超声无损评价金属材料晶粒尺寸的研究

利用超声波来评价金属材料的晶粒尺寸,与传统的金相法相比较,超声无损评价其特点是直接性和非破坏性,因此实用性强。综述了超声波无损评价金属材料晶粒尺寸各方法的原理和研究现状,并结合超声无损检测（评价）技术的应用需求及研究现状中的不足,对超声波无损评价金属材料晶粒度方法的设计方案的优化作了展望。     

304不锈钢固溶产物晶粒尺寸的超声无损表征研究

304不锈钢在1080℃下分别固溶1,2h,水淬后进行超声检测,以探讨无损评价304不锈钢固溶产物晶粒尺寸的可行性与表征参数。研究表明:固溶处理后,超声波速度逐渐降低,衰减系数明显增大;延长固溶时间,声速缓慢降低,衰减系数继续增大。频谱分析表明:固溶处理后,峰值频率明显降低,峰值幅度不断增大。分析认为:上述现象的产生与固溶处理对材料晶粒尺寸的作用以及晶粒尺寸对超声波传播的影响作用相关。基于最小二乘法拟合得到:横波声速vt、纵波声速vl与平均晶粒尺寸d线性相关:vt=-0.49254d+3188.40138,vl=-0.07632d+5772.88964;衰减系数与晶粒尺寸符合如下规律:α=1.2605×10-15 d6.5012+0.0995。     

复合材料损伤与断裂的动态无损评价

本文介绍声发射技术作为动态无损检测的有效方法评价纤维增强复合材料的损伤与断裂,其内容包括:评价纤维束丝的质量、层板的损伤与断裂,评价构件的结构完整性和预测玻璃钢气瓶的强度。     

超声焦散线法在材料定量无损评价中的应用

基于超声焦散线的形成原理,阐述了超声焦散线法在材料定量无损评价中的应用,指出了利用超声波的穿透性,结合断裂力学理论及声弹性理论,不仅可以探知材料中缺陷的有无,而且还可进一步确定缺陷附近的应力分布,从而达到材料进行定量无损评价的目的。     

基于临界折射纵波递归定量分析的纯铁疲劳损伤无损评价EI北大核心CSCD

利用超声检测技术无损评价金属材料的疲劳损伤程度,是保证高性能零部件承载性能和服役可靠性的重要手段。以工业纯铁低周疲劳损伤为研究对象,提出将临界折射纵波(critically refracted longitudinal,L_(CR))与递归定量分析相结合的无损评价方法。结果表明:拉-压加载过程中表现为循环硬化,随加载周次增加至1000周次,L_(CR)波幅值及对应归一化幅值差A_(dif)整体呈单调变化,5 MHz检测频率的灵敏度高于2.25 MHz。进一步对L_(CR)波进行递归定量分析,递归图随疲劳损伤发展变化明显,提取归一化递归度差RR_(dif)作为损伤指标,较时域、频域和时频域最大幅值等指标的灵敏度显著提升,增加幅度最大可达44%,为早期疲劳损伤的无损评价提供了新手段。     

基于频谱能量的材料晶粒尺寸表征方法

研究了利用超声频谱能量对材料晶粒尺寸进行表征的方法。通过不同的热处理方式获得了不同晶粒尺寸的奥氏体不锈钢材料,再分别利用衰减系数法、声速法和频谱能量法对材料的晶粒尺寸进行表征。结果表明:频谱能量法得到的衰减系数与平均晶粒尺寸呈非线性关系,晶粒尺寸的预测误差在4%~15%以内,优于传统的分析方法,证明了新方法的有效性。     

高频超声技术用于陶瓷零部件的无损评价和寿命预测

设计复合制作了工作频率在20～100MHz的纵波、横波以及曲面超声换能器．以延迟块直接耦合的方式对陶瓷零部件进行声参数和缺陷尺度的超声技术检测.以纵波（对气孔较灵敏）和横波（适于检测裂纹）换能器交替使用提高了可信度．在广泛检测的基础上,建立AVN（距离、波幅、当量）关系曲线,供作缺陷尺度的查判之用.基于无损的检测结果,根据断裂力学的基本原理,对陶瓷零部件作质量评价和级别判断以及取／舍裁决．     

脉冲反转技术在金属疲劳损伤非线性超声检测中的应用

材料性能退化总是伴随着某种形式的材料非线性力学行为,从而引起超声波传播的非线性,即高频谐波的产生。研究了利用脉冲反转技术测量金属材料超声学非线性系数的实验方法和信号处理算法,发展了一套可靠的测试实验系统,在相同条件下测量了同一试样在不同输入电压下的二次谐波和基波幅度,二次谐波幅度和基波幅度的平方近似成线性关系,表明实验系统是可靠的。利用该系统进行了一组LY12铝合金疲劳试样非线性超声检测实验。实验结果表明,超声非线性系数可以表征镁合金的疲劳早期退化,脉冲反转技术能够有效提取二次谐波时域信号,增强二次谐波的幅度,抑制主要由实验系统所产生的奇次谐波分量,为材料和结构早期力学性能退化的无损检测和评价提供一种有效的方法。     

超声探伤技术在无损检测中的应用

随着我国社会的发展和进步,当前我国的科学技术也取得了较好的发展,超声探伤技术在各个领域的无损检测中都有着较为广泛的应用,如建筑、机车、医疗、锅炉等领域,本文主要分析了超声探伤技术在无损检测中的具体应用。     

P91钢高温热损伤的二次谐波评价

P91钢是重要的核电承压钢结构材料,对其进行早期损伤评价具有重要意义。基于非线性超声理论,对P91钢不同温度的热损伤试样进行了非线性超声检测试验,逐级加大激励电压,基波幅度平方和二次谐波幅度呈现出良好线性关系,对基波和二次谐波进行频谱分析得到非线性系数,结果显示随着热处理温度的升高,非线性系数逐渐增大,可用于对这类材料热损伤进行有效评价。     

45号钢受热损伤的超声非线性检测实验研究

45 steel is a common material for parts manufacturing, and it is important to study its thermal damage detection for parts failure assessment.Here, in order to study ultrasonic nonlinear effects of 45 steel with different degrees of thermal damage, specimens with different degrees of thermal damage were made.Ultrasonic nonlinear detection tests were conducted for specimens using the RAM-5000 system made by RITEC company to obtain relation curves between ultrasonic nonlinear coefficients and heating temperature.These curves were deeply analyzed combining with the material’s metallographic microstructure evolution laws.Results showed that the ultrasonic nonlinear coefficient of 45 steel firstly increases, then decreases and increases again with increase in heating temperature;when heating temperature reaches 600 ℃, the ultrasonic nonlinear coefficient begins to increase; when temperature reaches 800 ℃, itreaches the peak value;thenit drops sharply, this is consistent with the coherent strain state of 45 steel between 700-800 ℃; finally, it at 1 300 ℃ rebounds slightly;the correlation between variation of ultrasonic nonlinear coefficient of 45 steel and its metallographic microstructure varying provides atest basis for the ultrasonic nonlinear detection of 45 steel thermal damage and the evaluation of its metallographic microstructure change.     

Remote nondestructive evaluation technique using infrared thermography for fatigue cracks in steel bridges

Long‐standing infrastructure is subject to structural deterioration. In this respect, steel bridges suffer fatigue cracks, which necessitate immediate inspection, structural integrity evaluation or repair. However, the inaccessibility of such structures makes inspection time consuming and labour intensive. Therefore, there is an urgent need for developing high‐performance nondestructive evaluation (NDE) methods to assist in effective maintenance of such structures. Recently, use of infrared cameras in nondestructive testing has been attracting increasing interest, as they provide highly efficient remote and wide area measurements. This paper first reviews the current situation of nondestructive inspection techniques used for fatigue crack detection in steel bridges, and then presents remote NDE techniques using infrared thermography developed by the author for fatigue crack detection and structural integrity assessments. Furthermore, results of applying fatigue crack evaluation to a steel bridge using the newly developed NDE techniques are presented.     

Thermographic nondestructive evaluation of steel-polypropylene laminates

The efficacy of passive thermography as a nondestructive evaluation technique for detection of voids and interlaminar flaws in steel-polypropylene laminates was investigated. Both analytical and experimental studies were conducted to assess the flaw resolution characteristics of the technique and to determine the effects of pertinent geometric and thermal parameters on resolution. The implications of the analytical and experimental results from the parametric studies are discussed in terms of their effects on flaw resolution and test technique optimization for development of on-line NDE for quality control monitoring.     

Ultrasonic evaluation of fatigue damage in metal matrix composites

This paper describes an experimental nondestructive technique for fatigue damage assessment in metal matrix composites by measuring ultrasonic phase velocity and attenuation. A [0/90] SiC/Ti---15V---3Cr---3Al---3Sn metal matrix composite is considered as a model system. Cyclic loading at 50 and 70% of the ultimate sample strength were used until failure. The ultrasonic phase velocities and attenuations were measured periodically and found to be very sensitive to fatigue damage. The fatigue-induced changes in the composite elastic constants were calculated from the measured ultrasonic velocity data. For samples heat treated prior to fatigue (815°C) above the matrix β transus (about 760°C), the dominant damage mechanism is debonding of the fiber/matrix interface. We found that when samples were fatigued for less than 50% of the lifetime, the reduction of the composite moduli was linearly dependent on the number of fatigue cycles, which is explained by extension of interfacial partial debonds. This was supported by micromechanical analysis based on a partial disbond model. The rate of decrease in the composite moduli in the second half of the fatigue life was found to be lower, which may serve as a basis for estimation of the remaining fatigue life of the composite from ultrasonic velocity and attenuation measurements. The attenuation data was obtained in directions perpendicular to the fiber. A single-fiber scattering model has been used to explain the effect of the fiber/matrix interface on attenuation. Good correlation between attenuation and moduli measurements was observed.     

Effects of ultrasonic vibration on SUS304 stainless steel subjected to uniaxial plastic deformation

In this study, a series of experiments was conducted in order to investigate the mechanisms of tensile force reduction and martensitic transformation in SUS304 stainless steel during ultrasonic vibration assisted tensile tests (UAT).

An independent analysis of the impact of the stress superposition effect in the ultrasound assisted tensile tests was done by finite element simulation, and metallographic analysis on the specimens showed that the increase of the amplitude of the ultrasonic vibration has a great influence on the martensite transformation in the material during deformation, reducing the elongation of the specimens. The results also pointed out that the tensile force reduction is caused by a combination of the effects of stress superposition and the energy absorption of dislocations over the hardening of the material due to the increase of dislocation density and induced martensitic transformation.     

超声捶击提高超细晶粒钢焊接接头的疲劳性能

焊接接头疲劳强度是其最重要的服役性能，由于焊接残余应力的作用和焊接接头处的几何不连续性，焊接接头的疲劳强度一般大大低于母材，采用超声捶击方法提高超细晶粒钢焊接接头的疲劳强度，通过对对接接头焊践处进行超声波冲击处理，对比超声波冲击处理后焊接接头的疲劳强度，实验结果表明：超声捶击使得S-N曲线右移，FAT（循环寿命为10^6时的疲劳强度）提高幅度达到66%，在应力范围为200MPa的疲劳寿命提高58倍，研究表明，经超声捶击处理，焊趾处的应力集中系数相应减小，焊接残余应力由拉应力转换为压应力，这是超声捶击提高焊接接头疲劳强度的主要机制。