基于空耦超声共振法的复合材料测厚技术研究

为解决当前传统超声检测技术对复合材料的检测耦合剂污染和检测效率低等问题,提出空气耦合超声共振法来检测复合材料薄板的厚度,从而确定缺陷的大小。利用 COMSOL 有限元仿真软件对复合材料进行建模,设置不同厚度及不同大小缺陷的物理模型来对比实验,后处理求解并进行快速傅里叶变换,提取谐振频率计算出复合材料的厚度。结果表明,超声共振法可对复合材料进行定性、定量检测;当复合材料的厚度越薄时,超声信号产生的谐振频率越大,则复合材料中所含缺陷范围越广,分层现象越严重;其检测精度可达 0.1 mm 左右,相对误差范围分布在 5% 以下。实验证明了该测厚技术的可靠性,为超薄复合材料板缺陷厚度的测量提供一定的参考和借鉴。     

基于声发射的Q235钢点蚀过程监测技术研究

以声发射技术为基础,针对油气储运常用材料Q235的点蚀过程,利用试件在模拟溶液中点蚀过程产生的声发射信号为样本,采用参量分析与波形分析相结合,重点研究Q235钢点蚀过程中产生的声发射信号的变化特征,得到了金属点蚀不同阶段的声发射信号特性,并通过声发射信号事件的分布规律,得到了Q235钢早期腐蚀与声发射信号演变的一致性结果。试验证明了声发射技术为基础的Q235钢点蚀过程监测具有良好效果。     

铝合金塑性损伤电磁超声谐振无损评估研究北大核心CSCD

针对传统线性超声方法难以有效检测金属构件微损伤的问题,使用电磁超声换能器,在6061铝合金试件内发射并接收超声信号,采用非线性电磁超声谐振方法对铝合金试件拉伸时产生的塑性损伤进行无损评估。基于非线性电磁超声谐振检测实验平台,对不同拉伸阶段的试件分别进行了非线性检测实验,通过基波与三次谐波的幅值比,定量地描述了铝合金材料的非线性参数与材料拉伸损伤程度相关关系。实验结果表明:弹性阶段的拉伸处理对试件的非线性情况影响较小,而塑性阶段的拉伸造成的微损伤对试件的非线性情况有较大影响,因此非线性电磁超声谐振技术可以有效评估铝合金塑性损伤。     

基于电磁超声技术的高强度螺栓轴力测量仪

基于电磁超声技术,研制了一款手持式高强度螺栓轴力测量仪,具有非接触、无需打磨、无需耦合剂和实时测量的特点.设计了可同时激发横波和纵波的电磁超声探头,实现了双波法轴力测量,能够解决在役螺栓长度未知的问题;设计了基于FP GA的高频大功率脉冲发射模块和低噪声信号调理模块,实现了电磁超声探头的激励与超声信号的接收;设计了基于...     

基于小波变换的薄层厚度电磁超声测量方法

机械结构(如齿轮、轴承、密封)中薄液体层对其性能有很大影响.针对传统超声反射回波方法时间分辨率低,难以实现薄层厚度测量以及压电换能器测量结果受界面耦合性能影响问题,提出了基于小波变换奇异点提取的薄液体层厚度电磁超声测量方法.同时,研究了小波变换基函数及分析尺度对薄液体层超声回波信号奇异点提取的影响,优化出适合薄层厚度测量的小波变换基函数和分析尺度范围.检测试验表明,基于小波变换奇异点提取的电磁超声技术可以很好地实现薄液体厚度测量.     

微观组织及测量信号对超声横波评价材料硬度影响

硬度是材料力学性能的重要指标之一,采用超声无损检测方法评价材料硬度指标目前还存在诸多挑战。通过搭建高精度声时测量系统,采用横波直探头脉冲反射回波法测量不同热处理45钢试件厚度方向超声横波传播声时和底面反射回波幅值,分别计算横波声速和衰减系数;在测量超声横波声时,改变测量声时门信号的测量方式,研究不同微观组织及测量信号对超声横波声速的影响,通过构建材料硬度-微观组织-超声横波声速及衰减系数之间的映射关系,建立超声横波评价45钢试件硬度指标的标定模型,并对标定模型进行验证。研究表明,横波声速可以作为评价45钢试件硬度的评价参数,测量误差满足工程应用误差10%的要求;测量横波衰减系数与材料硬度之间的变化没有明显的映射关系,不能作为评价45钢试件硬度指标的评价参数。     

电磁超声横波检测钢板减薄缺陷的有限元分析

电磁超声换能器(EMAT)在试件中激发的横波(剪切波)能够应用于试件厚度和内部缺陷检测,为了研究电磁超声激发横波的机理,采用有限元分析的方法,对其进行仿真分析。通过建立EMAT三维模型,进行电磁学耦合计算,获得被测试件表面磁场、涡流、洛伦兹力的分布规律,显示了EMAT激发横波的机理过程,为电磁超声换能器的设计提供参考;通过电磁学与动力学的耦合计算,获得横波在试件厚度方向的传播规律,结果表明,横波在试件中沿厚度方向传播,并且能量呈衰减趋势;对含缺陷钢板进行结构动力学分析,发现当波传播遇到缺陷时波动发生明显的改变和衰减,得出EMAT激发的横波可用以检测试件底面减薄缺陷,并通过试验验证提出横波检测缺陷时定量缺陷深度的方法。     

塔机材料常规缺陷的声发射定位与辨识技术

故障源的实时定位和特性辨识是塔机安全评价及故障预防的关键。试验采用塔机常用材料Q235无缺陷、裂纹及焊接缺陷试件,利用GPS-100高频疲劳试验机和SDAES数字型声发射仪采集在不同载荷下试样的声发射信号,通过结合信号分析技术得出缺陷试件的故障定位、信号的频谱特征和参数特征分析,总结了Q235常规缺陷试样典型声发射信号的主要特征参数的范围。论文研究工作为声发射技术在塔机危险源的检测研究提供了非常重要的学术价值和指导意义。     

基于宽频激励电磁声谐振 7075 铝合金板厚检出概率

电磁超声换能器(EMAT)换能效率低、激发信号弱,而基于长周期激励信号以产生声波共振的电磁声谐振技术(EMAR)虽然可以提高接收信号的信噪比,然而可能导致主脉冲加宽并扩大超声波检测盲区,降低测量精度。本文应用一种宽频激励电磁声谐振技术(BE-EMAR)和一种Halbach阵列纵波EMAT,以单周期宽频激励作为EMAT输入信号,并利用EMAR方法对7075型铝合金试件板厚进行测量,借助检出概率(POD)模型来表征该技术针对微金属板厚的测量精度。实验结果表明,在未降噪时BE-EMAR得到的三种信噪比下的POD曲线中,对应的a_(50)或a_(90/95)最大差异值为0.05 mm,同一信噪比下降噪前后的最大差异值为0.07 mm,而在时差法(ToF)得到的POD曲线中这一最大差异值则为0.21 mm,因此说明BE-EMAR降噪前后得到的结果并无较大差别,该方案对于常规噪声信号不敏感;且降噪前后,在BE-EMAR得到的POD曲线中,a_(50)和a_(90/95)均可稳定在0.55 mm以内,证明了BE-EMAR比ToF测厚具有更优的精度、稳定性和抗噪能力。     

电磁超声法测量结构内部温度场的试验研究

为实现结构内部温度场的无损、实时与高精度探测,研究设计一种可非接触式测量的电磁超声测温原理性试验系统。通过检测超声波回波信号在结构内部传递过程中波速的变化,根据热/声耦合理论,采用基于灵敏度法的温度场重建技术实现了对超声传播路径上温度非均匀分布状态的测量。基于钢试件的标定试验、稳态传热试验和瞬态传热试验,对超声测温系统及灵敏度测温方法的可靠性和准确性进行了试验研究。试验结果表明,采用灵敏度法的超声测温技术,结合无损非接触式探测的电磁超声方法,能够有效测量结构内部稳态/瞬态温度场分布状态,具有重要的工程应用价值。     

A methodology for assessing manufacturing cost due to tolerance of aerodynamic surface features on turbofan nacelles

A component of the direct operating cost of aircraft is that associated with the manufacturing cost. This affects depreciation, interest, insurance and maintenance charges. By relaxing the requirements for aerodynamic surface smoothness the manufacturing cost can be reduced at the expense of an increase in drag and corresponding fuel costs. This work is part of a study to examine this multidisciplinary problem. Only isolated turbofan nacelles are considered. The costs associated with assigning different tolerance levels to the feature dimensions on nacelles are assessed. A statistical procedure is employed to estimate the cost-tolerance relationship for eleven features involving gaps, steps, surface profile and fastener flushness. This procedure requires actual manufacturing and cost source data. A knowledge of the cost-tolerance relationships is useful in a concurrent engineering context. It will allow aerodynamicists to optimise surface smoothness in consultation with production engineers, thus achieving the best compromise between cost and drag.Nomenclature A ₁ statistic distribution area to the left ofL ₁ - A _u statistic distribution area to the right ofL _u - C manufacturing cost (£/piece) - C _a assembly process manufacturing cost (£/piece) - C _c cost per concession (£/concession) - C _ci interface component edgei manufacturing cost (£/piece) - C _i interface manufacturing cost (£/piece) - C _lmh labour man hour cost (£/piece) - C _ma management cost (£/piece) - C _mh man hour cost (£/h) - C _mmh management man hour cost (£/piece) - C _nr non-recurrent cost (£/piece) (cost of all the jigs and tools used in the assembly process divided by the number of units produced) - C _rd redeployment cost (£/piece) - C _smh skilled worker man hour cost (£/h) - C _su support cost (£/piece) - C _sumh support man hour cost (£/h) - C _usmh unskilled worker man hour cost (£/h) - C ₀ initial manufacturing cost (£/piece) - d _tma t _ma parameter - d _{N c} N _c parameter - d _{O f} O _f parameter - d _{t r} t _r parameter - d _{t rd} t _rd parameter - d _{t su} t _su parameter - E _i interface edgei - F _i featurei - G interface gap (mm) - G _n interface gap normal to air flow (mm) - G _p interface gap parallel to air flow (mm) - L _ef production line loss of efficiency factor due to redeployment - L ₁ dimension lower specified limit (mm) - L _u dimension upper specified limit (mm) - M mean - N dimension nominal value (mm) - N _c number of concessions (concession/piece) - O _f worker overtime fraction - P surface profile deviation (mm) - R _on ratio between the worker overtime and the normal man hour cost - S interface step or fastener flushness (mm) - standard deviation - S _n interface step normal to air flow (mm) - S _p interface step parallel to air flow (mm) - T manufacturing tolerance (mm) - T _a assembly process manufacturing tolerance (mm) - t _bw basic work time (hour/piece) - T _ci interface component edgei manuacturing tolerance (mm) - T _i interface tolerance (mm) - t _ma management time (hour/piece) - T _p performance tolerance - t _r rework time (h/piece) - t _rd worker redeployment time to other production line stations different to the usual one (h/piece) - t _su support time of the methods, quality and design departments to the line (h/piece) - T _t tolerance threshold between skilled and unskilled worker employment (mm) - T ₀ initial manufacturing tolerance (mm)     

Studies of high temperature sliding wear of metallic dissimilar interfaces IV: Nimonic 80A versus Incoloy 800HT

Wear variations of Nimonic 80A slid against Incoloy 800HT between room temperature (RT) and 750 °C, and sliding speeds of 0.314 and 0.905 m s⁻¹ were investigated using a ‘reciprocating-block-on-cylinder’, low debris retention configuration. These were considered alongside previous observations at 0.654 m s⁻¹.Different wear types occurring were mapped, including high transfer ‘severe wear’ (RT and 270 °C, also 0.905 m s⁻¹ at ≤570°C), low transfer ‘severe wear’ (0.314 m s⁻¹ at 390 °C to 510 °C oxide abrasion assisted at 510 °C), and ‘mild wear’ (0.314 m s⁻¹ at ≥570 °C; 0.905 m s⁻¹ at ≥630 °C). Wear surfaces at 750 °C were cross-sectioned and profiled.     

Reciprocating Sliding Friction and Wear Property of Fe<Subscript>3</Subscript>Si Based Alloys Containing Cu in Water Lubrication

Fe₃Si, Fe₃Si alloys containing Cu were fabricated by arc melting followed by hot-pressing. The friction and wear behaviors of Fe₃Si based alloys with and without Cu addition against Si₃N₄ ball in water-lubrication were investigated. The friction coefficient and the wear rates of Fe₃Si based alloys decreased as the load increased. The wear rate of Fe₃Si was higher than that of AISI 304. The addition of Cu can significantly improve the friction and wear properties of Fe₃Si based alloys and substantially reduce the wear rates of Si₃N₄ ball. The wear rate of Fe₃Si–10%Cu was 2.56 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 20 N and decreased to 1.64 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear rate of Si₃N₄ ball against Fe₃Si–10%Cu was 1.41 × 10⁻⁶ mm³ N⁻¹ m⁻¹, while the wear rate of Si₃N₄ ball against AISI 304 was 5.20 × 10⁻⁶ mm³ N⁻¹ m⁻¹ at load of 90 N. The wear mechanism was dominated by micro-ploughing. The combination of mechanical action (i.e., shear, smear and transference of Cu) and tribochemical reaction of Si₃N₄ with water was responsible for the improved tribological behavior of Fe₃Si alloys containing Cu under high loads.