金属表面疲劳损伤的非线性Rayleigh波检测方法

提出了一种非线性Rayleigh表面波检测方法来实现金属表面疲劳损伤的检测。搭建了非线性Rayleigh波检测平台,进行了金属材料表面疲劳损伤的检测,测量不同拉伸载荷周期数目下非线性系数的变化,结合金属材料表面微观形态,建立了非线性系数-材料微观结构-宏观力学性能之间的联系。试验结果表明,非线性Rayleigh波检测方法可用于金属表面疲劳损伤的检测,具有一定的应用价值。     

电阻法检测金属构件损伤及预测疲劳寿命

基于非线性连续疲劳损伤理论,考虑应力幅带来的非线性累积效应,以电阻值定义金属构件损伤参量,提出基于电阻变化的金属高周疲劳损伤累积模型及疲劳载荷应力幅对损伤参量的影响函数,给出通过测量电阻来检测金属构件疲劳损伤状态的方法及预测高周疲劳剩余寿命的理论公式,并通过45号钢高周疲劳试验进行验证。     

金属材料拉伸与疲劳性能预测研究取得新进展

<正>拉伸性能与疲劳性能是金属材料工程应用的关键指标,建立二者之间定量关系,实现金属材料不同力学性能之间关系的定量预测是金属结构材料领域重要研究目标之一。由于目前相关理论不够完善,基于微观变形与损伤机制的拉伸性能与疲劳性能定量预测模型并未建立起来。因此,虽有大量实验数据表明金属材料拉伸强度与塑性之间存在明确的倒置关系,拉伸强度与疲劳强度之间存在特定的关系,但至今仍缺乏定量模型来描述上述定量关系。因此,建立金属材料拉伸性能与疲劳性能定量预测具有重要科学意义。     

时效时间对7075铝合金疲劳裂纹扩展速率的影响

采用透射电镜、显微硬度仪、拉伸试验和疲劳试验等研究了 7075铝合金在欠时效(120℃×8 h)、峰时效(120℃×24 h)与过时效(120℃×48 h)状态下的微观组织、硬度、拉伸性能方面与疲劳裂纹扩展速率方面的差异.结果表明:3种时效状态的合金在高低应力强度因子范围时,疲劳裂纹扩展速率呈现不同的规律.在低应力强度...     

微纳米尺度金属导电材料热疲劳研究进展

世界已逐渐进入以物联网和智能制造为主导的工业4.0时代,特别是人工智能和大数据处理的强烈需求,微纳米尺度器件的研发制造及广泛使用的日趋活跃使得小尺度材料得到广泛关注。由于这些材料的几何尺度和微观结构尺度的约束效应,其热疲劳损伤行为与块体材料不同。同时,材料尺度由微米向纳米量级的转变也会引起损伤机制的转变,使材料表现出不同的损伤形式,产生显著的尺寸效应。本文综述了近年来国内外开展的有关金属薄膜/线的热疲劳实验方法、热疲劳损伤行为及演化和热疲劳影响因素的研究进展,探讨了微纳米尺度金属材料热疲劳的微观机制和尺寸效应,并对这一领域的研究前景进行展望。     

不锈钢管道焊缝金属疲劳短裂纹行为的实验研究Ⅰ.材料微观结构和研究方法

用金相、复型技术和硬度实验测试了1Crl8Ni9Ti不锈钢焊缝金属试样表面的微观结构组成.结果表明:奥氏体基体与富δ铁素体-带状结构组成的柱状晶是焊缝材料的微观结构特征,相邻富δ铁素体带间距离(约40 μm)是这一结构的特征参量.试样表面的微观结构依相对焊缝柱状晶取向的不同而不同.考虑疲劳损伤的局部性和区别试样表面不同尺度、位置微裂纹对疲劳损伤贡献的差异,提出了以"有效短裂纹准则"为核心的疲劳短裂纹行为研究方法.     

金属材料冲击疲劳损伤的涡流热成像检测

利用冲击疲劳损伤对材料微观结构和应力分布的改变导致的材料导热率和电阻率等参数变化的特性,提出了利用涡流热成像技术检测金属材料冲击疲劳损伤的无损检测方法,构建了检测系统。通过试验,获得了飞机刹车片的涡流热成像图像。结合对冲击疲劳损伤引起的塑性变形而导致的材料导热率和电阻率等的变化的分析,通过图像处理提取了试件的温升变化曲线,比对了受损区域和正常区域的红外图像差异,实现了对冲击疲劳损伤缺陷的判别。结果表明,涡流热成像法能够快速地判断材料受损位置。     

基于微观建模法的焊接接头低周疲劳寿命预测研究

提出一种微观尺度的有限元模型,模拟了焊接接头的变形和短裂纹的萌生寿命。该模型考虑了焊接接头晶粒取向的不同和焊缝不同区域力学性能的差异。塑性应变能被作为疲劳损伤参量,结合疲劳寿命的能量准则来预测疲劳裂纹的萌生寿命。通过分析钛合金电子束焊的实验数据对该模型进行了验证。结果表明,在恒幅载荷作用下,焊接接头裂纹萌生于焊缝区多个晶界交汇或者较大且轮廓有畸变的晶粒内;微裂纹主要以Ⅰ型裂纹扩展;该微观有限元模型结合疲劳寿命预测的能量法在微观尺度上能够较好地完成焊缝疲劳性能的表征和疲劳寿命的估算。     

不锈钢管道焊缝金属疲劳短裂纹行为的实验研究Ⅰ.材料微观结构和？…

用金相、复型技术和硬度实验测试了１Ｃｒ１８Ｎｉ９Ｔｉ不锈钢焊缝金属试样表面的微观结构组成。结果表明：奥氏体基体与富δ铁素体－带状结构组成的柱状晶是焊缝材料的微观结构特征,相邻富δ铁素体带间距离（约４０μｍ）是这一结构的特征参量。试样表面的微观结构依相对焊缝柱状晶取向的不同而不同。考虑疲劳损伤的局部性和区别试样表面不同尺度、位置微裂纹对疲劳损伤贡献的差异,提出了以“有效短裂纹准则”为核心的疲劳短裂纹     

预拉伸变形对欠时效7N01铝合金板材疲劳断裂的影响

针对工业化生产的7N01铝合金板材,采用拉伸实验、疲劳实验和微观组织结构表征等手段研究了预拉伸变形对欠时效态7N01铝合金板材疲劳性能和疲劳断裂特征的影响。结果表明,预拉伸变形量增大至20%,欠时效态7N01铝合金板材中合金相粒子的形状、尺寸、数量、分布以及薄带状晶粒的尺寸和形状基本保持不变。然而,板材表现出明显的加工硬化效应,其屈服强度、抗拉强度和显微硬度分别由181 MPa、233 MPa和95 HV增大至254 MPa、271 MPa和117 HV,延伸率从23.2%降低至5.2%。在应力175 MPa、应力比R=0的疲劳循环加载条件下,随预拉伸变形量的增加,欠时效态7N01铝合金板材的疲劳寿命呈现出先缩短再延长又缩短的趋势。未预拉伸变形试样的疲劳寿命为6.06×10⁵cyc,5%预拉伸变形可将铝板的疲劳寿命延长75%,达到了1.06×10⁶cyc,而3%和20%的预拉伸变形将铝板的疲劳寿命分别缩短至4.21×10⁵和2.89×10⁵cyc。5%～16%预拉伸变形使欠时效态7N01铝合金板材基...     

本底真空对磁控溅射镍铬合金薄膜电阻的影响

目的研究本底真空对溅射镍铬合金薄膜性能的影响。方法在不同溅射时间下制备了不同厚度的镍铬合金薄膜,采用4、6、8、10 h不同的抽真空时间制备薄膜样品,并在空气、氮气及真空气氛中,对同一工艺条件下制备的镍铬合金薄膜样品分别在300、400、500℃下进行热处理,所有样品分别测试方块电阻。结果不同厚度的镍铬合金薄膜的方块电阻与薄膜厚度之间存在非线性关系,样品的方块电阻随着溅射前抽真空时间的增加而降低。在真空和空气中进行热处理的薄膜的方块电阻变化规律一致,而在氮气中的则相反。结论本底真空残留气体对镍铬合金薄膜的氧化是引起薄膜电阻率增大的主要原因,即射频磁控溅射镍铬合金薄膜被氧化而使电阻率增大,随着溅射时间的增加,残留气体影响减小,导致电阻率降低。前期抽真空时间大于9 h,靶材溅射清洗时间大于110 min时,制备的镍铬合金薄膜电阻率才趋于稳定。     

Influence of loading holding time under quasistatic indentation on electrical properties and phase transformations of silicon

The quasistatic Vickers indentation of Si (100) were applied to investigate the influence of loading holding time on the changes of electrical resistance and phase transformation in the indentation zone. For all used loading regimes with different holding times (2 s, 10 s, 1 h and 10 h) in combination with constant loading-unloading rate (250 mN/s) the electrical resistance in the region of residual indentations was found to be lower than before indentation. It was shown that this is connected with the formation of semimetallic Si-III phase and amorphous Si of higher pressure induced by creep process developed under long lasting pressure. The longer the holding time, the greater lowering of electrical resistance in the indentation region was observed, with the exception of the holding time above 1 h, this being explained by a decelerating creep rate of Si for this interval of time leading to a halt of further extending of amorphous and Si-III regions of lower electrical resistance.     

半固态Al-7％Si合金二次加热及成形试验

采用电阻炉加热的方法对机械搅拌法制备的半固态Al-7％Si合金进行了二次加热及成形试验,观察了显微组织的变化;通过电阻炉加热,分别用半固态模锻和液态模锻的方法成功地试制了法兰盘零件。初步探讨了搅拌工艺参数和液态模锻(半固态模锻)工艺参数的选择问题。     

AgCuO电触头材料的接触电阻及电弧侵蚀形貌分析

采用原位反应合成法制备CuO含量为10%的AgCuO电触头材料,使用接触电阻参数测试仪对试样在不同电流条件下开闭次数与接触电阻的关系进行研究,并通过扫描电镜对试样的阴/阳极表面微观形貌进行电侵蚀特性分析。结果表明,低电流条件下AgCuO电触头材料的接触电阻基本都是先升高,然后在某一开闭次数时急剧下降,最后基本趋于一定值,且AgCuO电触头材料接触电阻会随着试验电流的增加而逐渐降低;当电流达到25A时,AgCuO电触头材料的接触电阻最低,且随开闭次数的增加其接触电阻变化不大,材料的接触电阻表现出极佳的稳定性。电弧侵蚀后的形貌分析发现,阳极表面呈凹凸状,并有气孔和裂纹,而阴极表面呈现浆糊状尖峰结构。     

基于电场定位的新型工件几何尺寸测定方法

针对数字化测量的技术特点,提出在三维电场定位原理基础上,依靠电阻抗模型的电势梯度进行工件几何尺寸测量的新方法。利用Maxwell电磁仿真软件对所建立的模型进行分析,得出定位极板参数的变化对电场均匀性和方向性的影响规律。实验结果表明:重构模型与实物的最大偏差和尺寸相对误差均在允许误差范围之内,验证了模型的正确性。     

High pressure electrical resistance behaviour of dialuminides of thorium and uranium

In this paper we report the pressure-induced electrical resistance behaviour of the dialuminides of thorium and uranium up to 8 and 11 GPa, respectively. ThAl₂ shows a rapid decrease in resistance up to 2.5 GPa and thereafter it decreases slowly. The electrical resistance of UAl₂ also decreases monotonically and it shows a collapse in resistance above a pressure of 9 GPa where our own previous high-pressure X-ray diffraction results indicated the occurrence of a structural phase transition from cubic (MgCu₂) to hexagonal (MgNi₂) phase. The marked difference in the pressure-induced electrical resistance behaviour of these two systems is discussed by taking into account the contributions from interband scattering and spin-fluctuation scattering mechanisms in ThAl₂ and UAl₂, respectively.     

氧化时间对微弧氧化膜电接触微动磨损行为的影响

目的研究不同氧化时间的铝合金表面微弧氧化涂层在电接触条件下的微动磨损行为,并探讨其磨损机理。方法通过控制氧化时间(10、20、30、40、50、60、70 min),在铝合金表面制备不同表面状态的微弧氧化涂层,并利用四线接触法研究其在电接触条件下接触电阻的变化,通过分析摩擦系数、F-D曲线、磨损形貌、三维轮廓及磨痕化学成分来揭示其微动磨损机理。结果电接触微动磨损下,氧化不同时间形成的微弧氧化涂层在相同电接触微动磨损条件下的耐磨性存在明显差异,进而影响其电接触行为。氧化10 min时,涂层磨损最严重,磨损区域的涂层迅速失效,从而导致铝合金基体外露,接触电阻骤降至零;氧化50 min时,涂层厚度最大,具有良好的耐磨性,缓减了接触电阻的衰减,接触电阻曲线在衰减过程中受到磨斑表面裂纹的影响而产生波动。结论氧化时间会影响微弧氧化膜表面形貌、粗糙度以及厚度,对其在电接触条件下的微动磨损行为影响较大。     

Numerical analysis on thickness effect of magnetic thin films on conduction noise absorption in microstrip line

Noise absorbing properties of two kinds of magnetic thin films (one is electrically conductive Co-Zr-O granular thin film and the other is Ni-Zn ferrite thin film with high electrical resistivity) are analyzed by the finite element method (FEM) with various film thicknesses. For the Ni-Zn ferrite film with high electrical resistivity (～2 × 10 ² Ωm), a low reflection parameter (S₁₁) value is predicted, and the value does not significantly change with increased film thickness up to 10 μm. However, the transmission parameter (S₂₁) is reduced with increased film thickness due to increased power absorption by magnetic loss. For the Co-Zr-O thin films with low electrical resistivity (～1.6 × 10^?5 Ωm), however, reflection signal is increased with increased film thickness due to diminished sheet resistance of the thin film. Transmission loss is not very sensitive to the thickness of the conductive film. Large power absorption is, therefore, predicted for conductive film of smaller thickness. It is concluded that film thickness is an important control parameter for the achievement of a highly absorptive thin film with increased electrical conductivity.     

Another approach in analysis of paint coatings with EIS measurement: Phase angle at high frequencies

Some electrical parameters could be extracted from EIS measurements of a coated metal like: coating capacitance, coating resistance, double layer capacitance, and charge transfer resistance. Although these elements are very valuable in analysis of electrochemical behavior of a coated system their extraction from EIS results is time consuming and always there are some error in calculation of the results with a model. In this paper an attempt is made to introduce a new parameter that could be easily extracted with no error in calculation. Theta at high frequencies has very good agreement with other extracted parameters.     

Effect of self-irradiation on the parameters of the α → β transformation of unalloyed plutonium

Damage of the structure of the α phase of plutonium as a result of repeated α ↔ β phase recrystallization and prolonged self-irradiation was estimated based on the changes in the electrical resistance measured at room temperature before and after phase recrystallization. Samples with different time of storage were used. An analysis of the results showed that the electrical resistance of samples grows linearly depending on the number of cycles of phase recrystallization. It has been established that the slope of the dependences obtained is determined by the maximum temperature of the sample in the cycle. At a maximum temperature in the cycle equal to 170°C, an increase in the relative electrical resistance of the samples was ∼2.5%/cycle; when heating to 125°C, ∼0.3%/cycle. The variation of the electrical resistance of the samples stored for ∼20 years depending on the number of cycles of phase recrystallization exhibited a single feature, namely, a decrease in resistance in the first cycle of heating to 170°C rather than an increase observed in the experiments with the samples stored for ∼2.5 year. This decrease is connected with the influence of the possible beginning of migration of radiogenic helium. In the subsequent cycles, the change in the electrical resistance of samples upon prolonged storage was analogous to that of the samples with a short time of storage.