利用磁声发射法对钢铁件微观损伤与残余应力的研究

本文通过４５钢和Ｔ１０钢在不同组织及应力状态下，磁声发射信号的强度，幅值和脉宽分布等特性的研究，表明了磁声发射特性的变化与材料内部应力状态有关。利用磁声发射可以无损地检测钢铁材料服役中出现的微观损伤和残余应力，避免应力，避免在役工件的意外事故发生。     

基于声发射监测的316LN不锈钢的疲劳损伤评价

疲劳裂纹的萌生与扩展容易导致压力容器及管道的严重疲劳失效.因此就设备的安全可靠性而言,非常有必要对疲劳裂纹扩展过程进行监测,并对疲劳损伤程度进行评估.本文针对316LN不锈钢材料进行疲劳实验研究,利用直流电位法测量实验中的裂纹长度,得到了材料的疲劳裂纹扩展曲线.利用声发射技术对疲劳裂纹扩展过程进行监测,通过声发射多参数分析对疲劳损伤状态进行评价,同时建立了声发射参数与线弹性断裂力学参数之间的关系,并进行寿命预测.研究表明:声发射能够对316LN不锈钢的疲劳裂纹损伤进行有效评估,声发射累积参数如累积计数、累积能量和累积幅值曲线上的转折点标志着疲劳裂纹进入快速扩展阶段,这可以为工程人员提供失效预警;声发射波形和频谱分析表明,噪声信号的幅值较小且信号持续时间较长,信号包含的频率成分比较复杂,而裂纹扩展信号是突发型信号,衰减较快,信号频率主要集中在80~170 kHz范围内;声发射计数率、能量率和幅值率与应力强度因子幅度以及疲劳裂纹扩展速率之间呈线性关系,裂纹长度预测结果与实测值接近.本研究工作对于工程结构的疲劳失效预警和剩余寿命预测具有重要意义.     

类岩石材料声发射参数与应力和应变耦合本构关系

利用液压伺服试验系统和声波监测仪开展了岩石和混凝土材料声发射特性试验研究,并在试验基础上研究了损伤变量与声发射参数之间的量化关系.结果表明,损伤变量与声发射参数呈线性关系.采用基于Weibull分布的损伤本构模型及损伤变量与声发射数间的经验公式,推导出应力、应变参量与声发射数参量的耦合模型,该模型参数可以根据应力-应变全曲线及损伤变量与声发射数关系曲线的几何边界条件确定其表达式,方式简单适用.通过与岩石和混凝土试样单轴压缩试验实测结果对比,证实模型可以很好地反映单轴受压状态下岩石和混凝土的应力、应变与声发射数的耦合关系.     

混凝土材料声发射过程及其自相似性的研究

将对材料声发射的研究同对力学过程的研究、材料断裂损伤等破坏过程的研究相结合,提出了声发射过程的概念。在此基础上,进一步给出了定量考察声发射过程自相似性的自相似特征函数.测试结果分析表明,混凝土试块在单轴压缩过程中,声发射过程的自相似程度随着应力状态的变化而变化.     

拉伸试验中充填体声发射特性及数值模拟研究

下向胶结充填采矿过程中, 胶结充填体顶板的破坏不仅受抗压强度的影响, 而且还表现为张拉破坏, 为了充分探索充填体顶板张拉破坏过程中的损伤演化规律, 对胶结充填体试件进行了单轴抗拉破坏声发射试验, 并利用RFPA2D软件对其拉伸破坏过程及声发射信号进行了数值模拟.模拟分析表明, 胶结充填体的抗拉破坏是始于试件圆盘中部, 沿着加载轴线方向出现裂隙萌生与扩展, 并汇聚成宏观的裂隙带, 最终导致整体失稳的破坏过程.模拟结果还再现了抗拉破坏时声发射的分布规律, 其结果对比室内试验的声发射特征规律, 具有很好的一致性.      

高速列车轻量化车体材料的选择研究

本文阐述了高速列车轻量化车体材料的选择,着重阐述铝合金车体材料及其焊接性的有关问题,总结了铝合金材料的焊接性方面的部分研究成果.     

铝合金919焊缝及热影响区的强度和硬度分析

采用铝合金材料制作车体是减轻车辆重量的有效途径之一.本文对高速列车用铝合金919焊缝及影响区的强度和硬度进行了分析讨论,对提高铝合金919焊缝的性能有一定的参考价值.     

基于声发射概率密度函数固废胶结充填体损伤分析

固废胶结充填体是保障矿山安全回采的关键承载结构,为探究其实际承载损伤破坏过程,在RMT-150C岩石力学测试系统上对不同粗骨料含量的4组胶结充填体试样进行了单轴压缩与循环载荷下的声发射试验。结果表明：循环载荷下,4组试样均具有显著的Kaiser效应,且含块石的3组试样声发射事件数更丰富,峰值应力前达到了纯尾砂试样的152%、225%和300%。同时,利用声发射概率密度与承载应力水平间的关联性,得到了4组不同块石含量胶结充填体的声发射概率密度方程,通过声发射概率密度函数实现了声发射参数量化分析胶结充填体承载损伤过程。对比损伤变量-应力水平曲线可以看出,块石的加入能够有效减缓并抑制前期损伤,当块石含量为20%时,效果最好。     

块石对充填体损伤演化影响的声发射表征

块石胶结充填体中块石含量是决定承载能力的关键因素,在RMT-150C材料试验机上进行不同块石含量的尾砂胶结充填体单轴压缩实验,利用1 MHz的宽频声发射传感器采集峰值破坏前各阶段声发射参量,试验结果显示了块石对充填体不同承载阶段应力-应变水平的影响。对比应力-应变-累计声发射事件数关系,发现块石的掺入有利于降低充填体裂纹产生与扩展的速率从而使其承载能力得到加强。分析试验数据得到用累计声发射事件数表征充填体损伤程度的关系式,并得到2组试件的损伤-应变水平关系曲线。分析表明,块石的加入有效抑制充填体前期的损伤增长速率,并使得损伤激增段出现后延趋势。     

国内最大截面铝合金预拉伸板在中铝诞生

<正>日前,中铝西南铝成功研制出的国内最大截面超宽超厚铝合金预拉伸板,顺利通过了由中国航空工业集团公司组织的专业评审.该产品配套航空航天飞行器后可有效减轻后者自身重量,提高其使用寿命和安全性能.2012年,西南铝就开始实施整体承力构件所需的超宽超厚铝合金预拉伸板材的材料研制.超宽超厚铝合金预拉伸板具有的高强韧、高损伤容限,尤其是优良的疲劳性能,对材料研制提出了更高更苛刻的技术要求,研制工作一时难以取得突破.因为随着材料规格的增大,工程     

A new quality index for characterizing aluminum cast alloys with regard to aircraft structure design requirements

A new quality index Q _D for characterizing aluminum cast alloys with regard to their suitability for use in damage-tolerant aircraft structures is introduced. The proposed quality index involves the material properties yield strength R _p and strain energy density W. The yield strength accounts for the region of allowable service stresses and strain energy density accounts for tensile ductility and fracture toughness. Both properties, R _p and W, are evaluated from the tensile test. The index Q _D was used to evaluate the quality of the cast aluminum alloys A357, A224, and 7475 and rank them accordingly. The evaluation results were compared against the results obtained by using the classical quality index currently involved by the industry to characterize the quality of aluminum cast alloys.     

Sources of acoustic emission generated during the plastic deformation of 7075 aluminum alloy

The plastic deformation of crystalline solids will in general result in the generation of acoustic emission. Identifying the actual sources of the acoustic emission is difficult since the data may be comprised of emissions from several sources which may be operating either independently or cooperatively. By using a series of testing procedures and simultaneously measuring the dislocation damping while testing, it has been possible to identify the major sources of acoustic emission in 7075-T6 and 7075-T651 aluminum alloys. For the 7075-T651 alloy essentially all of the emission is from the fracture of small intermetallic precipitates dispersed within the matrix. For the alloy in the T-6 temper there is additional acoustic emission occurring at the onset of plastic deformation due to break-away and subsequent motion of dislocation line segments from their pinning points. formerly graduate student at the University of Denver, Denver, CO.     

Effect of Process Parameters on Microstructure and Mechanical Properties in Friction Stir Welding of Aluminum Alloy

Friction stir welding process is a promising solid state joining process with the potential to join low melting point materials, particularly aluminum alloys. The most attractive reason for this is the avoidance of solidification defects formed during conventional fusion welding processes. Tool rotational speed and the welding speed play a major role in deciding the weld quality. In the present work an effort has been made to study the effect of the tool rotational speed and welding speed on mechanical and metallurgical properties of friction stir welded joints of aluminum alloy AA6082-T651. The micro hardness profiles obtained on welded zone indicate uniform distribution of grains in the stir zone. The maximum tensile strength obtained is 263 MPa which is about 85% of that of base metal. Scanning electron microscope was used to show the fractured surfaces of tensile tested specimens.     

高速切削铝合金用硬质合金刀具磨损机理研究

在高速切削加工铝合金涡轮过程中,硬质合金刀具的磨损会直接影响刀具的使用寿命和加工精度,导致加工精度无法满足设计要求,在磨损严重时还会引起刀具和零件的损伤。本文以高效切削铝合金涡轮用硬质合金刀具为研究对象,通过四因素三水平正交试验对刀具磨损行为进行研究,观测和分析不同切削参数下硬质合金刀具的磨损状态及微观形貌,讨论并提出有效控制刀具磨损的措施。结果表明,该控制刀具磨损的措施在保证零件加工精度的同时具有一定的实际推广价值。     

不同卸载应力对层状TiAl基合金损伤程度的影响

通过对层状TiAl基合金进行拉伸卸载试验，研究了不同预损伤对层状TiAl基合金断裂行为的影响。试验结果表明：随着损伤程度增加到一定程度，材料的弹性模量减小；随着预损伤程度的增加，裂纹面密度增大。通过统计分析发现裂纹面密度可以作为衡量损伤程度的损伤参量；但随着预损伤程度的增加，单位面积断裂功基本不变，进一步说明不同预损伤对层状TiAl基合金的最终断裂性能没有影响。     

A model for subgrain superplastic flow in aluminum alloys

Aluminum alloys that contain low angle boundaries exhibit different superplastic behavior than alloys consisting of high angle boundaries. On a relative basis, the low angle boundaries increase the flow stress, but impart a greater resistance to cavitation; the strain-rate sensitivity of this material is generally smaller and the change in the strain-rate sensitivity with strain rate shows a minimum instead of a maximum as observed in the large angle boundary materials. As a result, the subgrain material can be deformed to large tensile strains at fast strain rates. A kinetic model for subgrain superplasticity that invokes a balance between the arrival and emission rates of dislocations at low angle boundaries is presented. It explains several features of subgrain superplasticity. It also explains why ultrafine dispersoids of intermetallics appear to stabilize the subgrain structure in aluminum. Early work on the correlation between flow stress and the subgrain size in dynamic recrystallization of metals may also be consistent with the model.     

不同埋深灰岩岩爆倾向性及声发射特征试验研究

通过开展不同埋深灰岩的常规单轴试验,获取灰岩破坏过程中的应力—应变曲线和声发射时域特征参数.利用弹性能量指数WET、变形脆性指数Kε和线弹性能We指标,判别不同埋深灰岩岩爆倾向性.通过分析灰岩破坏过程的声发射特征参量及其变化规律,建立了发生岩爆的前兆信息特征.结果表明:随着埋深梯度递增,岩石岩爆倾向逐级增强,当埋深达1...     

泡沫铝主要性能特征研究及工业应用

本文对新型功能材料泡沫铝的性能和工业应用作了介绍。当前泡沫铝的研究主要集中在力学、隔热、声学、电磁屏蔽等方面,并证明泡沫铝是优秀的动能吸收材料、散热阻燃材料、隔声降噪材料以及电磁屏蔽材料,因此泡沫铝可作为良好的新型材料在生产建设中广泛应用。     

Fracture of boron particles in 2219 aluminum as a known acoustic emission source

Boron particles have been introduced into 2219 aluminum using a powder metallurgy approach. The only sources of detectable acoustic emission during deformation of the resulting material are decohesion of the boron particles from the matrix and particle fracture. The energy released by fracture of the boron particles during deformation was estimated from elasticity theory using measured diameters of the individual fractures. The energy in the acoustic emission signals produced by particle fracture (the integral of the signal voltage squared) was found to be proportional to the fracture energy released. Fracture energies were in the range 1–7 ergs for the larger fractures. The relation found between fracture energy and acoustic emission signal energy can be used to estimate the energy released by other comparable acoustic emission sources in samples of similar geometry from their acoustic emission signals. During the course of the acoustic emission measurements, the response of an rms voltmeter to an individual acoustic emission signal was found to be proportional to the energy of the signal.