An Analysis of a Quarter-Infinite Solid with a Corner Crack of Arbitrary Shape

In this paper, a versatile body force method for a quarter-infinite solid with a corner crack of arbitrary shape is proposed under two types of pressure: constant and linear. New numerical results are obtained for different corner crack cases. Fatigue crack growth from a corner crack has been analysed successively with the present method. Moreover, the stress intensity factor of a corner crack is proposed in a simple form for an arbitrary shape.     

Multiphysics Modeling and Analysis of the Photoinductive Imaging Effect for Crack Detection

Numerical multiphysics modeling of the photoinductive imaging (PI) effect was performed with a 2-D transient to characterize corner cracks at the edge of a specimen with a bolt hole. We present how the finite-element method (FEM) can be utilized to model the PI effect and observe the influence of critical factors on the coil probe impedance for a rectangular crack in the Ti-6Al-4V specimen. As anticipated, the proposed model can show that the PI method has a higher spatial resolution in the defect in 2-D models compared to the conventional eddy current testing method. The FEM simulation results for 0.25-, 0.50-, and 0.75-mm rectangular notches are shown and discussed. The effects of coil current frequency, laser-point temperature, and lift-off distance on the PI signal are also examined and analyzed. We demonstrate that the PI effect is a novel sensing method for characterizing the geometric shape of cracks and that the enhanced output signals of the coil probe can also be obtained given an appropriate quantity of factors.      

基于涡流方法的智能螺纹检测仪的研制

针对目前存在的内螺纹人工检测工作量大的问题,采用基于单片机技术的涡流方法研制了一种智能螺纹检测仪。先设计了一个简单的阻抗测量电路,建立了探头对不同螺纹状态试样和试验频率的阻抗图,然后通过分析该阻抗图找出了适合于用幅度法检测的频率范围,最后通过对探头施加合适的正弦激励信号,用测量探头两端电压的方法完成螺纹检测。对给定的螺纹试样检验结果表明,该仪器可以准确地判断出试样的半牙、无牙和合格状态,并能给出相应的输出信号。     

复合材料制件拐角部位超声检测技术

复合材料在航空、航天等领域应用不断增加,制件的结构形式越来越复杂,在很多复杂结构中存在拐角部位,这些拐角部位的检测给无损检测带来困难.通过对资料的分析和试验,介绍了解决复合材料制件复杂结构拐角部位无损检测的方案和思路,并对比分析了各种检测方法的优缺点,认为超声相控阵技术在未来复合材料拐角部位无损检测上具有比较好的应用前...     

钢坯表面裂纹的检测技术

表面裂纹的检测是生产高质量钢材的重要保证。目前,冶金企业已经开始应用一些检测技术对钢坯表面裂纹进行在线检测或离线检测。介绍了目前常用的几种钢坯表面裂纹检测技术的原理、特点、应用实例及其检测效果,这些技术包括涡流检测法、漏磁检测法、红外检测法和机器视觉检测法。在此基础上,总结了钢坯表面裂纹缺陷检测技术的发展方向。     

疲劳裂纹扩展速率试验中裂纹曲率修正方法研究

针对目前疲劳裂纹扩展速率试验标准中仅提出裂纹长度需进行曲率修正但未给出具体修正方法及步骤的问题,作者推荐了线性插值法和等比例法两种裂纹曲率修正方法,并通过分析两种方法的修正原理,结合试验结果,将两种曲率修正方法进行对比。结果表明,在双对数坐标系上,修正后的da/dN-ΔK曲线向低ΔK方向偏移,最大偏移量约15%,在利用da/dN-ΔK曲线进行选材对比或疲劳寿命评估时,修正后的曲线与未修正的曲线相比是偏安全的。基于两种方法修正后的da/dN-ΔK曲线之间差异较小,最大相差约2%,两种方法均可作为疲劳裂纹扩展速率试验中裂纹长度的曲率修正方法。     

基于仿真的计算尖角处应力的外推法

目的用有限元方法推算尖角处的应力。方法在对有限元模型进行第1次仿真的基础上,基于对等值线图的直观考察,确定应力梯度较小的方位。然后在尖角附近,沿此方位在几何体表面绘制一定大小的矩形,并在矩形上确定几个关键点。依次对该矩形进行网格细分,并考察几个关键点的应力变化情况。当这些点的应力趋于收敛时,根据这些点及其应力值创建一条三次样条曲线,然后利用此样条曲线进行外插,推测尖角处的应力。结果对于给定的算例,得到了尖角处的应力为1.46MPa。结论可以使用外插的方式来推算尖角处的应力。     

短裂纹密度场建模与CT成像仿真

以不同时刻的短裂纹密度场CT仿真成像为研究对象,提出了密度场建模原理,得到了局部质量不守恒和局部质量守恒两种裂纹扩展模型;利用亚体素模型、裂纹离散化、亚体素级的短裂纹扩展算法并扩展了建模软件的文件建模功能,分别得到了相应的CT检测样本模型文件,实现了局部质量不守恒和局部质量守恒两种情形下的裂纹扩展建模;通过获取不同时刻的CT检测样本模型文件,利用CT仿真系统重建了不同时刻的密度场图像,建立了不同裂纹扩展阶段的演化记录.     

Crack profiles and corner point singularities

Crack profiles in the vicinity of a crack tip were investigated both theoretically by using standard displacement field equations, and by experiments using foam plastic models. Particular attention was paid to crack profiles in the vicinity of a corner point where a crack front intersects a free surface. Crack profiles for single-mode and mixed-mode cracks, calculated from standard displacement field equations, are incorrect in the vicinity of a corner point. The use of foam plastic models permits the visualization of crack profiles in the vicinity of a corner point. Strictly speaking, stress intensity factors have no meaning in the vicinity of a corner point, but for practical purposes it is possible to calculate representative values. Failure to take into account warping of an initially plane-free surface, at a corner point, has led to some confusion in the finite element calculation of representative K _III values.     

用变频扫描励磁方法定量检测裂纹

目的 实现对疵病的定量检测和对材料的定性检测。方法 通过改变磁场交变频率从而引致导体中的涡流发生变化，来观测工件材料的疵病。结果 实验证明文该方法对于提高检测精度是有效的。结论 用变频扫描励磁方法进行裂纹定量检测可提高检测的可靠性。     

圆筒型容器接管外拐角表面裂纹疲劳扩展的有限元跟踪

运用1/ 4 点位移法和有限元技术对圆筒型容器接管外拐角表面裂纹扩展时应力强度因子的变化作了计算机数值跟踪。结果表明:表面裂纹各点的扩展速度与其所处的位置和容器接管的几何参数有关,且其扩展平衡状态为一不规则形状。     

Crack Characterization Method with Invariance to Noise Features for Eddy Current Inspection of Fasterner Sites

There is a need for research in eddy current (EC) nondestructive evaluation (NDE) to improve the reliability to detect, locate and size cracks around fastener sites in multi-layer structures while minimizing the overall cost of inspection. The objective of this work is to develop feature extraction and classification algorithms for crack characterization with invariance to noise features for eddy current inspection of fastener sites. Model-based parametric studies were first performed to explore potential features under a wide array of crack, noise and material conditions. Through these studies, several features were identified to have some invariance to the characteristic asymmetric response due to gaps between the fastener and hole, probe liftoff variation, and probe skew. In particular, a promising feature with noise invariance to all non-flaw conditions considered in this study was found through investigating changes in the eddy current response along a circumferential direction in an annulus region away from the hole center. To obtain a measure of this localized crack feature, an approach was developed using a fit of a characteristic function to the data through nonlinear least squares estimation. A model-based optimization approach was also implemented to evaluate the best signal processing algorithm design to distinguish between several classes of crack size. Using this approach, an optimized measure was found to be well correlated with subsurface crack size and insensitive to noise conditions included in this study.     

含铌、钒、钛微合金钢连铸坯角部横裂纹研究现状

在微合金钢连铸生产过程中,角部横裂纹一直未得到有效解决,裂纹的存在减少了铸坯热送量,严重影响生产顺行。综述了微合金连铸坯角部横裂纹的形成机理,重点分析了铌、钒、钛等微合金元素对角部横裂纹的影响,分析了防止横裂纹产生的措施,认为消除微合金钢连铸坯角部横裂纹的最有效方法是控制铸坯表层微观组织,使其具有较低的裂纹敏感性,克服连铸弯曲与矫直过程中产生的应力,而不产生裂纹。     

直流电压降法应力腐蚀裂纹扩展速率在线测定试验系统

介绍了应用直流电压降方法(DCPD)在线测量高温高压水环境中不锈钢应力腐蚀裂纹扩展的原理与试验系统,并采用商用301不锈钢对试验方法的准确性与系统的可靠性进行了验证。试验系统包括水化学回路、加热控制系统、动态加载系统与数据采集系统。在320℃,15.5MPa的去离子水中通过改变溶解氧含量和添加SO42-,Cl-等条件下完成了验证性试验。对材料的裂纹长度-时间曲线和断口形貌分析表明,该试验系统能够稳定而准确地在线测量应力腐蚀裂纹扩展速率。     

中碳钢连铸方坯内部角裂机制研究与优化

分别选取西钢某厂实际生产中易发生内部角裂缺陷的40Cr和45钢连铸坯为研究对象,通过对缺陷采用热酸浸低倍试验、金相法和探针能谱分析,发现缺陷处不存在明显的组织异常和质点沉淀。运用ANSYS软件对连铸结晶器凝固过程进行热模拟。研究结果表明,缺陷形成于结晶器内的凝固过程,根本原因是铸坯在结晶器中凝固传热不均导致出现铸坯偏角区热节区效应,从而诱导产生热应力,致使沿柱状晶晶间铁素体开裂,并伴随一定量的铸坯鼓肚现象。通过重新设定结晶器铜管圆角半径和优化生产部分工艺后,最终使连铸坯内部角裂评级在1.0级以上的比例下降到10.42%。     

数字式电脑多频涡流检测仪在电厂中的应用

目的 消除电站热交换管板信号干扰，提高检测信噪比。方法 采用4个独立频率的检测通道，混频处理后干扰信号，结果 在理论分析与实验室大量模拟试验基础上开发出国内第一台数字式电脑多频（四频）涡流检测仪，并在电厂中得到应用。结论 现场使用证明该仪器具有操作方便，检测速度快，抗干扰灵敏度高等特点。     

直流电位法检测高温合金的疲劳裂纹扩展性能

介绍了在高温下使用直流电位法测定疲劳裂纹长度的基本原理、试验方法及所需配置的仪器,并对有关影响因素进行了分析;并利用Johnson的分析型关系式,研究了一种适用于自动测定材料高温疲劳裂纹长度的直流电位法,该方法已成功应用于高温合金疲劳裂纹扩展试验,其测得的疲劳裂纹扩展速率da/dN-ΔK数据与长焦聚显微镜法测得的数据完全一致。     

X射线实时图象法在焊接检验中的应用

作者采用了不同型号高灵敏度的X射线工业电视探伤系统,对大直径钢制压力容器壳体焊缝进行了探伤灵敏度的测试,在对厚为8～20毫米的钢焊件进行测试的结果表明:其探伤灵敏度均小于等于2％。并通过录像和静态照相,可把探伤结果存档。 X射线实时图象法探伤是焊接检验中一种高灵敏度和很有发展前途的方法。     

Disilicide Diffusion Coating Inspection by Micro X-Ray Fluorescence Imaging

Space Shuttle orbiter thrusters fabricated from C-103 niobium alloy rely on a fused chromium disilicide coating as protection from high-temperature oxidation. Coating voids caused by high-temperature spalling, micrometeorite damage, or other impact damage must first be detected, and then characterized to measure the amount of remaining coating materials, since service life is directly proportional to coating thickness. Existing techniques to estimate the thickness of this diffusion layer are labor intensive, prone to error, and require contact with the coating. Alternative non-contact methods are sought that can automate the detection and characterization of coating defects.Micro X-ray fluorescence (MXRF) imaging is evaluated in this study as a potential NDE method to inspect the chromium disilicide coating. MXRF imaging, a relatively new technique to map the elemental composition of a surface, creates a high spatial resolution multispectral image that can be analyzed to detect coating voids and to quantify the remaining coating materials diffused in the alloy. Analysis of image data collected from sectioned thruster samples confirms that MXRF imaging is a viable detection and characterization method for the thruster coating inspection problem.     

基于Zynq的实时视频图像角点检测系统

针对机器视觉测量应用中,待测关键点的自动识别与定位中的角点信息提取问题,以ZYNQ系列可拓展平台内部ARM+FPGA的异构架构为基础,采用软硬件协同设计方法,搭建了一套可进行实时视频图像角点检测的系统。利用Vivado HLS工具,将角点检测算法封装成可以部署到PL端的IP核,极大地缩短了开发周期;对系统中各个模块进行了合理的任务分配,使得系统拥有ARM的灵活性以及FPGA的并行处理能力,展现了并行异构架构的优势。该系统中图像算法IP核可以进行灵活的算法替换和更新,为基于机器视觉检测的小型化应用提供了重要参考。