相控阵声束焦距及换能器孔径综合优化的实验研究

相控阵声束的聚焦受换能器频率、孔径、阵元尺寸、焦距以及扫查角度等诸多参数的影响,且各参数之间具有复杂的相互关联和制约关系。本文基于相控阵超声声束形成及聚焦原理,采用60阵元线型阵列换能器,通过实验方式研究了声束聚焦对成像质量的影响。在焦距为5mm-80mm和换能器孔径为5mm-30mm的范围内,分别测定了两参数匹配方式不同时,DB-H1标准试块上3横通孔的A扫描回波幅度。通过分析二者的最佳匹配方式证明了参数优化的必要性,研究结果对相控阵超声检测的工程应用具有重要参考价值。     

An ultrasonic testing method for detecting delamination of sprayed ceramic coating

The adhesion strength of thermal sprayed coatings is relatively low, and they sometimes tend to delaminate from the substrate during operation. In particular, sprayed ceramic coatings for thermal barriers, such as ZrO₂, often delaminate because of thermal shock; therefore, ceramic coatings are often submitted to thermal shock tests. A nondestructive inspection method using ultrasound to detect the delamination of sprayed coating was proposed. In this study, a coating model was made with acrylic plates, and an ultrasonic test was applied to investigate the precision of detecting delamination by the ultrasonic testing method. Results indicate that delamination more than 1mm in diameter can be detected by the ultrasonic testing method. Moreover, the delaminating process of sprayed coatings under thermal shock tests can be detected by this method.     

电磁超声技术在焊缝检测中的应用

电磁超声技术利用洛伦兹力或磁致伸缩原理在金属或磁性材料中激发出超声波,它是一种超声无损检测新技术。相对于其他无损检测技术而言,电磁超声具有所有的超声检测的优势。声波的激发发生在材料的表面而不是在传感器内部。所以它与传统的基于压电换能器的超声检测相比,具有无需耦合剂、可非接触、可适用于超低温或超高温环境、有利于工业自动化以及可方便有效地实现横波检测及导波检测等优势。Innerspec Technologies公司致力于电磁超声技术的研发和应用,在近十几年中开发了150多台工业在线电磁超声检测系统,广泛应用于钢铁、汽车制造、石油天然气管道和压力容器等领域。作为一种超声波技术,电磁超声可以应用于各种厚度测量、缺陷检测以及材料表征。举例讨论了电磁超声在焊缝检测中的应用。第一个应用是利用导波对激光拼焊板的检测。第二个应用是电阻焊钢管的在线检测。利用沿着周向传播的超声导波对焊缝进行检测,克服了由于焊缝位置偏转对传统超声焊缝检测设备带来的困难。第三个应用是水平横波以及多通道电磁超声相控阵技术实现奥氏体不锈钢焊缝的检测。     

钽钨合金薄板的兰姆波检测

采用超声兰姆波检测方法,和研制的1．25P15×20型38°入射角,大晶片专用换能器,对1．6mm（厚）×80mm（宽）的TaW合金板材实施了内部质量检测。试验表明,该超声换能器不但可以稳定检出1．6mm厚TaW板材内Ф0．4mm左右的缺陷,而且孔径与兰姆波反射幅值呈现出良好的线性关系,满足了生产中的质量控制要求。     

Fatigue Behavior of Bodies with Thermally Sprayed Metallic and Ceramic Deposits

This paper summarizes the basic results of fatigue testing of bodies with both metallic and ceramic thermally sprayed coatings. Three kinds of ceramic coatings (Al₂O₃, Cr₂O₃, and olivine) sprayed with DC plasma under identical conditions were investigated together with metallic Ni-5wt.%Al coatings sprayed by wire arc, DC plasma, and HVOF. The elastic modulus of the deposited coatings was investigated using four point bending and resonance method. Bending fatigue tests at resonance frequency were performed with cantilever beam specimens. The processes taking place during the fatigue test are identified and discussed. The morphology of the fracture surfaces was investigated together with microstructure and porosity of the coatings.     

Evaluation of thermal sprayed coating using ultrasonic inspection by means of bottom echo back reflection

Thermal spraying technique is widely used in various mechanical parts as a surface reforming technique. However, as demand to maintain superior mechanical performance in harsh operating environment increases, the need for non-destructive evaluation method for thermal spray coating becomes more important. For this purpose, we thinned the thickness of the thermal sprayed coating by abrasion with blasting and used ultrasonic inspection by means of bottom echo reflection for effective measurement of abrasion quantity in thermal sprayed coating. The results obtained are summarized as follows. When the thickness of thermal sprayed coating becomes thin, the echo height increases. This is because thermal sprayed coatings absorb ultrasonic energy. Ultrasonic energy absorbed by Al₂O₃ is smaller compared with Fe-13Cr coating. Thermal sprayed coatings submerged in water have a lower echo height compared with air. As mentioned above, the thermal sprayed coating thickness can be estimated using ultrasonic inspection by means of bottom echo back reflection.     

铸钢件超声波衰减系数测量及其影响因素

测定了铸钢件ZG0Cr13Ni4Mo超声波衰减系数并对其影响因素进行分析.试验结果表明,利用声压、声程乘积的对数函数ln(Px)与声程x的线性关系,来测量衰减系数是个较好的方法;探头晶片尺寸、频率对铸钢件超声波衰减系数有影响,随晶片尺寸增加,衰减系数呈先增后减趋势,而衰减系数随探头频率的增加而增加.从衰减系数对超声波检测影响来看,铸钢件纵波直探头超声波检测宜选用低频率、晶片直径约20 mm的探头.     

铅合金构件超声检测技术研究

针对40mm厚的铅合金构件质量检测,设计了不同深度的平底孔试块:Φ1mm、Φ2mm和Φ4mm。在分析和试验的基础上,优选了超声换能器参数,采用不同的超声波检测方法对缺陷检测能力进行验证,结果表明:铅合金构件的超声波检测频率不宜高于5MHz,在现有技术下,可以明显检出构件内部Φ2mm平底孔当量的缺陷,且超声相控阵技术缺陷的检出率高于常规超声检测方法,但也只能检出30mm深度范围内的Φ1mm平底孔缺陷。     

管道内检测的环形相控阵超声聚焦方法

针对管道内检测中相控阵超声聚焦的问题,分析了管道中环形相控阵超声辐射的超声波传播原理,建立了聚焦数学模型,计算了阵元间激励信号的延时;采用128阵元的换能器对直径为168mm的管道进行试验,结果表明,环形相控阵超声的延时法则实现了不同工作阵元数量以及不同焦距条件时,声束在管壁中的聚焦。在工作区间内,一定数量的阵元可获得良好的聚焦效果。     

小直径铜棒的超声波自动检测系统应用

针对φ2．5～15mm的铜质棒材,采用脉冲反射法的表面波和穿透法的纵波相结合的方法,可以较好地解决薄壁小直径铜质棒材的检测方法。研制了小直径铜棒超声自动检测系统。系统主要由上位机（即PC机）、下位机（即单片机控制系统）、发射／接收电路、探头和机械系统组成。上位机通过RS232串口与下位机通信,从而完成系统控制和数据采集。试验表明,系统可以检出φ2．5～15mm铜质棒材上直径为φ0．5mm,深度为1／4D的人工平底孔,可以实现定性定量检测。     

Multi-coil focused EMAT for characterisation of surface-breaking defects of arbitrary orientation

Electromagnetic Acoustic Transducers (EMATs) are a useful ultrasonic tool for non-destructive evaluation in harsh environments due to their non-contact capabilities, and their ability to operate through certain coatings. This work presents a new Rayleigh wave EMAT transducer design, employing geometric focusing to improve the signal strength and detection precision of surface breaking defects. The design is robust and versatile, and can be used at frequencies centered around 1 MHz. Two coils are used in transmission mode, which allows the usage of frequency-based measurement of the defect depth. Using a 2 MHz driving signal, a focused beam spot with a width of 1.3±0.25 mm and a focal depth of 3.7±0.25 mm is measured, allowing for defect length measurements with an accuracy of±0.4 mm and detection of defects as small as 0.5 mm depth and 1 mm length. A set of four coils held under one magnet is used to find defects at orientations offset from normal to the ultrasound beam propagation direction. This EMAT has a range which allows detection of defects which propagate at angles from 16° to 170° relative to the propagation direction over the range of 0–180°, and the setup has the potential to be able to detect defects propagating at all angles relative to the wave propagation direction if two coils are alternately employed as generation coils.     

表面粗糙度引起的超声波厚度测量误差的修正方法

根据对未经平整的粗糙锈蚀表面分别进行超声波厚度测量和机械测量的比较试验，发现超声波测量的平均误差为0．6～2．2mm。为解决该问题，建议使用一种表面回波持续时间的误差修正法，并选用合适的2．25MHz宽带换能器进行测量。该方法也适用于喷漆的表面检查。     

Model-based simulation of focused beam fields produced by a phased array ultrasonic transducer in dissimilar metal welds

Phased array ultrasound testing (PAUT) can produce steerable and tightly focused ultrasonic beams, so it is widely used for detecting flaws. However, inspection of dissimilar metal welds (DMWs) using phased array ultrasound is not easy at all, since ultrasonic beams are skewed and distorted severely in the welds that are anisotropic and inhomogeneous elastic media. So, to increase focusing efficiency and have optimized conditions for inspecting the welds, quantitative prediction of phased array ultrasonic beams is needed. This paper proposes a modeling approach that includes modeling the grain orientation of the welds with buttering, calculating the ray path for the determination of focal laws, and applying the linear phasing multi-Gaussian beam model in order to focus the ultrasonic beams produced by a phased array transducer mounted on a wedge contacted to the interrogated DMW. This paper also presents an example of the model-based simulation of the focused beam fields produced in the DMW. The proposed model allows us to increase the focusing efficiency by accurately simulating the ultrasonic testing of welded components and to propose a new tool to associate welding design with the ultrasonic assessment of structural integrity.     

Ultrasonic characterization of modified Cr_2O_3 coatings by reflection coefficient spectroscopy

Pores,microcracks and density of plasma sprayed Cr2O3 coatings before and after high-intensity pulsed ion beam(HIPIB) irradiation were investigated using the ultrasonic reflection coefficient spectroscopy(URCS).The URCS was analyzed based on an acoustic transmission model for the multi-layered structure.The longitudinal velocity in the coatings was calculated from the experimental URCS,and the attenuation coefficient expression was deduced by comparing the experimental and numerical fitting amplitude spectral lines.The longitudinal velocity of as-sprayed Cr2O3 coating is 2 002 m/s,and increases to 2 099 and 2 148 m/s after being irradiated by HIPIB with 1 and 5 shots.Correspondingly,the factor A changes from 0.046 to 0.026 and 0.020 and n from 1.702 to 1.658 and 1.649 in the attenuation coefficient expression of α=Af n.It is observed that the surface morphology of Cr2O3 coatings changes from rough and porous to smooth and uniform with the increase of shot number,which accords with the ultrasonic analyses reasonably.The URCS seems to provide a convenient and nondestructive method to characterize surface modification of the plasma sprayed coatings.     

径向振动匹配层换能器的设计参数及模态优化

设计基于匹配层外壳的径向振动换能器,分析匹配层材料、换能器直径、压电振子厚度对换能器模态振型的影响,并结合设计频率下最佳模态振型优化换能器设计参数。结果表明:树脂基匹配层显著提高换能器在空气介质中的发射效率。随着换能器直径减小、压电振子厚度增加,径向振动换能器激振效率提高。优化的换能器直径为100 mm,压电振子厚度为10 mm,在第三阶谐振频率为34 729 Hz时,可实现高效率、高质量振动辅助研磨加工。      

Ultrasonic testing of adhesive bonds of thin metal sheets

This article discusses the use of pulse-echo ultrasonic testing for the inspection of adhesive bonds between thin metal sheets (0.8 mm). The method is based on the measurement of the reflection coefficient at the metal/adhesive interface. After describing briefly the physical aspects of the phenomenon, an index is defined to detect defective zones of the joint (both for the lack of adhesive and for insufficient adhesion); the influence of the experimental variables (transducer frequency, coupling medium and contact force) on the measurement is discussed. The analysis shows that coupling medium and transducer frequency do not influence the results and that the method is robust with respect to the variation of contact force. By means of a control experiment it is shown that the statistical distribution of the index corresponding to good and defective adhesion zones are sufficiently separate to be distinguished. Finally, a procedure based on the statistical theory of decisions is proposed to evaluate the integrity of the joint under test.     

Dependency of fracture toughness of plasma sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript> coatings on lamellar structure

The fracture toughness of plasma-sprayed Al₂O₃ coatings in terms of critical strain energy release rate G _Ic was investigated using a tapered double cantilever beam (TDCB) approach. This approach makes the fracture toughness be measured only using the critical fracture load disregarding crack length during test. The Al₂O₃ coatings were deposited under different spray distances and plasma powers to clarify the effect of spray parameters on the G _Ic of the coatings. The fracture surfaces were examined using scanning electron microscope. On the basis of an idealized layer microstructure model for thermal sprayed coatings, the theoretical relationship between the cohesive fracture toughness and microstructure is proposed. The correlation between the calculated fracture toughness and observed value is examined. It was found that the fracture toughness of plasma sprayed Al₂O₃ coatings is not significantly influenced by spray distance up to 110 mm, and further increase in spray distance to 130 mm resulted in large decrease in the fracture toughness of the coatings. The G _Ic value predicted based on the proposed model using lamellar interface mean bonding ratio and the effective surface energy of bulk ceramics agreed well with the observed G _Ic data. Such agreement evidently shows that the fracture toughness of thermally sprayed ceramic coatings at the direction along coating surface is determined by lamellar interface bonding.     

强电流直流伸展电弧CVD纳米金刚石涂层微型工具

本文研制了强直流伸展电弧金刚石涂层沉积设备,它可产生长达400 mm的等离子体弧柱,可沉积金刚石涂层的区域大,能够在复杂形状硬质合金刀具上沉积金刚石涂层,有利于实现金刚石涂层硬质合金工具的产业化生产.在直径1 mm的微型铣刀上沉积了纳米金刚石涂层,研究了沉积压力对金刚石涂层组织的影响,沉积压力对金刚石涂层的晶粒尺寸和表面形貌有显著影响.随着沉积压力的降低,沉积的金刚石涂层晶粒尺寸减小,当沉积压力为0.80 kPa时,可沉积出纳米金刚石涂层.涂层的厚度均匀,其表面光滑、平整,且与硬质合金基体之间有较好的附着力.用激光Raman对金刚石涂层进行了表征.     

三种基于夹心换能器驱动的球形超声马达设计

文章在换能器设计理论基础上利用有限元方法对夹心换能器进行了优化设计,通过改变前端变幅杆的长度、底座高度以及前端厚度的几何参数进行分析,得到了换能器前端变幅杆几何参数与换能器性能之间的关系,变幅杆的长度与换能器固有频率成反比,与振幅成正比,变幅杆的底座高度和前端厚度与固有频率和振幅放大系数皆成反比.以夹心换能器为驱动,提出三种新型多自由度球型马达结构设计,分别介绍了三种马达结构,分析了驱动原理和运动轨迹的实现,对比了相互之间的优缺点.对四换能器球形马达进行了样机试验,实际工作频率为33.300kHz,在驱动电压110V时,最大输出力矩为0.13Nm,最高转速可达46r/min.     

中等厚度铅合金铸件的超声波检测

对铅合金铸件声学特征参数测试发现,铅合金的纵波声速较低,衰减系数较大,为超声的强衰减材料。对不同孔径的平底孔试样检测结果表明,目前采用超声水浸和直接接触法,均可较好地检出10mm厚板材内的1mm人工缺陷。因此采用超声方法检测中等厚度的铅合金铸件是可行的,重点是选取恰当的检测方法,以实现最佳的检测灵敏度。