接触疲劳伤损突出路段钢轨合理选用研究

在客货混运主干线的接触疲劳伤损突出路段,进行了1 100 MPa级热处理钢轨和U75V、U71Mn热轧钢轨的铺路试验.结果表明1 100 MPa级热处理钢轨的抗接触疲劳伤损性能明显优于U75V和U71Mn热轧钢轨.在客货混运主干线钢轨接触疲劳伤损突出的大半径曲线和直线路段选用1 100 MPa级热处理钢轨,将有效减少钢...     

Fretting fatigue behavior of surface modified biomedical titanium alloys

Fretting is a form of adhesive wear normally occurring at the contact points gradually leading to premature failure of load bearing medical implants made of titanium alloys. The aim of this work is to characterize the fretting fatigue damage features of PVD TiN coated, plasma nitrided, ion implanted, laser nitrided and thermally oxidized Ti-6Al-4V and Ti-6Al-7Nb contact pairs. The surface layers were characterized. The damage progression during fretting process is apparently explained with tangential force coefficient curves. Plasma nitrided pairs showed highest fretting fatigue life compared to others. PVD TiN coated pairs have experienced early failures due to third body mode of contact interaction with irregular tangential force coefficient pattern. Ion implanted layers showed similar damage as unmodified alloys. Laser nitrided and thermally oxidized pairs experienced early failures due to brittle and irregular modified layers.     

微动磨损对机械的危害及预防措施

在机械装备中,由于环境的影响和工况条件的复杂多变性,在接触面上很容易出现微动磨损造成接触表面的微动损伤。为此,主要介绍了机械中两固体接触面上因出现周期性小振幅震动造成损伤的微动磨损的特征;揭示了微动磨损机理是同时涉及到粘着、磨料、氧化和疲劳4种基本磨损机理的一种特殊磨损形式,通过实例论证了微动磨损对机械零件的危害以及通过结构改进设计、材料的选择和表面强化工艺等措施预防和减少微动磨损,提高机械运行的可靠性。     

Contact lens surface damage related to cases and case removal techniques

Surface damage incurred as a result of removing polymethyl methacrylate (PMMA) contact lenses form various contact lens carrying cases was monitored by photographic techniques. As compared to the controls, the experimental lenses showed consistent increases in surface damage, particularly if they were removed by a sliding (dragging) motion along the contours of the case.     

行星轧机角接触球轴承损伤原因探究及处理

针对连铸连轧铜管生产线三辊行星轧机角接触球轴承损伤形式的特征及产生的原因进行了深入的研究,研究表明行星轧机角接触球轴承损伤的形式主要有剥落、擦伤、破裂、压痕、咬粘等,提出了装配及配合、润滑、密封等合理的技术措施,为提高行星轧机角接触球轴承的使用寿命和延长轧机的工作时间提供帮助。     

行星轧机角接触球轴承损伤原因探究及处理

针对连铸连轧铜管生产线三辊行星轧机角接触球轴承损伤形式的特征及产生的原因进行了深入的研究,研究表明行星轧机角接触球轴承损伤的形式主要有剥落、擦伤、破裂、压痕、咬粘等,提出了装配及配合、润滑、密封等合理的技术措施,为提高行星轧机角接触球轴承的使用寿命和延长轧机的工作时间提供帮助。     

Corneal endothelial damage from previously implanted intraocular lenses

Intraocular lenses which had been surgically removed from human eyes were compared to new uncoated IOLs with regard to damage caused by dynamic and static contact with fresh rabbit corneal endothelium. Previously implanted IOLs caused consistently less endothelial damage. Possible mechanisms and the implications of these findings for the corneal surgeon doing pseudophakic keratoplasty are discussed.     

车速对钢轨接触疲劳伤损的影响及高速线路钢轨选用

采用专门的试验机对不同线路条件钢轨的接触疲劳伤损特点进行模拟试验研究.结果表明,车速在200km/h以下时,随车速提高钢轨的磨损量减小、接触疲劳伤损加剧;车速达300km/h时,钢轨的磨损量和接触疲劳伤损均减轻.该试验结果得到了计算机仿真计算结果相符.通过对试验结果的分析,认为车速在200km/h以下的客货共运快速线路,宜选用强度为1 100MPa级的热处理钢轨;车速达300km/h左右的高速客运专线,应考虑选用强度较低、但裂纹萌生和扩展速率较低、KIC值相对较高的U71Mn热轧钢轨,或成分性能与之相类似的其它钢轨.     

Damage phenomena in lubricated rolling-sliding wear of a gas carburised 0.85%Mo low-alloyed sintered steel: theoretical analysis and experimental verification

The resistance to surface and subsurface damage during lubricated rolling-sliding wear of a carburised low-alloy sintered steel and the effect of shot peening were investigated. The formation of both contact fatigue cracks and of brittle tensile cracks may be predicted by a theoretical model that was experimentally validated. Carburising is effective in increasing the resistance to contact fatigue, but pores in a hard and brittle matrix may act as pre-existing cracks. Shot peening increases the contact fatigue resistance since compressive residual stresses oppose the nucleation of surface cracks.     

Fatigue Damage Mechanism of Oil Film Bearing Sleeve

 With the rapid development of the steel industry, to keep pace with the current trend of high speed, continuous, and large scale production that focuses on automation and high levels of efficiency, many state owned steel companies are being equipped with oil film bearings. Through long term on spot inspection and research on the fatigue failure of oil film bearing, three segments of annulated fatigue breakage were found axially along the inner surface of the bearing sleeve. In order to elucidate the reason for the three segment annulated damage under rolling load, numerical boundary element method was adopted to analyze the contact behaviors between the sleeve and rollneck. Failure mechanism was discussed in detail, the distributions of contact stress were analyzed, and the service lives of the sleeve for different positions on the inner surface were quantitatively described, which provided an effective means to decrease wear and adhesive damage of the sleeve and to increase the load capacity of oil film bearing and its service life as well.     

Wound healing and soft tissue effects of CO2, contact Nd: YAG and combined CO2-Nd: YAG laser beams on rabbit trachea

Rabbit trachea was used as an experimental model to study tissue effects and healing of full-thickness tracheal lesions produced by CO2, contact Nd: YAG and combined, coaxial CO2-Nd: YAG (Combo) laser beams. Two power settings (10 W and 16 W) were used with CO2 and contact Nd: YAG lasers. Three different CO2/Nd:YAG power ratios (1:1, 1:2 and 1:4) and power settings (12 W 15 W and 16 W) were used with the Combolaser. Histological specimens for light and transmission electron microscopy were prepared immediately and 1, 3, 5, 7, 14 and 21 days postoperatively. The wound with the most precise and fastest healing was produced by contact Nd: YAG laser. CO2 laser produced a moderate amount of charring and the largest amount of coagulated tissue with a slightly prolonged healing period. In the acute phase, tissue defects produced by the Combolaser with power ratios 1:1 and 1:2 resembled the CO2 laser lesions but with slightly less charring. The power ratio 1:4 diminished the cutting properties of the beam considerably. During the healing period the Combolaser produced the most intensive inflammation and granulation tissue formation resulting in delayed regeneration of the lesion. In transmission electron micrographs the most severe damage to chondrocytes was seen after using the Combolaser. These findings indicate that the Combolaser produces deeper tissue damage than CO2 or contact Nd:YAG laser. However, the Combolaser appears to be suitable for tracheobronchial operations, owing to its good simultaneous cutting and haemostatic properties.     

Contact lens use after corneal trauma

BACKGROUND: This study was performed to explore the epidemiology and visual outcomes of major anterior segment trauma cases referred to the Contact Lens Service (CLS) in a large, urban, eye trauma center at a university hospital. METHODS: All eye trauma patients seen on the CLS at The University of Illinois in Chicago for a 2-year period were identified (n = 122). A search of all eye trauma cases seen at UIC (n = 2279) during the same period yielded 757 cases with the same diagnostic codes. RESULTS: CLS cases represent 16.1% of cases with similar diagnoses and 5.35% of all cases seen during the period of study. Cases were predominantly young men (mean age, 28 years). The mean age for CLS cases (mean age, 17 years) was significantly younger. Best-corrected visual acuity was 20/100 or better in 75% of cases with a contact lens and in 68% of cases with a spectacle lens; 82% of CLS cases had iris damage versus 14.5% of non-CLS cases; 73% of CLS cases were aphakic; 105 CLS cases were given contact lenses. Mean follow-up time was 24 months. Mean wearing time was 11 hours/day. On interview, 35 of 79 cases (44%) continued to wear lenses. CONCLUSIONS: Cases referred to the CLS tended to be young men with unilateral injuries-predominantly open globes-with resultant aphakia and iris damage. Good visual acuity was achieved in most cases. Long-term success wearing contact lenses for this population was poor, suggesting that alternatives to contact lens wear should be more actively considered.     

Analysis of Impact Response of Composite Laminates under Prestress

An analytical solution for the impact response is obtained for the central impact of mass on a simply supported laminated composite plate under prestresses based on the Fourier series expansion and Laplace transform technique. A linearized version of the elastoplastic contact law proposed was used in the analytical formulation to consider permanent indentation during the impact. Permanent indentation including damage effects was included in the elastoplastic contact law. The effects of initial stresses on the contact force, plate center displacement, as well as strain time histories are presented. It is shown that higher initial stresses increase the maximum value of the contact force but reduce the plate central displacement. Effects of impactor velocity, mass, interlaminar shear strength of the laminates, and plate thickness on the contact force and dynamic response of the plate under tensile prestresses are also discussed.     

White-Etching Matter in Bearing Steel. Part II: Distinguishing Cause and Effect in Bearing Steel Failure

The premature failure of large bearings of the type used in wind turbines, possibly through a mechanism called “white-structure flaking”, has triggered many studies of microstructural damage associated with “white-etching areas” created during rolling contact fatigue, although whether they are symptoms or causes of failure is less clear. Therefore, some special experiments have been conducted to prove that white-etching areas are the consequence, and not the cause, of damage. By artificially introducing a fine dispersion of microcracks in the steel through heat treatment and then subjecting the sample to rolling contact fatigue, manifestations of hard white-etching matter have been created to a much greater extent than samples similarly tested without initial cracks. A wide variety of characterization tools has been used to corroborate that the white areas thus created have the same properties as reported observations on real bearings. Evidence suggests that the formation mechanism of the white-etching regions involves the rubbing and beating of the free surfaces of cracks, debonded inclusions, and voids under repeated rolling contact. It follows that the focus in avoiding early failure should be in enhancing the toughness of the bearing steel in order to avoid the initial microscopic feature event.     

Wear mechanisms in brittle solids

The wear mechanisms of brittle ceramic and polymer surfaces have been studied. The tests span a wide range of sliding velocities—from 0.001 to 20 m/s. At the slower speeds the two surfaces remain completely cold, even on the scale of contacting asperities; at the highest speeds bulk heating is considerable and contact temperatures exceed the melting point. The appearance of the wear tracks correlates with the computed temperatures at the sliding contact. Models for wear damage are reviewed and related to these temperatures. The wear observations are summarised as a tentative wear-mechanism map.     

Damage mechanism of copper stave used in blast furnace

In order to prolong the life of copper stave, the damage forms and reasons for copper stave were studied through the investigation of 49 blast furnaces. The damage mechanism for copper stave was investigated through thermodynamic calculation, microstructure analysis and scanning electron microscope. The results show that the main reason for the damage of copper stave is mechanical wear owing to the slag layer peel off on the hot face. Thermodynamic calculation results show the hydrogen disease reaction occurs as long as the gas flow is directly contact with copper stave body, and the volume expansion rate of copper stave body is about 183%, a large number of micro pores appear in the microstructure forcing copper stave damage. The oxygen content in copper material is critical to hydrogen disease; the service life of copper stave will be extended by strictly controlling the oxygen content in copper material.     

Endothelial damage from intraocular lens insertion

Previous studies have shown that approximately 40 per cent of the corneal endothelial cells can be lost at the time of intraocular lens insertion. Momentary contact between the methacrylate surface and the endothelial cells causes an adhesion between these surfaces and results in extensive cell damage upon separation of the surfaces. This type of damage appears to be due to a biophysical interaction between these surfaces and may be avoidable by altering the surface of the lens.     

高速铁路用钢轨接触疲劳伤损的成因及预防

文章介绍了高速铁路用钢轨接触疲劳伤损的主要类型,主要表现斜线状裂纹踏面裂纹及蜂富状裂纹,分析了接触疲劳伤损的形成原因,进而提出了轨头接触疲劳伤损的预防对策。     

潜孔钻机冲击器接头拆装设备制作

钻机冲击器是一种冲击凿岩工具,工作过程中与坚硬的岩石直接接触,因而冲击器内部零件容易损坏,如何将损坏的冲击器接头拆开修复一直是困扰维修人员的难题。通过对冲击器结构进行分析,有针对性地制作出接头拆装设备,解决了固有难题。