工程车转向臂下端轴断裂原因分析

采用扫描电镜测试、金相检验、硬度测试、化学成分分析等方法对某型号重载工程车转向臂下端轴的断裂原因进行了分析。结果表明:该轴的断裂属于疲劳断裂,轴肩过渡处圆角未达到设计要求以及机加工刀痕、冶金缺陷引起该位置应力集中是导致其疲劳断裂的主要原因。     

某油田注水泵阀体弹簧断裂分析

对断裂弹簧进行化学成分分析、硬度测试、金相检验以及断口的宏观及微观分析。结果表明，该弹簧属脆性疲劳断裂失效，并提出改进措施。     

减振器前叉管断裂原因分析

本文通过对摩托车减振器前叉管的化学成分、断口形貌、硬度及金相组织进行检验，分析和讨论了前叉管的断裂性质及原因，从而得知该摩托车减振器前叉管的断裂是该材料中存在较严重的非金属夹杂物所导致的疲劳断裂。     

国产某型220T矿用自卸车转向臂受力分析及优化

近年来随着煤、铜等资源型企业不断扩大生产量,为降低运输成本,减少矿区范围内的汽车车流密度,提高生产运输效率,使得矿用运输车辆不断朝大型化方向发展,以减少车辆总数量,因此,矿用大型自卸车是目前大型露天矿山的主要运输工具。针对国产某型220t矿用自卸车个别转向臂在运行中由于局部地方因应力集中导致出现微裂纹的现象,通过workbench软件对转向臂受力分析,获得转向臂的应力分布状况,对转向臂应力集中部位进行优化设计,解决转向臂出现微裂纹的问题。     

55Cr3钢轿车稳定杆疲劳断裂失效分析

采用电子显微分析、金相组织分析和显微硬度分析等方法，对55Cr3钢轿车稳定杆疲劳试验过程中断裂的原因进行了分析。结果表明，发生断裂的稳定杆表面存在明显凹坑，导致其在疲劳试验过程中引起应力集中，是稳定杆发生早期疲劳断裂的主要原因。     

高速线材04H轧机减速齿轮断裂分析

应用硬度检验，化学分析及金相分析等方法对高速线材轧机减速机大齿轮断裂原因进行综合分析。结果表明，齿轮在制造过程中的机械加工不当，使齿轮产生磨削裂纹，渗碳层不均匀，在齿轮工作过程中裂纹进一步扩展导致齿轮断裂。     

45钢汽车半轴断裂原因探讨

通过检验45钢汽车半轴化学成分、金相组织、硬度、夹杂物，观察断口形貌及分析其热处理工艺，确定了造成汽车半轴断裂的主要原因，继而提出了改进措施。     

MC300K12塔吊鱼尾板断裂原因分析

本文利用化学成份测试，机械性能试验，金相组织检验，显微硬度测定及断口分析等手段对鱼尾板进行了断裂原因分析。结果表明，材料的原始晶粒粗大是产生裂纹的主要原因。     

铸机分节辊断裂原因及分析

针对目前铸机分节辊轴颈频繁断裂的问题，通过化学成分、表面硬度测定、低倍、高倍金相以及铸机分节辊的设计图等分析断裂形成原因，并建议通过采取一些措施，减少铸机分节辊轴颈的断裂。     

掘进机截割减速机输出轴断裂原因分析

掘进机截割减速机输出轴工作一段时间后发生断裂,该输出轴材质为35CrMo。为了分析断裂原因,在其断口处取样,通过化学成分分析、硬度检验和力学试验以及金相试验进行分析。分析结果表明,该输出轴的化学成分及热处理后硬度均能达到要求,但冲击功要求远低于技术要求,所以得出结论冲击韧性过低是该输出轴断裂的主要原因。     

Why should physicians worry about patient satisfaction? Applying some of the principles used in the emergency department to hospital and office-based practices

Dental porcelain has superior esthetics but may be subject to fracture during mastication. Residual compressive stresses on the porcelain surface after cooling enhance resistance of porcelain to crack initiation, as quantified by its fracture toughness (Kc). The effect of different cooling rates on Kc and hardness of a glazed porcelain reinforced with approximately 2% aluminum oxide was examined in 45 porcelain disks that were divided into three groups. After final glaze firing, one group was cooled rapidly, the second was cooled at a medium rate, and the third was cooled slowly. Fracture toughness was determined with a microindentation procedure. The mean Kc recorded for rapidly cooled porcelain (1.74 +/- 0.09 MN/m3/2), for medium-cooled porcelain (1.41 +/- 0.07 MN/m3/2), and for slow-cooled porcelain (1.29 +/- 0.07 MN/m3/2) was statistically different (p < 0.001, analysis of variance and Bonferroni post hoc test). No statistically significant differences in Vickers hardness values were recorded when porcelain was cooled at different rates (530 to 540) (analysis of variance). The faster cooling rate of a glazed alumina reinforced porcelain resulted in greater fracture toughness but had no effect on hardness.     

Selective Separation of Fe-Concentrates in EAF Slags Using Mechanical Dissimilarity of Solid Phases

We sought to develop an optimized particle size-dependent separation method to lower the Fe content of pulverized glass-ceramic electric arc furnace (EAF) slag for its improved reclamation as construction materials by considering the structures and the mechanical behavior of the discrete solid phases. After an isothermal crystallization process to enhance the spinel growth, the Vickers hardness and fracture toughness were measured on the spinel and amorphous phases separately from the solidified slag using indentation methods. The characteristic differences in the hardness of the phases were magnified when this glass-ceramic composite was isothermally crystallized. The hardness of the spinel was observed to be lower in slags with higher Fe_tO/Al₂O₃ mass ratios due to the triclinic unit cell expansion of the spinel, whereas the hardness of the amorphous phase decreased with increasing isothermal period because of the structural transformation into a silicate-dominant network. Fracture toughness could be calculated based on the hardness and crack length, where the Young’s modulus was determined using nanoindentation. The amorphous phase with a lower Fe content and lower fracture toughness resulted in finer powder distribution after pulverization, allowing better separation of the primary crystalline spinel containing higher Fe content from the Fe-deficient amorphous phase according to the particle size.     

微米／纳米Ti（C,N）基金属陶瓷刀具材料的研制

系统研究了添加纳米级Al2O3的含量对Ti(C,N)基金属陶瓷力学性能和显微结构的影响。结果表明:纳米Al2O3的添加可大幅提高Ti(C,N)基金属陶瓷的力学性能,特别是硬度和断裂韧性明显提高,克服了Ti(C,N)基金属陶瓷硬度较低的缺点,扩大了其应用范围。通过对微观结构观察和分析,可以看出,纳米Al2O3的添加细化了基体的晶粒,主要断裂模式为穿晶断裂,晶粒的细化和断裂模式的改变是材料力学性能提高的主要原因。     

Φ35mm40CrNiMoA钢剪切断面异常分析与改进

对比分析了不同批次Φ35mm40CrNiMoA钢剪切正常断面与异常断面的宏观形貌、化学成分、金相组织、硬度,综合分析确定钢材交货状态不同、金相组织差异较大、导致硬度差别大,是造成剪切断面异常撕裂的主要原因。热轧态钢材硬度高,剪切断面质量较好;退火态钢材硬度值低,剪切断面易出现撕裂。     

Effects of alloying elements on microstructure,hardness, and fracture toughness of centrifugally cast high-speed steel rolls

A study was made of the effects of alloying elements on the microstructure, hardness, and fracture toughness of centrifugally cast high-speed steel (HSS) rolls. Particular emphasis was placed on the role of hard carbides located along solidification cell boundaries and the type of the tempered martensitic matrix. Microstructural observation, X-ray diffraction analysis, hardness and fracture-toughness measurements, and fractographic observations were conducted on the rolls. The constitution and morphology of carbides observed within the intercellular boundaries varied depending upon the predominant alloying elements that comprised them. These massive carbide formations strongly influenced the bulk material hardness and fracture toughness due to their high hardness. The effects of alloying elements were analyzed on the basis of the liquidus-surface diagram which and indicated that the proper contents of the carbon equivalent (CE), tungsten equivalent, and vanadium were 1.9 to 2.0, 10 to 11, and 5 to 6 pct, respectively. The roll material, containing a small amount of intercellular carbides and lath-type tempered martensitic matrix, had excellent fracture toughness, since carbides were well spaced. Therefore, it was suggested that the optimization of alloying elements was required to achieve the homogeneous distribution of carbides.     

Effect of cerium on abrasive wear behaviour of hardfacing alloy

Hardfacing alloys with different amounts of ceria were prepared by self-shielded flux cored arc welding.The abrasion tests were carried out using the dry sand-rubber wheel machine according to JB/T 7705-1995 standard.The hardness of hardfacing deposits was meas-ured by means of HR-150AL Rockwell hardness test and the fracture toughness was measured by the indentation method.Microstructure characterization and surface analysis were made using optical microscopy,scanning electron microscopy(SEM) and energy spectrum analy-sis.The results showed that the wear resistance was determined by the size and distribution of the carbides,as well as by the matrix micro-structure.The main wear mechanisms observed at the surfaces included micro-cutting and micro-ploughing of the matrix.The addition of ceria improved the hardness and fracture toughness of hardfacing deposits,which would increase the resistance to plastic deformation and scratch,thus the wear resistance of hardfacing alloys was improved.     

SDAS对A357合金时效过程的影响

铸造Al-Si-Mg合金是典型的可热处理强化铝合金,二次枝晶臂间距（SDAS）对合金力学性能有非常显著的影响,研究SDAS对合金时效动力学的影响有重要意义.采用硬度计进行力学性能测试、光学显微镜分析金相组织,研究了SDAS对A357合金时效动力学的影响.研究发现,在相同的固溶处理条件下,随着A357合金试样二次枝晶臂间距的增大,固溶处理后达到的硬度值减小;不同壁厚的合金试样的时效峰随SDAS增大而延后;对时效处理实验结果进行回归分析和量纲分析,得到时效力学性能的数学模型,并证明了该数学模型的有效性.     

N80钢级外加厚油管断裂失效分析

文章通过力学性能测试、化学成分分析、显微组织和微观断口分析等分析手段,综合分析了N80钢级外加厚油管断裂失效原因。结果表明,该油管为典型的脆性断裂失效,由于模具冷却操作不当导致油管淬火产生了马氏体组织,使油管冲击功低于标准要求,高硬度、低韧性是油管在管坯镦粗过程中发生脆性断裂失效的主要原因。     

The effects of surface hardening on fracture toughness of carburized steel

This research program was carried out to evaluate the effects of surface hardening on the fracture toughness of carburized steel. The materials AISI 8620 steel was machined into compact-tension (CT) specimens. The specimens were pack carburized at 930°C (1706°F) for different periods of time, cooled to ambient temperature and subsequently tempered at various temperatures for one hour. The fractured specimens were examined by hardness tests, metallography, X-ray diffraction analysis for retained austenite in the case, and scanning electron microscope fractographic analysis of the fracture surfaces. The experimental results revealed that theKIC values of the carburized, AISI 8620 steels were improved by the increase in case depth. Martensitic/tempered-martensitic structure in the case was the major constituent contributing to the improved toughness. The amount of retained austenite at the case increased as the thickness of the hardened layer increased. But retained austenite as well as large grain size were found to have adverse effects on fracture toughness of the carburized steel. The tempering temperature of 500°C (932°F) provided maximumKIC values. Higher tempering temperatures resulted in sharp decrease of fracture, toughness values. W{upeio}-Y{upoue} H{upo}, formerly a Graduate Student, in the Department of Materials Engineering Tatung Institute of Technology, is in compulsory 0 ROTC military service of Republic of China.     

Effect of Segregation of Secondary Phase Particles and “S” Line on Tensile Fracture Behavior of Friction Stir-Welded 2024Al-T351 Joints

A 5-mm-thick 2024Al-T351 plate was friction stir welded (FSWed) at welding speeds of 100, 200, and 400 mm min^?1 with a constant rotation rate of 800 rpm, and the microstructure and tensile fracture behavior of the joints were investigated in detail. FSW resulted in the redistribution of secondary phase particles along the recrystallized grain boundaries at the nugget zone (NZ), forming linear segregation bands consisting of secondary phase particles. The segregation bands, mainly present in the shoulder-driven zone, were believed to result from periodic material flow, with the average band spacing on the longitudinal and horizontal cross sections equal to the tool advancement per revolution. At a low welding speed of 100 mm min^?1, in spite of the highest density of segregation bands, the FSWed 2024Al-T351 joint fractured along the low hardness zone (LHZ) of the heat-affected zone because of large hardness gap between NZ and LHZ. Increasing the welding speed to 200 and 400 mm min^?1 reduced both the hardness gap between NZ and LHZ and the density of segregation bands. In this case, the segregation bands played a role, resulting in unusual fracture of the joints along the segregation bands. The “S” line originated from the oxide film on the initial butting surfaces and did not affect the fracture behavior of the FSWed 2024Al-T351 joints.