Effect of oil environments on the initiation of fatigue cracks and propagation of small cracks in plain carbon steel specimens

In fatigue tests of plain carbon steel specimens in air, fatigue life is taken up mainly by the life in which a crack propagates from its initial size up to about 1 mm. This means that the behaviour of a small crack in the oil environment must be known in order to evaluate the effect of oils on fatigue life. In this paper, using a series of base oils of different viscosity grades, the effects of oils on fatigue damage are investigated in rotating bending fatigue tests of annealed 0.34% carbon steel plain specimens. Successive detailed observations of the specimen surface are made in order to study the fatigue processes of micro-crack initiation and small crack propagation. The physical background of the effect of oil environments on fatigue behaviour is shown, and a method for predicting fatigue life in oil environments is discussed.     

光学玻璃微切削时材料去除机理和表面质量的研究

通过显微压痕和纳米压痕试验,研究了Soda-lime光学玻璃在微/纳米尺度下的材料去除机理,发现外加载荷的幅值对脆性材料变形方式有直接影响。对光学玻璃的金刚石普通切削和超声振动切削试验结果表明,超声振动切削的实际有效切削深度与名义切削深度有着较好的一致性,合理选择金刚石超声振动切削参数可实现光学玻璃的塑性域切削。     

Tool wear and its effect on surface roughness in diamond cutting of glass soda-lime

For the technology of diamond cutting of optical glass, the high tool wear rate is a main reason for hindering the practical application of this technology. Many researches on diamond tool wear in glass cutting rest on wear phenomenon describing simply without analyzing the genesis of wear phenomenon and interpreting the formation process of tool wear in mechanics. For in depth understanding of the tool wear and its effect on surface roughness in diamond cutting of glass, experiments of diamond turning with cutting distance increasing gradually are carried out on soda-lime glass. The wear morphology of rake face and flank face, the corresponding surface features of workpiece and the surface roughness, and the material compositions of flank wear area are detected. Experimental results indicate that the flank wear is predominant in diamond cutting glass and the flank wear land is characterized by micro-grooves, some smooth crater on the rake face is also seen. The surface roughness begins to increase rapidly, when the cutting mode changes from ductile to brittle for the aggravation of tool wear with the cutting distance over 150 m. The main mechanisms of inducing tool wear in diamond cutting of glass are diffusion, mechanical friction, thermo-chemical action and abrasive wear. The proposed research makes analysis and research from wear mechanism on the tool wear and its effect on surface roughness in diamond cutting of glass, and provides theoretical basis for minimizing the tool wear in diamond cutting brittle materials, such as optical glass.     

Contact fatigue and wear behaviour of bismaleimide polymer subjected to fretting loading under various temperature conditions

Cracking and wear induced by fretting is a critical problem for industrial composite structures. Thermosetting bismaleimide resin is a promising material due to its good mechanical and thermal properties. The effect of temperature regarding fretting cracking and fretting wear is presently investigated. The temperature effect on crack initiation and propagation is quantified combining experiments and modelling. The fretting wear is explained using a friction energy wear approach. A bilinear evolution of wear volume versus the dissipated energy is identified and related to a protective third body layer. These various damage evolutions are compared to the viscoelastic properties of the polymer.     

Computational simulation of three-dimensional neck propagation in polymeric specimens under tension and hybrid identification of constitutive equation

The three-dimensional neck propagation behavior of a glassy polymer under tension, which obeys a constitutive equation based on the molecular chain network theory, was investigated numerically. An experimental observation of tension in polycarbonate (PC) specimens was performed. A hybrid identification procedure of the parameters in the constitutive equation was developed by employing the least mean squares method with an evaluation function which is defined by the square of the difference of the computational and experimental results for nominal stress at specific deformation stages. Application of the proposed procedure to PC led to a very smooth convergence process and accurate results. The validity of the results was also examined through a comparison of the calculated lateral contractions of the specimens at different points in different stages of the deformation with those obtained by experiments.     

Relationship between the propagation of fatigue cracks and the behaviour of plastic flow under rolling/sliding contacts - effect of slip ratio

The relationship between the propagation of fatigue cracks and the behaviour of plastic flow in the surface layer was experimentally investigated under lubricated rolling-sliding contact. The test specimen material was medium carbon steel (S45C) with hardness H_v 187 after annealing. Results show that the displacement of plastic flow in the surface layer of the follower increased with increasing number of revolutions. Crack propagation occurred in the surface layer of the follower when the displacement of plastic flow on the centre of the contact reached a saturated value. On the contact surface of the follower, the propagating angle of the fatigue crack was found to be correlated to the angle of plastic flow, which was independent of the slip ratio. The rate of plastic flow increased with increasing slip ratio, resulted in a reduction of fatigue life. The displacement of plastic flow beneath the contact surface could be evaluated from the profile change of the plastic flow on the contact surface.     

涡盘在气体力和温度载荷作用下的应力及变形分析

采用有限元方法，对涡旋压缩机动涡盘在气体力及温度载荷作用下应力分布特点及变形规律进行了分析。结果表明最大应力发生在齿头根部，对变形的分析中得到气体力主要影响径向及周向变形。而温度载荷主要影响轴向变形。     

An evaluation of the errors in the yield surface for a rotationally symmetric thin shell due to neglecting transverse normal stresses and shell curvature

An estimate has been made of the errors introduced in the plastic analysis of rotationally symmetric shells by the neglect of transverse normal stress σ_z, and the ratio of thickness to the radii of curvature in comparison to unity. It is shown that the latter effect will generally be negligible and that the more important factor is that due to σ_z. An example of a complete sphere under internal pressure is considered, and the further effect of moving the pressure onto the centre line examined.     

Changes in the microstructural and electrical behavior of poly-Si films subjected to ion implantation and annealing process modifications

Polycrystalline silicon (poly-Si) films implanted with arsenic using beam currents of 500 μA (400°C) and 230 μA (room temperature) have been investigated via transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), and spreading resistance analysis (SRA). Experimental observations demonstrated the annealed high beam current-implanted poly-Si to possess inferior electrical properties compared with that implanted at a lower beam current. The reduced electrical activity of the high beam current-versus the low beam current-implanted poly-Si was directly related to the postimplant microstructure (small grains ～140 nmvs. amorphous) and the mechanism of the subsequent anneal (grain growth vs. recrystallization). The recrystallization mechanism augmented the electrical activation of the As dopant (decreased sheet resistivity) via a reduction of total grain boundary area. Further improvement in the electrical performance of the low beam current-implanted poly-Si, a resistivity decrease of up to 28%, was incurred via a two-step annealing process. This process induced grain growth, which in turn minimized total grain boundary area and dopant trapping.     

Surface roughness and the use of a peak to background ratio in the X-ray microanalysis of bio-organic bulk specimens

The use of a net peak intensity and of a peak to background (P/B)-ratio of sulphur and chlorine is examined in the X-ray microanalysis of a 2·4% w/w S bulk standard in Spurr's epoxy resin. In calculating the P/B-ratio, the background intensity is calculated for the same energy region as for the net peak. Analyses were carried out on the flat top of the standard and on the slope running down from the top on the side not facing the X-ray detector. The results obtained for the peak to local background ratios from the top and the slope yielded a relatively small mean deviation (11%) while net peak intensities ultimately were reduced to 7% or less of the initial value for the flat top. This indicated that a peak to local background ratio is to be preferred in the quantitative analysis of bulk specimens which have poorly defined local tilt and takeoff angles. A second advantage is the inherent correction for beam current fluctuations.     

QT800-6曲轴磨削裂纹产生的原因分析及对策

通过金相分析及工艺试验 ,研究了 QT80 0 - 6曲轴表面中频淬火后磨削裂纹产生的原因及解决办法。淬火组织中马氏体与残余奥氏体的成分不均匀及磨削用量参数选择不当是导致裂纹出现的主要原因。通过改善热处理工艺 ,优化磨削用量参数 ,优选冷却液等办法可以解决问题。     

Evaluation of machinability according to the changes in machine tools and cooling lubrication environments and optimization of cutting conditions using Taguchi method

This study analyze the effect of machine tools, cooling lubrication environments and cutting conditions on surface roughness and cutting force, and propose the combination of cutting conditions which minimizes the effect of machine tool variables on the dispersion of cutting force and surface roughness by treating the changes in machine tool itself and the installation environments as a noise factors. To do so, the Taguchi method is used to establish an experiment plan, and flat end milling is carried out to measure cutting force and surface roughness. The research results show that in the case of cutting force, the effect of cutting conditions is dominant, and changes in machine tools and cooling lubrication environments barely have effect on cutting force. However, in the case of surface roughness, all of the cutting conditions, machine tool and cooling lubrication environment variables have impact. In order to select a combination of cutting conditions insensible to changes in machine tools, considerations for feed per revolution and axial depth of cut turn out most important in the aspect of cutting force, and considerations for feed per revolution is most important in the surface roughness.