Kou G.,Northwestern Polytechnical University |
Guo L.-J.,Northwestern Polytechnical University |
Li Z.-Q.,Shanghai Aerospace Equipment Manufacturer |
Peng J.,Northwestern Polytechnical University |
And 2 more authors.
Journal of Alloys and Compounds | Year: 2017
Carbon nanotubes (CNTs) reinforced carbon/carbon-copper (C/C-Cu-CNTs) composites were fabricated by thermal gradient chemical vapor infiltration (TGCVI). The effect of copper and CNTs on the microstructure and flexural properties of carbon/carbon (C/C) composites were investigated. Results showed that the flexural strength of C/C-Cu-CNTs composites was larger than that of pure C/C composites and C/C-Cu composites. Copper particles coated on carbon fibers reduced the contact area between pyrolytic carbon matrix and carbon fibers, leading to the decrease of flexural strength by 17.34% in direction Z and 22.44% in direction X, respectively. However, CNTs catalyzed by copper particles linked adjacent pyrolytic carbon layers together as a bridge and made propagation resistance of cracks increased, which strengthened the matrix. The flexural strength of C/C composites was improved by 33.61% in direction Z and 23.94% in direction X, respectively. © 2016 Elsevier B.V.
Su Y.,Shanghai JiaoTong University |
Chu X.,Shanghai JiaoTong University |
Chen D.,Shanghai JiaoTong University |
Sun X.,Shanghai Aerospace Equipment Manufacturer
Journal of Intelligent Manufacturing | Year: 2015
Operation sequencing in CAPP aims at determining the optimal order of machining operations with minimal machining cost and satisfying all the precedence constraints. The genetic algorithm (GA) is widely used to solve precedence constrained operation sequencing problem (PCOSP) due to its efficiency and parallel processing capability. How to guarantee the precedence constraints is always a hot research topic and there are mainly two classes of methods. The first ones use additional adjustment approaches to repair the infeasible solutions that break precedence constraints. It is unreliable and low efficient. The second ones avoid infeasible solutions in initialization through some encoding approaches such as topological storing based encoding approach, but the premature convergence problem may occur facing some complicated PCOSPs. To solve these problems, an edge selection strategy based GA is proposed. The edge selection based strategy could produce feasible solutions in initialization, and assures that every feasible solution will be generated with acceptable probability so as to improve GA’s converging efficiency. Then the precedence constraints are kept by order crossover. Modified mutation operator is designed to optimize the selection of machine tool, tool access direction and cutting tool for each operation. The experiments illustrate that the proposed algorithm is effective and efficient. © 2015 Springer Science+Business Media New York
Zhao S.,Shanghai JiaoTong University |
Huang Y.,Shanghai JiaoTong University |
Wang H.,Shanghai JiaoTong University |
Liu C.,Shanghai JiaoTong University |
And 2 more authors.
2016 IEEE International Conference on Prognostics and Health Management, ICPHM 2016 | Year: 2016
The ball screw's health assessment is significant to keep accuracy and reliability of the motion axes in the CNC machine. Mahalanobis-Taguchi System (MTS) is considered to be an effective non-parametric approach to carry out the health assessment. In this paper, a Laplacian Mahalanobis-Taguchi system (referred as LMTS) analytical model is proposed to establish a nonlinear mapping relationship between the features of sensor information and the ball screw performance. In order to utilize the limited sensor data effectively, LMTS method is only performed on the speed and motor current signals which are available in CNC secondary-develop interface. Because of the complexity of processing high dimensionality nonlinear features, Laplacian Eigenmaps is utilized to reduce the feature data dimension before they were sent to Mahalanobis-Taguchi System as inputs. Compared with the classical dimension reduction methods, the intrinsic low dimensionality manifold by Laplacian Eigenmaps in Mahalanobis feature space characterizes the performance degradation more accurately and robustly. Among many ball screw assessment technologies, this LMTS assessment is a promising data driven based approach because of less influence in the machining process and few changes in the original structural design. The results show that LMTS monitoring may enable the practical application of online real-time assessment for ball screws. © 2016 IEEE.
Wang F.,Shanghai JiaoTong University |
Fang Z.,Shanghai JiaoTong University |
Xu C.,Shanghai JiaoTong University |
Yin Y.-H.,Shanghai Aerospace Equipment Manufacturer |
Chen K.,Shanghai JiaoTong University
Hangkong Cailiao Xuebao/Journal of Aeronautical Materials | Year: 2015
2195-T8 and 2219-T87, the two widely used high-strength aluminum alloys in aerospace industry, were successfully joined together by friction stir welding (FSW). The variation of microstructure and mechanical properties with different travel speeds was studied at a fixed tool rotation speed. Distinct interface was observed at the top part of weld nugget, and the morphology of this interface was influenced significantly by travel speed. Meanwhile, a new fracture mode of FSW joint was discovered at high travel speed. The fracture mode is related to the morphology and metallurgical bonding strength of the interface between dissimilar materials at the top part of weld nugget. The cause for this fracture mode and its effect on mechanical properties of the joints were investigated. ©, 2015, Chinese Journal of Aeronautics. All right reserved.
Zhao W.,Nanjing University of Aeronautics and Astronautics |
Chen C.,Nanjing University of Aeronautics and Astronautics |
He N.,Nanjing University of Aeronautics and Astronautics |
Li L.,Nanjing University of Aeronautics and Astronautics |
And 2 more authors.
Nanjing Hangkong Hangtian Daxue Xuebao/Journal of Nanjing University of Aeronautics and Astronautics | Year: 2015
Minimum quantity lubrication (MQL) has been accepted as a successful semi-dry application because of its satisfactory performance in practical machining operations. However, the oil mist generated from MQL machining process has a direct impact on the ambient air quality, and then does harm to those who permanently work in this environment. Using the weighing method, the oil mist concentration in machining workshop is measured. The effect of milling speed on the oil mist concentration under different MQL system parameters such as oil flow rate, air pressure, spray distance to target and jet temperature, is analyzed. The research results show that, the oil mist concentration PM10 and PM2.5 in machining workshop will increase with the increase of milling speed due to the secondary atomization, which results from the fierce collision between oil mist particles generated from MQL system and cutting tool with high rotation speeds. But the varying patterns of oil mist concentration PM10 and PM2.5 are changing with the increase of milling speed at different MQL system parameters. © 2015, Editorial Department of Journal NUAA. All right reserved.
Zhang D.,Shanghai Aerospace Equipment Manufacturer |
Chen W.-H.,Nanjing University of Aeronautics and Astronautics |
Sun Y.-H.,Shanghai Aerospace Equipment Manufacturer |
Dong F.-B.,Shanghai Aerospace Equipment Manufacturer
Hangkong Cailiao Xuebao/Journal of Aeronautical Materials | Year: 2013
Electron beam welds, Friction stir welding and gas tungsten arc welds of aluminum alloy 2219 were made and their mechanical properties were compared by tensile testing and micro-hardness. The reasons for the difference of mechanical properties were researched by scanning electron microscopy and optical microscope. It is shown that the tensile strength of EBW joints is about 79% of base metal and hardness of the joints reaches 97HV. The tensile strength of FSW joints is about 74% of base metal and hardness of the joints reaches 97.6HV. But the tensile strength of TIG joints is only about 53% of base metal and hardness of the joints reaches 72HV. The EBW joints and the FSW joints had better performances than the TIG joints. According to the microstructures, fracture and section morphology analysis, fine equiaxed grains, distribution more evenly of copper elements and less defects that the EBW joints and the FSW joints have are the main reasons for superior mechanical properties.
Xue J.,Nanjing University |
Su P.,Shanghai Aerospace Equipment Manufacturer |
Dong W.,Nanjing University |
Jiang X.,Nanjing University |
And 2 more authors.
Applied Surface Science | Year: 2015
In this study, a series of anodic aluminum oxide (AAO) ordered nanoporous matrix layers were prepared, and hydrophobic (perfluoroalkyltriethoxysilanes, PFO) and hydrophilic (3-Aminopropyltrimethoxysilane, APTS) materials were modified on these surfaces. The static contact angle of these specimens was in the range of 30-153°. By using the f values in the theory equation and comparing with the experiment value, the wetting state of the surface was determined. Under impact pressure, the wetting states of the porous surface with the hydrophobic PFO-modified material were more stable, and the contact angle on these surfaces under external pressure remains constant. However, the hydrophobicity of the surface modified with APTS was metastable, and the surface hydrophobicity decreased as the impact pressure increased. Under sufficient hydraulic pressure, the liquid would wet a rough structure, and the hydrophobic state would be lost and not automatically restored. In addition, the change in the wettability of the APTS-modified surface occurs spontaneously due to the immersion conditions. Finally, the critical pressure of the PFO-modified surfaces was investigated. Although the critical pressure of the surface is on the micrometer level, which is similar to the static energy barrier (ΔP), our experimental data are smaller and on the nanometer scale, which is discussed in this study. © 2015 Elsevier B.V. All rights reserved.
Qiao F.,Shanghai Aerospace Equipment Manufacturer |
Cheng K.,Brunel University |
Wang L.,Shanghai Aerospace Equipment Manufacturer |
Wang L.,Tongji University |
And 2 more authors.
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture | Year: 2016
This article presents an industrial feasible approach to robustly joining dissimilar materials of AA6061-T6 and 1Cr18Ni9Ti using refill friction stir spot welding processes and the associated joints assessment. The microstructure and shear strength property tests are taken on the dissimilar joints of 2-mm-thick plates. The results indicate that the microstructure change of the joints can be categorized in stir zone, heat-affected zone, thermomechanically affected zone and base material. The 1Cr18Ni9Ti material is squeezed toward the 6061-T6 material and forms the hook tissue, which enhances the mechanical properties of the refill friction stir spot welding-enabled joints of two dissimilar materials. The shear strength of the joints increases at first and then decreases with increase in the tool rotational speed, the indentation depth, the axial force and welding time. When the welding process is carried out at the tool rotational speed of 1800 r/min, indentation depth of 2.3 mm, the axial force of 15.65kN and the welding time in 7.5 s, the maximum shear strength of the joints can be achieved as being able to take the loading of 8650N as experimentally tested. © 2015 IMechE.
Li Z.Q.,Shanghai Aerospace Equipment Manufacturer |
Nan B.H.,Shanghai Aerospace Equipment Manufacturer |
He T.F.,Shanghai Aerospace Equipment Manufacturer |
Feng G.X.,Shanghai Aerospace Equipment Manufacturer
Materials Science Forum | Year: 2015
As an ideal layout scheme for launch vehicle, bearing co-bulkhead tank can improve the slenderness ratio of launch vehicle, reduce structure weight and increase structure efficiency. In this paper, a novel cryogenic tank co-bulkhead was fabricated by vacuum assisted resin transfer molding (VARTM) process. Consisting of LD10 alloy and polymethacrylimide (PMI) foam-sandwich, the new cryogenic tank co-bulkhead was designed with variable-thickness, hemi-ellipsoid structure, thermal insulation and bearing function. Fundamental temperature distribution, thermal stress and low-temperature load sensitivity of the foam-sandwich co-bulkhead were also assessed by finite element analysis and environment tests in simulated service environment. The results showed that the analog values highly agreed with the test results, and thermal insulation and bearing function of the foam-sandwich co-bulkhead could satisfy the design requirement, which proved the reliability of bonding quality and feasibility of the bonding technique. © (2015) Trans Tech Publications, Switzerland.
Yu X.,Chongqing University |
Shen S.,Shanghai Aerospace Equipment Manufacturer |
Jiang B.,Chongqing University |
Jiang B.,Chongqing Academy of Science and Technology |
And 5 more authors.
Applied Surface Science | Year: 2016
This paper studies the effect of the existing state of Y element on the high temperature oxidation resistance of magnesium alloys. Different levels of Al element were added into Mg-2.5Y alloy to obtain different existing state of Y. The oxidation rate of Mg-2.5Y-2.5Al alloy is the highest among Mg-2.5Y, Mg-2.5Y-2.5Al and Mg-2.5Y-4.2Al alloys at 500 °C. An effective and protective Y2O3/MgO composite oxide film was formed on the surface of Mg-2.5Y alloy after oxidized at 500 °C for 360 min. The results show that the dissolved Y element in the matrix was beneficial to improve the oxidation resistance of magnesium alloys. Once Y element transformed to the high temperature stable Al2Y compound, its ability in preventing oxidation would disappear. The formation of Al2Y compound severely deteriorated the oxidation resistance of Mg-2.5Y alloy. In addition, the dissolved Al can also cause the rise of oxidation resistance at a certain extent. © 2016 Elsevier B.V. All rights reserved.