基于BP神经网络的焊接冷裂纹声发射信号特征识别

声发射技术能够监测焊接冷裂纹,但由于焊后冷却过程中干扰信号很多,并且监测时间长,使得人工分析、评价困难较大。以5个典型声发射信号参量为输入单元、开裂信号和噪声信号特性为输出单元,建立了一个能识别焊接冷裂纹开裂信号的BP神经网络。通过对SPV490Q钢平板刚性拘束焊接裂纹试验的数据进行训练和测试,验证了该网络的可行性。     

基于结构负载声发射检测的低碳钢板电阻点焊飞溅表征

利用实时检测结构负载声发射信号实现了低碳钢电阻点焊过程中的焊接飞溅现象的检测与定量评估。试验结果表明,根据焊接飞溅声发射信号特征,焊接飞溅主要分为三种模式。随着焊接飞溅的模式不同,也意味着焊接飞溅能量当量的区别。焊接飞溅的结构负载声发射信号特征可以用于对焊接飞溅的定量评估。实现焊接飞溅定量评估的两个声发射信号特征参数分别为振铃计数和正峰值。焊接飞溅事件的声发射振铃计数和正峰值越大,说明焊接飞溅的能量当量越大;反之,则说明焊接飞溅的能量当量越小。在低碳钢的电阻点焊中,作为引发焊接飞溅的主要因素,焊接电流所起的作用应该比焊接时间和电极压力更为重要。其中,焊接电流和焊接时间越大,焊接飞溅的能量当量越大;电极压力越大,焊接飞溅的能量当量越小。     

金属裂纹扩展声发射信号特性研究

机械结构件中的应力集中使得结构极易产生裂纹并逐渐扩展,裂纹扩展时伴有声发射信号,因此有必要对结构件中裂纹扩展时的声发射信号进行特征研究。为研究金属板件中的裂纹声发射源特征行为,通过分析板件中的裂纹声发射源,从理论上推导了裂纹声发射的幅值和频率特征表达式。在裂纹扩展过程中,金属板件的裂纹声发射信号幅值与声发射源的开裂长度和拉伸应力的乘积成正比,频率与裂纹开裂速度成反比,且与裂纹开裂长度成正比。用声发射检测系统对预制有初始裂纹的金属板件进行拉伸状态下的声发射监测,通过对声发射信号求取功率谱密度估计,实现不同声发射信号以功率谱在频域的分布为信号特征的有效区分。实验结果与理论分析相符合,研究结果对金属板件的裂纹声发射检测技术具有重要意义。     

转轴裂纹声发射监测研究

声发射技术作为一种无损检测方法,可以找到声发射信号和裂纹扩展之间的关系,分析材料变形与断裂机制。介绍了声发射技术用于转轴裂纹监测的研究,分析了声发射信号与转轴裂纹扩展之间的关系。实验表明采用声发射技术可以对转轴裂纹进行监测,证明了声发射技术在转轴监测上的可行性。     

基于光纤光栅和支持向量机的声发射定位系统

利用光纤光栅传感器和边缘滤波原理构建传感系统,结合小波分解与重构和支持向量机算法,对铝合金板声发射定位进行了研究。根据划分区域进行声发射实验,探索声发射源所在区域与信号特征之间的关系。在对声发射信号进行小波分解的基础上,使用近似系数和细节系数进行重构,并对重构后的各信号计算其振荡能量作为信号特征,进行声发射区域识别。以重构信号的振荡能量作为输入、声发射区域位置类别作为输出构建支持向量机多分类模型,实现了声发射区域定位识别。实验结果表明,在400mm×400mm×2mm的铝合金板上对36个测试样本进行了多次声发射区域定位识别,在180次模拟实验中实现了176次声发射区域准确定位,正确率达到97.78%,声发射区域识别精度为30mm×30mm。该研究结果为机械结构的声发射区域定位检测提供了有效方法。     

BK7光学玻璃金刚石划刻声发射信号的特征提取

以金刚石压头划刻BK7光学玻璃为研究对象,分析了脆性材料脆性去除过程中的声发射机制,研究了声发射信号的特征提取技术。多种切深实验显示:BK7光学玻璃发生脆性去除的特征主要集中在[100,200]kHz、[300,400]kHz两个频段,对应不同的声发射机制,其中[100,200]kHz频带的滤波信号呈现明显的、时间间歇的突发式声发射现象,与脆性材料裂纹的生成与扩展密切相关。基于上述实验结果,提出了以突发式声发射事件为单位的特征监测方法。针对该带通滤波信号的均方根值(RMS),研究了基于凸优化理论的声发射事件识别算法,得到了脆性材料裂纹扩展的时刻及能量信息。得到的结果表明:以声发射事件为单位的特征监测具有明确的物理意义,能够更加客观地表征脆性材料的去除过程。     

风力机叶片疲劳裂纹AE信号的小波变换优化方法

为实现风力机叶片的及时有效地监测和维护,使用声发射技术采集疲劳裂纹信号,从而提取裂纹特征。而声发射信号的突发性和冲击性需要具有时频分析能力的信号处理方式来提纯和降噪,小波变换方法作为常用的时频处理方式油漆有效性,但是现有的小波基函数不足以适应该信号的分析。提出基于Shannon熵理论计算疲劳裂纹扩展的声发射信号的小波基函数带宽参数,得到最适合此裂纹声发射信号的Morlet小波基函数,计算优化基函数的小波,获得风力机疲劳裂纹特征成分在时间尺度平面的高幅值能量分布。实验研究表明,优化小波基的方法具有很好的时频聚集性和抗噪能力,实现了风力机叶片裂纹声发射信号的时频特征清晰准确的提取。     

基于声发射技术的金属高频疲劳监测

采用声发射技术监测高频疲劳条件下金属材料裂纹的扩展。介绍了如何运用软硬件处理的方法，从采集到的信号中分离出裂纹扩展的声发射信号。从处理后的声发射信号与观察得到的裂纹扩展对比来看，声发射参数的变化能够有效地反映材料疲劳裂纹扩展的过程，并且能更早地发现试样内部微小裂纹的变化。通过试验，得出了紧凑拉伸试样在裂纹稳定扩展阶段声发射信号能量率与应力强度因子幅值之间的关系式。     

DP780胶接点焊试件拉伸损伤过程的声发射特征分析

针对1.2 mm厚的DP780高强钢板,进行胶接点焊响应面实验.采集胶焊接头拉伸过程的声发射信号,拟合拉伸过程撞击计数的历程图,对信号进行小波包分解并分析归一化能量特征,对比分析胶焊接头界面撕裂与基板撕裂失效形式声发射信号时域及频域特征,并建立胶层失效时的累计撞击计数与焊接工艺参数之间的回归模型.结果表明:界面撕裂与基板撕裂失效形式在屈服和断裂阶段产生声发射信号,且两种失效形式对应阶段频率分布相似,屈服阶段与断裂瞬间频率分别分布于31.25～281.25 kHz和31.25～125 kHz,但界面撕裂失效在胶层断裂瞬间比基板撕裂失效产生更多组声发射信号;胶层失效时累计撞击计数与焊接电流存在负相关性.     

基于声发射信号的多种光学玻璃特征尺寸测量的压痕实验

主要介绍使用声发射信号技术对压痕实验过程进行监测。在实验过程中,对每个不同压力载荷情况下进行声发射信号的采集,建立声发射有效监测压痕试件状态的机制从而配合压痕实验来提高实验精度和稳定性,最终得到在所施加载荷状态下的各种光学玻璃试件的特征尺寸值及压痕形貌显微照片,确定侧向裂纹和中介裂纹的形核、发展过程,从而为提高光学玻璃的加工质量和表面精度做出理论铺垫。     

Characterization of nugget nucleation quality based on the structure-borne acoustic emission signals detected during resistance spot welding process

Acoustic emission signals detected during the resistance spot welding of aluminum alloy were studied in order to assess the characterizations of welding process, the characterizations of the effect of welding parameters to nugget nucleation and the characterizations of the nugget quality by the analysis to acoustic emission signals. The results showed that the physical phases of nugget nucleation can be characterized by the acoustic emission signals detected during the resistance spot welding process. The effects of welding current and current duration to nugget nucleation can be characterized by the characteristic parameters of acoustic emission signals. The characteristic parameters of acoustic emission signals had a better relevance to nugget dimensions and weld strength, which made it possible to measure or predict the weld strength by the characteristic parameters of acoustic emission signals detected during the resistance spot welding process.     

电弧声信号与铝合金MIG焊缝塌陷的相关性

针对铝合金MIG焊过程热积累作用强容易产生焊缝突然塌陷从而导致焊接过程失败的问题,建立电弧声信号传感系统并以焊接电弧声为研究对象,运用小波分析方法研究焊接电弧声信号与焊缝塌陷的相关性。研究表明电弧声信号的能量变化与焊缝塌陷有着明显的对应关系,电弧声总能量随着焊缝开始塌陷而增加,对电弧声进行小波分解发现不同频带有着不同的变化规律。研究结果为铝合金MIG焊实时焊接塌陷缺陷的检测提供一种新型有效的方法。     

铝合金电阻点焊多信息融合与质量分类

采用分布式多传感器同步采集系统实现铝合金点焊质量实时监测,并利用LABVIEW图形化语言编制相关数据处理软件。研究发现：焊点内喷溅与点焊电压和电极位移信号波形“下榻”现象相关联;电极压力所产生的高频脉冲强度和持续时间与内喷溅强弱有关,三种特征信息根据内喷溅严重程度,同时发生或个别出现。所提取的9种特征信息能够反映点焊质量,信噪比高,可为实现铝合金点焊质量分类奠定基础。采用主成分分析可进一步实现信息融合和数据压缩,点焊质量判断准确率达98 %。     

铝合金电阻点焊中电极点蚀对焊接质量的影响

采用有限元和物理模拟方法,考察了铝合金AA5182电阻点焊过程中电极点蚀对焊接质量的影响。结果表明:当电极尖端点蚀面积增加时,电极与试件界面上的实际接触面积基本不变,而试件与试件界面上的接触面积显著增加,电流密度大大减小,形成熔核的厚度和直径都减小。物理模拟试验所得熔核的形状和尺寸与有限元法预测结果符合很好。物理模拟和数值模拟都表明,点蚀孔直径为5.0mm时,只能形成厚度十分有限的环状熔核。研究揭示:电极尖端点蚀导致被连接试件之间的接触面积增大是其影响焊接质量的主要原因之一。     

2A14铝合金法兰焊接裂纹修复

铝合金以其良好的力学性能、防锈性能和轻量化而被广泛用于航空、航天等领域。但铝合金特有的物理-化学性质导致其焊接性极差,极易产生气孔、裂纹等焊接缺陷。主要对2A14铝合金法兰焊接裂纹的产生原因和补焊工艺特点,各种注意事项以及对铝合金焊接裂纹补焊工艺规范进行了详细讨论和探索,同时制定了严格的和细化的补焊工艺流程,完成了该法兰的补焊操作。     

逆变电阻点焊多参数单片机测试系统

针对传统的点焊监测与控制系统参数单一的缺点，研制了一种点焊电压、电流实时检测系统。通过合理、简单、可靠的硬件电路及软件计算实现了对点焊电流、电极间电压、能量和焊接时间等参数的数据采集和处理。     

The effect of welding parameters on fracture toughness of resistance spot-welded galvanized DP600 automotive steel sheets

The aim of this study was to evaluate the fracture toughness of resistance spot welded (RSW) lap joints of galvanized DP600 steels. RSW lap joints galvanized DP600 steel sheets were performed on spot welded in a pneumatic, phase-shift-controlled, and 0–9?kA effective weld current capable AC spot welding machine. Defect-free RSW lap joints were produced on galvanized DP600 steel sheets. Fracture toughness of RSW lap joints were calculated from the results of shearing tensile tests: the dependence of fracture toughness to welding current, welding time, and hardness of welding zone for galvanized DP600 steel sheets. According to the experimental data, the fracture toughness increases as welding current and welding time increase up to a certain value, then the fracture toughness starts to decrease. Also, it was seen that the fracture toughness varies with the hardness of the welding zone. This variation is related to welding current.     

Modeling small-scale resistance spot welding machine dynamics for process control

Electrode displacement is generally regarded as a variable that can provide real-time information useful for monitoring and controlling resistance spot welding (RSW) process quality. However, in small-scale RSW production, it is difficult to measure the displacement because its magnitude is very small. By contrast, force signals are relatively large and thus are less susceptible to measurement noise. In this article, an empirical model is proposed to simulate the dynamics of an SSRSW head with the objective of calculating electrode displacement from the variation of electrode clamping force measured during welding. The parameters in the model were determined by fitting experimental force and displacement signals with polynomials and then performing an optimization search for parameters of first-order dynamic models. To verify the models’ accuracy, they were subsequently applied to simulate the electrode displacement curves of welds with expulsion and without expulsion. The calculated displacement curves agreed well with experimental measurements, and the occurrence of expulsion was clearly indicated by the model predictions. A more comprehensive model is under construction with an objective to eliminate displacement sensor in the monitoring and control of SSRSW process.     

Studying the deformation and temperature distributions in a specimen during acoustic-emission testing of the weld-seam welding and cooling process

The results of experimental studies of the weld-seam welding and cooling process in steel specimens using acoustic emission (AE) and strain gauging are presented. Deformation was measured by high-temperature strain gauges welded to specimens using spot welding. Temperature was measured by chromel-alumel thermocouples. Measurements were performed with measured with an MMTC-64.01 microprocessor strain-gauging system and a C??a?? ?16.10 AE system. Computers of these two systems exchanged information. Residual strain deformations were recorded on a specimen after cooling of a weld seam. Metallographic studies of transverse sections, which were were cut out from the clusterization zones of a weld seam, confirmed the presence of cracks, pores, and faulty fusions.