Autofocusing ultrasonic imagery for non-destructive testing and evaluation of specimens with complicated geometries

This paper introduces the autofocus problem for non-destructive testing and evaluation of specimens with complicated geometries using ultrasonic arrays. We present an algorithm for autofocusing imagery of point-like defects obtained from a flexible array with an unknown profile. The relative positions of the array elements are parameterised using a cubic spline function and the spline control points are estimated by iterative maximisation of an image contrast metric via simulated annealing. The resultant spline gives an estimate of the array profile and the profile of the surface that it has conformed to, allowing the generation of a well-focused image. The algorithm is demonstrated on experimental data obtained using a flexible array prototype.     

蜂窝状微坑结构的电化学加工研究

在摩擦副表面加工蜂窝状微坑作为改善滑动摩擦的途径已成为研究热点.研究了电解加工蜂窝状微坑结构的方法,介绍了加工原理和试验过程,分析了加工电压、加工时间、阴极贯穿孔尺寸、电解液等加工参数对所加工微坑的影响,优化了加工参数和加工条件,提高了所加工微坑的精度.     

数控机床定位精度检测方法比较

评定机床性能的一项重要指标是机床的定位精度大小。文章介绍了两种常用的数控机床定位误差测量方法：一维球列法和激光干涉仪测量法的原理。在分析比较了两种方法的特点后，得出一维球列法在测量机床定位误差时的一些不足。向时，通过对一台数控铣床的测量后，发现激光干涉仪测量法更适合于机床定位精度的快速评定。     

A hybrid process of raining co-deposition and rotary wire spark erosion in the development of a custom CBN tool for making a biochip injection mold

This study examines a hybrid process combining raining co-deposition and rotary wire spark erosion with one-off grinding to generate an array of microgrooves in the fabrication of biochip injection molds on NAK80 steel. A precision composite electroforming device that can create a rain like co-deposition effect to uniformly grow a Ni-based Cubic Boron Nitride (CBN) abrasive layer onto a wheel-blank substrate is proposed and employed. Slicing and dressing are conducted by using rotary wire spark erosion to make the co-deposited wheel-blank into a thin CBN wheel-tool with a grinding edge array that alternates between coarse and detailed. A multiple microgroove array on NAK80 steel is one-off generated by using the developed CBN wheel-tool array, swiftly creating a superior surface finish for biochip injection molding. A comprehensive examination of the quantitative and qualitative properties of the CBN wheel-tool was undertaken. Experimental results have been evaluated in terms of CBN grit content, accuracy of co-shaft machining, influence of grinding depth, shape of microgroove and tool wear as well as an estimation criterion for the CBN wheel-tool array.     

相控阵超声检测技术应用

相控阵超声技术在无损检测行业中已经得到广泛的应用,该技术根据电子延时控制,利用波的叠加和干涉原理,形成动态扫查声束,最终合成扫查图像,比传统超声波探伤具有时更高的缺陷检出率。围绕相控阵技术原理、设备的使用和校准,介绍了相控阵技术在一些领域的经典应用。     

Accurate depth measurement of small surface-breaking cracks using an ultrasonic array post-processing technique

In this paper, the half-skip configuration of the Total Focusing Method (TFM) is used to image and size surface-breaking cracks. The TFM is an ultrasonic array post-processing technique which is used to synthetically focus at every image point in a target region. This paper considers the case of inspecting for cracks which have initiated from the far surface of a parallel-sided sample using an array on the near surface. Typically, only direct ray paths between the array and image points are included in the TFM algorithm and therefore the image obtained for this case consists only of root and tip indications; no specular reflection from the crack faces is captured. The tip indication often has such a poor signal-to-noise ratio that reliable crack depth measurement is challenging. With the Half-Skip TFM, instead of using directly-scattered signals, the image is formed using ultrasonic ray paths corresponding to the ultrasound that has reflected off the back surface and has then undergone specular reflection from the crack face back to the array. The technique is applied to experimental and simulated array data and is shown to measure the depth of small cracks (depth <1 mm) with greater reliability than methods which rely on tip diffraction.     

塑封球栅阵列焊点热疲劳寿命预测有限元方法

选取典型的塑封球栅阵列封装器件,将其建模为由封装外壳、硅芯片和基板组成的三层结构,采用粘塑性材料模式描述锡铅钎料的力学本构关系,建立器件的三维有限元模型,通过有限元仿真得到焊点的应力应变分布云图、应力应变回线及关键焊点的应变范围,最后根据基于应变的Engelmaier疲劳模型预测塑封球栅阵列焊点的寿命.结果表明,在热循环条件下,塑封球栅阵列封装器件的关键焊点的位置位于器件芯片边缘的正下方,并不位于最边缘的焊点处,为改进塑封球栅阵列焊点的热疲劳可靠性提供了依据.     

Effect of interface anisotropy on spacing selection in constrained dendrite growth

The selection of spacing in directional dendritic solidification is investigated numerically using the phase-field method in two and three dimensions. A criterion for the critical spacing below which no stable array growth can exist is derived from analysis of individual tip shapes. Constricted solute diffusion in the array leads to a deformation of the dendrite tip shape that competes with the deformation due to surface tension anisotropy. At the critical spacing both effects balance and a stable growth solution is destroyed. This mechanism is identified to determine the critical spacing of a dendritic array and leads to a dependence of the spacing on the anisotropy of the solid–liquid interface energy in a similar way as for the dendrite tip radius.     

Ultrafast hardware-based focal law calculator for automatic focusing

Phased array ultrasonic imaging of arbitrarily shaped components at high scanning speed demands computing an adapted set of focal laws before each new image. This requires computing the individual time-of-flight (TOF) from array elements to foci in a two media scenario. Most precedent approaches to this problem were based on iterative search for the minimum TOF in a sampled interface (Fermat׳s principle). This work follows a different approach by implementing a specialized processor that performs TOF computations. Several algorithms are implemented using High Level Synthesis (HLS) for state-of-theart FPGAs: Fermat iterative search, Newton–Raphson, Illinois and a combination of the latter.     

Lamb wave generation with an air-coupled piezoelectric concave array using square-wave burst excitation

In this paper, an improved pulse generator is proposed to emit a low-voltage square-wave burst. This generator will be used to excite a concave piezoelectric transducer array. Unlike classical single-pulse excitation circuits, this generator is also able to generate a square-wave burst signal. The Lamb waves generated in an aluminium plate with the square-wave burst generator are compared with those obtained using a classical single-pulse generator. Also, the signal conditioning system for all the transducer array elements has been implemented and tested.     

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.     

An eddy current array instrument for application on ferritic welds

This paper describes a multi-element, eddy current array for the local testing of ferritic specimens including welds. A novel transient method is used to extract coil impedance parameters, and has the advantage of fast measurement, digital compatibility and a minimum of front-end components; a useful feature when large element numbers are involved. The problem of displaying lift-off and flaw information from an array is solved by using a novel ‘volcano display’, which provides a simple two-dimensional image of conditions under the array. However, to produce this display, the burden of interpreting the coil element responses must be left to the instrument. The resident analysis software contains a number of operating modes which provide options for single element and multi-element operation. The array has been applied to the detection of cracks in the HAZ of a weld, where the large surface area of the probe permits a coarser scanning pattern to be used whilst providing a high probability of detection due to the number of elements deployed.     

电火花摇动加工微细阵列轴和孔的试验研究

针对微细阵列轴和孔的电火花加工,提出了利用数控电火花加工机床摇动功能的摇动加工微细阵列轴和孔的方法.此法是基于电火花反拷贝加工的原理,先用丝电极在薄平板(中间电极)上按要加工的阵列轴和孔间距或数倍间距加工阵列小孔(直径0.1 mm以上),然后用加工的薄平板(中间电极)作电极,电火花摇动加工微细阵列轴(电极),最后用此微细阵列电极加工阵列孔.进行了电火花摇动加工微细阵列电极试验,得到了单电极直径为50 μm、长径比为16的3×3阵列电极,并用此电极在70 μm厚的不锈钢板上加工出单孔直径为70 μm的3×3微细阵列孔.试验结果表明,电火花摇动加工方法可实现微细阵列轴和孔的加工.     

Accurate two-dimensional modelling of piezo-composite array transducer elements

The assumption of piston-like behaviour is widely applied when modelling ultrasonic transducers. Experimental measurements of the directivity patterns of piezo-composite array transducers have shown that this assumption is not valid for small element sizes. An alternative modelling approach has been developed based on the assumption that the variation in pressure across the face of each array element can be described by a Hanning window. The effect of inter-element cross talk has been included in the model by using a window larger than the nominal size of the element. This approach has been shown to produce excellent results via validation against experiment for directivity patterns and array surface displacement.The improved modelling method has been used to quantify the errors introduced by the assumption of piston-like behaviour by comparison of modelled beam profiles generated using simple delay and sum beam forming. This has been performed by simulating a variety of different beam types and monitoring the following parameters: beam width, maximum amplitude, and beam angle. These simulations show that the only parameter significantly affected is the relative amplitude of different beam angles. The improved directivity model predicts that the maximum beam amplitude decreases with increasing beam angle at a higher rate than directivity models based on piston-like behaviour; the maximum error recorded was approximately 3 dB.     

微喷部件阵列孔电火花加工工艺试验研究

比较各种微细阵列孔的电火花加工方法,分析了单电极加工微细阵列孔方法的优点。以去离子水作为工作液,在已研制成功的微喷部件阵列孔电火花加工机床上进行单电极加工微细阵列孔的工艺试验,研究电源参数对微细阵列孔的孔径一致性、加工效率及电极损耗的影响规律。优化微细阵列孔加工的电参数,实现稳定的一次性加工256个直径小于50μm、偏差小于2μm的微细阵列孔。     

基于电火花线切割加工的微细阵列电极加工

介绍了微细阵列电板的应用情况及其电火花线切割加工的特点.以硬质合金为材料,采用电火花线切割加工方法进行了微细阵列电极的加工实验,总结出了不同加工因素对加工结果的影响规律.     

FPGA焊点连接失效故障诊断

利用焊点内建自测(solder joint built-in self-test,SJ BIST)方法,建立球栅阵列(ball grid array,BGA)封装现场可编程门阵列(field programmable gate array,FPGA)焊点连接失效故障诊断的模型,用multisim进行仿真,并在Altera DE2平台上进行验证.结果表明,相比已有的文献资料,文中对SJ BIST诊断方法进行了更详细论证,更详细地确定了焊点阻抗大小,从而可得到更准确的FPGA焊点健康状态信息.     

玻璃纤维结构风电叶片的超声相控阵检测方法研究

随着中国风电行业的兴起和逐渐成熟,对风电系统本身的质量要求也越来越高,尤其是叶片检测越来越受到各个叶片制造企业的关注。但常用的敲击手段、光照手段等已经无法满足更高的质量要求,即使是使用常规超声技术,由于探头尺寸的限制,无法实现大面积的快速扫查,且数据判读和缺陷检出率受人为因素影响较大。基于上述原因,介绍了一种利用超声相控阵技术,并结合专用的风电叶片检测探头对风电叶片进行检测的方法。通过近3年的实验,证明了使用超声相控阵技术可以快速准确地检测风电叶片内部缺陷,包括玻璃纤维外壳内部的分层和干丝缺陷,以及玻璃纤维外壳和内部支撑结构之间的脱粘缺陷,并基本掌握了风电叶片的检测方法和要点。其优势包括直观C扫描成像、检测效率高、易于存储记录等诸多优点,因而在风电制造行业有着广泛地应用前景。     

小径管焊缝相控阵超声检测新动态

介绍小口径薄壁管环焊缝用横向曲面相控阵超声探头进行探伤与定量的新方法。制作了φ70×6．5和φ38×4两种钢试样管,试样管中加工了φ1mm通孔和深×宽=0．5mm×0．5mm（长分别为6．9mm和6．6mm）的线槽。相控阵图像仿真显示验证结果表明：曲面相控阵聚焦的缺陷定量准确度明显优于平面相控阵和矩阵探头,而且,该方法简单、经济。     

超声相控阵检测高速数据采集系统设计

提出了一种超声相控阵高速数据采集系统的设计方案,该方案基于ADC＋FPGA＋ARM架构,实现多路高速数据的采集传输。重点研究了ADC、FPGA接口设计。采用AD9272作为相控阵模拟前端,实施前端模拟信号预处理及多路高速数据并行采集;采用Spartan-6XC6SLX150进行多路高速数据的实时传输转换,在FPGA内实现了32路600M、DDR、串行LVDS数据高速接收恢复;最后通过上位机观测采集传输的超声相控阵回波信号。该设计充分利用当前高集成度芯片,为超声相控阵检测系统小型化的实现提供了参考。