超细晶Laves相NbCr2颗粒增强Nb基复合材料的制备及其组织性能研究

采用机械合金化 热压工艺制备了Laves相NbCr2增强的Nb基复合材料。研究了Nb-22.5Cr配比成分的Nb,Cr元素粉经MA30h后在1250℃分别热压10min,20min和30min所获得的Nb/NbCr2复合材料的组织和性能。结果表明:三种热压时间均可制备出组织均匀,致密度高的Nb/NbCr2复合材料,体积分数约为30%的近等轴状的Laves相NbCr2颗粒弥散分布于Nb固溶体基体中。热压20min的试样具有最佳的组织和性能,其Laves相NbCr2的晶粒尺寸达到亚微米级,致密度达到99.2%,维氏硬度为9.41GPa,屈服强度为2950 MPa,抗压强度为3345 MPa,塑性应变达到了7.01%,充分实现了Laves相NbCr2颗粒强化和细晶强韧化的效果。     

Influence of processing and external storage conditions on the performance of envelope materials for stratospheric airships

Envelope materials are extremely vital for stratospheric airships, which are widely used in numerous applications. The influence of processing as well as the storage and utilization conditions on the performance of envelope materials has been studied systematically for the first time. Results show that the performance of envelope materials depends largely on the hot-pressing temperature and the flexing during processing. The tensile strength of samples dropped to 289.1 ± 8.0 MPa from 346.6 ± 9.3 MPa when pressed at temperature above 180 °C and helium leakage appeared. The outer layers would be worn off when flexed no matter by manual or machine, resulting in dramatic increase of helium permeability and even leakage as well as varying decrease of mechanical properties. Hence, suitable hot-pressing temperature and limitation of flexing as little as possible during processing are essential to obtain products with suitable properties. Besides, the storage and utilization conditions are also critical to the properties of envelope materials. Both naturally aged samples in outdoor storage on ground and samples recovered from actual flight on stratospheric airship exhibited reduced mechanical properties and even helium leakage due to excess solar irradiation, ozone concentration and energetic particles interaction compared with those stored indoors. The weatherability of envelope materials should be further strengthened in the next few years. This research could provide a theoretical guidance for actual practice.     

Brazing of C/C composite and Ti-6Al-4V with graphene strengthened AgCuTi filler: Effects of graphene on wettability,microstructure and mechanical properties

Graphene nanosheets(GNSs) strengthened AgCuTi composite filler(AgCuTi_G) was used to braze C/C composite and Ti-6Al-4V. The effects of GNSs on the wettability of AgCuTi_G filler on the C/C composite surface and the interfacial microstructure and mechanical properties of brazed joints were investigated. The results indicate that the addition of GNSs reduced the wettability of AgCuTi_G. The interfacial microstructure of brazed joints evolved with the addition of GNSs, where Ti_3Cu_4 and TiCu_4 were converted to TiCu and the thickness of the reaction layer adjacent to the base material decreased. The maximum shear strength of joints brazed at 0.3 wt% GNSs was 23.3 MPa(880℃/10 min). Further adding GNSs deteriorated the shear strength of the joints. Fracture of the joints occurred in the C/C composite substrate and the TiC layer adjacent to C/C composite.     

C/C喉衬近净尺寸制备及性能

采用径向针刺工艺制备了近净尺寸针刺C/C喉衬预制体,通过热梯度CVI和树脂浸渍碳化复合工艺对预制体进行了致密,利用μ-CT、光学显微仪表征了C/C喉衬材料微观孔隙和热解碳织构,分析了喉衬材料的弯曲性能。结果表明,径向针刺过程形成的损伤型孔隙通道与碳源气体传输方向一致,提高了碳源气体传输效率,使径向针刺喉衬CVI增密效率比传统轴向针刺喉衬提高10.9%。预制体近净尺寸成型缩短了烧蚀区域碳源气体的渗透距离,喉衬材料烧蚀区域形成了高织构热解碳,有利于喉衬烧蚀性能的提高。径向针刺喉衬的轴向弯曲强度比轴向针刺喉衬提高150%。     

Estimation of sediment settling velocity in estuarine and coastal waters using optical remote sensing data

A robust method has been developed for estimating sediment settling velocity (w_s) from high resolution optical remote sensing data in estuarine, coastal and harbor waters. This method estimates settling velocity as a function of the drag coefficient (C_d), Reynolds number (Re), grain size (D₅₀), specific gravity (Δ_SG) and grain shape (in terms of the Corey Shape Factor – CSF). These parameters were derived from the particulate inherent optical properties such as backscattering (b_bp), beam attenuation (c_p), suspended sediment concentration and turbidity using Landsat 8 OLI and HICO data. Preliminary results for the Gulf of Cambay in the eastern Arabian Sea and Yangtze river estuary in the East China Sea, showed that satellite-retrieved settling velocities (m?s^?1) varied from very low values in clear oceanic waters, intermediate values in coastal waters, to very high values in river plumes and sediment-laden coastal waters. The remote sensing retrievals of sediment properties and their settling velocities were generally consistent with the field and laboratory results, which indicate that the proposed methodology will have important implications in various coastal engineering, environmental and management studies.     

Lakshita – Mining and research hub at L5

In this paper, the design of an orbital space settlement named Lakshita located at L5 for 10,000 residents having area of 1 × 10⁶ m² has been proposed, with the aim of fulfilling mining activities and space research in micro – g. All calculations are made in the perspective of a dynamic demography which could lead to the doubling of the population in next 25 years with initial population of 4500. The settlement consists of one residential torus, one agricultural torus, industrial cylinder and two docking cylinders rotating coaxially at 1 rpm. 2.3% of the total volume of settlement is provided for two docking cylinders with 6 docking ports enabling the elastic flow of space traffic, thereby providing continuous loading and unloading of cargo and passengers. Four pressurized sliding cylinders with 5.7 × 10⁵ m³ volume above the down surface area moving along the spokes fulfill the need of adaptation of visitors at half the gravity level of primary settlement volumes, as well provide wobble control. 1.1 × 10⁵ torr of pressure is provided above the down surface area of the residential torus. The power generation of 400 Mw, required for the functional need of Lakshita, will be obtained through SPS located at L4. The 14 h day and 10 h night cycle will be maintained by four mirrors attached on either side from the central cylinder. The walls of the settlement will be made up of three consecutive layers of super adobe, Nextel and Kevler-49 respectively to provide radiation and debris protection. An assortment of various facilities like appropriate distribution and management of water through an intended network of pipelines, accurate management of waste within the settlement has been provided.     

Vectran纤维复合材料拉伸与撕裂性能研究

文章对Vectran纤维织物及Vectran纤维织物复合材料的拉伸和撕裂性能进行了试验研究;分析了环境温度对Vectran纤维织物拉伸性能的影响;讨论了不同涂层厚度下织物复合材料的抗拉特性与破坏模式。试验结果表明Vectran纤维织物材料的拉伸性能明显的受环境温度影响;材料失效破坏模式,对Vectran纤维织物主要为纤...     

辅助摩擦电铸Ni-Mn合金的力学性能

利用一种新的电铸技术--游离粒子辅助摩擦电铸技术进行Ni-Mn合金的电铸试验.研究了工艺参数对Ni-Mn合金电铸层显微硬度和拉伸性能的影响规律.试验结果表明,游离粒子的辅助摩擦作用和电铸层中的锰元素共同影响着电铸层的力学性能.随着阴极旋转速率的提高,电铸层中锰含量不断增加,且游离粒子对电铸层的摩擦、挤压作用随之加强,电...     

改性羰基铁粉/ 硅橡胶材料的制备及其力学性能

以微米级改性羰基铁粉为填充剂,甲基乙烯基硅橡胶为基体,制备了高温硫化的羰基铁粉/硅橡胶复合材料.研究了偶联剂种类、用量及羰基铁粉填充量对复合材料力学性能的影响,利用扫描电镜对硫化胶断面的微观结构进行了观察.结果表明,采用硅烷偶联剂KH570、KH151改性羰基铁粉都能提高复合材料的拉伸强度,其中KH151的改性效果要优于KH570;KH151的最佳用量为羰基铁粉质量的1%;在一定范围内随着改性羰基铁粉体积分数的增加,复合材料的拉伸强度增大.羰基铁粉体积分数超过60%后,混炼困难.     

Multi-objective optimization of different dome reinforcement methods for composite cases

A multi-objective optimization method was proposed for different dome reinforcement methods of a filament-wound solid rocket motor composite case based on a Radial Basis Function (RBF) model. Progressive damage of the composite case was considered in a simulation based on Hashin failure criteria, and simulation results were validated by hydraulic burst tests to precisely predict the failure mode, failure position, and burst pressure. An RBF surrogate model was established and evaluated by Relative Average Absolute Error (RAAE), Relative Maximum Absolute Error (RMAE), Root Mean Squared Error (RMSE), and R² methods to improve the optimization efficient of dome reinforcement. In addition, the Non-dominated Sorting Genetic Algorithm (NSGA-II) was employed to establish multi-objective optimization models of variable-angle and variable-polar-radius dome reinforcements to investigate the coupling effect of the reinforcement angle, reinforcement layers, and reinforcement range on the case performance. Optimal reinforcement parameters were obtained and used to establish a progressive damage model of the composite case with dome reinforcement. In accordance with progressive damage analysis, the burst pressure and performance factor were obtained. Results illustrated that variable-angle dome reinforcement was the optimal reinforcement method compared with variable-polar-radius dome reinforcement as it could not only ensure the reinforcement angle’s continuous changing but also decrease the mass of composite materials. Compared with the unreinforced case, the reinforced case exhibited an increase in the burst pressure and performance factor of 36.1% and 23.5%, respectively.