Dynamic response and acoustic radiation of double-leaf metallic panel partition under sound excitation

The transmission of sound through a rectangular double-leaf metallic panel partition clamp mounted on a rigid acoustic baffle has been investigated analytically. It is found that, at a specific frequency, sound transmission through the structure is significantly enhanced for incident sound with a certain incidence angle. This physical phenomenon, namely, transparent effect, is analyzed in terms of both dynamical panel modal responses and radiating acoustic pressure. The enhanced transmission is attributed to the unique mass-air-mass effect of the double-panel partition system. Numerical results clearly demonstrate that this effect does not completely stem from the point-to-point out-of-plane motion of the two panels, due to the additional constraining effect of the clamped supports.     

Design systems for gear elements made of cotton fiber-reinforced plastics

We look on the cotton fiber reinforced plastics as industrial gear materials, and have been developing design systems for industrial gears made of cotton fiber-reinforced plastics. In this report, we deal with a method estimating for tooth root stresses caused by bending movements under running conditions. The gear material used was cotton fiber plain woven cloth reinforced phenolic resin laminates. Paper-reinforced phenolic resin laminates, a commonly used material, was used as a control for comparison. The main dimensions of the gears were module 3–5 mm and tooth width 25 mm. First, accelerations of gears were measured under running conditions to estimate dynamic performance. Second, fracture tests of gear teeth were carried out under bending loads. Different fracture modes at tooth roots for cotton fiber-reinforced plastics and phenolic resin gears were observed. The fractures occurred at a high position from the tooth root in the case of the cotton fiber-reinforced plastics gear because the cotton fiber-reinforced plastics had excellent cleavage and shear strength. This gear also had higher strength for tooth bending loads. Third, the mechanical properties of the gears were researched by tensile, bending, and shearing tests. It was clear that the cotton fiber-reinforced plastics had excellent properties in cleavage fracture between laminates and shear strength. Finally, we proposed a design method for this gear, which considers the cleavage and shear strength.     

噪声异常压缩机的声诊断分析

通过声品质评价方法分析了噪声异常转子压缩机试验样机,并计算出A声级、响度、粗糙度和尖锐度作为声品质的客观评价指标,结果表明与正常压缩机相比,该噪声异常压缩机具有较差的声品质。声阵列技术能够精确定位复杂形状的目标声源,与传统采用声级计测试相比,能够获得更加丰富的声场信息。为了诊断出压缩机的异常噪声,通过声阵列技术在全频段对该异常压缩机进行了声源识别定位分析,找到了影响压缩机噪声的关键频率点及相应的噪声源,从而为压缩机噪声的改善提供了有力证据。     

声强法在柴油机表面辐射噪声源识别中的应用

根据声强测试原理，应用B＆K 3560C便携式振动与噪声测试系统中的声强测试模块，对4190型柴油机的表面辐射噪声源进行识别。绘制了三维声强图，找出了该发动机的各个辐射面上的主要噪声源，并对其进行了排序，分析了这些噪声源的产生根源。提出了控制主要噪声源的一些建议，以便于进一步降低该柴油机的噪声水平。     

基于小波-倒频谱的齿轮故障诊断方法及应用

利用振动信号采集到的齿轮故障信息,依据点蚀的故障机理和频谱特征,采用小波分解将信号分解在不同频带,有效抑制了背景噪声,从而得到故障特征频带,获得周期性突变的故障信息。选择故障所处频带重构信号,对故障进行诊断。结合倒频谱方法可以有效地识别故障特征频率。结果表明小波分析与倒频谱相结合是齿轮故障检测中一种有效的诊断方法。     

Special manufacturing and characteristics of basalt fiber reinforced hybrid polypropylene composites: Mechanical properties and acoustic emission study

Basalt fiber reinforced, polypropylene matrix hybrid composites were manufactured in the process of carding, needle-punching and pressing. Hemp, glass and carbon fibers were applied besides basalt fiber in these composites. In order to achieve a sufficient interfacial adhesion, the fibers were treated with the reaction mixture of maleic acid anhydride and sunflower oil. The hybrid effect in these composites was examined as a function of fiber content and fiber combination. The strength properties of hybrid composites improved owing to surface treatment and this was proven by mechanical tests and microscopic analysis, as well. Acoustic emission methods revealed that there is a correlation between the physical parameters of sound waves that occurred during failure and the mechanical properties.     

Failure Analysis of Cracked Gear Shafts

Two gear shafts cracked during the fabrication. The cracks are through the grooves associated with the gear teeth and propagated completely across the shaft. Fractography on the cracked teeth indicates that the crack origins are about 3.5 to 4.0 mm from the groove and exhibit pointlike features. Fracture surfaces near the crack origin regions were intergranular, and the fracture appeared to have occurred instantaneously. Metallurgical analysis indicates that decarburization had occurred on the surfaces of the gear shafts, but occurrence of decarburization has no relation to the cracking. Cracking occurred during the carburization-quenching process and originated at a cluster of Al₂O₂ complex inclusions. The thermal stress produced by quenching drove the cracking process.     

Failure Analysis of a Diesel Engine Gear System Consisting of Camshaft and Crankshaft Gears

A failure investigation was conducted on a diesel engine gear system consisting of a driven camshaft and drive crankshaft gears that were used in a truck. The gears are made from a nitrided 42CrMo steel. Adjacent teeth fracture and plastic deformation regions appeared on the gears after a 400 h run test of the gear system. Fractography indicates that fatigue fracture is the dominant failure mechanism for the gear teeth. Although the appearance of needle-like nitrides in the nitrided layer and the narrow depth of the compound layer may decrease the fatigue strength of the camshaft gear, these do not suffice to lead to the premature fracture of the gear teeth. Geometrical analysis of the gears was performed and compared with an analysis of unfailed gears that had experienced a run test for 1800 h. The comparison reveals that the small fillet radius at the root area of the camshaft gear concentrated the stresses and is mainly responsible for fatigue fracture of the teeth. The camshaft gear is the component that initiated trouble in the gear system. The appearance of severe plastic deformation on the gear faces is caused by the fractured teeth crushing the teeth faces and being embedded in the grooves between teeth.     

Wavelet transform of acoustic emission signals in failure of model composites

The fundamental characteristics of acoustic emission (AE) signals, such as the attenuation, and frequency dependency of AE signals, were investigated and the fracture process of the single fiber composite (s.f.c.) was examined. As a result, the frequencies of AE signals were almost unchanged, while the amplitudes attenuated greatly with the increment of the propagation length. This proved that the frequency analysis is an effective way in processing AE signals of composite materials. In the fracture process of the s.f.c., the number of AE events was in a good agreement with the number of fiber breakages, and the sources of AE signals were the failure modes at fiber breakages. Using the proposed time-frequency method of wavelet transform (WT) to process AE signals, the microfailure modes at a fiber breakage and the microfracture mechanism, such as the sequence of each failure mode and their interaction, were made clearer. These indicated that both processing methods of AE signals, fast-Fourier transform and WT, were powerful for identifying the microfailure modes and for elucidating the microfracture mechanisms in composite materials.     

Identification of Fiber Breakage in Fiber Reinforced Plastic by Low-Amplitude Filtering of Acoustic Emission Data

A new low-amplitude filtering technique has been developed for the identification of fiber breakage in fiber reinforced plastics from acoustic emission data. In this approach, the acoustic emission hits associated with fiber breakage are separated from the hits associated with other failure mechanisms by filtering out the low amplitude hits from the measured data. The lowest remaining amplitude upon the cumulative plot of the remaining hits vs. load coinciding with the cumulative signal strength vs. load plot is taken as the borderline between fiber breakage hits and non-fiber breakage hits. Experiments were conducted on unidirectional-fiber specimens and complex-fiber specimens to examine the efficacy of the proposed technique. Evaluation of the experimental results by visual inspection and extensive scanning electron microscope studies verifies the low-amplitude filtering technique as a reliable tool for identifying fiber breakage in fiber reinforced plastics.     

Identification of microbiologically influenced corrosion (MIC) in industrial equipment failures

The present study demonstrates different approaches towards MIC identification in three real cases of technological equipment failures.

In the first case the failure of carbon steel heat exchanger as a result of tubes, lids, tube sheets, and connection pipes clogging was investigated. Chemical analysis of cooling water and precipitates, as well laboratory screening of deposits for bacteria, revealed that activity of iron-oxidizing bacteria present in cooling water led to heat exchanger blockage.

The second case is related to MIC detection on floating roofs made of magnesium–aluminum alloy following a 3-weeks hydro-test. Corrosion tests carried out on the original and sterilized water used in hydro-test confirmed MIC process.

In the third case the potential of MIC occurrence in engine cooling system made of cast aluminum alloy and filled with 20% ethylene glycol coolant solution was evaluated. The simulation tests allowed determining the real causes of the severe corrosion attack of examined system, including MIC high probability.     

双目系统中图像随机噪声的分析

图像立体匹配的精度是保证双目系统测量准确性的重要因素,也是系统研制过程中需要解决的难点问题。对影响双目系统中图像立体匹配精度的随机噪声建立了一种局部统计量符合高斯分布的简化统计模型,基于这个噪声模型设计了滤波方案。实验表明,滤波后图像立体体匹配的精度优于1／4像素。     

Characterization of lead-based relaxor ferroelectric crystals by acoustic emission

The acoustic emission (AE) method is presented as a useful complementary tool for nondestructive characterization of selective relaxor ferroelectrics. Combined measurements of the dielectric permittivity and AE activity as a function of temperature and externally applied electric fields have been carried out using Pb(Mg_1/3Nb_2/3)O₃–33%PbTiO₃ (PMN-0.33PT) single crystals and Pb(Sc_0.5Ta_0.5)O₃ (PST) single crystals. Anomalous behavior in the electric field dependencies of the characteristic temperatures, T_m (diffuse permittivity maximum in PMN-PT) and T_n (formation of incommensurate antiferroelectric domains in PST), and the associated AE intensities has been observed. Both T_m and T_n exhibit minima coinciding with the AE activities maxima at critical values of the applied dc electric fields, 0.5 and 0.13 kV respectively. These phenomena are discussed mainly in terms of the interaction of the external field with the random electric fields originating from the polar nanoregions in relaxor ferroelectrics.     

声发射和小波包分解技术在刀具磨损状态中的应用

随着现代加工工业的发展,对刀具磨损的监测在保障生产安全和产品质量中发挥着越来越重要的作用。声发射技术是刀具磨损监测的一种新方法。在车削加工过程中采集声发射信号,用声发射信号对刀具磨损状态进行识别。利用小波包分解技术对信号进行分析,得到有效的特征量作为BP神经网络的输入样本,并对网络进行学习训练,完成对刀具磨损状态的有效识别。     

Gabor小波时频分析在声发射信号处理中的应用

介绍Gabor小波时频分析的基本理论,用数值仿真举例验证Gabor小波时频分析可同时在时域和频域上来表征信号分布的特点。利用该方法可得到声发射源定位中传感器接收到的声发射信号在时域和频域上的分布,并用于区分声发射信号的传播模式和不同的信号组成,得到声发射波群的准确到达时间,从而提高时差定位的精度。     

金属疲劳断裂的声发射检测技术

疲劳断裂是金属结构的主要失效形式,通过金属疲劳断裂时声发射特征参数的提取,建立了声发射特征参数和裂纹扩展速率之间的关系,由试样的三点弯曲疲劳试验,证明采用声发射技术监测疲劳裂纹的扩展,不仅与疲劳裂纹扩展的变化规律相似,而且能实时的捕捉到疲劳裂纹的产生。     

离散频谱分析中两邻近谱峰参数的识别

在理论概括比值法原理的基础上,提出一种新的自动识别和修正离散频谱中两邻近谱峰参数的方法.它保留了比值法计算简单的特点FFT谱分析时无需增加样本长度,谱峰参数修正识别的算法简单,无迭代搜索过程.不仅能识别间距不到一个频率分辨率的两个密集频率成份,而且能识别峰间距为1～6个频率分辨率的邻近谱峰参数,从而与比值法相辅相成,形成了一套完整的离散频率信号分析方法.仿真研究表明,该方法能有效克服窗谱函数主瓣干涉和旁瓣泄漏的影响,识别精度较高当峰间距大于0.2倍频率分辨率时,对于两个频率分量的各种截断情况,均能保证幅度误差小于6%,相位误差在5°以内.     

Cause and effect assessment after a complex failure of a large ethylene compressor

A rusted cylinder liner and excessive wear of piston rings forced several maintenance disassemblies in a 1000 kW ethylene reciprocating compressor. Several months later the compressor failed due to growth of cracks in the crosshead of one of the cylinders. The initiation site was located in material defects near a stress raiser. In order to identify the root cause of the failure, crack growth time calculations were required. The applied stress field near the initiation sites and along fatigue paths were FEM estimated. Stresses vary steeply and become partly compressive along a large part of one of the fatigue crack paths. A recently developed weight function based numerical method was used to assess total fatigue crack growth time; this method also predicts the shapes of the crack front during propagation. Fatigue crack initiation was traced to a disassembly six months before final failure, which was found to be a joint result of non-conformities in manufacture and maintenance.     

Identification of process and distribution characteristics by testing monotonic and non-monotonic trends in failure intensities and hazard rates

Statistical tests are developed for testing monotonic and non-monotonic trends in failure data. A procedure is presented, by using a set of six tests as an example, to determine whether a failure process is a renewal process, a homogeneous or a non-homogeneous Poisson process, or none of these. The same tests with different data transformations can also be used for testing the goodness of fit of candidate hazard rates (i.e. distributions) and failure intensities. Several examples illustrate the potential power of these tests and the importance of testing for non-monotonic as well as monotonic trends. The efficiency of these tests is discussed in several special cases.     

基于切削声发射信号测量的刀具磨损状态判别

针对刀具磨损状态判别方法在变化的加工条件下判别正确率低的问题,通过实时采集刀具的切削声发射信号,提出了一种自适应获取声发射信号中刀具磨损状态特征的方法和基于磨损状态特征数据序列之间灰色关联分析结果的刀具磨损状态判别方法。以4把WNMG080408-TM T9125型号车刀在ZCK20数控车床上进行了车刀的切削磨损实验和磨损状态判别,实验结果表明:该方法能够自适应获取车刀的磨损状态特征,车刀的磨损状态判别结果与实际相符,具有较高的判别正确率。