基于LMD与多重分形寻优的往复压缩机故障特征识别方法

针对往复压缩机振动信号的非平稳和非线性特性,多重分形广义谱是一种简便、快速有效的特征参数提取方法;但其对噪声敏感,使得谱值波动,部分故障类间特征可分性差。利用经小波降噪后的优化LMD算法,并结合相关系数提取PF主分量以突出状态主信息,将多尺度整数寻优观点引入广义维,基于最佳可分性角度计算状态间最大平均距离,构造广义维数特征矩阵;通过SVM与增量学习K邻近(IKNNModel)统计算法训练和识别样本,对比证明该法能提高故障特征类间可分性和识别准确性。     

Combined effect of the prior deformation and applied stress on the bainite transformation

There has been a continued interest over the past years in the effects of external stress or prior deformation on the bainite transformation. In this study, the combined effect of prior deformation and stress on the bainite transformation was investigated and the interaction between the effects of prior deformation and stress was discussed in detail. The results show that although single deformation and single stress promote the bainite transformation, their combination cannot promote the bainite transformation to a much larger degree. In addition, at the early stage of transformation, the promotion effects of prior deformation and stress on the amount of the bainite transformation are enhanced by each other. However, at the latter stage, the deformation weakens the promotion effect of the stress. Moreover, prior deformation at a low temperature accelerates the kinetics of the bainite transformation with stress, but it decreases the amount of the bainite transformation even if the deformation is small.     

The Portevin–Le Chatelier (PLC) effect and shear band formation in an AA5754 alloy

A non-contact strain measurement technique, based on digital image correlation (DIC) analysis, has been utilized in order to observe Portevin–Le Chatelier (PLC) band behaviour during tensile deformation of AA5754 sheet and subsequently to measure the level of incremental plastic strain carried within the bands. In addition, PLC banding was studied as a function of prior deformation under positive strain rate sensitivity conditions (i.e., at low temperature). Small prestrains (of the order of the Lüders strain) do not affect subsequent room-temperature deformation. However, prestrains of 0.1 or higher change the nature of the PLC bands that form at room temperature. Finally, careful experiments were performed involving low-temperature prestrains sufficient to cause immediate necking when deformation was continued at room temperature. These suggest that shear localization is independent of existing PLC bands.     

塑性变形对渗钛过程的影响

用正交试验方法对１６Ｍｎ钢形变渗钛过程进行了探讨。根据实验结果分别讨论了温度、时间、形变量对渗钛过程的影响规律，实验结果表明预先室温塑性变形对置换原子钛的渗入有促进作用，存在一个最佳形变量。     

INFLUENCE OF HEAT TREATMENT PROCESSES ON MECHANICAL PROPERTIES OF ACu－Ni－AI－Ti ALLOY

ＩＮＦＬＵＥＮＣＥＯＦＨＥＡＴＴＲＥＡＴＭＥＮＴＰＲＯＣＥＳＳＥＳＯＮＭＥＣＨＡＮＩＣＡＬＰＲＯＰＥＲＴＩＥＳＯＦＡＣｕ－Ｎｉ－ＡＩ－ＴｉＡＬＬＯＹＩＮＦＬＵＥＮＣＥＯＦＨＥＡＴＴＲＥＡＴＭＥＮＴＰＲＯＣＥＳＳＥＳＯＮＭＥＣＨＡＮＩＣＡＬＰＲＯＰＥＲ...     

Ti53311S钛合金热变形的组织和机制分析

用Gleeble-1500型热模拟试验机对Ti53311S钛合金在温度为880～1080℃,应变速率为0.001～10 s-1的条件下进行高温压缩变形行为的研究.测试了其真应力.真应变曲线,采用双曲正弦本构方程计算出激活能,双相区为641 kJ/mol,β相区为244 kJ/mol.观察了变形后的显微组织,并分析了其变形机制.结果表明:该合金对温度和应变速率敏感,不同变形条件下应力值变化很大;应变速率敏感指数(m)随温度升高而降低,而变形激活能(Q)随温度升高而增大.合金的变形机制在双相区为晶界滑移和晶粒球化,在β单相区为动态回复.     

电化学充氢条件下TWIP钢应力腐蚀敏感性的研究

通过慢应变速率拉伸和观察断口形貌等方法,研究了TWIP钢在电化学充氢条件下的应力腐蚀敏感性.结果表明,在电化学充氢条件下,TWIP钢具有应力腐蚀敏感性.恒定应变速率6.67×10-6 s-1时,具有单向奥氏体结构的TWIP钢有较小的应力腐蚀敏感性,具有形变孪晶的TWIP钢有较高的应力腐蚀敏感性.这是因为孪晶的形成导致氢在局部浓度更高,因而促进了局部塑性变形,降低了内氢压,导致TWIP钢的应力腐蚀敏感性上升.     

Static recrystallization behavior of a martensitic heat-resistant stainless steel 403Nb

A static recrystallization behavior between the rolling passes of a martensitic heat-resistant stainless steel 403Nb has been studied by OM,TEM and double-hit thermo-mechanical simulator to explore the effects of deformation temperature,strain rate,strain and the prior austenite grain size. The results show that increases of deforma-tion temperature and strain rate and strain can promote the static recrystallization of 403Nb steel. Static recrystallization also proceeds faster when the prior austenite grain...     

Effects of nanocrystalline and ultrafine grain sizes on constitutive behavior and shear bands in iron

The mechanical behaviors of consolidated iron with average grain sizes from tens of nanometers to tens of microns have been systematically studied under uniaxial compression over a wide range of strain rates. In addition to the well-known strengthening due to grain size refinement, grain size dependence is observed for several other key properties of plastic deformation. In contrast with conventional coarse-grained Fe, high-strength nanocrystalline and submicron-grained Fe exhibit diminished effective strain rate sensitivity of the flow stress. The observed reduction in effective rate sensitivity is shown to be a natural consequence of low-temperature plastic deformation mechanisms in bcc metals through the application of a constitutive model for the behavior of bcc Fe in this strain rate and temperature regime. The deformation mode also changes, with shear localization replacing uniform deformation as the dominant deformation mode from the onset of plastic deformation at both low and high strain rates. The evolution and multiplication of shear bands have been monitored as a function of plastic strain. The grain size dependence is discussed with respect to possible enhanced propensity for plastic instabilities at small grain sizes.     

Low temperature deformation and dislocation substructure of ruthenium aluminide polycrystals

The flow behavior and dislocation substructure present in ruthenium aluminide polycrystals due to deformation at room temperature and 77 K have been studied. Dislocations with three different types of Burgers vectors have been identified after 1–2% deformation in compression at 77 K and room temperature: 〈100〉, 〈110〉 and 〈111〉. The 〈100〉 and 〈110〉 dislocations are present with approximately equal densities, while the 〈111〉 are only occasionally observed. Trace analyses show that the majority of the dislocations are mixed in character and lie on {110} type planes. The implications of these observations with regard to the number of independent slip systems and the intrinsic deformability of this material are discussed.     

Effect of silicon and prior deformation of austenite on isothermal transformation in low carbon steels

Isothermal transformation (TTT) behavior of the low carbon steels with two Si con-tents (0.50 wt pct and 1.35 wt pct) was investigated with and without the prior deformation. The results show that Si and the prior deformation of the austenite have significant effects on the transformation of the ferrite and bainite. The addition of Si refines the ferrite grains, accelerates the polygonal ferrite transformation and the formation of M/A constituents, leading to the improvement of the strength. The ferrite grains formed under the prior deformation of the austenite become more ho-mogeneous and refined. However, the influence of deformation on the tensile strength of both steels is dependent on the isothermal temperatures. Thermodynamic calcu-lation indicates that Si and prior deformation reduce the incubation time of both ferrite and bainite transformation, but the effect is weakened by the decrease of the isothermal temperatures.     

U. R. Evans Award 1977

Abstract

Nucleation and growth of transgranular stress corrosion cracks has been studied in Type 316 austenitic steel stressed in MgCl₂ solutions of various degrees of acidity and under a narrow range (?0·24 to ?0·40 V SCE) of controlled potential. Slip line attack occurs in relatively acid solutions and is accompanied by the formation of {110} slots which are covered with a chromium rich oxide. In well boiled solutions, which are of low acidity, nucleation occurs at inclusions. MnS particles are efficient crack nuclei, but for other inclusions the size and geometry is of greater importance than chemical composition. High potentials favour pitting and crevice corrosion and such sites are particularly important crack nuclei at low stresses.

Edge notched sheet specimens have shown very low threshold stress intensities for crack growth and a sensitivity to prior deformation. Crack tips are extremely narrow and the crack sides show evidence of corrosion. Data pertinent to aslip dissolution model are discussed.     

FRACTURE MECHANISM OF PRE-DEFORMATION-AGED Al-2.73Li ALLOY

The fracture mechanism of deformation-aged Al-Li alloy was approached by investigatingthe influence of prior cold deformation on the precipitation kinetics as well as the behavioursof work hardening and fracture for Al-2.73Li alloy.The experimental results show that thework hardening rate and the strength are increased and the ductility is decreased by prior colddeformation.The decrease in ductility is mainly due to the cell dislocaton substructure distrib-uted inhomogeneously and the hardening of precipitate free zones at grain boundaries causedby prior cold deformation.The failure mode in the alloy is a mixed integranular andtransgranular one.The tendency of intergranular fracture is intensified through thedeformation-aging.The mechanisms of intergranular failure in the alloy are different undervarious deformation-aging treatments.     

Density Dependence of the Compressive Behaviors of Closed-Cell Al Foams Manufactured Through Powder Metallurgy Route

The compressive deformation behaviors of closed-cell Al foams manufactured through powder metallurgy route with various relative densities have been studied. The high-density specimens displayed smoother stress-strain curves and more stable compressive behaviors. The stress-strain curves for low-density specimens displayed a regular fluctuation and more than one stress drop were observed. This can be attributed to the different deformation mode due to density variation. The effect of relative density on the stress drop ratio was studied. The results show that the stress drop ratio decreases with relative density. The compressive deformation mode changes as the relative density is <0.15.     

多应变率下Ti-811钛合金针状组织压缩变形及断裂机制

采用Instron力学试验机及分离式Hopkinson压杆系统,分别对Ti-811钛合金针状组织进行静、动态压缩实验,以研究其不同应变率下的变形及断裂机制。结果表明:随应变率升高,针状组织屈服强度依次呈现正-负-正的应变速率敏感性,其内在原因是位错滑移机制和孪生变形机制的相互竞争。针状组织在静态和动态加载下的断裂机制明显不同,分别呈现为双剪切及单剪切断裂模式。动态加载试样端面部位可形成连续锯齿形金属屑,这是由高速变形过程中主剪切带两侧金属的剧烈错动被入射杆与透射杆遏制所导致。     

多晶与单晶铜塑性变形行为的相关性

利用TEM分析拉伸变形多晶铜中不同取向晶粒的位错组织, 研究了多晶与单晶形变行为的相关性. 结果发现, 多晶铜中诸晶粒的形变显微组织可分为3种不同类型, 而且组织类型与其相应晶粒的晶体学取向存在密切的相关性; 根据多晶中不同类型组织的体积含量, 结合相应取向单晶的应力应变曲线, 计算出了多晶的应力应变曲线, 其结果与实测曲线相似.     

Admissibility of Bayes estimate with inaccurate prior in surveying adjustment

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Mechanical behavior of LC_4 alloy in semisolid state at high volume fractions of solid

1　ＩＮＴＯＲＤＵＣＴＩＯＮＡｌｌｏｙｓｗｉｔｈｅｑｕｉａｘｅｄｍｉｃｒｏｓｔｒｕｃｔｕｒｅｅｘｈｉｂｉｔｓｉｇ ｎｉｆｉｃａｎｔｌｙｌｏｗｅｒｆｌｏｗｒｅｓｉｓｔａｎｃｅｉｎｔｈｅｓｅｍｉｓｏｌｉｄｓｔａｔｅｔｈａｎａｌｌｏｙｓｗｉｔｈｄｅｎｄｒｉｔｉｃｍｉｃｒｏｓｔｒｕｃｔｕｒｅ .Ｔｈｅｉｒｄｕａｌ(ｔｈｉｘｏｔｒｏｐｉｃ)ｂｅｈａｖｉｏｒ (ｓｏｌｉｄ ｌｉｋｅｉｎｔｈｅｕｎｐｅｒｔｕｒｂｅｄｓｔａｔｅａｎｄｌｉｑｕｉｄ ｌｉｋｅｄｕｒｉｎｇｓｈｅａｒｉｎｇ)ｈａｓｂｅｅｎｔｈｅｂａ ｓｉｓｆｏｒｓ…     

Superplastic behavior of magnesium-based Mg-10 wt % Gd alloy after severe plastic deformation by torsion

Characteristic features of superplastic behavior of Mg-10 wt % Gd alloy with an ultrafine-grained structure produced by severe plastic deformation by high-pressure torsion have been considered. The ultrafine-grained structure has been studied by transmission electron microscopy and X-ray diffraction. The optimum temperature-strain-rate regime of superplastic deformation of the ultrafine-grained alloy and the magnitudes of the strain-rate sensitivity parameter of the flow stress have been determined.     

On conditions of single- and multiphaseness of adsorption layer on solid surface with regard to deformation

The isotherm equation of single-component adsorption from a liquid solution on a solid metal surface bearing an electric charge is discussed involving the model of two parallel capacitors taking into account the small deformation of surface in terms of the thermodynamic theory proposed earlier. The isotherm equation is studied with regard to the uniqueness or nonuniqueness of its solution with respect to the surface concentration of an adsorbate in the case when the initial isotherm (before deformation) is a Frumkin isotherm. The conditions of uniqueness or nonuniqueness are derived, having traditionally been interpreted in the second case as the capability of the adsorption layer to be multiphase by analogy with the Van der Waals equation.