结构钢残余应力的电磁法测量优化研究

采用万能试验机、金相显微镜、X射线衍射仪及电磁应力仪,研究了电磁法测残余应力灵敏系数与层深之间的关系,对相应工件不同层深残余应力进行测量,并提出了使用线性拟合法取得更合适的灵敏系数,最后使用X射线衍射法进行了验证.结果表明:灵敏系数随着层深增加,先增大后减小;工件近表层残余应力分布与深层有着显著区别,在0.6 mm以上...     

工程陶瓷磨削表面残余应力的测量新方法

磨削加工后工程陶瓷零件表面会产生残余应力。X射线衍射法是用来测量磨削加工后工程陶瓷中残余应力的可靠测量手段。传统的X射线衍射法称之为sin^2ψ法，通常只能测量工件表层的残余应力；本文介绍了一种残余应力测量新方法，该方法联合使用sin^2ψ法和掠入射X射线衍射法从而得到残余应力在试件中的深度分布。如果考虑X射线的折射，在一系列掠射角下采集到的X射线衍射花样的有效穿透深度和衍射角必须进行折射校正。最后，用这种方法得到的残余应力值是X射线照射的所有层的平均值。     

GH4169疲劳试样加工残余应力的表征及其对低周疲劳寿命的影响

为了探究GH4169合金低周疲劳试样加工过程中表面残余应力的变化及残余应力对低周疲劳性能的影响，采用X射线衍射法对“车 磨 抛”不同加工工艺的试样表面残余应力进行表征及对成品试样进行残余应力层深度测试，通过中子衍射法对试样内部进行残余应力测试。采用电液伺服万能试验机进行了低周疲劳试验。结果表明：GH4169合金低周疲劳试样加工表面残余应力随着切削量的增加由表面残余压应力变为残余拉应力。根据残余应力层深度测试，机加工对试样表面造成残余应力层深度小于0.01 mm，内部残余拉应力减小；根据疲劳试验结果，GH4169合金疲劳寿命与表面轴向残余压应力呈正相关关系。     

GH4169疲劳试样加工残余应力的表征及其对低周疲劳寿命的影响

为了探究GH4169合金低周疲劳试样加工过程中表面残余应力的变化及残余应力对低周疲劳性能的影响,采用X射线衍射法对“车 磨 抛”不同加工工艺的试样表面残余应力进行表征及对成品试样进行残余应力层深度测试,通过中子衍射法对试样内部进行残余应力测试。采用电液伺服万能试验机进行了低周疲劳试验。结果表明：GH4169合金低周疲劳试样加工表面残余应力随着切削量的增加由表面残余压应力变为残余拉应力。根据残余应力层深度测试,机加工对试样表面造成残余应力层深度小于0.01 mm,内部残余拉应力减小;根据疲劳试验结果,GH4169合金疲劳寿命与表面轴向残余压应力呈正相关关系。     

FV520B钢等离子喷焊组织性能及残余应力分析

针对残余应力及组织性能对再制造修复叶轮的影响,运用等离子喷焊技术,在叶轮材料FV520B基体上进行喷焊试验,通过金相显微镜观测其组织形貌,采用X射线应力分析仪测试喷焊层表面的残余应力和厚度方向的应力梯度。结果表明:喷焊层界面组织成分分布均匀,没有明显缺陷;拉应力出现在工件热影响区边界、结合层及工件背面,最大拉应力分布在热影响区边界处。以工件表面热影响区边界处残余应力为指标,采用正交试验法对等离子喷焊工艺参数进行优化,最终减小了喷焊后的表面残余拉应力。     

基于化学腐蚀法的激光淬火表层残余应力测量

为了进一步揭示激光淬火提高工件表面耐磨性机理,根据激光淬火区尺寸小、不易制备利用曲率变化的剥层法测量残余应力的缺点,提出了化学腐蚀剥层法与X射线法相结合测量表层残余应力的方法。并以测量结果说明了激光淬火提高耐磨性的残余应力影响机理。     

40Cr钢磨削淬硬层残余应力的试验研究

以平面磨削淬硬加工试验为基础,利用X射线应力测定仪对40Cr钢磨削淬硬层残余应力进行了研究.结果表明,磨削淬硬层表面均存在残余压应力,次表层出现最大残余压应力.随着磨削速度的提高、磨削深度的增加或工件进给速度的降低,磨削淬硬层表面残余压应力值相应减小,但最大残余压应力和应力作用深度相应增加.采用单程干式磨削淬硬可增加淬硬层的最大残余压应力及应力作用深度.     

X80管线钢电磁超声残余应力检测精度的影响因素

管道运输中X80管线钢应用较为广泛，实际管道焊接大多使用半自动焊，难免存在焊接缺陷，在使用过程中会造成应力集中，可能导致管道破裂、石油泄漏等重大事故。为了促进电磁超声残余应力检测在管线钢中的应用，采用电磁超声系统，测试了X80管线钢残余应力检测的最佳参数。试验结果表明，电磁超声残余应力检测系统的6次回波测试精度为60 MPa;得出了电磁超声残余应力检测应力系数、信噪比随回波次数的变化关系，回波次数和应力系数、信噪比之间存在最佳取值，最后对薄板、厚板的电磁超声残余应力检测提出了一些建议。     

大型冷轧辊机加工残余应力沿层深分布的测定

利用X射线应力分析法和电解剥层法测定了大型轧辊机加工后的残余应力沿层深分布,结果表明：选择较小的工艺参数时,磨削加工应力层为250－300um,车削加工应力层为800－900um,从而为测定冷轧辊在淬,回火后残余应力沿截面分布时,去除表面机加工应力层,减少X射线法的测量误差提供了科学依据。     

闭挤式精冲成形表面残余应力与耐腐蚀性实验分析

为了研究闭挤式精冲成形后工件的残余应力分布规律以及耐腐蚀性能,对闭挤式精冲件进行了表面和层深残余应力分析,同时通过极化曲线试验法研究了工件在3.5%NaCl溶液中的腐蚀电化学行为。结果表明:工件表面残余应力为压应力,压应力随变形程度增大而增大,最大值为150MPa;随着层深的增加,残余压应力先增大后减小,在次表层达到最大值,残余应力场的深度为200μm左右;在极化曲线试验中,闭挤式精冲件初期耐蚀性优于车削件和坯料,但随着腐蚀的进行,耐蚀性反而下降,且闭挤式精冲件最终钝化现象较车削件和坯料延迟。     

弹簧钢60Si2Mn疲劳试验断裂分析

对60Si2Mn弹簧钢进行了疲劳寿命试验。试验结果表明，疲劳寿命较低，未达到标准要求(不低于20万次)。采用化学成分检测、断口扫描观察、能谱分析和金相检验等方法，对疲劳试验中断裂弹簧进行了分析、检测。分析结果表明，钢丝表面微裂纹是导致弹簧疲劳断裂的直接原因，该裂纹是由于母材表面存在轧制缺陷，经过拉拔表面产生硬化组织，由于塑性不足，产生微裂纹；钢丝近表面存在超尺寸夹杂物，该夹杂物属于连铸过程中典型的外来宏观夹杂物，间接加速了弹簧疲劳断裂。     

多壁纳米碳管／Cu基复合材料的摩擦磨损特性

利用销－盘式磨损试验机研究了粉末冶金法制备的多壁纳米碳管／Cu基复合材料的稳态摩擦磨损行为,并用扫描电镜分析了复合材料的磨损形貌。结果表明：多壁纳米碳管／Cu基复合材料具有较小的摩擦系数,并随纳米碳管质量分数的增加而逐渐降低;由于复合材料中纳米碳管的增强和减摩作用,在低载荷和中等载荷作用下,随着纳米碳管质量分数的增加,复合材料的磨损率减小;而在高载荷作用下,由于发生表面开裂和片状层剥落,含纳米碳管质量分数高的复合材料的磨损率增高。     

碳纤维表面生长纳米碳管及其增强的炭/炭复合材料

采用化学气相沉积工艺在碳纤维表面生长了纳米碳管,将此种碳纤维作为增强材料,以中间相沥青为基体炭前驱体采用浸渍炭化工艺制备了炭/炭复合材料.观察了所得复合材料断口的微观形貌,测试了抗弯强度及热物理性能.结果表明,碳纤维表面的纳米碳管可以有效地提高纤维与基体的粘结力,复合材料的抗弯性能提高了50%,而对复合材料的导热性能影响较小.     

Processing and characterization of carbon nanotube mat/epoxy composites

A carbon nanotube mat (CNT mat) with long (∼1 mm) multi-walled carbon nanotubes (MWCNTs) was used to process MWCNT/epoxy composites at high concentrations (4.4 and 10.0 wt.%) of MWCNTs by a simple method without the use of a solvent. The CNT mat circumvents several cumbersome processing steps, including the dispersion of CNTs in a solvent. Two different resin-impregnation processing methods were explored. The processing steps were chosen to prepare composite samples based on the performance of the composites and the simplicity of the processing techniques. Scanning electron microscopy (SEM) was used to examine the microstructures of the CNT mat and its composites. The mechanical and electrical properties were tested. The tensile strengths of the composites with 10.0 wt.% MWCNTs were increased by 17% to 90% when compared to that of neat epoxy samples. The electrical conductivity of the composite is 36.1 S/cm. 4.4 wt.%-MWCNT composites show very large strain valuesupon fracturing (> 15 %), and their electrical conductivity is 14.9 S/cm. These results show that CNT mat/epoxy composites can be used as flexible electrodes and as a matrix system for advanced fiber composites.     

Friction and Wear Behavior of Carbon Fabric-Reinforced Epoxy Composites

Besides intrinsic material properties, weight/energy savings and wear performance play an important role in the selection of materials for any engineering application. The tribological behavior of carbon fabric-reinforced epoxy composites produced by molding technique was investigated using a reciprocating pin-on-plate configuration. It was shown that the wear rate considerably decreased (by a factor of approx. 8) with the introduction of the reinforcing carbon fabric into the epoxy matrix. It was observed that the wear rate of the tested composites increased with an increase in normal load. Moreover, the coefficient of friction for epoxy/steel and composites/steel tribo-pairs was also determined and decreased with increasing load. By means of scanning electron microscopy of the wear tracks, different wear mechanisms such as matrix wear, matrix fatigue and cracking, matrix debris formation for neat epoxy together with fabric/fiber thinning, fabric breakage and fabric/matrix debonding for the reinforced epoxy could be distinguished.     

Structural interpretations of deformation and fracture behavior of polypropylene/multi-walled carbon nanotube composites

The deformation and crack resistance behavior of polypropylene (PP) multi-walled carbon nanotube (MWNT) composites have been studied and their interrelation to the structural attributes studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarization light microscopy has been discussed. The composites were produced from industrial available MWNT by extrusion melt-mixing and injection-molding. In stress–strain measurements a strong increase in the yield stress and the Young’s modulus at low MWNT contents has been observed, which was attributed to an efficient load transfer between the carbon nanotubes and polypropylene matrix through a good polymer–nanotube adhesion as indicated by SEM. The extent of enhancement in mechanical properties above 1.5 wt.% of MWNT decreased due to an apparently increased tendency of clustering of carbon nanotubes. Several theoretical models have been taken into account to explain the mechanical properties and to demonstrate the applicability of such models to the system under investigation. The crack resistance behavior has been studied with the essential work of fracture (EWF) approach based on post-yield fracture mechanics (PYFM) concept. A maximum in the non-essential work of fracture was observed at 0.5 wt.% MWNT demonstrating enhanced toughness compared to pure PP, followed by a sharp decline as the MWNT content was increased to 1.5 wt.% reveals a ductile-to-semi-ductile transition. Studies on the kinetics of crack propagation aspects have revealed a qualitative picture of the nature of such a transition in the fracture modes.     

Synthesis of MWNT-based composite materials with inorganic coating

Multiwalled carbon nanotube (MWNT) based metal oxide composites were prepared by an impregnation method using organometallic compounds as precursor. Aluminium isopropoxide (AlIP), tetraethyl orthosilicate (TEOS), and tetraethyl orthotitanate (TEOTi) were used as inorganic sources and decomposed by hydrolysis on the surface of carbon nanotubes. The composites were subsequently investigated by transmission electron microscopy and their coverage was compared. A direct, solvent-free impregnation technique turned out to be the most successful for all organometallic compounds and provided homogeneous inorganic cover layer on the surface of purified MWNTs.     

Electrochemical synthesis of polypyrrole films over each of well-aligned carbon nanotubes

Polypyrrole (PPy) films were uniformly electropolymerized over each carbon nanotube of the well-aligned carbon nanotube arrays. For comparison, PPy films were also coated on flat metallic titanium (Ti) and platinum (Pt) substrates by the same technique. The synthesis and the redox performance of the PPy films were conducted by cyclic voltammetry (CV). The structural characterization including the thickness and uniformity of the PPy films was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is observed that the coating of the PPy film over carbon nanotubes is much faster than that on flat Ti/Pt surface. Furthermore, the redox performance of the PPy-coated carbon nanotube electrodes over flat Ti/Pt electrodes was significantly improved due to the high accessible surface area of the carbon nanotubes in the aligned arrays, especially in large film formation charge (Q_film). It is very promising that the electrode developed in this study could be used as high performance electrode in rechargeable batteries.     

Dependence of dielectric properties on BT particle size in EP/BT composites

The polymer-ceramic composites of epoxy resin (EP) and barium titanate (BT) were prepared.BT powders of different BT particle sizes from 100 nm to 1 μm were used in the preparation.The dielectric properties, such as dielectric constant, dielectric loss and electrical breakdown strength, of the EP/BT composites were studied.The morphology of the composites was characterized by the means of scanning electron microscopy (SEM).The results show that the dielectric constant of the composites is much higher than the epoxy matrix at frequency range from 1 kHz to 10 MHz, and it is also obviously dependent on the size of BT particles.The electrical breakdown strength of the composites decreases with the increase of the BT content.The dependence of electrical breakdown strength on BT particle sizes was also discussed.     

中间相沥青基炭/炭复合材料的微观结构与力学性能

借助偏光显微镜、扫描电镜、透射电镜以及力学性能测试研究了微观结构对中间相沥青基炭/炭复合材料力学性能的影响.结果表明基体炭在偏光显微镜下呈现出光学各向异性,在SEM和TEM下呈片层条带状结构.基体炭与纤维之间的界面不连续,为"裂纹型"界面.材料受载破坏时裂纹通过改变扩展路径而延缓其扩展速度,在纤维-基体界面处以及基体炭层片之间引起滑移,在断口形貌上体现出断裂台阶适中且与纤维拔出交替进行,表现出韧性破坏的断裂特征.材料具有较高的力学性能,抗弯强度达到257MPa.