Comparison Between Using Longitudinal and Shear Waves in Ultrasonic Stress Measurement to Investigate the Effect of Post-Weld Heat-Treatment on Welding Residual Stresses

Fusion welding is a joining process widely used in the industry. However, undesired residual stresses are produced once the welding process is completed. Post-weld heat-treatment (PWHT) is extensively employed in order to relieve the welding residual stresses. In this study, effect of PWHT time and temperature on the residual stresses of a ferritic stainless steel is investigated. Residual stress distributions in eight welded specimens were measured by using an ultrasonic method. Ultrasonic stress measurement is a nondestructive method based on acoustoelasticity law, which correlates mechanical stresses with velocity of an ultrasonic wave propagating within the subject material. The ultrasonic wave employed could be longitudinal or shear wave produced by the longitudinal (normal) or transverse (shear) transducers, respectively. Ultrasonic stress measurements based on longitudinal waves use longitudinal critically refracted (L_CR) waves in this direction, while shear wave methods use an ultrasonic birefringence phenomenon. The results show that the effect of PWHT can be successfully inferred by both longitudinal and shear wave methods, but the former is found to be more sensitive to stress variation. Furthermore, the distribution of subsurface residual stresses is found to be more distinguishable when the L_CR method is employed.     

用于瞬态高温测试超声波传感器

目的　研究一种用于测试瞬态高温的传感器 .方法　设计超声波发射和接收装置用来测量超声波声速 ,根据超声波的相关原理 ,声速的大小可以反映被测气体的温度值 .结果与结论　超声波瞬态高温传感器是一种非接触式测量传感器 ,动态响应好 ,可用于气轮机进气、火箭排气、汽缸燃烧气体、火炸药爆破燃烧等场合的温度测试     

激光致声技术的研究

从热弹与烧蚀机制两个方面，讨论了激光超声表面波的产生。通过对点光源激励声表面波的机理进行分析，出线光源激励的表达式。进行了表面波同线光源能量、方向角、位置、长度关系的实验研究。实验结果验证了激光超声表面波理论模型的合理性，证实了线光源产生的表面波具有信号强、方向性好等优点。     

高温管道超声波测厚方法影响因素仿真研究

针对石化行业中在高温工作状态下的管道测厚问题,本文研究了超声波高温管道测厚方法中的一些影响因素,并实现了一套高温管道超声波测厚的仿真系统。实验中讨论了不同厚度、不同材料、不同噪声水平以及不同温度对超声波管道测厚结果的影响。此外,比较了不同测厚方法对管道厚度测量的影响。实验结果表明,该系统能够较好的模拟高温超声波测厚系统,能够实现高温管道厚度的测量。     

桩内应力波的频散现象及数学模型

本文采用广义变分原理建立了一种考虑圆杆内横向运动影响的纵波理论,用于求解锤击杆端所生成的波场.所得到的解包括两部分:局限于杆端的驻波场和具有频散的行波场;理论结果与实验结果吻合较好,对于桩的动测技术具有指导意义.     

Nondestructive Evaluation of Welding Residual Stresses in Austenitic Stainless Steel Plates

This article investigates the nondestructive capability of ultrasonic waves in residual stress evaluation of austenitic stainless steel plates (AISI 304L). Longitudinal critically refracted (L _CR ) waves are employed to measure the residual stresses. Measuring the acoustoelastic constant through the tensile test is eliminated on the main investigated sample to keep it intact. Another welded plate with the same welding specification, geometry, thickness, and the same material is used to extract tensile test samples. To find the acoustoelastic constant of the heat affected zone (HAZ), a metallographic investigation is done to produce microstructure similar to that of the HAZ in a tensile test sample. A finite element model of welding process, which is validated by hole-drilling method, is used to verify the ultrasonic results. The results show good agreement between finite element and ultrasonic stress measurements which is accomplished nondestructively.     

Propagation of Ultrasonic Lamb Waves in Aluminium Adhesively Bonded LAP Joints and in Single Plates

The analysis of the propagation of Lamb waves in multi- and single-layer systems is presented in this work. The study of this propagation problem is developed from matrix formulations, which describe elastic waves in layered media. The behavior of the different modes that propagate in the overlapped region is characterized. It is found that their relative amplitudes can be estimated based on the properties of the incident wave mode. It was verified that the excitation of these modes is ruled by the degree in which the shapes of both modes match each other.

Other result of this method refers to the evaluation of the attenuation of both longitudinal and transversal waves in plates, which is usually difficult, especially in thin plates by using the conventional pulse-echo technique. By using the immersion pitch and catch setup, the total attenuation, the sum of the losses due to the leaking in the fluid and to the material damping can easily be obtained through two measurements at different distances. The leaking losses are calculated by the bulk properties of both the fluid and the plate, and, consequently, the attenuation of the longitudinal and the transversal waves (material damping).     

退火温度对溅射Al膜微结构及应力的影响

用直流溅射法在Si基片上制备了 2 5 0nm厚的Al膜 ,并在不同退火温度下进行退火处理 ,用X射线衍射和光学干涉相位移法对薄膜的微结构及应力随退火温度的变化进行了研究。结构分析表明 :退火后的Al膜均呈多晶状态 ,晶体结构仍为面心立方 ;随着退火温度由 2 0℃升高到 4 0 0℃ ,薄膜的平均晶粒尺寸由 2 2 8nm增加到 2 5 1nm ;薄膜晶格常数在不同退火温度下均比标准值 4 0 4 96 A稍小。应力分析表明 :随退火温度的升高 ,Al膜应力减小 ,30 0℃时平均应力减小为 2 730× 10 8Pa且分布均匀 ;在 4 0 0℃时选区范围内应力差仅为 3 82 8× 10 8Pa。     

Ultrasonic and Microscopic Investigation of Impact Damage in GFRP Composites

Abstract

Some aspects of ultrasonic evaluation of impact damage in glass fiber-reinforced plastic (GFRP) composites are discussed in this paper. First and foremost, results of a microscopic investigation are reported which illustrate the structural properties of GFRP composites and show that, contrary to the assumption used in the current literature, no delamination occurred in the samples examined in this work when the energy of impact was lower than 9 J. Second, a simple ultrasonic approach to assess the maximum spatial extent of the damaged volume is presented. The evaluation of the damage spatial extent obtained by this method is shown to correlate well with that recovered by a direct microscopic investigation. Finally, in view of the findings obtained by the microstructural analysis, a brief discussion is presented which reviews the properties a nondestructive method should possess in order to provide reliable quantitative assessment of impact damage in GFRP composites.     

超声冲击处理对铝合金焊接应力的影响

为了探究超声冲击处理(UIT)对铝合金材料焊接应力的影响,采用有限元分析软件AQAQUS建立了7A52铝合金双丝熔化极隋性气体保护焊(MIG)焊接模型和超声冲击处理耦合模型,得到了冲击后的应力场,分析了冲击前后残余应力分布特点;通过改变冲击针移动速度、冲击位置以及冲击针直径,分析其对焊接应力的影响规律,旨在探讨超声冲击处理对铝合金焊接应力改善的影响规律。计算结果表明,超声冲击处理能够显著改善焊缝和热影响区的焊接残余应力,且超声冲击处理对焊趾处的冲击比对焊缝处冲击产生的压应力数值大、范围宽;随着冲击移动速度的增加,焊接接头处压应力值逐渐减小,且移动速度增加到一定程度将会出现欠处理状态,达不到产生压应力的效果;冲击针直径对焊后残余应力影响较大,随着冲击针直径的增大,其接头处压应力值会增加,且产生的纵向残余压应力区间会增大;经过超声冲击处理后的试验和数值计算表明,材料模型中是否考虑应变率对应力结果影响很大,应该根据实际材料的应变率硬化程度建立准确的材料模型。     

导电聚合物的温度效应

研究炭黑填充的聚合物电阻率与温度之间的关系表明,当炭黑浓度在临界区域或晶质聚合物在较窄的熔化区域,材料都能呈显高的正温系数(H-PTC)效应;而炭黑浓度很大时,具有负温系数(NTC)效应。这些是探索新型功能导电材料——温度自控塑料发热体的理论基础。     

磁流变液的屈服应力与温度效应

通常磁流变液的屈服应力大约比电流变液大一个数量级，磁流变学液由于具有较强的屈服应力而受到广泛的重视。我们用多畴的软磁材料同连续相一起充分混事获得的磁流变液，在３×１０＾５Ａ／ｍ的场强下静态屈服应力达到６０ｋＰａ以上，而其零场时的粘度仅为１５ｍＰａ．ｓ，本文报道了匀们研制的拖板式磁流变仪的性能。同时，我们比较了几种磁流变液在零场下的沉淀性，以及外加磁场，屈服应力，温度，永磁材料，表面处理剂，添加剂和     

微电铸层内应力超声去除实验

针对Ni微电铸层中内应力过大的问题,提出用超声时效技术去除铸层内应力的方法.利用自行研制的超声设备对铸层内应力进行去除,借助X射线衍射仪和应力测量公式求得超声前后的内应力大小,并对实验结果进行对比.结果显示,铸层内应力在50min时去除最为明显,平均应力由-209.0MPa减小到-109.0MPa,减小了100MPa,消除率达到47.9%.可知在合适的实验参数下利用超声时效技术可以有效地减小和消除电铸层的内应力.超声时效去应力效果与热处理效果相当,能够满足微器件的使用要求,具有一定的实用价值.     

初始应力对瑞利波无损评价45钢表层应力的影响

基于瑞利波声弹效应理论,在瑞利波无损表征45钢表层应力的基础上分析了45钢表层初始应力状态对应力评价结果的影响。采用声程固定不变中心频率为5MHz的双瑞利波探头对45钢表层应力进行评价,在归一化互相关函数基础上计算了应力引起的瑞利波信号间时间差。结果表明:初始应力不会影响瑞利波在45钢表层中传播速度随拉伸应力的变化规律,即随拉伸应力的增加,瑞利波在45钢表层中的传播速度基本呈线性规律增加,当应力达到一定值时,再随应力的增加,瑞利波传播速度不再呈线性规律变化;但初始应力和去应力退火状态45钢的名义瑞利波声弹性系数不同,分别为0.838和1.041,最大时间差对应的应力值也不同,去应力退火前后应力评价结果的误差约为22%。     

Strategies for Reducing Stress in Ultrasonic Cutting Systems

Abstract:  Ultrasonic cutting is an established technology in the cutting of food products. As the high-cost components of an ultrasonic cutting system are the ultrasonic generator and transducer, some designs have concentrated on running several cutting blades from a single power source. This strategy is undoubtedly economic, but problems remain with reliability. Blade failure during cutting is a common problem in ultrasonic systems and therefore strategies are proposed to reduce stress levels at the failure locations. Many alternative blade profiles are investigated using finite element (FE) models, which are validated by experimental modal analysis (EMA) using a 3D laser Doppler vibrometer (LDV). Combining three strategies can reduce the stress level at the failure location on cutting blades. The first investigates the blade profile at the failure location with the aim of incorporating sufficient gain at reduced stress levels. The second concentrates on detuning the block horn and blades in order to move the longitudinal node away from the highest stressed section of the blade. Finally, a redesign of the block horn is studied in order to eliminate the effects of blade flexural vibrations in the longitudinal cutting mode.     

X70管线钢的室温蠕变及其对流变应力的影响

利用MTS万能试验机研究了X70管线钢在不同应力加载速率和不同加载过程下的室温蠕变现象,以及室温蠕变对流变应力的影响.结果表明,X70管线钢有明显的室温蠕变现象存在,应力加载速率和加载过程对室温蠕变变形量有明显的影响,而且室温蠕变显著提高了材料的流变应力.并根据位错理论对实验结果进行了分析解释.     

超声纵波换能器用于平测时的测距修正方法研究

研究了超声纵波换能器用于平测时的测距修正方法.首先,根据弹性波理论分析了利用平测布置代替对测布置测量波速时的实际物理意义;然后,分析了两种换能器布置方式的真实传播距离并通过设计混凝土试件切割-测量实验进行了两种布置方式的声时对比;最后,根据实验数据在对测回归直线方程的基础上提出了计算换能器平测布置修正测距的最小二乘法....     

高温合金锻件超声波检测显示信号分析

根据超声波形变化的静态和动态特征与缺陷分布状况，结合被检工件的加工工艺，综合评价分析了长期积累的高温合金锻件超声波检测显示信号的特点和规律，为无损检测质量评定可靠性提供了参考依据。     

表面温度传感器时间常数测量方法研究

介绍了一种表面温度传感器时间常数测量的新方法,并对该方法测量的结果进行了分析。     

电脉冲辅助超声冲击技术对焊缝残余应力及显微硬度的影响

焊接结构件中存在焊接残余应力,使得焊接构件在使用过程中容易发生断裂,缩短构件的使用寿命.以D36钢焊缝为研究对象,使用电脉冲辅助超声冲击技术处理D36钢焊接件,研究了电脉冲辅助超声冲击技术对焊缝残余应力和显微硬度的影响.研究结果表明:电脉冲辅助超声冲击技术在适当的电流密度和处理时间下消除焊接残余应力和表面强化的作用优于传统的单一超声冲击技术,不仅能够比单一超声冲击技术降低焊缝的残余应力最多达23 MPa,提高焊缝表层的最大硬度达109HV,同时增加强化层深度最多达250μm.