Temperature accelerated storage test method for composite solid propellant

Abstract

According to the invention, research is carried out around a damage mechanism and an aging model of a propellant in a temperature cycle accelerated aging test, and the problems that a 71 DEG C method and an Arrhenius model are single in form and the environmental stress is not fully considered in the industry are solved. On the basis of analyzing a typical failure mechanism of the propellant, a temperature cycle accelerated aging test is carried out on the propellant, the influence of temperature alternating stress on the microstructure of the propellant is analyzed from the perspective of a damage mechanism based on a scanning electron microscope and an infrared spectrum result of the propellant, and the acceleration of the temperature alternating stress on a degradation state is verified; on the basis of a mechanical property test result, a propellant temperature alternating accelerated aging model is constructed from the perspective of a physical-like model, model parameters are fitted, a theoretical method and data support are provided for a high-confidence equivalent method for a propellant accelerated aging test, a new way is provided for a propellant accelerated aging method, and the method is suitable for popularization and application. And the storage life extension, scientific life determination, service life edge-touching bottom detection and other work of the solid rocket can be supported.

Description

Technical Field

[0001] The invention belongs to the field of accelerated test methods in reliability engineering, and in particular relates to a temperature accelerated storage test method for composite solid propellant. Background Art

[0002] Composite solid propellants (hereinafter referred to as "propellants") are multiphase mixtures composed of a polymer binder as an elastic matrix, filled with a solid oxidizer, a metal fuel, and a small amount of other components. They are the core power unit of solid rockets. Throughout their lifecycle, they undergo storage, field duty, loading, and transportation, among other mission conditions. Their performance significantly impacts the operational effectiveness and service life of solid rockets. Propellant components have distinct interfaces. With extended service life, propellants are susceptible to microscopic failure modes such as interface damage, matrix tearing, and particle fracture. At the macroscopic level, these failure modes manifest as changes in internal stress within the engine grain due to factors such as temperature fluctuations and transportation vibrations, leading to crack initiation and propagation. The presence of cracks can lead to abnormal combustion surfaces during ignition, deviations from interior ballistic parameters, and engine deflagration. Therefore, engine life has always been a matter of great concern within the industry. To support storage life extension, scientific life determination, and lifespan estimation for solid rockets, accelerated storage testing of engine propellants is necessary to address the current shortage of flat storage samples.

[0003] In recent years, accelerated storage testing of propellants within the industry has been primarily conducted based on high-temperature stresses. Acceleration factors are determined using the 71°C method outlined in GJB 736, "Test Methods for Initiating Pyrotechnic Devices," or by using the Arrhenius model to determine acceleration factors under multiple constant high-temperature stresses. However, propellants are viscoelastic materials, exhibiting mechanical behavior intermediate between that of elastic and viscous materials. These materials exhibit typical viscoelastic phenomena such as creep, stress relaxation, and mechanical loss under external forces. While these viscoelastic phenomena contribute to the time-temperature equivalence principle (the same mechanical relaxation phenomenon can be observed at both higher temperatures and shorter times, and at lower temperatures and longer times, with increasing temperature and extending observation time being equivalent to molecular motion), the temperature stresses to which propellants are subjected during long-term service are not constant but rather fluctuating. These fluctuating temperature stresses generate internal stresses within the motor grain, making the conventional time-temperature equivalence principle and Arrhenius model inapplicable. Therefore, it is necessary to investigate equivalent characterization methods for propellant degradation under temperature-induced stress. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a temperature accelerated storage test method for composite solid propellant.

[0005] Composite solid propellant is the core power unit of solid rockets, and its performance stability is significantly affected by temperature cycles. This patent focuses on the damage mechanism and aging model of propellant in temperature cycle accelerated storage test. First, by analyzing the failure mechanism of solid propellant temperature load, it is preliminarily determined that accelerated storage test by applying temperature cycle stress can accelerate the degradation state of propellant; then, based on the failure mechanism, a propellant temperature cycle acceleration model is constructed, and a test plan is designed; finally, by conducting temperature cycle accelerated storage test on the propellant, the consistency of the failure mechanism under temperature cycle accelerated stress is verified by infrared spectroscopy detection results, and the development trend of propellant damage mode with stress and time is analyzed based on SEM, and an accelerated aging model of propellant mechanical properties is formed.

[0006] Step 1: Analysis of propellant temperature load failure mechanism

[0007] Accelerated storage testing presupposes that the propellant failure mechanism remains unchanged; only research based on this is effective. Consistency in the propellant failure mechanism can be demonstrated by no substantial changes in the physical microstructure or in the chemical composition.

[0008] The failure mechanism of propellant under temperature alternating load. From a macroscopic perspective, propellant is a viscoelastic material. When subjected to cyclically changing loads, the strain of the propellant lags behind the stress. There is a phase difference between stress and strain, resulting in residual strain and energy dissipation. It is a process of entropy increase, which causes the mechanical properties of the propellant to continuously degrade. From a microscopic perspective, the propellant is mainly based on a polymer adhesive, to which solid oxidant particles and metal powder combustion agents are added. In addition, there are a small amount of curing agents, plasticizers, antioxidants and other components. The performance of these components continues to degrade under temperature alternating stress.

[0009] The impact of high-temperature chemical aging on the mechanical properties of propellants is primarily manifested in changes in the matrix binder network structure. These changes occur through two pathways: oxidative crosslinking and degradation chain scission. These two types of changes are observed during the aging process of nearly all propellant types. The higher the storage temperature, the lower the maximum elongation and elongation at break for the same aging time. This is because higher storage temperatures lead to more pronounced post-curing, oxidative crosslinking, and degradation chain scission reactions. Furthermore, since oxidative crosslinking is stronger than degradation chain scission in the propellant, this results in lower maximum elongation and elongation at break. Furthermore, the propellant adhesion index increases with storage time, with the trend becoming more pronounced at higher temperatures. After high-temperature accelerated aging, the microstructural changes and chemical reactions, as evidenced by physical and chemical parameters, do not fundamentally alter. Higher temperatures and longer aging times promote more complete chemical reactions, such as oxidative crosslinking and degradation chain scission, leading to more pronounced changes in performance parameters. Therefore, accelerating the chemical aging process by increasing the temperature is reasonable.

[0010] From the perspective of propellant micromorphology, temperature stress can also cause the propellant filler / matrix interface to become less bonded, resulting in "dehumidification". Propellants have three microscopic damage modes under tensile stress, namely matrix tearing, particle tearing, and interface damage, such as Figure 1 shown.

[0011] The interface between the binder matrix and the solid filler in unaged propellants is fuzzy. At fracture surfaces subjected to tension at room temperature and low strain rates, the oxidizer and other solid fillers bond well to the binder, forming a nearly integrated whole with no apparent dewetting. The damage pattern consists solely of matrix tearing and interface failure between the particles and the matrix. Under low temperature and low strain rate tension, a small amount of particle fracture occurs. After prolonged high-temperature aging, at low strain rate tension surfaces at room or low temperature, the interface between the binder matrix and the solid filler becomes clear, with numerous pits and exposed solid filler. The filler has debonded, forming cavities, indicating poor interfacial adhesion. Furthermore, the distribution density of particle fractures is significantly higher than that of unaged propellants.

[0012] Analysis suggests that under high-temperature loads, the gases released by the slow decomposition of the oxidizer AP disrupt the adhesion of the adhesive adsorbed on its surface. Furthermore, thermal stress causes the adhesive network to shrink, leading to collapse of the polymer network structure and damage to interfacial adhesion points. These factors can lead to voids at the interface between the oxidizer, aluminum powder, and other solid fillers, and the adhesive, causing dehumidification. Furthermore, high-temperature aging causes the AP particles to slowly decompose, resulting in a decrease in their strength.

[0013] Because propellants are often cast within solid rocket motors and tightly bonded to the motor casing via insulation and lining, their thermal expansion coefficient is significantly greater than that of the metal casing (approximately 10 times). Under low-temperature loading, the grain's cooling contraction is constrained by the casing, generating tensile stresses and strains within the grain. At low temperatures, the propellant's tensile strength and modulus increase, as does the interfacial bond strength between the grain and the matrix. However, after high-temperature aging, the strength of the AP grain decreases. This makes it more likely for microcracks generated under tensile stress to initiate and propagate within the AP grain. Although the tensile stress magnitude caused by this thermal mismatch is far below the yield limit of the propellant material (typically in the tensile range of tensile to hundreds of kPa), under long-term alternating high-temperature and low-temperature loading, the propellant undergoes a cycle of high-temperature aging, interfacial dewetting, AP grain strength reduction, low-temperature tensile stress, interfacial failure under tensile stress, and AP grain fracture. This cycle of microcrack damage increases internally. As this damage develops and accumulates, macrocracks develop in the grain, significantly degrading the propellant's mechanical properties. Lowering the minimum test temperature will increase the tensile stress value inside the grain. The higher the stress value and the greater the rate of stress change, the faster the rate of microcrack damage will form.

[0014] During engine service, high-temperature aging causes "dehumidification" at the interface between the grain and the matrix, reducing the strength of the AP grain. Low temperatures, on the other hand, create tensile stresses within the grain, leading to the accumulation and development of internal microcracks. In the natural high-low temperature cycle, these two effects alternate, causing the accumulation and development of microcracks, which manifests as a macroscopic degradation of mechanical properties. Therefore, temperature cycling stress can better reflect the aging mechanism of propellants in solid motors under real-world service conditions than simple constant-temperature acceleration. The accelerated effect is more pronounced, the test cycle is shorter, and it facilitates the assessment of product life. Therefore, temperature cycling stress was selected as the accelerated test stress.

[0015] X-ray photoelectron spectroscopy, CT detection, SEM electron microscope scanning, Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, etc. can be used to conduct qualitative or quantitative tests on the elemental composition, chemical valence, content, functional groups, and components of damaged materials / components before and after aging, analyze the changes in the tissue composition such as oxidation, decomposition, and segregation of the material matrix and surface / interface, and determine whether a physical reaction or a chemical reaction occurs; use metallography, scanning electron microscopy, transmission electron microscopy, X-ray microtransmission and other detection technologies to characterize the microscopic morphology and tissue results of damaged materials / components, and analyze changes in damage structures such as cracks, voids, and grain boundaries.

[0016] Step 2: Construction of an accelerated model based on failure mechanism

[0017] In recent years, the Arrhenius model has been widely used in engineering as a model for accelerated propellant aging. However, this model assumes that reaction rates are affected solely by temperature and not by other factors, and that it is only applicable under constant temperature stress. However, temperature cycling stresses can cause internal stress changes in the propellant within the engine casing, and the degradation characteristics of the engine charge are also affected by factors such as the stress state. This makes it difficult to accurately predict the service life of propellants using billets. Therefore, the traditional Arrhenius model and billet-based testing methods are no longer applicable. Based on the previously mentioned analysis of propellant failure mechanisms under temperature loading, a model for accelerated propellant aging under temperature cycling is constructed.

[0018] Based on the principle of damage equivalence, lowering the minimum temperature can increase the extreme tensile stress. At the same time, increasing the temperature difference can increase the amplitude of the tensile stress alternating load, thereby increasing the damage caused to the propellant by each stress cycle and reducing the number of cycles to achieve the purpose of acceleration. Phenomenological methods study the fatigue damage of materials based on the changes in mechanical parameters such as strength and stiffness during the material fatigue process, and then predict fatigue life. The traditional stress-life formula is as follows:

[0019]

[0020] Where: k, n——constants related to material properties; N f ——The number of loading cycles when the material fatigues and fractures, that is, the fatigue life; S——is the applied stress amplitude.

[0021] When considering the tensile stress caused by thermal mismatch at low temperatures, the lower the temperature, the greater the tensile stress. S is the difference between the maximum response stress inside the grain at the highest and lowest temperatures in a cycle. The maximum response stress inside the grain at different temperatures is closely related to the propellant material parameters and the grain geometry. Therefore, under temperature cycle loads, S can be expressed by the following function:

[0022] S=H(T max ,T min ,α,ψ)

[0023] Where: T max ,T min ——absolute temperature extreme value in the temperature cycle, K; α——constant related to material properties; ψ——constant related to the geometric shape of the grain.

[0024] Regarding the effect of cyclic loading frequency, there are currently two views on the relationship between fatigue life and frequency for materials with constant strain: one is that at high frequencies, the heat generated by cyclic loading cannot be dissipated quickly, causing temperature rise, thermal softening, and reduced fatigue life; the other is that at low loading frequencies, stress relaxation damage increases with each cycle, thus reducing fatigue life. Temperature cycles typically last from a few to tens of hours, allowing the heat generated by cyclic loading to dissipate quickly and temperature rise to be negligible. Considering the effect of stress relaxation, the stress at a given strain decreases logarithmically with time, while the damage caused by stress relaxation increases logarithmically with time.

[0025] Therefore, for temperature alternating stress, based on the traditional Arrhenius model, the fatigue damage caused by temperature change is introduced, and the relationship model between the performance degradation rate θ and the temperature environment stress under the temperature cycle of solid rocket propellant is established as follows:

[0026]

[0027] Where: θ is the material performance degradation rate, which is the performance degradation amount for each temperature cycle; E is the activation energy, J; K B —Boltzmann constant, 1.38×10 -23 J / K; A, B - constants related to material properties, geometry, and test methods, obtained by fitting test data; f - frequency of temperature cycle, h -1 .

[0028] The acceleration factor of temperature cycle accelerated stress relative to the natural temperature environment can be expressed as:

[0029]

[0030] Where, T m Represents the mean temperature of the natural environment, T q Indicates the natural ambient temperature amplitude, Indicates the maximum temperature under accelerated conditions, f * Indicates the cycle frequency under accelerated conditions, S * represents the cyclic stress under accelerated conditions.

[0031] Step 3: Accelerated storage test plan design

[0032] (1) Test sample status

[0033] Propellant accelerated storage test was carried out using propellant dumbbell specimens.

[0034] (2) Ultimate stress

[0035] The accelerated storage temperature stress limit value is determined based on the temperature limit that the propellant can withstand. The accelerated storage test temperature must not exceed the temperature limit that the propellant can withstand.

[0036] In order to ensure the stable performance of the propellant, the maximum limit of the ambient temperature T is specified when the propellant is stored and used. max Therefore, in order to ensure that the failure mechanism of the product in the accelerated test is consistent with that in normal use, the maximum value of the accelerated stress selected in the accelerated test is To meet the product requirements, namely:

[0037] Propellants have not only a maximum temperature limit for storage and use, but also a minimum temperature limit. When the temperature is too low, the propellant will transform into a glassy state, and the failure mechanism will change.

[0038] (3) Temperature change rate

[0039] The temperature change rate should be determined based on the actual temperature change of the propellant during storage.

[0040] (4) Temperature cycle frequency

[0041] The temperature cycling frequency primarily affects the rate of temperature change and the degree of stress relaxation in the propellant under a certain strain. When the temperature change rate exceeds a certain limit (different requirements for different products), a temperature shock effect occurs, which differs from the product failure mechanism under the slower temperature change rate in the natural environment. The temperature holding time of the propellant specimen is set in conjunction with the thermal stability time of the propellant specimen to calculate the temperature cycling frequency.

[0042] (5) Test level

[0043] Within the extreme temperature stress range of the propellant, temperature cycling stress levels of different magnitudes are set, generally not less than 4 groups of temperature cycling stress levels.

[0044] (6) Test profile

[0045] Based on the formed accelerated storage test plan, formulate the accelerated storage test profile.

[0046] (7) Test Node

[0047] After the accelerated storage test reaches a certain cycle, a propellant sample is taken at each stress level for uniaxial tensile testing, and some of the stretched specimens are selected for scanning electron microscopy and infrared spectroscopy analysis.

[0048] Step 4: Accelerated aging test data analysis

[0049] By conducting uniaxial tensile tests on dumbbell-shaped propellant specimens after accelerated aging, the degradation of the elastic modulus, tensile strength, maximum elongation and elongation at break of the aged propellant under different temperature cyclic stresses were obtained. The rate of change of the mechanical properties of the propellant with the number of cycles at different temperature cyclic stress levels was fitted using the least squares method, and the acceleration factors at different temperature cyclic stress levels were obtained. The equivalent acceleration model of the propellant under temperature cyclic stress was then fitted using the least squares method.

[0050] The beneficial effects of the present invention are as follows:

[0051] The present invention conducts research on the damage mechanism and aging model of propellants in temperature cycle accelerated aging tests, solving the problems in the industry of the single form of the 71°C method and Arrhenius model and insufficient consideration of environmental stress. Based on the analysis of the typical failure mechanism of propellants, temperature cycle accelerated aging tests were carried out on propellants. Based on the results of propellant scanning electron microscopy and infrared spectroscopy, the influence of temperature alternating stress on the microscopic morphology of propellants was analyzed from the perspective of damage mechanism, and the acceleration of temperature alternating stress on the degradation state was verified. Based on the results of mechanical property tests, a propellant temperature alternating accelerated aging model was constructed from the perspective of a quasi-physical model, and the model parameters were fitted. This provides theoretical methods and data support for the realization of a high-confidence equivalent method for propellant accelerated aging tests, and provides a new approach for propellant accelerated aging methods, which can support the storage life extension, scientific life determination, and life exploration of solid rockets. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings, which constitute a part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an improper limitation of the present invention.

[0053] Figure 1 Schematic diagram of three typical mesoscopic damage modes of propellant under tensile stress;

[0054] Figure 2 is the external dimensions of the propellant sample;

[0055] Figure 3 It is the propellant accelerated storage test profile;

[0056] Figure 4 is the Mises stress distribution of the grain at -40℃;

[0057] Figure 5 is the Mises stress of the grain middle cross section at different temperatures;

[0058] Figure 6 It is the result of infrared spectrum detection;

[0059] Figure 7 This is the SEM morphology of the specimen at different aging times from -25℃ to 65℃;

[0060] Figure 8 This is the SEM morphology of the specimen under different aging stresses at the 35th cycle;

[0061] Figure 9 It is the test result of the specimen's cyclic stress performance under different temperatures. DETAILED DESCRIPTION

[0062] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0063] This embodiment provides a temperature accelerated storage test method for composite solid propellants. A certain type of composite solid propellant is selected as the implementation object, and research is carried out around the damage mechanism and aging model of this type of propellant in the temperature cycle accelerated storage test. First, by analyzing the failure mechanism of solid propellant temperature load, it is preliminarily determined that the accelerated storage test by applying temperature cycle stress can accelerate the degradation state of the propellant; then, based on the failure mechanism, a propellant temperature cycle acceleration model is constructed, and a test plan is designed; finally, by conducting a temperature cycle accelerated storage test on the propellant, the consistency of the failure mechanism under temperature cycle accelerated stress is verified using infrared spectroscopy detection results, and the development trend of the propellant damage mode with stress and time is analyzed based on SEM, and an accelerated aging model of the mechanical properties of the propellant is formed.

[0064] Step 1: Analysis of propellant temperature load failure mechanism

[0065] Accelerated storage testing presupposes that the propellant failure mechanism remains unchanged; only research based on this is effective. Consistency in the propellant failure mechanism can be demonstrated by no substantial changes in the physical microstructure or in the chemical composition.

[0066] During engine service, high-temperature aging causes "dehumidification" at the interface between the grain and the matrix, reducing the strength of the AP grain. Low temperatures, on the other hand, create tensile stresses within the grain, leading to the accumulation and development of internal microcracks. In the natural high-low temperature cycle, these two effects alternate, causing the accumulation and development of microcracks, which manifests as a macroscopic degradation of mechanical properties. Therefore, temperature cycling stress can better reflect the aging mechanism of propellants in solid motors under real-world service conditions than simple constant-temperature acceleration. The accelerated effect is more pronounced, the test cycle is shorter, and it facilitates the assessment of product life. Therefore, temperature cycling stress was selected as the accelerated test stress.

[0067] Step 2: Construction of an accelerated model based on failure mechanism

[0068] For temperature alternating stress, based on the traditional Arrhenius model, fatigue damage caused by temperature change is introduced, and the relationship model between the performance degradation rate θ and temperature environmental stress under temperature cycling of solid rocket propellant is established as follows:

[0069]

[0070] Where: θ is the material performance degradation rate, which is the performance degradation amount for each temperature cycle; E is the activation energy, J; K B —Boltzmann constant, 1.38×10 -23 J / K; A, B - constants related to material properties, geometry, and test methods, obtained by fitting test data; f - frequency of temperature cycle, h -1 .

[0071] The acceleration factor of temperature cycle accelerated stress relative to the natural temperature environment can be expressed as:

[0072]

[0073] Where, T m Represents the mean temperature of the natural environment, T q Indicates the natural ambient temperature amplitude, Indicates the maximum temperature under accelerated conditions, f * Indicates the cycle frequency under accelerated conditions, S * represents the cyclic stress under accelerated conditions.

[0074] Step 3: Accelerated storage test plan design

[0075] (1) Test sample status

[0076] The accelerated storage test of propellant was carried out using a dumbbell-shaped propellant specimen. The dimensions of the propellant specimen are as follows: Figure 2 The curing cooling simulation of the engine containing propellant is carried out, and the calculation results are shown as follows. Figure 4 and Figure 5 As shown in the figure, the maximum Mises stress of the grain at low temperature is located at the tip of the charge.

[0077] Under the normal storage temperature of 20°C, the stress at the tip of the charge is 0.01764 MPa, which is equivalent to applying an 8% constant strain to the propellant dumbbell specimen. Therefore, the propellant dumbbell specimen with an 8% constant strain was used as the test sample.

[0078] (2) Ultimate stress

[0079] From a safety perspective, the maximum test temperature for high-energy propellants generally does not exceed 343K (70°C). The glass transition temperature of this type of propellant is approximately -50°C. Based on measured environmental data, the lowest temperature in the engine's full lifecycle temperature load spectrum can reach approximately -40°C. Taking all factors into consideration, the lowest temperature in the acceleration spectrum was set at 233K (-40°C). Therefore, the low-temperature ultimate stress of this type of propellant is -40°C, and the high-temperature ultimate stress is 70°C.

[0080] (3) Temperature change rate

[0081] Considering the temperature change rate in the natural environment, the temperature change rate of the accelerated storage test was set to 1°C / min.

[0082] (4) Temperature cycle frequency

[0083] Since the temperature stabilization time of the propellant specimen is 0.5h, the high and low temperature holding time of each temperature cycle level is set to 0.5h, and the temperature cycle frequency is calculated to be about 1h -1 .

[0084] (5) Test level

[0085] Within the extreme temperature stress range of the propellant, five temperature change levels are selected, namely 20℃~65℃, 10℃~70℃, -10℃~50℃, -25℃~65℃, and -40℃~70℃.

[0086] (6) Test profile

[0087] According to the accelerated storage test plan, the accelerated storage test profile is formed as follows Figure 3 As shown, the test conditions are as follows.

[0088] Table 1 Accelerated storage test conditions

[0089] Serial number Temperature cycling stress level High temperature / low temperature holding time Number of cycles 1 cycle test time 1 20℃～65℃ 0.5h 35 2.5h 2 10℃～70℃ 0.5h 35 3h 3 -10℃～50℃ 0.5h 35 3h 4 -25℃～65℃ 0.5h 35 4h 5 -40℃～70℃ 0.5h 35 4.7h

[0090] (7) Test Node

[0091] After 7, 14, 21, 28, and 35 cycles, one specimen at each stress level was taken for uniaxial tensile testing to measure the mechanical properties of the propellant specimens, including modulus, tensile strength, maximum elongation, and elongation at break. Some of the stretched specimens were selected for scanning electron microscopy and infrared spectroscopy analysis.

[0092] Step 4: Accelerated aging test data analysis

[0093] To investigate the microscopic damage mechanisms and mechanical property changes of propellants after accelerated aging through temperature cycling, uniaxial tensile tests were conducted on propellant specimens before and after accelerated aging. Scanning electron microscopy (SEM) and infrared spectroscopy were also performed on some of the fractured specimens. The following sections analyze the microscopic damage mechanisms and mechanical property degradation, ultimately developing a propellant accelerated aging model through temperature cycling.

[0094] (1) Consistency analysis of failure mechanisms based on infrared spectroscopy

[0095] The consistency of the failure mechanism of the propellant can be demonstrated by the absence of significant changes in the main chemical components. Infrared spectroscopy can be used to analyze the changes in the groups in the organic matter or polymer in the binder network of the propellant.

[0096] Figure 6 Infrared spectroscopy results are presented for the initial state and the 35th cycle under stress conditions of 20°C-65°C, 10°C-70°C, -10°C-50°C, -25°C-65°C, and -40°C-70°C. Comparison of the molecular composition of the components in the initial state and after aging reveals no significant changes, and no new characteristic functional groups are generated, indicating that the propellant failure mechanism remains unchanged under stress conditions of 20°C-65°C, 10°C-70°C, -10°C-50°C, -25°C-65°C, and -40°C-70°C.

[0097] (2) Microscopic damage mechanism analysis based on SEM electron microscope scanning

[0098] From the perspective of aging time, the effect of extending the accelerated aging time on the microscopic damage mechanism is compared. Figure 7 The scanning electron microscopy results of the 21st and 35th cycles under -25℃~65℃ stress are given. From the perspective of aging stress, the effect of stricter accelerated aging stress on the microscopic damage mechanism is compared. Figure 8 The scanning electron microscopy results of the 35th cycle under stress conditions of 20℃~65℃, 10℃~70℃, -10℃~50℃, -25℃~65℃, and -40℃~70℃ are given.

[0099] The areas exhibiting "grain fracture" are marked in red, those exhibiting "interface damage" are marked in yellow, and the remaining areas exhibit "matrix tearing" damage. None of the propellant samples exhibited the "grain fracture" damage mode during the 21st cycle, but all did after the 35th cycle. This indicates that with increasing temperature cycling aging time, the probability of propellant exhibiting "grain fracture" increases significantly, and "dehumidification" becomes increasingly pronounced. The probability of the "grain fracture" damage mode increases with increasing temperature cycling stress levels, indicating that increasing temperature cycling stress worsens propellant degradation.

[0100] Prolonging the temperature cycle accelerated aging time and increasing the temperature cycle stress can both achieve the goal of accelerating the degradation state of the propellant, which can also be understood as the "time-temperature cycle equivalence" effect of the propellant under temperature cycle stress.

[0101] (3) Analysis of mechanical property degradation laws

[0102] By conducting uniaxial tensile tests on dumbbell-shaped propellant specimens after accelerated aging, the degradation of the elastic modulus, tensile strength, maximum elongation, and elongation at break of the propellant after aging under different temperature cycle stresses is obtained. Figure 9 shown.

[0103] Using the least squares method, the changing rates of the mechanical properties of the propellant with the number of cycles at different temperature cycle stress levels are fitted and are shown in the following table.

[0104] Table 2 Performance change rate of temperature cycle accelerated test

[0105] Stress level 20℃～65℃ 10℃～70℃ -10℃～50℃ -25℃～65℃ -40℃～70℃ Modulus 0.0837 -0.0090 -0.0036 0.0403 0.0024 tensile strength 0.0005 0.0038 0.0026 0.0045 0.0144 Maximum elongation -0.1909 0.1291 0.1300 -0.2451 -0.1890 Elongation at break -0.1614 0.0360 0.2437 -0.0446 -0.2894

[0106] The aforementioned performance change rates indicate that the degradation rate of tensile strength increases with increasing temperature differences. Therefore, we further analyzed the degradation rate of tensile strength under different temperature cycling accelerated stress levels. The acceleration factors for propellants at various temperature cycling stress levels relative to 20°C to 65°C are shown in the table below.

[0107] Table 3 Acceleration factors of propellants in temperature cycle accelerated test

[0108] Stress level 20℃～65℃ 10℃～70℃ -10℃～50℃ -25℃～65℃ -40℃～70℃ Speed ​​of change 0.0005 0.0038 0.0026 0.0045 0.0144 Acceleration Factor - 7.6 5.2 9 28.8

[0109] The equivalent acceleration model of propellant under temperature cycling stress is obtained by fitting using the least squares method as shown below.

[0110]

[0111] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A composite solid propellant temperature accelerated storage test method, characterized in that: The method includes the following steps: (1) analysis of the failure mechanism of propellant temperature load; (2) construction of an accelerated model based on the failure mechanism; (3) design of an accelerated storage test program; and (4) analysis of accelerated aging test data.

2. A composite solid propellant temperature accelerated storage test method according to claim 1, characterized in that: The step (2) is specifically: For temperature alternating stress, based on the traditional Arrhenius model, fatigue damage caused by temperature change is introduced, and the relationship model between the performance degradation rate θ and temperature environmental stress under temperature cycling of solid rocket propellant is established as follows: Where: θ is the material performance degradation rate, which is the performance degradation amount for each temperature cycle; E is the activation energy; K B is the Boltzmann constant, 1.38×10 -23 J / K; A and B are constants related to material properties, geometry, and test methods, obtained by fitting test data; f is the frequency of temperature cycling; S is the applied stress amplitude; k and n are constants related to material properties; T max , T min is the absolute temperature extreme value in the temperature cycle; α is a constant related to the material properties; ψ is a constant related to the geometric shape of the grain; The acceleration factor of temperature cycle accelerated stress relative to the natural temperature environment can be expressed as: Where, T m Represents the mean temperature of the natural environment, T q Indicates the natural ambient temperature amplitude, Indicates the maximum temperature under accelerated conditions, f * Indicates the cycle frequency under accelerated conditions, S * represents the cyclic stress under accelerated conditions.

3. The temperature accelerated storage test method for composite solid propellant according to claim 2, characterized in that: The step (3) specifically includes: determining the state of the test object, ultimate stress, temperature change rate, temperature cycle frequency, test magnitude, test profile, and test nodes.

4. The method for accelerated storage test of composite solid propellant according to claim 2, characterized in that: The step (4) is specifically as follows: a uniaxial tensile test is performed on a dumbbell-shaped propellant specimen after accelerated aging to obtain the degradation of the elastic modulus, tensile strength, maximum elongation, and elongation at break of the propellant after aging under different temperature cyclic stresses; using the least squares method, the rate of change of the mechanical property value of the propellant with the number of cycles under different temperature cyclic stress levels is fitted, and the acceleration factor under different temperature cyclic stress levels is obtained, thereby using the least squares method to fit the equivalent acceleration model of the propellant under temperature cyclic stress.

5. The method for accelerated storage test of composite solid propellant according to claim 2, characterized in that: After obtaining the degradation of the aged propellant under different temperature cyclic stresses, some stretched specimens were selected for scanning electron microscopy and infrared spectroscopy analysis.

6. The method for accelerated storage test of composite solid propellant according to claim 5, characterized in that: The analysis includes: Failure mechanism consistency analysis based on infrared spectroscopy detection, microscopic damage mechanism analysis based on SEM electron microscope scanning, and mechanical property degradation law analysis.

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