High speed forging of solid powder discs of large slenderness ratio

The paper reports an investigation into the forging of a solid powder circular disc with large slenderness ratio(L/D) between two flat dies at high speed. The deformation pattern during the operation is influenced by many factors, which interact with one another in a complex manner. The decisive factors are the interfacial conditions, initial relative density of the preform and the geometry of the preform. An attempt has been made to determine the die pressures developed during such forging, using an upper bound approach. The results so obtained are presented graphically and discussed critically to illustrate the interaction of various process parameters involved.     

Pad flattening ratio, coefficient of friction and removal rate analysis during silicon dioxide chemical mechanical planarization

Pad flattening ratio (PFR) was investigated as a non-destructive pad surface analysis method on the IC1000 K-groove pad during silicon dioxide chemical mechanical planarization. The PFR defines as the ratio of the bright area to the total image area. A series of marathon polishing runs were performed under ex-situ diamond disc pad conditioning, ex-situ high-pressure micro jet (HPMJ) pad conditioning and no pad conditioning methods where PFR analysis was performed to estimate the amount of pad surface flattening or glazing under these conditions. With no conditioning, PFR increased rapidly to 40% indicating severe glazing. With ex-situ diamond disc pad conditioning, PFR remained relatively constant below 12%, suggesting a rough and stable pad surface for polishing, while with ex-situ HPMJ conditioning it increased gradually and stabilized at the value of about 23%. Real-time analysis of friction force and silicon dioxide removal rate showed a clear correlation among the PFR, the coefficient of friction and the removal rate during the silicon dioxide chemical mechanical planarization.     

循环荷载作用下钢梁临界侧向长细比研究

针对我国《建筑抗震设计规范》推荐的临界侧向长细比计算公式来源于单调荷载研究结果,并未反映不同抗震等级影响问题,基于抗震等级应与适宜的转动能力相匹配准则,对循环荷载作用下钢梁进行非线性有限元分析。所建模型考虑初始几何缺陷、残余应力影响,并得到试验验证。通过对钢梁端部弯矩比、腹板高厚比、翼缘宽厚比、残余应力分布图式及平面外边界约束条件等5类影响因素数值分析,提出循环荷载作用下钢梁临界侧向长细比计算公式。该公式具有计算精度高、表达形式简单等特点。     

On the processing properties and friction behaviours during compaction of powder mixtures

ABSTRACT

Iron-based powder mixtures were prepared by dry and wet mixing method. The friction properties during compaction were tested by measuring the internal and external friction coefficient. The test results showed that the wet mixing process could realise the homogeneity of lubricant and improve the processing properties of the powder mixtures. With 0.6 wt-% lubricants, wet mixing powder mixtures have a flow rate of 29.6 s/50?g, an apparent density of 3.18?g?cm^–3, a repose angle of 35.5°, and the friction coefficient during the compaction is 0.223. An equation to calculate the total (both internal and external) friction forces during the compaction process is proposed, and then the factors influencing the friction coefficient during compaction were quantitatively analysed.     

Effect of carbon-fibre powder on friction and wear properties of copper-matrix composites

ABSTRACT

The copper-matrix composite contains carbon-fibre powder which is prepared using a powder metallurgy sintering process in an effort to examine the effects of 50-mesh (270?μm) carbon-fibre powder on the microstructure and, friction and wear properties of copper matrix composites at high speed. When carbon-fibre powder is added within a certain range, the friction coefficient of the composite material is increased and the amount of wear is greatly reduced, When the content of carbon-fibre powder is 0.2wt-%, the hardness, density, friction and wear properties of the copper-based composite material has the best combination.     

填料长径比对导电胶渗流阈值的影响

采用微波辅助乙二醇还原法制备了不同长径比的银纳米方块及银纳米线, 并对其进行了SEM、 XRD表征。以不同长径比银纳米线作为导电填料制备了各向同性导电胶。对导电胶的填充渗流阈值的研究发现, 填料的长径比对填充渗流阈值的影响很大, 长径比越大, 渗流阈值越小。运用修正的阈值理论对这一实验现象进行了合理解释, 模拟结果表明修正的阈值理论与实验结果非常吻合。      

A treatment of interfacial cracks in the presence of friction

Frictional sliding on interface crack surfaces results in weak crack tip stress singularity and zero strain energy release rate. A fracture criterion based on finite extension strain energy release rate, is proposed to capture the intrinsic fracture toughness. The finite extension strain energy release rate is shown to represent the magnitude of the singular stress field. Numerical simulations of a center crack in a bimaterial infinite medium under remote shear as well as fiber pull-out and push-out in composite materials are presented to illustrate the frictional effect in both small and large scale contacts near the crack tip.     

Effect of friction factor on barrelling in elliptical shaped billets during cold upset forging

This work deals with the effect of friction factor of different lubricants on barrelling in elliptical shaped billets during cold upset forging. Experiments were carried out to generate data on cold upset forging of commercially pure aluminium solid of elliptical billets with different lubricants applied on both sides in order to evaluate the effects of friction factor on the forming behavior of barrelling phenomenon under plane stress state condition. The radius of curvature of both major and minor bulge measured conformed to the calculated one using experimental data and the calculations were made with the assumption that the curvature of the bulge followed the form of a circular arc. Three different b/a ratios (ratio of minor to major diameter) namely, 0.6, 0.7 and 0.8 and aspect ratio (ratio of height to diameter) of 0.75 were prepared and cold upset forged. The relationship was also established between the various bulge parameters like the hoop strain, the axial strain, the new geometric shape factor, the stress ratio parameters, the major and minor radius of curvature of the bulge and the friction factor ‘m’ of different lubricants.     

C/C/Cu及C/Cu复合材料摩擦磨损行为比较

采用无压熔渗工艺制备一种新型的具有优异耐磨性能的碳纤维整体织物/炭/铜(C/C/Cu)复合材料,在UMT23多功能摩擦磨损测试仪上考察复合材料的摩擦磨损行为,并与粉末冶金方法制备的滑板用炭/铜(C/Cu)复合材料进行了对比分析。结果表明：C/C/Cu复合材料形成了连通状的网络结构,其导电性能及力学性能明显优于传统C/Cu复合材料;2种复合材料摩擦系数相近;2种复合材料及其对偶的磨损率随载荷增大而增大;与C/Cu相比,C/C/Cu的耐磨性较优,且对对偶损伤较小,在70N载荷下更为明显。连通状的网络结构及磨损表面形成的磨屑保护层是C/C/Cu复合材料具有良好摩擦磨损特性的主要原因。     

固化压力对一种纸基摩擦材料摩擦性能的影响

基于本实验室制备的一种炭纤维增强纸基摩擦材料, 研究了固化压力对材料孔隙率, 动摩擦系数, 静动摩擦系数之比, 摩擦力矩曲线的影响。研究结果表明: 孔隙率随固化压力增加而下降; 动摩擦系数随制动压力的增加均呈下降趋势; 静动摩擦系数比值随制动压力的增加分布趋势较为复杂: 较低的固化压力条件下, 静动摩擦系数之比略有上升, 而较高的固化压力条件下静动摩擦系数之比则略有下降趋势; 摩擦力矩曲线随固化压力升高有轻微翘曲出现。综合考虑固化压力对动摩擦系数、 静动摩擦系数比值以及摩擦力矩曲线的影响, 在这种纸基摩擦材料成分不变的条件下, 其对应较为合适的固化压力约为3.4MPa。      

基于搅拌摩擦的金属固相增材制造研究进展EI北大核心CSCD

基于搅拌摩擦的固相增材制造是大型轻质合金构件成形制造的新技术,已成为国内外先进成形制造领域研究的热点之一。本文对目前国内外基于搅拌摩擦的金属固相增材制造技术及其相关工艺机理的研究现状进行了分析和总结。常见的基于搅拌摩擦的固相增材制造技术可分为三类:基于搅拌摩擦搭接焊原理,使板材逐层堆积,从而获得增材构件的搅拌摩擦增材制造(friction stir additive manufacturing,FSAM)技术;采用中空搅拌头,通过添加剂(粉末或丝材)进行固相搅拌摩擦沉积的增材制造(additive friction stir deposition,AFSD)技术;采用消耗型棒材,通过棒材的摩擦表面处理,形成增材层的摩擦表面沉积增材制造(friction surfacing deposition additive manufacturing,FSD-AM)技术。重点分析了金属材料基于搅拌摩擦的固相增材制造技术的国内外研究与应用现状,对比了三类基于搅拌摩擦的固相增材制造技术的特征及其工艺优缺点。最后指出增材工艺机理、形性协同控制、外场辅助工艺改型、新材料应用和人工智能优化是基于搅拌摩擦的固相增材制造技术未来研究的重点方向。     

Internal friction of solid neon and argon films

The internal friction of solid neon and argon films, with thicknesses of several hundred nanometers, was measured at temperatures up to 25% of the triple point temperature, T_tr. At temperatures higher than 0.12T_tr, the internal friction increased strongly, following an Arrhenius law. The activation energy scaled with triple point temperature and was independent of film thickness. The value suggests that lowered energy barriers for dislocation motion enhance the plasticity and give rise to the internal friction peak.     

Workability studies on powder metallurgy pure iron preforms during hot forging under triaxial stress state condition

An experimental research work was performed for the understanding of the workability behavior of pure iron preforms produced through powder metallurgy route during hot forging under triaxial stress state condition. Relationship was established between the formability stress index and the axial strain. A relationship between the relative density and the axial strain was also established. Various stress ratio parameter under triaxial stress state condition which indicates the workability behavior of the material namely, , and were studied. An attempt has also been made to relate the stress ratio parameters with the relative density (R).     

Al_2O_3颗粒镀铜对铜基粉末冶金摩擦材料Al_2O_3-Fe-Sn-C/Cu摩擦磨损性能的影响

通过对陶瓷摩擦组元的表面进行化学镀铜来改善铜基粉末冶金摩擦材料中陶瓷相与基体间的结合效果,从而提高材料摩擦磨损性能。分别采用镀铜Al2O3颗粒和未镀铜Al2O3颗粒与铜粉和铁粉等经混合、压制、加压烧结制备Al2O3-Fe-Sn-C/Cu摩擦磨损试样。测试并分析了摩擦材料的微观结构、力学性能及摩擦磨损性能。结果表明:摩擦组元镀铜可使硬质颗粒与铜基体结合紧密;摩擦材料的布氏硬度增加了12%,弹性模量提高了约7%,摩擦系数提高了5%~10%,线磨损量降低了20%~50%;表面镀铜后的Al2O3颗粒不易脱落,摩擦系数稳定性提高了13%~23%。研究结果表明,摩擦组元表面镀铜可提高材料的综合性能。     

Molecular dynamics study of solid state interfacial reaction in the Ni-Mo system

Based on the Finnis–Sinclair formalism, an n-body Ni-Mo potential is constructed and the potential with optimized parameters is able to reproduce some physical properties of several Ni-Mo alloy phases. Molecular dynamics simulation with the constructed potential is performed to study the detailed process of solid-state interfacial reaction in the Ni/Mo multilayers upon isothermal annealing at medium temperatures. It is found that in the sandwich model or the bilayer model, interfacial reaction can take place down to 350 °C and is initiated through interface-crossing atomic diffusion, resulting in alloying and amorphization. The planar growth of the amorphous interlayer shows an asymmetric behavior, i.e., consuming the Ni lattice at a higher speed than the Mo lattice, leading to some intermediate stages where an Ni-enriched amorphous phase coexists with a small amount of unreacted Mo crystal. Moreover, it is revealed that 21 at.% Mo atoms in the Ni lattice reaches a critical value, resulting in a crystal-to-amorphous transition, while the critical concentration for collapsing of the Mo lattice is up to 25 at.% Ni. It follows that the above difference in the solubilities is regarded as the physical origin of asymmetric growth. Kinetically, the growth of the amorphous layer is found to follow a t ^1/2 law, indicating that solid-state amorphization is indeed through a diffusion-limited reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

轮缘固体润滑剂对轮轨减摩及损伤性能影响

用MMS-2A滚动摩擦磨损试验机完成试验工作,对比干态和3种不同固体润滑剂作用工况,分析干态和3种不同固体润滑剂作用后的轮轨摩擦性能和固体润滑剂的有效作用时间,探究固体润滑剂对轮轨摩擦性能的影响;分析不同工况下轮轨表面磨损量和表面裂纹,同时对裂纹的长度、角度、深度进行统计,分析固体润滑剂作用对轮轨损伤性能影响。结果表明:固体润滑剂具备减摩润滑作用,其中1号效果最佳,将干态下的摩擦系数0.5降低到0.2左右;固体润滑剂通过降低接触界面的摩擦系数减小轮轨界面的切向摩擦力,降低轮轨表面的磨损量,其中固体润滑剂1降低车轮和钢轨的磨损量最大,分别降低95.3%和97.1%;固体润滑剂主要通过抑制疲劳裂纹的长度来抑制轮轨疲劳裂纹的生长和扩展,通过正应力挤压作用使轮轨表面疲劳裂纹开口紧闭,缓解裂纹根部分支现象,有效抑制轮轨疲劳裂纹生长与扩展行为.     

Optimum rolling speed and relevant temperature- and reduction-dependent interfacial friction behavior during the break-down rolling of AZ31B alloy

The present study aimed to determine the optimum rolling speed for break-down rolling of as-cast AZ31B alloy and investigated the friction behavior associated with temperature- and reduction-sensitivity at the roll/plate contact interface. Tensile testing, formability evaluation and microstructural studies relevant to different rolling speeds were performed and finally the optimum operating rolling speed (50.0 ± 0.8 m/min) was obtained. Further, the effects of rolling reduction and initial temperature were assessed on the temperature variation, lateral spread and interfacial friction behavior at optimum rolling speed. The results showed that lower rolling speed (18.0 ± 0.8 m/min) resulted in an incompletely recrystallized structure where twins occupied relatively high volume fraction. Twinning dominated the deformation at rolling speed exceeding the optimum, resulting in the local recrystallization with shear bands and coarse grains. Rolling at 50.0 ± 0.8 m/min could get the best overall tensile properties and rolling formability due to the relatively high recrystallization degree and microstructure uniformity. An inverse method has been developed to determine the interfacial friction coefficient during interaction of AZ31B alloy with roll surfaces. When rolling at the optimum speed, the interfacial friction coefficient ranged from 0.16 to 0.58, which was strongly positively correlated with the reduction but slightly positively correlated with the initial temperature. Depended on the rolling characteristics, external friction effect coefficient ranged from 1.25 to 2.35 and it exhibited positive correlation with both the initial rolling temperature and rolling reduction.     

固体润滑剂对磁流变液摩擦性能的影响

从磁流变液的配方设计入手,采用四球摩擦磨损实验机研究了不同类型的固体润滑剂对磁流变液摩擦性能的影响,并考察了固体润滑剂在不同触变剂体系和不同基础油体系磁流变液中的配伍性,记录了摩擦系数随时间的变化曲线。结果表明,无机层状结构类固体润滑剂和高分子化合物类固体润滑剂的加入均能有效地改善磁流变液的润滑性能,其中MoS2在无机层状结构类固体润滑剂中的润滑效果最佳,氮化硼的润滑效果最差。固体润滑剂在以SiO2为触变剂的磁流变液体系中的减摩效果优于以高岭土为触变剂的磁流变液体系。与硅油磁流变液体系相比,在矿物油磁流变液体系中聚四氟乙烯和氮化硼能能起到明显的润滑效果,MoS2和石墨的润滑效果变弱。     

亚胺化温度对聚酰亚胺固体润滑膜摩擦性能的影响

在镀Ni基材上制备PAA薄膜并加热亚胺化,改变最终的亚胺化温度,所得产物经红外光谱分析均为PI薄膜。考察在不同亚胺化温度下制备的PI薄膜的亚胺化程度,物理机械性能和摩擦性能。试验结果显示,随亚胺化温度的升高,亚胺化程度逐渐提高,到了300℃亚胺化基本完成,继续升高温度,亚胺化程度反而有所降低。300℃制备的PI膜具有最好的物理机械性能,在MM 200摩擦磨损试验机上同偶面摩擦时获得最低的摩擦系数和较高的使用寿命。     

Microstructure and enhanced atomic diffusion of friction stir welding aluminium/steel joints

Lap joints of friction stir welding between aluminium and stainless steel sheets were conducted using a welding tool with a cutting pin. The atomic diffusion of Fe–Al system during the severe plastic deformation was investigated. The interfacial microstructure and metallurgical reaction was analysed. The metallurgical reaction layers were identified as a compounds containing a phase of Al₃Fe, partial solid solution of Fe and Al, and amorphous with a thickness of 0.9–3.3?μm which depending on the process parameters. The interdiffusion coefficient between Al and Fe atoms is about 4 orders of magnitude compared with that under thermal equilibrium state. The nanocrystalline and partial amorphous were formed near the interface which may caused by the enhanced atomic diffusion.