NEPE推进剂低温力学性能研究

为分析硝酸酯增塑聚醚(NEPE)推进剂低温力学性能,通过低温和低温恢复常温单轴拉伸试验,考察了低温条件下NEPE推进剂力学性能的变化情况。采用原位拉伸扫描电镜和环境扫描电镜分别观察了推进剂拉伸过程中和拉断后的微观表面形貌,对比分析了推进剂的动态力学性能。结果表明:在低温拉伸条件下,NEPE推进剂主要表现为基体撕裂;而在低温恢复常温拉伸条件下,主要以颗粒与基体的"脱湿"破坏为主。在低温和低温恢复常温条件下的推进剂力学性能变化不大,结合定应变实验结果,表明NEPE推进剂低温下具有较强的抵抗损伤能力。     

HTPB推进剂的低温力学性能

通过低温和低温恢复常温单轴拉伸试验,考察了低温条件下HTPB推进剂力学性能的变化情况,用SEM扫描电镜观察了推进剂拉伸断面形貌,分析了所得HTPB推进剂的拉伸应力-应变曲线和力学性能特性。结果表明,在低温拉伸条件下,HTPB推进剂主要表现为基体撕裂和颗粒脆断,而在低温恢复常温拉伸条件下,主要以"脱湿"破坏为主。推进剂的低温拉伸曲线具有明显的屈服现象发生,说明推进剂的屈服现象与低温有关。推进剂在低温和低温恢复常温条件下的最大抗拉强度、弹性模量和延伸率等力学性能呈现出不同的变化规律。     

温度和拉伸速率对NEPE推进剂力学性能影响研究

采用单轴拉伸和扫描电镜（SEM）法,研究了硝酸酯增塑聚醚（NEPE）推进剂在宽温域（–30～70℃）、宽拉伸速率（0.5～12 000 mm/min）下应力–应变曲线和拉伸断面形貌变化。结果表明,NEPE推进剂的力学性能曲线受温度和拉伸速率影响较大。随温度降低和拉伸速率升高,其应力–应变曲线从逐渐上升的曲线转变为阶跃两段式上升形状,推进剂拉伸断面颗粒脱离和基体撕裂越来越明显,高温和慢拉、低温和快拉的“偶合”作用,均加剧了推进剂内部损伤的发生。最大抗拉强度（最大拉伸应力）与拉伸速率具有较好的线性双对数关系,该变化规律可采用高分子链段的应力松弛理论进行解释,而最大伸长率（最大拉伸应变）受拉伸速率影响无明显规律。     

利用选择性溶解法研究NEPE推进剂的微观结构

为探索NEPE复合固体推进剂的微观结构特征,了解各组分在推进剂中的微观形态,对NEPE复合固体推进剂在水和三氯甲烷中的溶解过程进行了现象观测,得到了质量损失及离子浓度变化数据.用扫描电子显微镜对溶解剩余物进行了形貌观测.结果表明,NEPE推进剂中的黏合剂把固体颗粒粘结在一起.从微观结构上看NEPE推进剂比较致密,水和三氯甲烷都只能以渗透方式缓慢进入.推进剂中黏合剂的交联程度不高,未交联的黏合剂很容易被溶解;黏合剂受力伸长时包覆在其中的固体颗粒易脱离出来.     

硝酸酯增塑聚醚固体推进剂力学性能研究进展

从黏合剂基体网络结构、固体填料及固体填料/黏合剂基体界面特性等3个方面概述了硝酸酯增塑聚醚(NEPE)固体推进剂力学性能和固体推进剂力学模型的研究进展,并指出改善NEPE推进剂力学性能的方向。     

原位拉伸扫描电镜法研究GA P推进剂的损伤行为

采用原位拉伸扫描电镜研究了GAP推进剂的损伤演化过程,并结合数字图像技术和分形维数的方法对裂纹演化进行了定量分析。结果表明,GAP推进剂在拉伸过程中的破坏首先发生在大粒径的AP颗粒集中分布区域,紧邻AP颗粒间少量的黏合剂基体断裂及脱粘;然后再到分散分布区域的AP颗粒及其附近位置处与黏合剂基体的脱粘;拉伸前期裂纹增加较为迅速,其后缓慢增加直到推进剂整体断裂;拉伸速率越慢,拉伸前期裂纹增加越快,且整个拉伸过程损伤程度越大;其中,拉伸速率为0.05 mm/min的拉伸过程损伤程度最为显著。     

利用选择性溶解法研究NEPE推进剂的微观结构

为探索NEPE复合固体推进剂的微观结构特征，了解各组分在推进剂中的微观形态，对NEPE复合固体推进剂在水和三氯甲烷中的溶解过程进行了现象观测，得到了质量损失及离子浓度变化数据。用扫描电子显微镜对溶解剩余物进行了形貌观测。结果表明，NEPE推进剂中的黏合剂把固体颗粒粘结在一起。从微观结构上看NEPE推进剂比较致密，水和三氯甲烷都只能以渗透方式缓慢进入。推进剂中黏合剂的交联程度不高，未交联的黏合剂很容易被溶解；黏合剂受力伸长时包覆在其中的固体颗粒易脱离出来。     

NEPE推进剂的细观力学性能研究

采用原位拉伸扫描电镜技术对NEPE推进剂的单轴拉伸破坏过程进行了研究.结果表明,固体粒子与黏合剂基体的脱湿是破坏的主要因素.采用数字图像分析方法对此破坏过程进行定量化研究,对图像的分形维数进行了计算,发现随着拉伸破坏过程的进行,分形维数逐渐增大.采用此方法计算的细观结构分形维数可以作为研究NEPE推进剂细观损伤演化的定量指标.     

NEPE推进剂老化过程中结构与力学性能的关系

为考察NEPE推进剂的老化特性,在60,65,70和75℃老化了推进剂样品,研究了其在常温时的抗拉强度σm,初始模量E0与黏合剂母体凝胶质量分数ω、化学交联密度υe、物理交联密度υp之间的关系.用动态热机械分析仪(DMA)测试了多个频率下老化样品的损耗因子tanδ、损耗模量半高峰宽D h/2.结果表明,高温加速老化过程中NEPE推进剂样品σm和E0下降的原因是推进剂黏合剂母体结构的ω,υe 和υp下降.NEPE推进剂降解和解聚由黏合剂母体结构变化引起.     

嵌段型中性聚合物键合剂在NEPE推进剂中的初步应用

采用扫描电镜和力学性能测试技术,对比研究了嵌段型中性聚合物键合剂QD–06和中性聚合物键合剂(NPBA)对黑索今(RDX)粒子的包覆性能以及在硝酸酯增塑聚醚(NEPE)推进剂中的键合效果。结果表明,QD–06包覆RDX的表面更加圆滑,颗粒间团聚现象明显,其包覆能力优于NPBA;QD–06能显著提高固体推进剂的常温和高温力学性能,大幅改善推进剂脱湿现象,其键合效果优于NPBA。     

星型PAO黏合剂在NEPE推进剂中的应用

星型PAO作为一种新型高能固体推进剂用黏合剂,其特有的3星或4星结构,能提高NEPE推进剂交联网络的交联比例,且交联点间有较长的柔韧结构,能充分抵抗拉长和撞击的破坏,可有效改善NEPE推进剂的力学性能,并在一定程度上降低推进剂的感度。文中主要对星型PAO的结构特点及其在NEPE推进剂中的应用情况进行了评述和总结。     

Experimental Investigation on High Strain Rate Tensile Behaviors of HTPB Propellant at Low Temperatures

To study the high strain rate tensile behaviors of hydroxyl‐terminated polybutadiene (HTPB) propellant at low temperatures, uniaxial tensile tests were conducted at different strain rates (0.4–42.86 s⁻¹) and temperatures (233–298 K) using an INSTRON testing machine. Scanning electron microscopy (SEM) was employed to observe the tensile fracture surfaces. Experimental results indicate that strain rate, temperature and test environment remarkably influence the tensile behaviors of HTPB propellant. The stress‐strain curves exhibit three different shapes. The elastic modulus and maximum tensile stress increase with decreasing temperature and increasing strain rate. However, the strain at maximum tensile stress decreases with increasing strain rate at low temperatures and there is a maximal value at 298 K and 14.29 s⁻¹. The effects of strain rate, temperature and test environment on the tensile behaviors are closely related to the changes of properties and fracture mechanisms of HTPB propellant. The dominating fracture mechanism depends on not only temperature but also strain rate, and it changes from the dewetting and matrix tearing at room temperature and lower strain rate to the particle brittle fracture at low temperatures. Based on the time‐temperature superposition principle (TTSP), the master curves of mechanical parameters for HTPB propellant were obtained.     

A new test method to obtain biaxial tensile behaviors of solid propellant at high strain rates

A new test method was proposed and applied for studying the biaxial tensile behaviors of hydroxyl-terminated polybutadiene (HTPB) propellant at high strain rates. The biaxial tensile stress responses of the propellant at room temperature and at different strain rates (0.40–85.71 s^?1) were obtained through the use of biaxial tensile strip samples, a new designed aluminum apparatus and a uniaxial Instron testing machine. A high-speed camera and scanning electron microscop (SEM) were employed to observe the biaxial tensile deformation and the damage of HTPB propellant under the test conditions. The results indicated that strain rate could remarkably influence the biaxial tensile behaviors of HTPB propellant. The effect of strain rate on the characteristics of stress–strain curves, mechanical properties and fracture mechanisms was consistent with that in uniaxial tension. However, the biaxial weakening of HTPB propellant was obvious. The strain at biaxial maximum tensile stress was between 10 and 30 % lower than that at the corresponding uniaxial case. Finally, the correlations between the fracture mechanisms and the mechanical properties of HTPB propellant, stress state and the damage of HTPB propellant were discussed. The damage of the propellant under the biaxial tensile test was less serious than that under uniaxial tension at the same strain rate. In addition, continuously increasing strain rate could change the fracture mechanism of the propellant under the biaxial and uniaxial tensile tests. In this investigation, the dominating fracture mechanism of HTPB propellant changed from the dewetting and matrix tearing at lower strain rate to the particles fracture at higher strain rate.     

Tensile mechanical properties and constitutive model for HTPB propellant at low temperature and high strain rate

To investigate the mechanical properties and fracture mechanisms of hydroxyl‐terminated polybutadiene (HTPB) propellant at low temperature and high strain rate, uniaxial tensile tests were conducted over the range of temperatures 233 to 298 K and strain rates 0.4 to 14.14 s^?1 using an INSTRON testing machine, and scanning electron microscope (SEM) was employed to observe the tensile fracture surfaces. The experimental results indicate that the deformation properties of HTPB propellant are remarkably influenced by temperature and strain rate. The characteristics of stress–strain curves at low temperatures are different from that at room temperature, and the effects of temperature and strain rate on the mechanical properties are closely related to the changes of properties and the fracture mechanisms of HTPB propellant. The dominating fracture mechanism depends much on the temperature and changes from the dewetting and matrix tearing at room temperature to the particle brittle fracture at low temperature, and the effect of strain rate only alters the mechanism in a quantitative manner. Finally, a nonlinear viscoelastic constitutive model incorporating the damage evolution and the effects of temperature and strain rate was developed to describe the stress responses of this propellant under the test conditions. During this process, the Schapery‐type constitutive theories were applied and one damage variable was considered to establish the damage evolution function. The overlap between experimental results and predicted results are generally good, which confirms that the developed constitutive model is valid, however, further researches should be done due to some drawbacks in describing the deformation behaviors at very large strain. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42104.     

Experimental Investigation on Laser Ignition and Combustion Characteristics of NEPE Propellant

The ignition and combustion property of solid propellant is the main content in internal ballistic research, which has a great significance for propulsion application and combustion mechanism. In this study, the detailed gas‐phase reaction mechanism of Nitrate Ester Plasticized Polyether Propellant (NEPE) was developed. It is helpful to understand the intricate processes of solid‐propellant combustion. The factors which may have influences on ignition delay time and temperature distribution of propellant surface was analyzed by laser ignition experiment. Using high‐speed camera and an infrared thermometer, the ignition and combustion process and the surface temperature distribution of NEPE propellant under laser irradiation were measured. Laser heat flux, ambient pressure and initial temperature of NEPE propellant have an influence on the ignition delay time and the surface temperature. Results show that the ignition delay time decreases with the increase of laser heat flux, ambient pressure and initial temperature of NEPE propellant. At the same time, with the increase of laser heat flux, the influences of ambient pressure and initial temperature on the ignition delay time decrease. Besides, laser irradiation, ambient pressure and initial temperature have significant influences on the surface temperature distribution of the propellant.     

三官能度PET对胶片和NEPE推进剂力学性能的影响

为了改进NEPE推进剂常温力学性能,研究了三官能度环氧乙烷-四氢呋喃共聚醚(PET)对PET/N100胶片及NEPE推进剂力学性能的影响。结果表明,在胶片固化比R分别为1.0、1.1、1.2时,随着三官能度PET(f=3.2)在预聚物中所占质量分数的增大,胶片交联密度相应提高,最大增幅达45.69%,胶片强度随之提高,最大抗拉强度σm增幅达101%,断裂伸长率εb相应减小;三官能度PET应用于NEPE推进剂时,能有效改善推进剂常温力学性能,强度与延伸率均有所提高,当粘合剂预聚物中三官能度PET的质量分数达62.5%时,σm可达0.570 4 MPa,比空白样提高了50%以上。     

Applying modified hyperbranched polyester in hydroxyl‐terminated polyether/ammonium perchlorate/aluminium/cyclotrimethylenetrinitramine (HTPE/AP/Al/RDX) composite solid propellant

Composite solid propellants demand fine and stable mechanical properties, creep resistance and stress relaxation performance during their long storage and usage time. In this study, modified hyperbranched polyester (MHBPE) was prepared and introduced into HTPE/AP/Al/RDX (HTPE, hydroxyl‐terminated polyether; AP, ammonium perchlorate; RDX, cyclotrimethylenetrinitramine) solid propellant as an effective additive. The static tensile and dynamic mechanical properties of this propellant before and after the introduction of MHBPE were evaluated. The elevated interfacial interaction by using MHBPE between the binder and RDX fillers improved the toughness and elasticity of the propellant. The enhancement mechanisms were also confirmed by the influence on the fracture surface morphology of the binder which was investigated by SEM. In addition, some influence on the dynamic mechanical properties of HTPE/AP/Al/RDX propellant caused by MHBPE was investigated by dynamic mechanical analysis. The creep behaviors of the HTPE/AP/Al/RDX propellants with and without MHBPE were also investigated at different stresses and temperatures. Reduced creep strain rate and strain were obtained for the modified propellant, implying enhanced creep resistance performance. The creep properties were quantitatively evaluated using a six‐element model and the long‐term creep performance of the propellant was predicted using the time–temperature superposition principle. A creep behavior of nearly 10⁶ s at 30 °C could be acquired in a short‐term experiment (800 s) at 30–70 °C. Moreover, the stress relaxation investigation of the propellants with and without MHBPE at ?40 °C, 20 °C and 70 °C suggested that MHBPE/HTPE/AP/Al/RDX propellant possessed better response ability to deformation. Thus, the application of MHBPE provides an efficient route of reinforcement to enhance the creep resistance and stress relaxation properties. © 2020 Society of Chemical Industry     

含CL-20 NEPE推进剂的力学性能

采用光电子能谱(XPS)和显微红外光谱(M IR)研究了4种键合剂(M APO,22#,HX-752,T 313)与CL-20的相互作用。结果表明,键合剂可以作为CL-20的包覆剂;由于海因和三聚异氰酸酯键合剂(22#)的环状结构以及具有较多的极性基团,对CL-20的包覆性最好。含CL-20的NEPE推进剂力学性能测试结果表明,22#键合剂对提高含CL-20的NEPE推进剂体系的力学性能非常有利,其拉伸强度和断裂延伸率均有较大的提高,分别增加了18.8%和103.4%。     

Life Prediction of NEPE Propellants

NEPE propellants were prematurely aged at 65, 70, 75, and 80 °C, respectively. The strength limit of NEPE propellants was tested by the uniaxial tension test. Based on the aging mechanism of the micro‐phase structure and the macro‐mechanical properties of NEPE propellants, the aging process was divided into three stages: post curing stage, microstructure gradual degradation stage and accelerated chemical aging stage. Because nitrate ester is hardly to decompose at ambient temperatures, the post cure of NEPE propellants only occurs at higher temperatures. Thus, the life prediction of NEPE propellants should ignore the time of post cure. The service life of NEPE propellants at ambient temperatures should be determined by the second stage of high temperature accelerated aging. By analyzing the tensile strength of NEPE propellants aged at 65, 70, 75, and 80 °C, the service life prediction equation of NEPE propellants was established and the service life was predicted.