Determining Mode-I Cohesive Parameters for Nugget Fracture in Ultrasonic Spot Welds

Ultrasonic spot welds have been used as a model system to investigate how to determine the mode-I cohesive parameters associated with interfacial fracture of a spot weld. Numerical analyses indicated that, while multiple combinations of the two cohesive parameters (characteristic strength, , and toughness, Γ _I) could result in virtually indistinguishable behaviors for individual geometries, only a single pair of parameters can provide a unique set of behaviors for different test geometries. This provides the basis for determining the cohesive parameters by comparing numerical predictions to experimental observations. In particular, a direct uniaxial tensile test was found to be particularly useful for measuring the characteristic strength of an ultrasonic weld. With the characteristic strength known, the toughness of the weld was determined by fitting numerical predictions to experimental observations of the load–displacement curves obtained from T-peel specimens bonded with the ultrasonic weld. These two parameters were then used without modification to predict the performance of welded U-peel specimens. The numerical predictions for this third configuration were in excellent agreement with the experimental results, verifying that it may be possible to use cohesive-zone parameters to predict the behavior of different geometries of spot welds formed under nominally similar conditions.     

焊缝超声检测缺陷类型的模糊C均值聚类识别

提出了一种采用模糊C均值聚类的方法来识别焊缝超声检测缺陷类型的方法.以夹渣、气孔、未焊透、未熔合4种焊缝常见缺陷为对象,对25个实际焊缝样本进行识别计算,并与射线检测结果进行比对.结果表明:该方法正确识别率达88%,具有较好的识别效果.     

超声冲击处理2A12铝合金焊缝表层微观组织结构变化

采用超声冲击工艺对母材为2A12铝合金焊接接头进行了焊后处理.利用扫描电镜、X射线衍射分析了超声冲击处理前后焊缝表面层的微观组织结构特征.结果表明,超声冲击处理可以在焊缝表面形成约为300μm的致密塑性变形层,晶粒明显细化.对X射线衍射峰的观察分析表明,处理后焊缝表层材料衍射峰明显宽化,这是超声冲击处理使焊缝表层材料粒子细化和晶格结构的微观应变引起的.利用谢乐方程和威尔逊公式对超声冲击处理后焊缝表层的晶粒度和微观应变进行了定量分析,结果表明,处理层的晶粒平均尺度为123nm,平均微观应变为0.134%.最后,对晶粒细化的机理进行了分析.     

Grain Size Measurement of Copper Spot Welding Caps Via Ultrasonic Attenuation and Scattering Experiments

During ultrasonic testing of resistance spot welds in real time, the probe sends the sound waves through the thickness of the copper electrode cap into the materials being welded. Characteristics of the reflected waves from the weld interfaces allow a reliable decision to be made on the quality of the joint. Transmission of high frequency sound waves through the relatively thick copper welding cap cause the signal to be greatly attenuated due to grain scattering. For this reason, close monitoring of the copper cap properties prior to installation is essential for adequate performance. Finding copper alloys with a small average grain size is essential in order to minimize the attenuating effects. The conducted backscatter and attenuation experiments indicate correlation between the ultrasonically measured parameters and the optically found copper grain size. This correlation suggests that the attenuation or backscatter technique could be used alone in order to validate the proper copper alloy to be used in spot weld probes. Using nondestructive testing techniques for this purpose greatly reduces the time and cost involved compared to optical techniques.     

Microstructure and Property Relationships in Resistance Spot Weld between 7114 Interstitial Free Steel and 304 Austenitic Stainless Steel

Due to the differences in physical, chemical and mechanical properties of the base metals, the resistance spot welding of dissimilar materials is generally more challenging than that of similar materials. The influence of the primary welding parameters affecting the heat input such as peak current on the morphology, microhardness, and tensile shear load bearing capacity of dissimilar welds between 304 grades austenitic and 7114 grade interstitial free steel has been investigated in this study. The optimum welding parameters producing maximum joint strength were established at a peak current of 9 kA, where the electrode force is kept 6×10-5 Pa and weld time is kept constant 17 cycles, respectively. The primary cause of weakening the weldment is identified as the excessive grain growing region of heat affected zone (HAZ) in case of 7114 grade interstitial free steel.     

T91／P91钢管焊接接头的超声波探伤

通过对T91／P91钢中声速的理论计算和实际测试,利用声波的反射规律和运用几何关系,计算了常用不同K值探头在对T91／P91钢进行超声波探伤中的K值变化、深度和水平距离的差异。用常用探头和普通试块即可完成T91／P91钢管焊接接头以及与T91／P91钢对接的普通低合金钢焊接接头的超声波探伤。     

焊接微缺陷磁光成像检测有限元分析

目的 研究铁磁材料焊接微缺陷的磁光成像规律.方法 运用漏磁检测原理和法拉第磁致旋光效应,建立微缺陷三维有限元模型,分析微缺陷磁光成像过程与磁场之间的关联,研究不同提离值、励磁电流、缺陷宽度、缺陷深度下的磁光成像,以及探索这些因素对磁光图像特征的影响.在此基础上,对最小宽度为0.05 mm的微缺陷进行磁光成像检测实验,并...     

高频焊接钢管焊缝的超声波自动检测工艺

在高频焊接钢管焊缝自动超声波检测的实际工作中,精确的焊缝跟踪较难实现,易影响检测的可靠性.通过对超声波检测技术进行分析,利用6 dB声束全壁厚覆盖区进行检测,提出了一套超声波检测新工艺.实践证明:该工艺可以在焊缝跟踪不精确的情况下实现可靠的超声波检测,为高频焊接钢管焊缝自动超声波检测提供了一套有效的检测方法.     

GH169合金制件中黑斑和白斑偏析的超声检验

通过对所搜集到自然缺陷试样的超声检验，研究ＧＨ１６９合金中黑斑和白斑偏析的可探性。     

电容式微加工超声传感器(cMUT)的结构设计及仿真

与传统的压电传感器相比,电容式微加工超声传感器(cMUT)性能优良,有着广泛的应用前景．为此．介绍了cMUT的基本结构和工作原理,并提出了一种新型结构．利用有限元分析软件ANSYS对这种结构进行模态分析．得到其共振频率和一阶振动图;利用ANSYS的耦合场分析模块和参数化设计语言(APDL),对结构进行力电耦合仿真,获得其直流偏压和作为发射器时所需的交流电压值．分析结果表明,所设计的结构符合设计要求．     

SUS304不锈钢板点焊接头超声成像及力学性能EI北大核心CSCD

利用超声波水浸聚焦入射法,对1mm厚的SUS304奥氏体不锈钢板点焊接头进行超声C扫描成像检测,研究不同焊接工艺参数下接头的C扫描图像特征,检测分析点焊的熔核直径,并对点焊接头进行拉伸-剪切实验。结果表明：超声波水浸聚焦C扫描成像法能够有效检测点焊熔核直径,为4．76～5．25mm,比金相实测值大2．6％～5．3％;随着焊接电流的增加（4-8kA）,接头的失效载荷均值从7116．8N增加到9707．1N,能量吸收均值从66．3J增加到196J,同时反映在C扫描图像上的熔核直径也从4．76mm增加到5．11mm;当焊接电流增加至9kA时,接头的失效载荷均值下降至6799．5N,能量吸收均值下降至41．3J,此时在C扫描图像上反映出飞溅、焊穿等典型的焊接缺陷。     

超声检测信号的特征分析

目的 在无损检测中提高疵病实时检测和识别的正确性和可靠性。方法 提出了利用检测信号的波形特征分析进行疵病实时检测和识别的方法。结果 通过一应用实例,表明该方法对于提高检测可靠性是行之有效的。结论 用波形特征分析的方法可实现疵病的实时检测和提高检测精度。     

Development of damage in a 2D woven C/SiC composite under mechanical loading: II. Ultrasonic characterization

The non-linear mechanical behavior of a CVI-processed 2D woven C/SiC composite has been investigated by means of an ultrasonic method. This method provided the complete variation of the stiffness tensor of the material required to fully identify anisotropic damage, which was otherwise inaccessible by classical strain measurements. The various damage mechanisms induced by mechanical loading and their influence on the tensile behavior were determined and analyzed by comparing the variations of the components of the stiffness tensor obtained from the ultrasonic measurements with the prediction of microcracks by a system of slit cracks derived from a micromechanical model. Two damage modes were thus emphasized: transverse microcracking characterized by a deterministic accumulation and a random development of longitudinal microcracking, i.e. fiber/matrix and bundle/matrix debonding. Comparisons with the results obtained in Part I from both classical strain measurements and microstructural observations are also made and discussed, whenever possible.     

Failure Analysis of Friction Weld (FRW) in Truck Axle Application

A section of a fractured spindle from an axle housing was metallurgically examined. The axle fractured at the friction weld (FRW) interface and was from a truck with only about 8,000 miles of service. SEM and metallographic examinations of the weld fracture revealed that a ferritic band existed at the weld interface. A significant amount of oxides and some micro-porosity was observed in the ferrite. The existence of this type of microstructure compromised the strength of the weld and resulted in the overload fracture of the axle. FRW is supposed to be a solid-state process; however, melting-solidification was evident in this case, as suggested by the band of oxides caused by liquid phase oxidation of the molten layer at the interface and micro-shrinkage porosity formed during solidification of the liquid film. Process conditions that resulted in high heat input and liquidizing of the weld interface before the upsetting stage of the friction welding process should be mitigated. This article was published in Materials Science & Technology 2007 Conference and Exhibition: Exploring Structure, Processing, and Applications Across Multiple Materials Systems (Detroit, MI), September 17–20, 2007, What We Can Learn from Failure Analysis Symposium, ASM International, Materials Park, OH, 2007.     

超声微粒检测换能器的分析与设计

利用超声波在传播过程中遇障碍物会产生散射信号的特性进行微粒检测时,超声换能器的设计非常关键.通过对平面圆形活塞声源和凹球面聚焦声源的轴向声场分布比较分析,完成了超声微粒换能器的选型;基于一个假设的应用实例,对影响换能器性能的三个重要参数(焦距 D、晶片半径 a、和谐振频率 f)的确定原则进行了理论研究和仿真分析,给出了...     

奥氏体不锈钢管母材和焊缝的显微组织对超声检测的影响

采用金相试验手段研究了在不同焊接方法下同种奥氏体不锈钢管母材及焊缝的显微组织特性,以及在相同焊接方法下奥氏体钢管和碳钢钢管母材及焊缝的显微组织特性。用超声检测方法对试样焊缝中的人工刻槽缺陷和边缘端角进行灵敏度和信噪比的定量检测,研究了超声波在奥氏体不锈钢管和碳钢钢管中的传播特性差异。结果表明:在两种不同的焊接方法下,奥氏体不锈钢管母材及焊缝的显微组织状态基本相同,对超声检测的影响差异不大;在相同的焊接方法下,304奥氏体不锈钢管和20碳钢钢管的焊缝显微组织明显不同,超声波在奥氏体不锈钢管焊缝内的传播效果较差,检测存在一定困难;临界纵波双晶探头的灵敏度和信噪比均很高,在检测表面缺陷时能获得较好的效果。     

2A12与2A11铝合金超声波焊接工艺与组织研究

对2A12-T3和2A11-O铝合金进行了超声波焊接,研究了不同超声波焊接工艺参数对焊接界面结合状况的影响.采用扫描电镜、电子背散射衍射和透射电镜研究了焊接界面的组织结构.结果表明,当超声波焊接振幅为30μm,焊接时间为0.2s,焊接界面结合状况较好,焊接界面的线性焊接密度接近100％.氩气保护也会对线性焊接密度产生影响.当焊接振幅为15μm时,氩气保护可提高线性焊接密度;但当焊接振幅为30μm,氩气保护对线性焊接密度无明显影响.超声波焊接过程中,焊接界面上产生波纹和漩涡状塑性流动,发生动态回复和连续动态再结晶,形成由位错缠结、位错胞、亚晶和细小晶粒组成的焊接界面组织.     

Ultrasonic 2D SH Crack Detection in a Layered Anisotropic Plate

The 2-D scattering problem of an internal crack in a layered anisotropic plate is considered in this paper. In the model, two ultrasonic SH probes are attached on the upper surface of the plate and the incoming displacement field is generated by one of the probes and the other probe is acting as a receiver. The transmitting and the receiving probe may be the same. The problem is solved by deriving the Green function for the layered plate and then using the integral representation for the total field to obtain an integral equation for the crack opening displacement. The integral equation is solved by expanding the crack opening displacement (COD) in Chebyshev functions. A crucial part of the method is the expansion of the Green function in a free space part, expressed in the crack coordinate system, and a reflection part, expressed in the plate coordinate system. The electrical signal response is calculated by an electromechanical reciprocity relation. Numerical examples are given for a transversally isotropic graphite-epoxy plate, where the symmetry axes are mutually perpendicular in the layers. The results are presented as A-scans, i.e. the electrical response as a function of time.     

基于CAE耦合分析的注塑件熔接痕性能优化

采用Moldflow对注塑件的熔接痕进行CAE模拟,将Moldflow模拟注射成形后的结果数据导入到Algor中对制件做特征值屈曲分析,并将屈曲载荷因子作为注塑件熔接痕性能的评价指标。通过正交试验,分析了熔体温度、模具温度、保压压力、保压时间对制件屈曲载荷因子的影响。结果表明：熔体温度对熔接痕力学性能的影响最为显著,保压时间和模具温度次之,保压压力的影响最小。     

粘接结构超声信号的小波分解与特征提取

粘接结构因其独特的物理、机械和声学特性在诸多领域具有非常广泛的应用,对于铝合金-橡胶这样一种金属-非金属粘接结构的超声检测信号,本文利用了小波变换的多分辨率分析(时频分析)的方法,有效地提取出了反映多层材料粘接状况的信号特征,该特征提取方法可用在粘接结构的无损检测中。