Q235钢板局部腐蚀声发射信号特性研究

为解决腐蚀声发射源特征提取和识别的难题,直接从理论上证明了腐蚀声发射监测的有效性并推导出声发射信号特征。气泡破裂声发射信号幅值近似与气泡半径平方和液位高度成正比,频率与气泡半径成反比;钢板及其腐蚀产物开裂声发射信号幅值与开裂位置局部应力强度成正比,频率与裂纹扩展速度成正比,与裂纹扩展距离成反比。用低频和高频两套声发射系统,同时长时间监测Q235钢板在10%FeCl_3·6H_2O、10%FeCl_3·6H_2O加0.01 mol/L HCl混合液、5%CuSO_4·5H_2O溶液中的腐蚀情况,辅以监测钢板及钢板腐蚀产物开裂作为验证实验。通过对声发射信号的参数及谱分析,得出不同声发射源可以通过撞击数及功率谱在频域的分布来有效区分。实验结果与理论分析相吻合,研究结果对腐蚀声发射监测技术具有重要指导意义。     

腐蚀声发射信号降噪方法

为了从复杂背景噪声中有效地检测出腐蚀声发射信号,采用短时分形维数和离散分数余弦变换相结合的降噪方法,利用声发射检测系统,对6% FeCl₃·6H₂O溶液中Q235钢板的全面腐蚀和局部腐蚀声发射信号进行了降噪处理。实验结果表明,腐蚀声发射信号分别加入白噪声、有色噪声和粉红噪声,在输入信噪比为0~15dB的条件下,此方法降噪效果与标准离散余弦、离散分数余弦变换方法相比,输出信噪比最高可提升8 dB。所述降噪方法对检测腐蚀声发射信号以及对金属剩余寿命的评价具有一定意义。      

不同硬度钢质破片侵彻Q235A钢板试验研究

为研究不同硬度钢质破片的静动态力学性能及侵彻能力,通过准静态及动态力学性能试验确定了不同硬度D60钢的力学性能参数。采用弹道枪发射破片并撞击钢板的试验方法,获得了不同着速破片对有限厚Q235A钢板的侵彻过程参数,分析了材料力学性能与破坏模式的相关性。结合量纲分析法,得到不同硬度钢质破片侵彻Q235A钢板的弹道极限速度经验关系式。结果表明:破片的质量损失程度随着破片硬度的增加而降低,剩余破片的长度随着硬度的增加而减少,破片的侵彻能力随着硬度的增加而增加,HRC36破片贯穿钢板后剩余速度相对HRC20破片大幅度提高。所确定的弹道极限速度经验关系式预测值与试验结果吻合较好。     

油罐声发射检测信号数据库研究及应用

分析了油罐声发射检测技术特点和弱点,基于对检测影响因素的分析研究提出了油罐声发射信号特征数据库系统。采用盐水腐蚀真实罐底板,模拟油罐腐蚀。以Matlab软件为基础,提取全波形文件中被识别为腐蚀类别的特定帧信号,选取合适的自适应阈值电压得到信号特征参数,将全波形信号和信号特征参数入库。根据数据库特征参数训练支持向量机分类器,应用到实际油罐检测中并与开罐检测结果作对比,达到预期油罐分类效果。     

流化床燃烧声发射与气固两相流特性研究

１引言燃烧流化床声发射是一个极其复杂的过程,它是气因流态化两相流运动,气体湍动和燃烧化学反应复合作用的结果,其发射声谱中包含了上述运动过程的丰富信息山,对其发射声谱进行系统深入的研究,对寻求流态化两相流的运动规律有重要意义。本文试图以大量的实验研究为基础,以声波数字计算技术和现代分析理论手段,对气因流态化两相流运动规律进行了研究。２实验简介实验装置主要有燃煤流化床燃烧实验台和声波测量系统组成。燃煤流化床燃烧实验台如图１所示,声波测量系统见图２,从燃烧室不同位置测得的声波信号,一路送声波数字化处理…     

铝合金材料腐蚀损伤的声发射评价

为了研究如何利用声发射(AE)技术监测飞机主结构件的腐蚀损伤从而为确定飞机日历寿命提供科学依据。首先介绍了航空铝合金材料在加速腐蚀过程中的AE信号特征,说明如何利用AE技术来监测腐蚀损伤,进而讨论如何对材料的安全性能和剩余寿命进行评估。试验表明, AE能比超声和涡流等常规无损检测方法更早地发现铝合金材料的腐蚀损伤。通过研究加速腐蚀过程中腐蚀损伤程度及腐蚀AE信号随加速腐蚀时间的变化规律,获得了腐蚀损伤与AE参数之间的变化关系。说明AE技术可用于探测早期腐蚀、研究腐蚀发展规律及监测和评估腐蚀损伤方面。     

声发射特性与材料断裂韧性相关性研究

以高强度铝合金的断裂过程为研究对象，利用先进的声发射试验系统，考察了拉伸试样和带有预制疲劳裂纹的DCB试样在断裂时的声发射事件特性，揭示了材料断裂韧性和声发射特性 间的关系.试验结果表明，材料稳态裂纹扩展起始于K_1C并发射出许多幅值超过 阈值35 dB的信号，材料裂纹失稳扩展时爆发出强烈的声发射信号，材料断裂的累积声发射能与宏 观断裂能呈线性关系. 关键词： 声发射 断裂韧性 铝合金     

纳米混凝土声发射特性分析及其力学参数与声发射参数关系的研究

本文对不同二氧化硅掺量的纳米混凝土进行单轴压缩声发射试验。试验结果表明:当二氧化硅掺入量不超过3%时,纳米混凝土的声发射活性随着二氧化硅掺入量的增加而明显增强。从时间角度出发,在以时间参数作为中间变量的基础上推导出声发射能量累计数与应变的耦合关系。利用基于weibull分布的混凝土损伤本构模型,进一步推导出声发射累计数与应力以及损伤之间的耦合关系。结果表明理论曲线和试验数据结果吻合程度较好。     

神经网络在声发射信号模式识别中的应用

介绍了人工神经网络中的BP网络、RBF网络、Hamming网络、BP－Hamming网络在声发射信号模式识别中的应用现状，并对这些方法的优缺点进行了比较。     

网箱养殖大黄鱼合成声信号特性研究

对所采集到网箱中人工养殖的两组不同年龄大黄鱼(Pseudosciaena crocea)产生的声信号进行定量分析和比较,运用分段指数振荡函数合成大黄鱼声信号,并利用振荡频率和衰减指数定量地描述了鱼声信号特性。结果显示,合成的大黄鱼声信号在时频域都显示出很好的拟合优度,13—15月鱼龄组的平均振荡频率和衰减指数均低于7—8月鱼龄组。结果表明函数的振荡频率和衰减指数与大黄鱼发声的物理过程及年龄特征存在一定的联系,为今后人工养殖大黄鱼中声学技术的相关应用提供一定的科学参考和基础。     

Research on acoustic emission characteristics of local corrosion on Q235 steel

To solve the problem of corrosion acoustic emission(AE) source feature extraction and recognition,the AE detection validation and the amplitude-frequency characteristics were derived in theory.The amplitude of AE signal generated by bubble burst is proportional to its radius square and the liquid level,while the AE signal frequency is inversely proportional to the bubble radius.The AE signal amplitude of the steel and the steel corrosion product cracking is proportional to the local stress,and the AE signal frequency is proportional to the crack propagation velocity and inversely proportional to the crack propagation distance.Three Q235 specimens were separately immersed in the solution of 10%FeCl_3·6H_2O,5%CuSO_4·5H_2O and10%FeCl_3·6H_2O with 0.01 mol/L HCL.The AE systems with high frequency and low frequency were used to detect the whole corrosion process AE signals.The AE signals of Q235 steel and the steel corrosion products cracking were detected as the verification experiment.The AE signals from different sources could be distinguished by AE hits count and the power spectrum.It is coincident with theoretical analysis.These conclusions have significant guidance for the corrosion detection and evaluation by on-line acoustic emission detecting.     

Research on acoustic emission monitoring of pitting corrosion on 304 stainless steel

In order to study acoustic emission(AE) characteristics of pitting corrosion on 304 stainless steel under higher than normal temperature,pitting corrosion process of 304 stainless steel in 6%ferric chloride solution at 70°was monitored by AE technology.Conventional parameter-based approach and signal-based analysis were combined to deal with recorded AE signals,and micrographic observation was performed for further verification.The results showed that AE hit and energy increased gradually with time and reached the peak at certain time, and then declined and maintained a stable condition.Signal waveform was mainly composed of low-frequency(< 100 kHz) flexural wave with larger amplitude and energy and high-frequency (> 100 kHz) expansion wave with lower amplitude and energy.The research results have some certain significance for AE monitoring of pitting corrosion on 304 stainless steel under higher than normal temperature.     

304不锈钢点蚀声发射监测研究

为研究304不锈钢在高于常温条件下的点蚀声发射特性,对70℃下6%氯化铁溶液中304不锈钢点蚀过程进行了声发射监测。采用参数和波形分析相结合的方法处理信号,并通过点蚀形貌观察进行验证。结果表明声发射撞击和能量随时间逐渐增加,在某一时段达到峰值,随后下降并维持平稳状态。信号波形主要由幅度、能量较大的低频段(<100kHz)弯曲波和幅度、能量较小的高频段(>100 kHz)扩展波构成。研究结果对304不锈钢高于常温条件下声发射点蚀监测具有一定意义。     

Noise reduction algorithm of corrosion acoustic emission signal based on short-time fractal dimension enhancement

The general corrosion and local corrosion of Q235 steel were tested by acoustic emission(AE) detecting system under 6%FeCl_3-6H_O solution to effectively detect the corrosion acoustic emission signal from complex background noise.The short-time fractal dimension and discrete fractional cosine transform methods are combined to reduce noise.The input SNR is 0~15 dB while corrosion acoustic emission signals being added with white noise,color noise and pink noise respectively.The results show that the output signal-to-noise ratio is improved by up to 8 dB compared with discrete cosine transform and discrete fractional cosine transform.The above-mentioned noise reduction method is of significance for the identification of corrosion induced acoustic emission signals and the evaluation of the metal remaining life.     

Application of signal processing to acoustic emission signals emitted by steel specimens during tensile tests

We show that time and spectral properties of ae signals emitted by steel specimens during a tensile test depend, in a large part, on the characteristics of the acquisition set-up. Then we apply signal processing techniques (FFT, normalized energy, etc) to ae signals and we make here a comparative study between the acoustic emissions of different types of steel used in nuclear reactor technology.     

Detection of stress corrosion cracking of high-strength steel used in prestressed concrete structures by acoustic emission technique

The stress corrosion cracking (SCC) of high-strength steel used in prestressed concrete structures was studied by acoustic emission technique (AE). A simulated concrete pore (SCP) solution at high-alkaline (pH ≈ 12) contaminated by sulphate, chloride, and thiocyanate ions was used. The evolution of the acoustic activity recorded during the tests shows the presence of several stages related respectively to cracks initiation due to the local corrosion imposed by corrosives species, cracks propagation and steel failure. Microscopic examinations pointed out that the wires exhibited a brittle fracture mode. The cracking was found to propagate in the transgranular mode. The role of corrosives species and hydrogen in the rupture mechanism of high-strength steel was also investigated. This study shows promising results for an potential use in situ of AE for real-time health monitoring of eutectoid steel cables used in prestressed concrete structures.