The curing process of nitrate ester plasticized polyether (NEPE) propellants involves complex interactions between heat generation, heat transfer, and mechanical evolution, which fundamentally determine the structural integrity of solid rocket motors. In particular, the exothermic nature of the curing reaction leads to non–uniform temperature fields, giving rise to heterogeneous curing behavior and residual stress accumulation. In this study, a fully coupled thermo–chemo–viscoelastic finite–element model is developed to simulate the curing–cooling process and validated by experiments. Simulations were then performed to quantify the effects of temperature–pressure coupling on residual stress evolution during the curing process. A four–factor Box–Behnken design combined with Response Surface Methodology (RSM) is employed to evaluate the influence of curing temperature, curing pressure, cooling rate, and depressurization rate. Analysis of variance shows that curing temperature and pressure dominate stress formation, exhibiting a pronounced synergistic amplification, whereas rate–controlled factors play a secondary role. Optimization yields an optimal parameter combination—50.0 °C, 3.33 MPa, 0.064 °C/min, and 0.007 MPa/min—reducing maximum residual stress to 0.018 MPa, a 53.6% decrease compared with atmospheric curing. The findings provide a quantitative framework for optimizing pressurized curing and improving structural reliability in polymer–based energetic materials.

To address the issue of randomness in the mechanical properties of the hydroxyl‐terminated polybutadiene (HTPB) propellant, a stochastic constitutive model (SCM) with a lognormally distributed random parameter Λ was proposed to describe their mechanical behaviors, and the structural integrity of a HTPB propellant grain was analyzed based on it. The results indicate that the stress‐strain curves predicted by the SCM have a good agreement with the experimental curves, and the experimental curves fall within a 95 % probability interval predicted by the SCM. The mechanical response of HTPB propellant grain under ignition pressurization is associated with the random parameters Λ. The maximum equivalent stress and safety factor increase approximately linearly with the increase of random parameters Λ, while the maximum equivalent strain and maximum damage coefficient decrease approximately linearly with the increase of random parameters Λ. The error in the mechanical response of the grain obtained based on the SCM and the experimental constitutive model is basically not more than 2 %, the SCM can effectively characterize the randomness in the mechanical response of propellant grain caused by the dispersion of HTPB propellant mechanical properties.

In order to investigate the formation mechanism of the residual stress and residual strain in a nitrate ester plasticized polyether (NEPE) propellant grain during the curing and cooling process, the temperature, curing degree and stress/strain of the NEPE propellant grain during the curing and cooling process were analyzed via ABAQUS finite element software. The results indicate that there is a temperature gradient in the NEPE propellant grain during curing at 50 °C. The maximum temperature difference is about 5 °C and the maximum temperature is located on the center of propellant grain. At the end of curing, the temperature in the interior of the grain tends to be uniform. The curing degree in the NEPE propellant grain during the curing process has the same trend as temperature. The residual stress/strain of the NEPE propellant grain during the curing and cooling down processes are mainly composed of curing shrinkage stress/strain in the curing process and thermal stress/strain in the cooling down process. The curing shrinkage stress and strain in the curing process account for 19% and 31% of the whole process, respectively. The thermal stress and thermal strain in cooling down process account for 75% and 69% of the whole process, respectively. The thermal stress and thermal strain in the curing process can nearly be ignored. The residual stress and residual strain calculated by the traditional method is larger than that obtained in this paper. The maximum deviation of the residual stress and residual strain are about 8% and 17%, respectively.

This paper presents a servo control method for the multiple launch rocket system (MLRS) launcher during marching fire operations. The MLRS, being a complex nonlinear system, presents challenges in designing its servo controller. To address this, we introduce the fuzzy adaptive sliding mode control (FASMC) approach. The permanent magnet synchronous motor (PMSM) and controller of the MLRS were simulated in the MATLAB/Simulink environment. The dynamic model of the MLRS during marching fire was established using multi-body system theory, vehicle mechanics, and launch dynamics. The dynamic model was then integrated with the FASMC-based controller using the Adams/View module. Numerical calculations were performed to demonstrate the control performance and the effectiveness and applicability of the proposed approach were validated through a comparison experiment between FASMC and other common control methods.

To study the formation mechanism of residual stress/strain of the nitrate ester plasticized polyether （NEPE） propellant grain during curing and cooling process， the temperature field， curing degree field and stress/strain field of the propellant were numerically analyzed based on ABAQUS finite element software. The results show that there are temperature gradient and curing rate gradient in the NEPE propellant grain during the curing process at 50 ℃. The temperature and the curing rate are notably higher at the center of the grain， and they eventually reach a consensus at the completion of curing. The temperature difference in the propellant does not affect the final residual stress/strain. The total residual stress/strain during curing and cooling obey the principle of stress/strain superposition， and they are mainly composed of the curing shrinkage stress/strain and thermal stress/strain during cooling. For the total residual stress， the proportions of the two stages are approximately 20% and 80%， respectively， and for the total residual strain， the proportions are about 30% and 70%， respectively. Compared with the traditional method， the residual stress/strain calculated in this study have the same distribution characteristics， but the values are smaller.

In order to investigate the effect of tension–compression asymmetry of propellant mechanical properties on the structural integrity of a Nitrate Ester Plasticized Polyether (NEPE) propellant grain, the unified constitutive equations under tension and compression were established, a new method for grain structural integrity assessment was proposed and the structural integrity of the NEPE propellant grain under the combined axial and transverse overloads was evaluated. The results indicate that the mechanical state of the NEPE propellant grain is in the coexistence of tension and compression under the combined axial and transverse overloads, and the tension and compression regions in the propellant grain is independent of the propellant constitutive behavior. The tension–compression asymmetry of the propellant mechanical properties has a certain impact on its mechanical response. The maximum equivalent stress and strain considering the tension–compression asymmetry falls between that obtained through the tension and compression constitutive model, and is the same as damage coefficient. The safety factor of the NEPE propellant grain considering the tension–compression asymmetry of its mechanical properties is larger than that non-considering, and the traditional method of structural integrity assessment is conservative.

To investigate the structural effects of the mechanical heterogeneity of Hydroxyl-terminated polybutadiene (HTPB) propellant grain under ignition pressurization, a gradient finite element method was proposed to evaluate its structural integrity. The heterogeneous mechanical properties of the propellant grain were constructed and assessed. The results demonstrate that the mechanical properties of the propellant grain are spatially variable when taking into account the effect of the load. The range of variation in the mechanical properties is related to the size of the load and its effect on the mechanical properties of the propellant. Two key parameters that affect the mechanical response of the grain are the non-uniform distribution of the modulus and the damage strain threshold. An increase in the propellant modulus leads to an increase in the stress response and a decrease in the strain response of the propellant grain under ignition pressurization. Meanwhile, an increase in the damage strain threshold improves the propellant's modulus in the linear elastic stage in a disguised form. This also leads to an increase in the stress response and a decrease in the strain response when the strain response exceeds the damage strain threshold. The safety factor, based on the equivalent strain failure criterion of the grain, directly depends on both the strain response of the propellant grain and the maximum elongation of the propellant. Furthermore, the change in the safety factor of two propellant grains is primarily affected by the maximum elongation of the propellant.

为研究端羟基聚丁二烯(HTPB)推进剂力学性能非均匀性对药柱结构完整性的影响,针对HTPB推进剂在定应变载荷作用下的两类典型本构响应特性构建药柱力学性能非均匀场,采用梯度有限元法开展药柱在点火增压载荷作用下的结构完整性评估.结果表明,HTPB推进剂力学性能的非均匀性引起的药柱等效应变响应的变化,以及定应变引起的药柱最大延伸率的非均匀分布是影响药柱结构完整性的两个直接因素;药柱中模量的不均匀分布是影响其在点火增压载荷下应变响应的主要因素;药柱力学性能的非均匀分布对其在点火增压载荷下的安全系数有较大的影响.考虑药柱力学性能非均匀性时,Ⅰ型推进剂药柱安全系数由 2.32 上升到 3.14,上升幅度约为 35.34%;Ⅱ型推进剂药柱安全系数由 2.13 下降到 1.48,下降幅度为 30.52%,其中药柱等效应变响应的变化对两型推进剂药柱安全系数的影响度分别为-10.15%与31.63%,最大延伸率的变化对两型推进剂药柱安全系数的影响度分别为 110.15%与 68.37%.药柱安全系数变化主要由推进剂最大延伸率变化决定.

Although the ignition-and-growth model can simulate the ignition and detonation behavior of traditional energy materials well, it seems insufficient to simulate the impact-induced deflagration behavior of reactive materials (RMs) using current finite element codes due to their more complicated ignition threshold and lower reaction rates. Therefore, a simulation method for the impact-induced deflagration behavior of a reactive materials projectile (RMP) is developed by introducing tunable ignition threshold conditions for RMs, and a user-defined subroutine is formed by the secondary development on the equation of state (EOS). High-velocity impact experiments were performed to prove the validity of simulations. The results show that the user-defined subroutine for RMs is competent in simulating the ignition and deflagration behavior under impact conditions, because the reaction ratio, morphology and temperature distribution of RMP fragments are all well consistent with experiments, theory, and current reports from other researchers. In this way, the quantitative study on the deflagration reaction of RMs can be implemented and relevant mechanisms are revealed more clearly.

为研究围压效应对NEPE推进剂药柱结构完整性的影响,对包含围压效应的含损伤非线性粘弹性本构模型进行了增量推导,编制本构模型的UMAT子程序对NEPE药柱在点火增压载荷下的力学响应及结构完整性进行了分析.结果显示:围压效应对NEPE推进剂药柱力学响应的影响与损伤应变阈值有关,当药柱的应变响应低于0围压下NEPE推进剂的损伤应变阈值时,围压效应对药柱的力学响应的影响可忽略;当药柱的应变响应高于0围压下NEPE推进剂的损伤应变阈值时,药柱应力响应增大、应变响应降低.5.4MPa围压作用使药柱最大等效应力增加约26％,等效应变降低约12％.围压的压实作用能够大幅降低药柱的损伤程度,5.4MPa的围压作用可降低损伤系数约40％左右.考虑围压效应时采用双剪强度准则和Von Mises应力准则计算得到药柱安全系数分别为3.06和2.11,未考虑围压效应时采用传统的Von Mises应力准则计算得到药柱安全系数为1.97,围压效应可明显提高药柱安全系数,传统的发动机药柱结构完整性评估方法趋于保守.

In order to investigate the effect of confining pressure on the structural integrity of Nitrate Ester Plasticized Polyether (NEPE) propellant grain, a NEPE propellant, whose maximum tensile stress increased from 0.71 MPa to 1.30 MPa and ultimate strain increased from 81% to 175% at 0.0667 s-1 strain rate with the confining pressure increased from 0 to 5.4 MPa, was chosen to be analyzed and discussed. An existing three-dimensional viscoelastic damage model considering confining pressure effect developed for solid propellant was generalized for wider use in a finite element model. The structural integrity of NEPE propellant grain under ignition pressurization was evaluated. The results indicate that the effect of confining pressure within 5.4 MPa on the mechanical response of NEPE propellant grain is related to the strain damage threshold, when the equivalent strain of NEPE propellant grain is lower than the strain damage threshold of NEPE propellant without confining pressure, the confining pressure has little effect on the mechanical response of grain; otherwise, the confining pressure increases the equivalent stress and decreases equivalent strain of NEPE propellant grain under ignition pressurization. The maximum equivalent stress increased 24% and maximum equivalent strain decreased 10% under the confining pressure of 5.4 MPa. The confining pressure can reduce the "dewetting" damage, the "dewetting" damage coefficient can be reduced about 40% under the confining pressure of 5.4 MPa. When considering the confining pressure effect, the safety factor of the grain obtained by twin shear strength criterion and Von Mises stress criterion are 8.57 and 4.36, respectively. The safety factor obtained by the traditional Von Mises stress criterion is 2.38 with non-considering confining pressure effect. The confining pressure effect can improve safety factor of NEPE propellant grain significantly, and the traditional method of structural integrity assessment is conservative.

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

针对定应变贮存条件下HTPB推进剂的微损伤特性,采用临界“脱湿”应变值表征推进剂界面的微损伤.通过开展HTPB推进剂定应变加速老化试验,得到了试样的应力-应变曲线,拉伸断面形貌及耗散能密度的变化趋势.结果 表明:宏观上9％以下的定应变不会引起推进剂明显的“脱湿”现象,但仍会引起界面的微损伤;定应变对推进剂界面的微损伤可用临界“脱湿”应变值表征,其微损伤程度与贮存时间及定应变水平基本符合线性规律;在9％以下定应变作用下,贮存温度是影响HTPB推进剂基体与固体填料界面的黏接性能的主要因素,且存在温度阈值,当温度高于此阈值时,推进剂耗散能密度整体下降较快.

为研究定应变对固体火箭发动机药柱概率贮存寿命的影响,对推进剂高温加速老化力学性能数据进行了统计分析,利用随机有限元法分析了发动机药柱在内压和过载的联合作用下Von Mises应变的均值和标准差,采用应力-强度干涉模型计算了药柱结构可靠性随应变敏感系数的变化趋势,据此分析了定应变对发动机药柱概率贮存寿命的影响.结果显示,定应变对发动机药柱概率贮存寿命影响显著,以0.97为可靠性下限,当应变敏感系数为2.94时,其寿命约为30.98年,应变敏感系数为-2.94时,其寿命约为0.92年,在此范围,药柱概率贮存寿命随应变敏感系数的增大而延长.

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

Accelerated aging tests at the conditions of 3%, 6% and 9% strain levels were conducted on HTPB propellant with the goal of studying effects of constant strain on its maximum elongation. An elongation ag?ing model was developed to analyze the effects of constant strains and temperature on model parameters by fitting the experimental data. Results show that physical tension effect caused by constant strains can increase elonga?tion significantly, and the increasing amplitude exhibits a linear relationship with aging temperature and pre-strains. Physical tension effect shows obvious characteristics of stress relaxation with aging times at various con?stant strains, increasing elongation exponentially. There is a critical temperature between 65℃and 70℃in the aging process of propellant. Constant strains have almost no effect on elongation aging rate below critical tempera?ture,but they decrease elongation aging rate above critical temperature.

Accelerated aging tests under constant strain were conducted on HTPB propellant with the goal of investigating its mechanical properties and constitutive behaviors. Considering the random distribution of inter-nal defect in propellant,a statistical damage constitutive model of propellant was established. The initial damage coefficient,making aging process of propellant equivalent to a form of damage,was introduced to construct the damage variable. Based on the uniaxial tension test of propellant samples aged under constant strain , the model was validated. Results show that theoretical model has good agreement with experimental results and can accurate-ly describe the mechanical behavior of propellant during the constant strain aging. Further analysis indicated the damage effects caused by chemical aging and constant strain can be identified from the equation of initial damage coefficient. Chemical aging can not only influence the tensile strength of propellant in damage phase , but also change the shape characteristics of stress-strain curve. There are obvious yield zones in the stress-strain curves when aging time is below 284 days while there are nonsignificant yield zones at aging time above 284 days under the aging temperature of 55 ℃. The constant strain only decreased the tensile strength in damage phase. The strain threshold value decreased linearly along with the aging time and constant strain level during aging process.

In this study, the effects of accelerated ageing under pre-strain on the maximum elongation of composite solid propellants were investigated. The maximum elongation of aged composite solid propellants at different ageing times, temperatures and pre-strains were determined. An ageing model was developed to analyse the effects of pre-strain and temperature on model parameters. Results show that pre-strain can increase the maximum elongation significantly during accelerated ageing, and the increasing amplitude exhibits a linear relationship with ageing temperature and pre-strain. The physical tension effect caused by pre-strain is a cumulative effect of the stress on samples and shows obvious characteristics of stress relaxation. The relaxation time is independent of pre-strain and exhibits an exponential relationship with ageing temperature. The effect of pre-strain on chemical ageing is related to a critical temperature T-C. For the HTPB propellant investigated in this study, the T-C is between 65 degrees C and 70 degrees C. When the ageing temperature is below T-C, pre-strains have almost no effect on the ageing rate constant for maximum elongation k(epsilon); however, at temperatures above T-C, they may promote chain scission reactions and decrease k(epsilon). (C) 2016 Elsevier Ltd. All rights reserved.