-terminated polyether (HTPE) propellant during impact loading is essential for assessing the structural reliability and impact safety of HTPE propellant. In this study, a modified split Hopkinson pressure bar (SHPB) apparatus has been developed to research the stress–strain behavior of the HTPE propellant over strain rates ranging from 470 to 5910 s−1 at room temperature, and the validity of the SHPB test is analyzed in detail. Meanwhile, the evolution of deformation to failure of the HTPE propellant was recorded by a high-speed digital camera synchronized with the SHPB test, which revealed the correlation between mechanical response and failure mode. Scanning electron microscopy was applied to investigate the microscopic failure mechanism of the post-test HTPE propellant, which indicated two characteristic failure modes: cracking propagates along the (1) debonding surface and (2) transgranular damage path. Finally, based on the stress–strain plots derived from the SHPB tests, the ultimate stress, strain energy density, and adiabatic temperature-rise effect of the HTPE propellant were seen to show strong strain rate dependence by following an empirical power law function.