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71.
M. M. I. HAMMOUDA I. G. EL-BATANONY H. E. M. SALLAM 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(7):627-639
An understanding into the macro kinetic and kinematic behaviour of fretted surfaces is provided. Making use of a modified version of a previously developed in‐house two‐dimensional elastic–plastic finite element analysis numerically simulates flat contact pad fretting fatigue tests. Basic macro mechanics concepts are adopted to idealise two bodies with rough contact surfaces and loaded at two different sites with arbitrary axial loading profiles. A time scale factor is devised to recognise the earliest candidate out of the events possibly accommodated at each loading increment. The present analysis utilises a relevant experimental set up developed in the Structural Integrity Research Institute of the University of Sheffield as an application. Computational results accurate to within 1.2% and corresponding to one contact pad span and six constant normal loads acting individually with four amplitudes of two sinusoidal axial load cycles are presented. The present computations include (1) the development of the global and local normal and tangential reactions and relative sliding displacement acting along the fretting surfaces and (2) contact pad deformation, generated stress fields and plasticity development within the neighbouring region of the fretted area. 相似文献
72.
73.
Giovanni Maizza Salvatore Grasso Yoshio Sakka Tetsuji Noda Osamu Ohashi 《Science and Technology of Advanced Materials》2007,8(7-8):644
A combined experimental/numerical methodology is developed to fully consolidate pure ultrafine WC powder under a current-control mode. Three applied currents, 1900, 2100 and 2700 A, and a constant pressure of 20 MPa were employed as process conditions. The developed spark plasma sintering (SPS) finite-element model includes a moving-mesh technique to account for the contact resistance change due to sintering shrinkage and punch sliding. The effects of the heating rate on the microstructure and hardness were investigated in detail along the sample radius from both experimental and modeling points of view. The maximum hardness (2700 HV10) was achieved for a current of 1900 A at the core sample, while the maximum densification was achieved for 2100 and 2700 A. A direct relationship between the compact microstructure and both the sintering temperature and the heating rate was established. 相似文献
74.
The effects of boiling Aqua Regia (AQ), N2/Cl2 plasma followed by AQ and O2 plasma followed by AQ surface treatments prior to Ni/Au (20 nm/20 nm) metallization to p-GaN:Mg (∼ 3 × 1017 cm− 3) have been investigated. N2/Cl2 plasma was employed in a bid to lower the Ga/N and O/Ga ratios of the GaN surface to improve the contact properties to p-GaN, while O2 plasma was employed as an alternative to incorporate O into the Ni/Au system. Results show that a low Ga/N ratio does not necessarily correspond to a better contact. The positive effect of O2 over N2 anneal is observed only for the AQ-treated sample, although the mechanisms responsible for its positive effect: NiO formation and Ni/Au layer-reversal were observed for all O2-annealed contacts. We conclude that the effect of O2 anneal on the Ni/Au contact is dependant on the p-GaN surface prior to metallization. 相似文献
75.
反复荷载下钢筋混凝土剪力墙的非线性有限元分析 总被引:1,自引:0,他引:1
本文介绍了反复荷载下非线性有限元分析程序,该程序针对钢筋混凝土剪力墙类结构的特点,采用了钢筋与混凝土复合单元计算模型,考虑混凝土裂面接触效应的反复加载混凝土应力-应变关系。在钢筋应力-应变关系中,还同时考虑了混凝土开裂后钢筋的拉伸强化效应及反复荷载下钢筋的Bausinger效应。本文还介绍了作者利用该程序对反复荷载试验的试件及Ger-venka的剪力墙板进行的计算分析。结果表明,本文所采用的分析模型是合理、准确的;和国内外以往的分析比较,本文的方法成功地消去了力-位移滞回曲线中的拐点现象,而且计算的混凝土裂缝开闭也能和实测较好地吻合。表明本文方法能为分析反复荷载下钢筋混凝土剪力墙类结构性能提供一个准确、有力的工具。 相似文献
76.
接地电阻对地电场观测的影响及克服方法 总被引:1,自引:0,他引:1
论述了测量电极的接地电阻对振幅和相位测量精度的影响规律,提出了克服接地电阻影响,提高野外观测精度的切实可行的方法和技术。 相似文献
77.
A. P. Umanskii V. P. Konoval A. D. Panasyuk E. P. Dvornik 《Powder Metallurgy and Metal Ceramics》2007,46(1-2):90-94
The kinetics of wetting double titanium and chromium diboride by iron-based alloys with different chromium content is studied.
It is shown that contact angles are formed in such systems over the range 0–10°. The energy parameters of wetting are calculated.
It is established that chromium as a surface-active element promotes Fe-Cr alloy spreading on the diboride surface. The microstructure
of the interaction area is studied. It is shown that terminal solid solutions and eutectics are formed in the TiCrB2-(Fe-Cr) system. The optimum compositions of the metallic binder are determined for TiCrB2-based composite materials.
__________
Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 109–115, 2007 相似文献
78.
79.
Adhesion studies of diamond-like carbon films deposited on Ti6Al4V substrate with a silicon interlayer 总被引:2,自引:0,他引:2
Diamond-like carbon (DLC) films have proven quite advantageous in many tribological applications due to their low friction coefficient, their extreme hardness, and more recently their high adherence on different substrate materials. However, for many applications, DLC films as thick as 2 μm are required, which cause high residual stress. In order to overcome this problem, this study observed the behavior of different thicknesses of silicon interlayer between DLC films and Ti6Al4V substrates. The study also analyzed the relation of growth parameters to the mechanical properties of DLC films. Silicon and DLC films were grown by using a rf-PECVD at 13.56 MHz with silane and methane atmospheres, respectively. The contribution of an interlayer thickness to the adhesion between the DLC films and Ti6Al4V substrate was evaluated by using a micro-scratch technique. The hardness and friction coefficient were evaluated by using microindentation and lateral force microscopy (LFM), respectively. Raman scattering spectroscopy was used to characterize the film quality. A correlation was found between the intrinsic stress and adhesion of DLC film and the parameters of the silicon interlayer growth. The addition of a silicon interlayer successfully reduced intrinsic stress of the films, even as measured by using a perfilometry technique. 相似文献
80.
The employment of the Zn(Se,Te) pseudo-graded contacting scheme to p-type ZnSe-based alloys contributes directly to the recent
demonstration of room temperature continuous-wave operation of II– VI green-blue laser diodes. Contact ohmicity is maintained
down to cryogenic temperatures which enabled the investigation of electrical transport properties associated with the p-type
nitrogen-doped ZnSe, Zn(S,Se), and (Zn,Mg)(S,Se). The observation of both persistent photoconductivity and a metastable population
of holes which are in thermodynamic equilibrium with hydrogenic acceptors having reduced activation energy suggests the presence
of a DX-like behavior for holes in p-type (Zn,Mg)(S,Se). 相似文献