四旋翼无人机反步积分自适应控制器设计

针对四旋翼无人机在实际应用过程中出现质量变化的情况,基于自适应控制理论设计质量观测器,用于实时观测无人机的质量并修正其质量参数。在经典反步控制器 (CBC)基础上,结合质量观测器和第一类控制误差积分,提出反步积分自适应控制器 (BIAC), 用于无人机的轨迹跟踪控制。该控制器的设计过程基于Lyapunov稳定性理论,能够保证系统的控制误差渐进稳定。应用MATLAB/Simulink软件环境完成轨迹跟踪仿真实验。仿真结果表明：在无人机存在质量慢变或质量突变情况下,BIAC可以更好地估计无人机实时质量;与CBC相比,地球坐标系Exeyeze下ze轴 轨迹误差减小80%左右,跟踪精度大为提高。     

Mechanical,tribological and anti-corrosive properties of polyaniline/graphene coated Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys

The mechanical, tribological and corrosion protection offered to Mg-9Li-7Al-1Sn and Mg-9Li-5Al-3Sn-1Zn alloys by the epoxy coating containing polyaniline/graphene (PANI/Gr) pigments is undertaken in the current work. PANI/Gr containing coatings were observed to be strongly adherent with a higher scratch hardness (H_s) and plowing hardness (H_p), i.e. H_s of 0.43 GPa, and H_p of 0.61 GPa, respectively when compared to that of neat epoxy coating (H_s of 0.17 GPa, and H_p of 0.40 GPa, respectively). Due to their higher H_s and H_p values, PANI/Gr based coatings displayed an enhanced wear resistance (Wear volume, W_v = 4.53 × 10^-3 m³) than that of neat epoxy coating (W_v = 5.15 × 10⁻³ m³). The corrosion protection efficiency in corrosive environment of 3.5 wt% NaCl solution was obtained to be >99% for PANI/Gr containing coatings when compared to that of neat epoxy coating. The charge-transfer resistance (R_ct) of the PANI/Gr containing coatings were estimated to be >10⁶ Ω cm², which indicates their highly protective nature when compared to that of neat epoxy coating (R_ct ˜10⁵ Ω cm²). Hence, PANI/Gr containing coatings can be potentially used for wear resistance and corrosion protection applications in marine environments.     

Study of the interaction between microstructure,mechanical and tribo-performance of a commercial brake lining material

The interaction between microstructure, mechanical, and frictional properties of a commercial brake lining material (BLM) was investigated in order to correlate them to braking performance. For this purpose, a Scanning Electron Microscope (SEM) with energy dispersive X-ray (EDX) mapping and spectrum were used to identify and analyze different constituents. The mechanical properties were determined using compression test. Relevant physical properties (density and porosity) were determined using standard test methods. The friction coefficient and wear behavior of the friction material on contact with the grey cast iron disc were established using a pad-on disc tribometer. The results have shown that the brake lining material contains phenol resin such as the matrix and other various ingredients, including silica, rock and mineral filler reinforcement, barium sulfate and carbon-rich particles as filler and brass particles as friction modifier. It had a varied amount and size up to 1 mm for brass particles. The density and porosity were 1.8 g cm⁻³ and 7%, respectively. The investigated material exhibited excellent mechanical properties in the normal solicitation direction. The average friction coefficient was about 0.65, whereas the friction coefficient was stable. The different actions of various ingredients in terms of their effects on the friction and wear behavior of the BLM could be related to their different bonding strengths with the resin matrix and their different abilities to form friction films (third-body layer) on the surfaces of the material and transfer films on the counterpart cast iron surface in relation to the surface temperature evolution and mechanical properties.     

Effects of SiC interphase by chemical vapor deposition on the properties of C/ZrC composite prepared via precursor infiltration and pyrolysis route

Silicon carbide (SiC) interphase was introduced by chemical vapor deposition (CVD) process to prevent carbon fiber degradation and improve fiber–matrix interface bonding of C/ZrC composite prepared via precursor infiltration and pyrolysis (PIP) process. Moderate thickness of SiC interphase in fiber bundles could increase the density of the composite, but when the thickness of SiC interphase was over 0.5 μm, more close pores formed and the density of the composite decreased. The SiC interphase could protect carbon fiber effectively from carbo-thermal reduction, but could not enhance the mechanical properties of C/ZrC composite. The flexural strength and fracture toughness of C/ZrC composites with 0.05 μm thickness SiC layer were 252 MPa and 13.6 MPa m^1/2, and for those with 0.5 μm thickness SiC layer 240 MPa and 12.8 MPa m^1/2, both close to the value of the composite without SiC interphase (254 MPa and 14.5 MPa m^1/2), while those with 0.7 μm thickness SiC layer were only 191 MPa and 10.8 MPa m^1/2, respectively. Moderate content of SiC interphase could improve the ablation property of C/ZrC composites; however excessive content of SiC interphase would decrease the ablation property.     

Effects of polymer derived SiC interphase on the properties of C/ZrC composites

Polymer derived silicon carbide (SiC) interphase was introduced by precursor infiltration and pyrolysis (PIP) to prevent carbon fiber erosion and to improve the fiber–matrix interface bonding of C/ZrC composites prepared by PIP. Introducing SiC interphase increased the density of the composites. The SiC interphase not only protected carbon fibers effectively from erosion by carbo-thermal reduction, but also enhanced the mechanical properties of C/ZrC composites by strengthening the interface bond. The flexural strength and fracture toughness of C/ZrC composites with SiC interphase prepared by two PIP cycles were 319 MPa and 18.8 MPa m^1/2 respectively. The ablation properties of C/ZrC composites were with rising content of SiC interphase but then decreased when excessive. The mass loss rate and the linear recession rate of the C/ZrC composites with SiC interphase prepared by one PIP cycle were 0.0079 g/s and 0.0084 mm/s, respectively.     

Mechanical and tribological properties of ceramic-matrix friction materials with steel fiber and mullite fiber

The purpose of the present work was to investigate and compare the mechanical and tribological behaviors of ceramic-matrix friction material (CMFM) with steel fiber (SF), mullite fiber (MF), and mixing SF and MF. The CMFM was prepared by hot-pressing sintering, and the tribological behaviors were determined using a constant speed friction tester. The worn surfaces and wear debris were observed by a scanning electron microscopy (SEM). Experiment results show that the combination of SF and MF can improve the mechanical properties that each single fiber does not have. The sever fade for the specimen reinforced by single MF during the whole friction testing can be attributed to the poor interface cohesive strength between MF and matrix. Mixing the SF and MF can improve the friction stability, and the friction coefficients for friction material with a mixture of the SF and MF increases with increasing MF content. For all specimens, increasing in the friction temperatures result in the increase of wear rates.     

Effects of isothermal process parameters on the microstructure of semisolid AZ91D alloy produced by SIMA

The effects of isothermal process parameters on the microstructure evolution of semisolid AZ91D alloy produced by strain-induced melt activation (SIMA) were investigated using the self-programmed analysis software based on quantitative metallography. The results showed that long isothermal time could make the semisolid particles more globular, but the size of the particles would grow larger; high semisolid isothermal temperature would reduce the solid volume fraction and accelerate the spherical evolution of the solid particles. It was found that the optimal process parameters should be 570 °C and 10–20 min of isothermal temperature and time respectively based on the conditions of this paper. The mechanism of the particles’ formation was also discussed during the isothermal treatment.     

Improved corrosion resistance of AZ91D magnesium alloy coated by novel cold-sprayed Zn-HA/Zn double-layer coatings

In order to improve the corrosion resistance and bioactivity of biodegradable Mg alloy substrate, novel Zn-HA/Zn double-layer coatings with different HA/Zn ratios in weight were deposited on AZ91D substrates by cold spraying. Phase compositions and microstructures of as-sprayed coatings and coatings after corrosion tests were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Electrochemical corrosion behaviors of both Zn-HA/Zn double-layer coatings were investigated in Hanks’ simulated body fluid using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that both the pure Zn coating and HA/Zn composite coatings presented the similar phase compositions with their primary powders in addition to Zn oxidizations. Zn powders were plastically deformed and partially oxidized due to its low melting point, while HA powders were mainly crashed into fragments and hill-like splats. Both Zn under layer and HA/Zn upper layer were well bonded and presented dense structures, differences in HA/Zn upper layers were related to the HA/Zn ratios. Potentiodynamic polarization and EIS measurements illustrated that the cold-sprayed Zn-HA/Zn double-layer coatings not only improve the corrosion resistance of Mg alloy substrates, but also enhance its bioactivity due to the HA existed in composite upper layer.     

球磨制备Mo-B-Co-Cr热喷涂复合粉体研究

目的通过机械球磨加粘结破碎法制备可用于超音速火焰喷涂制备MoB-CoCr涂层的Mo-B-Co-Cr复合粉末。方法通过机械球磨加粘结破碎法制备m(MoB):m(CoCr)分别为1:1、2:1和3:1复合粉末,研究所制备的三种复合粉末的组织形貌及物相,并将所制备的m(Mo B):m(CoCr)=1:1复合粉末进行超音速火焰喷涂实验制备MoB-CoCr涂层,研究所制备涂层的组织结构。采用扫描电子显微镜观察粉末和涂层的形貌,通过X-射线衍射仪分析复合粉末的物相,通过图像法测量涂层的平均孔隙率和厚度。结果制备的三种复合粉末各相之间结合良好,组织形态呈近球形。经过X-射线衍射发现,三种复合粉末中未发现杂质及氧化现象,复合粉末的物相主要为Mo、Co和Cr三相,随着MoB质量比的增加,复合粉末中Mo相的峰值逐渐增高。通过对m(MoB):m(CoCr)=1:1复合粉末进行超音速火焰喷涂技术制备涂层,发现所制备的MoB-CoCr涂层形态呈典型的层状结构,涂层组织致密性较好,且涂层各相间及涂层与基体界面结合良好。结论采用机械球磨加粘结破碎法可制备近似球形的Mo-B-Co-Cr复合粉末,通过超音速火焰喷涂技术可成功制备组织结构较好的MoB-CoCr涂层。     

机床平面度检测机构设计及时空映射算法研究

为了实现机床导轨安装表面平面度误差在线测量,文章设计出了包含检测机构与参考板的检测系统,利用测量过程中检测机构与参考板对应的位置关系开发出了时间-空间映射算法。给出了算法原理,建立了算法的数学模型,并进行了测量试验,得到的三组空间序列测量值趋势线在所有检测位置中的最大误差为1.8μm,约占趋势线极差的1%,对曲线形状影响很小。结果表明:检测机构设计合理且时间-空间映射算法可以正确的将检测机构时间序列的测量值转换为对应检测位置的空间序列测量值。