航空材料学报

Research on mechanism of LY12CZ aluminum alloy fretting damage

TAO Feng, ZHANG Yu

2002, 22(2): 1-4.

[Abstract](1365) [PDF 486KB](243)

Abstract:
The fretting wear of aluminum alloy is a very complicated process, and it involves four subprocesses adherence、rubbing、oxidation、surface fatigue. In those subprocesses surface takes up a dominant status, and the effect of oxidation should not be neglected. The fretting fatigue cracks of aluminum appear on the common boundary of slide and none slide, because on that boundary there is the highest stress which makes microcracks initiating and expanding. The pit produced by fretting wear strengthens stress concentration and makes microcracks changing into expandable fretting fatigue crack.

Effect of experimental parameters on small fatigue crack growth threshold in high-strength steel

WANG Lifa, LIU Jianzhong, DING Chuanfu, WU Xue ren, HU Benrun

2002, 22(2): 5-7,28.

[Abstract](1424) [PDF 778KB](284)

Abstract:
Effect of experimental parameters on small fatigue crack growth threshold test in 9310 steel was investigated. Through experimental and analytical investigation, the following results were obtained: Influence of both K gradient and Δa on small fatigue crack growth threshold is not significant. When Kmax was selected in linear elasticity range, fracture mechanism of crack tip process zone under different Kmax-values was the same. No obvious effect of Kmax-values on small fatigue crack growth threshold test was found.

The dynamic recrystallization properties of superalloy GH4169 inertia friction welding joint

YANG Jun, LOU Songnian, ZHOU Yun, YAN Junmin, SHI Weiqing

2002, 22(2): 8-11.

[Abstract](1453) [PDF 663KB](329)

Abstract:
It is easy to start dynamic recrystallization of GH4169 superalloy inertia friction welding when the temperature, strain and strain rates reach at a certain conditions. The research result shows, it has been found some crystallization process are still at the nucleation stage in the dynamic recrystallization, because the inertia friction welding time is very short so that the dynamic recrystallization process is sufficient and the dynamic restoration is insufficient. It is the reason that fine grain and superfine grain microstructure produced in the joints of inertia friction welding.

Study on mold filling velocity in AZ91 magnesium alloy LFC process with vacuum

LIU Zili, WU Guohua, DING Wenjiang, ZHU Yanping, LI Qiang

2002, 22(2): 12-16.

[Abstract](1218) [PDF 618KB](400)

Abstract:
Full factorial experiments were carried out to study the effects of vacuum, pouring temperature and pattern thickness on the mold filling velocity in AZ91 magnesium alloy lost foam casting (LFC) process. The results show: all of them play a positive effect on the velocity, and vacuum is a crucial parameter in determining the velocity. Without vacuum, the velocity is very small and continually decreases as the pattern is displaced, the effect of pouring temperature on velocity is minor; when vacuum is applied, the velocity during mold filling process varies greatly and displays indefinitely,and the fluctuation of the changing velocity increases with increasing vacuum, pouring temperature and the pattern thickness. At low vacuum, as vacuum and/or pouring temperature increase, the average velocity increases rapidly, and the interaction effect between vacuum and pouring temperature on the velocity is enhanced; at still higher vacuum, the average velocity increases with increasing pouring temperature all the same, but the average velocity increase rate decreases as vacuum further increases, and the interaction between vacuum and the pouring temperature is insignificant. The effect of pattern thickness on the velocity is somewhat modified under vacuum.

Feature-based classification for forging and feature-based numerical simulation

LIU Yuhong, LI Fuguo, WU Shichun

2002, 22(2): 17-20.

[Abstract](1480) [PDF 177KB](340)

Abstract:
Based on analyzing the form and deforming characters of forging parts, the definitions and construction of forging feature and its form feature are presented, and an feature based classification for forging is developed. The concept model and parameterized data model of the feature class are proposed by introducing object oriented technology. The method of expressing boundary restriction conditions and load conditions, which are complicated and the key factors in FEM simulation, in the feature class construction is discussed and the relation concept of feature classed is presented. Based on the feature based classification for forging, we reduce two types of the parts deforming, which posses the characters of "extrusion" or "upsetting", so that feature based finite element method (FFEM) is presented. In this paper, we develop the idea of integrating FFEM with adaptive FEM, concurrent FEM and knowledge based FEM to simulate the deforming of large complicated forging parts.

Influence of surface integrality on fatigue limit for 30CrMnSiNi2A steel

GAO Yukui, LIU Tianqi, YIN Yuanfa, LI Xiangbin

2002, 22(2): 21-23.

[Abstract](1408) [PDF 569KB](417)

Abstract:
The changes of surface integrality caused by shot peening and vibration peening were investigated and its influence on fatigue limit of 30CrMnSiNi2A steel for 107 cycles was determined. Due to the local plastic deformation, residual stresses are developed and the surface topography is changed. Results on the influence of shot peening and vibration peening on 30CrMnSiNi2A steel are compared. The results indicate that the fatigue endurance limit of the shot peened specimens is higher than the corresponding limit of the virgin specimens by about 16% and the fatigue limit of vibration peened specimens is higher than that of virgin specimens by about 11%. The reason why fatigue limit is improved is that surface integrality is modified by mechanical surface treatment such as shot peening and vibration peening.

Preparation of nanometer thin films by nanosecond pseudospark beam ablation

HAN Lijun, JIANG Xingliu, WEN Xiongwei

2002, 22(2): 24-28.

[Abstract](1187) [PDF 255KB](358)

Abstract:
Similar to film deposition of laser beam ablation the pseudospark electron beams with nanosecond duration can be used for film preparation through the interaction of beam and target to cause rapid melting, vaporization and explosion of clusters of target materials and nucleation crystallization of ablated target cluster with similar ratio of components occur on the surface of substrates. Physical processes of the ablation and deposition of this new technology have been investigated. Experimental results show that a variety of multilayered films with the oxides of multiple elements, and metals/oxides layered films can be deposited by using the new approach of pseudospark electron beam ablation. The observation of high resolution electron microscopy, X-ray diffraction, photo-electronic energy spectroscopy have been presented. Experimental results show that such a new approach of film deposition with made application possess some unique advantages.

Study of high performance resin formula for composite skirt

GUO Yalin, LIANG Guozheng, LI Ying, QIU Zheming

2002, 22(2): 29-32.

[Abstract](1137) [PDF 725KB](331)

Abstract:
The study of high performance resin formula for composite skirt is presented. The tensile strength for cast of the formula is 107.4MPa and the tensile modulus 4.05GPa. If the CF prepreg is stored in refrigerator, it can be used in seven days. The formula perfectly matches the fiber. The tensile strength of NOL ring is above 2000MPa.

Fabrication of 3D Nextel^TM720/Mullite at low temperature

Litong, CHENG Laifei, XU Yongdong

2002, 22(2): 33-36.

[Abstract](1287) [PDF 844KB](312)

Abstract:
3D NextelTM720/Mullite composites were fabricated by precursor infiltration pyrolysis method. Influence of the matrix component control,the dense of composite and the treating temperature on the fracture strength of composites was studied. The results indicted that the dense composite were obtained by using the mixture of TEOS(Si(OC2H5)4) and aluminum s butoxide (Al(OC3H7)3) as precursor through cycle infiltration at relative low temperature(≤1200℃).

Studies on matching rules for microwave electromagnetic parameters of single-layer homogeneous absorber

GAN Zhiping, GUAN Jianguo, WANG Wei

2002, 22(2): 37-40,61.

[Abstract](1461) [PDF 235KB](410)

Abstract:
The prerequisites of microwave electromagnetic parameters and the border curves for a single layer homogeneous absorbing coating backed by a perfectly conducting plate to produce zero specular reflection are obtained by the Steffensen speedup approach to solve the complex transcendental equation. The numerical simulation equations of the border curves in term of δm～δe and δm～Atn(μ′/ε′), as well as the matching rules and the frequency dependence of microwave electromagnetic parameters of a broad band homogeneous absorbing coating with a finite value of reflection loss are available.

Study on the mechanical properties of the moderate and high density Nomex honeycomb

HAO Wei, LI Yong, LUO Yuqing

2002, 22(2): 41-45.

[Abstract](1531) [PDF 751KB](538)

Abstract:
The mechanical properties of three kinds of moderate and high density Nomex honeycomb used as aeronautical materials were studied.Furthermore,the effects of aramid paper's thickness,sollvent impregrated resin's concentration and environmental moisture on the mechanical properties of Nomex honeycomb were investigated.The results show that the moderate and high density Nomex honeycomb of good quality can be produced under the following conditions:moderate thickness aramid paper is chosen,the environmental moisture is controlled strictly,and penetrating agent is added to the solvent impregnated resin whose concentration is 35%～50%.The properties of this kind of honeycomb are comparable to that of the same kind of inputed product.

Study of influences of the complete-moving-hysteresismodel partial parameters on the hysteresis loops

LUO Guangsheng, GE Hai, WANG Jing, YIN Jinhua, ZHANG Hongwei

2002, 22(2): 46-48.

[Abstract](1532) [PDF 311KB](213)

Abstract:
The influences of complete-moving-hysteresis model parameters on the hysteresis loops were studied.While the saturation magnetization Ms and moving parameter α were improved two times,the major loops altered slightly,but the influence of the parameter γ was obvious and the slope of major loops increased with increasing parameter.

Strengthening mechanisms of metal matrix composites

CHEN Jianfeng, WU Gaohui, SUN Dongli, JIANG Longtao

2002, 22(2): 49-53.

[Abstract](5187) [PDF 1023KB](1406)

Abstract:
The strengthening mechanisms and strength prediction have always been the focus of investigation, because these are critical to the design of metal matrix composites (MMCs). Numerous strengthening mechanism and theoretical models have been developed to correlate the mechanical behaviors of MMCs with their microstructure characteristics, but no one accords with the experimental results very well. An overview of recent studies on strengthening mechanisms and models for MMCs is presented. The disadvantages, appropriate research orientation are also discussed.

Present progress on studies of reinforcement carbon, silicon carbide and alumina surface coatings in aluminium metal matrix composites

YU Zhiqiang, CHEN Jianfeng, WU Gaohui, SUN Dongli

2002, 22(2): 54-61.

[Abstract](1501) [PDF 1067KB](691)

Abstract:
The interface between the matrix and reinforcement plays a crucial role in determining the properties of metal matrix composites (MMC).Surface treatments and coating of the reinforcement are some of the important techniques by which the interfacial properties can be improved . Reinforcement coatings are classified as metallic,ceramic,bilayer and multilayer coatings. Fabrication methods often include electroless plating ,chemical vapor deposition,and sol gel technique, etc. Coatings on three important reinforcements, such as carbon, silicon carbide (SiC) and alumina (Al2O3) and their effects on the interface and properties of aluminium alloy matrix composites are reviewed.

2002 Vol. 22, No. 2