真空技术在固体火箭发动机装药及总装检测中的应用

本文介绍了真空技术在固体火箭发动机推进剂原材料准备、燃烧室绝热、推进剂药柱浇注成型、发动机总装检测中的应用,真空技术在提高固体火箭发动机制造质量方面发挥了积极作用。     

高能复合固体推进剂的研究进展

高能化始终是复合固体推进剂的研究热点.介绍了当今复合固体推进剂高能化研究进程中国内外在氧化剂、金属燃烧剂和含能粘合剂体系方面的主要研究成果.借助先进的技术途径改善氧化剂和金属燃烧剂的燃烧性能是目前国内复合固体推进剂的研究重点.超高能量密度材料(氮原子簇化合物和多异氰基立方烷类化合物)和贮氢类金属燃烧剂三氢化铝以及一些新型的含能粘合剂等新型含能材料的出现,为下一代高能复合固体推进剂的研究指明了方向.     

复合固体推进剂细观界面脱粘有限元分析

针对复合固体推进剂细观损伤的特点,在颗粒与基体之间引入了粘结界面单元,采用双线性关系模型描述其界面损伤扩展特性,并对双线性关系模型中初始线性模量、最大粘结强度和最大张开位移等参数进行了预测.结合复合固体推进剂的填充模型,对推进剂内部细观界面脱粘过程进行了有限元分析.研究表明,采用粘结界面单元可以有效模拟推进剂颗粒的界面...     

复合固体推进剂的溶解特性研究

对复合推进剂在水、乙醇、乙酸乙酯和二氯甲烷溶剂中的溶解特性进行了研究,用显微镜对溶解剩余物的形貌进行了扫描观测,得到了复合推进剂微观结构的溶解机理。结果表明,复合推进剂中粘合剂系统的交联程度比较高,结构比较致密,粘合剂把固体颗粒粘结在一起,从微观结构上看,溶剂只能以渗透的方式缓慢进入,未交联的粘合剂很容易被溶解。     

细观结构参量对推进剂力学性能影响的数值研究

为了更好地理解并预测复合固体推进剂组分、界面对其宏观力学性能的影响，在细观层次上建立了考虑界面和颗粒形貌的代表性体积单元(Representative volume elements,RVE)计算模型，通过引入内聚力模型(Cohesive zone model,CZM)研究了界面刚度、强度及最大失效位移对推进剂力学性能的影响，并对比分析了颗粒形貌与界面对其力学性能的贡献。研究结果表明：界面刚度为0.004～400 MPa/mm时，推进剂初始模量从0.67 MPa提升到3.67 MPa；界面强度从0.05 MPa提高至30 MPa时，推进剂拉伸强度从0.15 MPa提高到了0.76 MPa，即界面刚度增加对推进剂初始模量的提高有限，而界面强度对其拉伸强度的提高非常显著；然而，较高的界面强度可能导致细观结构出现“损伤局部化”，从而降低延伸率。相对于界面对推进剂实际力学性能的提升，颗粒级配、形状的作用显得较小，说明界面是决定推进剂拉伸性能的主要因素之一。最后基于以上分析结果，对另一种推进剂在不同应力下的蠕变性能进行了预测，发现蠕变断裂时间的对数与恒定应力满足线性关系。     

复合固体推进剂基体/填料界面研究现状

复合固体推进剂广泛应用于航天火箭及常规战备武器中,其基体与填料间的界面问题一直是科研工作者关注的焦点。因基体/填料界面属于推进剂的弱作用点,研究界面问题可在一定程度上反映推进剂的整体结构完整性。简要介绍了目前关于固体推进剂中基体/填料界面的主要研究方法,从物相表征和力学测试两方面进行分类,分别介绍了红外光谱、显微镜、X射线光电子能谱、接触角测量及拉伸测试法和动态力学性能测试法在基体/填料界面处的应用,并介绍了几种常见界面作用理论。通过总结和对比,展望了固体推进剂基体/填料界面研究的发展方向,指出界面研究将朝着对单一界面进行研究、从微观角度测试力学性能以及界面分子动力学研究的方向发展。     

BT20钛合金激光焊接接头的断裂韧性研究

对BT20钛合金及其激光焊接接头的断裂韧性进行了研究.同时分析了合金及激光焊接接头的硬度分布及显微组织.断裂实验表明,除了一个焊接接头紧凑拉伸(CT)试样是脆性启裂外,其它CT试样均在裂纹延性启裂并缓慢扩展后,发生脆性失稳断裂.母材的断裂韧性明显高于焊接接头,轧制方向对母材断裂韧性的影响不明显.焊接热影响区的断裂韧性介于母材和焊缝金属之间.本研究采用的焊后热处理没有改善焊接接头的断裂韧性,还有进一步恶化的趋势.添加活性剂对焊缝金属的断裂韧性没有明显作用,但对延性裂纹扩展长度有所改善.     

高强钢断裂韧性K_(IC)的小尺寸试样评价方法

研究了不同尺寸的0Cr13Ni8Mo2Al沉淀硬化高强钢断裂韧性试样的断口形貌和断裂机理。结果表明:断裂韧性试样的拉断区可分为裂纹慢速扩展区(解理区)和快速扩展区(韧窝区);而断裂能,则主要消耗在裂纹慢速扩展区内。本文建立了断裂韧性K_(IC)的小尺寸试样评价方法。根据该方法,使用小尺寸试样测得的断裂韧性K_(IC)值与使用标准试样测得的断裂韧性K_(IC)值之间的相对误差为9%,没有超过10%。这个结果表明,使用小尺寸试样评价方法测出的金属材料的断裂韧性K_(IC)值是十分可靠的。     

少烟PBT推进剂制备及性能研究

为获得少烟且高能量的复合固体推进剂，使用含能PBT黏合剂，制备了铝粉质量分数为5%的PBT叠氮三组元推进剂，研究了推进剂的能量、燃烧及力学性能。结果表明，推进剂在固体质量分数78%时能量和工艺性能最优，使用φ118标准发动机测试能量比冲达246.4 s；压强指数随燃速铜铬催化剂RC和增塑剂ATC用量的增加而降低；燃烧速度随RC和超细高氯酸铵AP用量的增加而升高；固化参数或键合剂用量增加后，推进剂抗拉强度升高、伸长率降低。制备的少烟叠氮配方综合性能良好，可供高性能少烟推进剂装药。     

Bi2O3／氧化石墨烯复合催化剂的制备及其爽双基推进剂燃烧催化性能的研究

以氧化石墨、五水硝酸铋等为原料,通过液相化学沉积法制备出Bi2O3／氧化石墨烯（Bi2O3／GO）复合催化剂,采用扫描电镜（SEM）、透射电镜（TEM）和X-射线粉末衍射（XRD）对产物的粒子形貌、粒径和物相结构进行了表征,并考察了Bi2O3／GO复合催化剂对双基推进剂燃烧性能的影响,结果表明,产物中Bi2O3以球状粒子的形式均匀地负载在氧化石墨烯表面,平均粒径约40nm。Bi2O3／GO复合催化剂能明显改善推进剂的燃烧性能,使推进剂的燃速提高了139％f4MPa）,压强指数（14～20MPa）从0．650降低至0．253,降低了61．0％。     

Investigation of microstructure and mechanical properties of steel fibre–cast iron composites

Abstract

The aim of the present experimental study was to investigate improvement of the toughness and strength of grey cast iron by reinforcing with steel fibres. The carbon content of the steel fibres was chosen to be sufficiently low that graphite flakes behaving as cracks were removed by carbon diffusion from the cast iron to the steel fibres during the solidification and cooling stages. To produce a graphite free matrix, steel fibres with optimum carbon content were used and the reinforced composite structure was cast under controlled casting conditions and fibre orientation. Three point bend test specimens were manufactured from steel fibre reinforced and unreinforced flake graphite cast iron and then normalising heat treatments were applied to the specimens at temperatures of 800 and 850°C. The fracture toughness and strength properties of the steel fibre reinforced material were found to be much better than those of unreinforced cast iron. The microstructures of the composite at the fibre–matrix transition zone were examined.     

Effect of heat treatment on fracture behavior of steel-wire-reinforced gray cast iron

In this experimental study, fracture toughness of heat-treated metal matrix composite was investigated. The gray cast iron was reinforced with steel wire of volume fraction of V_r = 0.05 and three-point bend specimens were manufactured to determine fracture toughness. Heat treatment was applied to the specimens at the normalization temperatures of 850°C and then cooled in three distinct environments (water, air, and furnace). Fracture toughness of the metal matrix composite was calculated by unloading compliance method. The study shows that the fracture toughness of the steel-wire-reinforced gray cast iron increases with the increase in cooling rate. Scanning electron microcopy (SEM) analyses were used to examine the microstructure and fracture surface. It is observed that the carbon diffuses from the gray cast iron to the steel wire and transition region having partially dissolved graphite was observed due to carbon diffusion, and it plays an important role in the fracture toughness depending on the cooling media.     

Fracture toughness of sub-zero-chilled cast iron

A series of fracture toughness experiments were carried out involving sub-zero-chilled (using liquid nitrogen) cast iron containing 1.5% Cu, and chromium contents ranging from 0.0%–0.2%. By using copper chills of different thicknesses, the effect on fracture toughness of varying the chill rate was also examined. The fracture toughness tests were carried out using three-point bend specimens, each with a chevron notch, as per ASTM E 399-1974 standards. It was found that fracture toughness is highly dependent on the location on the casting from where the test specimens are taken and also on the chromium content of the material. Chill thickness, however, does not significantly affect the fracture toughness of the material. There was found to be an approximately linear relationship between fracture toughness and pearlite content, in which fracture toughness increases as pearlite content decreases and vice versa.     

Fracture behavior and microstructure of steel fiber reinforced cast iron

In this study, improvement of fracture toughness and strength of gray cast iron by reinforcing steel fiber was investigated. Three point bend specimens were used to calculate the flexural strength and fracture toughness. Fracture toughness of the reinforced cast iron with two distinct volume fraction (Vf = 0.05 and 0.08) were calculated by compliance method and J-integral method using single specimen technique. The study shows that fiber reinforced composite has higher fracture toughness and flexural strength than cast iron without reinforcement. Also, fracture toughness increases with increasing volume fraction of reinforcement. Optical and scanning electron microcopy (SEM) analyses were used to examine the microstructure and fracture surface. It is noted that the carbon diffuses from gray cast iron to steel fiber and graphite free transition regions with high hardness were observed due to the carbon diffusion.     

高能固体推进剂工艺助剂研究进展

综述了提高高能固体推进剂加工工艺性能助剂的研究进展.从稀释药浆、延迟固化反应、改善颗粒流动性能等改善推进剂药浆加工性能的措施出发,分别介绍了相应工艺助剂的研究及应用情况.对近年来研究报道较多的可同时改善加工过程中固体颗粒流动性能及推进剂力学性能的多功能性工艺助剂的研究情况进行了重点介绍.对高能固体推进剂多功能性工艺助剂...     

Influence of heat treatment and hot working on fracture toughness of cast aluminium base composites

Abstract

Evaluation of toughness in terms of the fracture energy E*, obtained using Charpy impact testing and the fracture toughness K_Ic obtained from bend tested specimens, has been carried out for various cast particle reinforced aluminium base composites, namely, A356–SiC, A357–SiC, 6061–Al₂O₃, and 2014–Al₂O₃. In practice, the first two are used in the as cast foundry condition and the last two in the cast and extruded condition. Hot extrusion or rolling to reduction ratios between 2 : 1 and 50: 1 was conducted on the 6061 and 2014 composites to characterise the influence of working processes. Heat treatment conditions considered included the as cast (or as worked), solid solution treated, and T6 temper. The results show that extrusion or rolling can markedly improve the toughness, but on thermal aging the toughness is reduced. The increase in total fracture energy by hot working is mainly caused by the increase of initiation energy, whereas the decrease of fracture energy by artificial aging is controlled by the propagation energy. The values of K_Ic obtained for these composites are from 15 to 25 MN m^?3/2. Comparisons and interpretations of the dynamic Charpy fracture energy, quasistatic fracture toughness, and fracture surface of the four composites are also presented.

MST/1806     

Manufacturing Influence on the Delamination Fracture Behavior of the T800H/3900-2 Carbon Fiber Reinforced Polymer Composites

'Torayca' T800H/3900-2 is the first material qualified on Boeing Material Specification (BMS 8-276) which utilizes the thermoplastic-particulate interlayer toughening technology. Two manufacturing processes, the autoclave process and the fast heating rated Quickstep™ process, were employed to cure this material. The Quickstep process is a unique composite production technology which utilizes the fast heat transfer rate of fluid to heat and cure polymer composite components. The manufacturing influence on the mode I delamination fracture toughness of laminates was investigated by performing double cantilever beam tests. The composite specimens fabricated by two processes exhibited dissimilar delamination resistance curves (R-curves) under mode I loading. The initial value of fracture toughness G_IC-INIT was 564 J/m² for the autoclave specimens and 527 J/m² for the Quickstep specimens. However, the average propagation fracture toughness G_IC-PROP was 783 J/m² for the Quickstep specimens, which was 2.6 times of that for the autoclave specimens. The mechanism of fracture occurred during delamination was studied under scanning electron microscope (SEM). Three types of fracture were observed: the interlayer fracture, the interface fracture, and the intralaminar fracture. These three types of fracture played different roles in affecting the delamination resistance curves during the crack growth. More fiber bridging was found in the process of delamination for the Quickstep specimens. Better fiber/matrix adhesion was found in the Quickstep specimens by conducting indentation-debond tests.     

Effect of compressive transverse normal stress on mode II fracture toughness in polymeric composites

Effect of transverse normal stress on mode II fracture toughness of unidirectional fiber reinforced composites was studied experimentally in conjunction with finite element analyses. Mode II fracture tests were conducted on the S2/8552 glass/epoxy composite using off-axis specimens with a through thickness crack. The finite element method was employed to perform stress analyses from which mode II fracture toughness was extracted. In the analysis, crack surface contact friction effect was considered. It was found that the transverse normal compressive stress has significant effect on mode II fracture toughness of the composite. Moreover, the fracture toughness measured using the off-axis specimen was found to be quite different from that evaluated using the conventional end notched flexural (ENF) specimen in three-point bending. It was found that mode II fracture toughness cannot be characterized by the crack tip singular shear stress alone; nonsingular stresses ahead of the crack tip appear to have substantial influence on the apparent mode II fracture toughness of the composite.     

On the relation between the mode I fracture toughness of a composite laminate and that of a 0° ply: Analytical model and experimental validation

This paper proposes a simple model to predict the fracture toughness of multidirectional carbon–epoxy composite laminates using the fracture toughness of the 0° ply. The model is based on a combination of Linear-Elastic Fracture Mechanics and lamination theory, and uses as material properties the ply elastic properties and the fracture toughness of the 0° ply measured in compact tension test specimens. A good correlation is obtained by comparing the model predictions and experimental data obtained in center-cracked specimens manufactured using different lay-ups and materials.