Crack closure and stress intensity factor measurements in nodular graphite cast iron using three-dimensional correlation of laboratory X-ray microtomography images

Three-dimensional (3-D) tomographic images of a nodular graphite cast iron obtained using a laboratory X-ray source were used to analyze the opening of a fatigue crack during in situ mechanical loading. Direct image analysis and digital image correlation are utilized to obtain the 3-D morphology and front location of the crack, as well as the displacement fields in the bulk of the specimen. From digital image correlation results it is possible to extract the crack opening displacement (COD) map in the whole sample cross-section and to compute stress intensity factors (SIFs) all along the crack front, even for COD values that are less than the image resolution. The comparison of COD maps with local values of the SIF enabled for an estimation of the opening SIF (K_op) equal to 6 MPa m^1/2.     

远距离采集图像损伤区域三维重建仿真研究

远距离采集图像的损伤区域形状基属性形变和噪音难以消除,三维重建难度大,传统重建方法不能有效修复损伤区域.提出基于体像素插值的图像损伤区域三维重建方法,在远距离图像采集中形变不规则的前提下,利用产生奇异点的规律进行奇异点插值补偿,提取到图像仿真投射映像属性点的非齐次矩阵后,利用体像素补偿损伤区域奇异点,并通过边缘冲突原理进一步消除奇异点,获取到更加真实的远距离采集三维重建图像.实验结果证明:所提方法增强了远距离采集图像损伤区域三维重建的信息量.     

红透山铜矿外围隐伏矿体三维定量预测

介绍红透山铜矿外围隐伏矿体三维定量预测的技术组合和方法体系。首先,借助三维可视化仿真环境,实现红透山铜矿的地表面、矿体、断层、地层实体模型的三维可视化。其次,将成矿信息场、地层形态场、断裂影响场、地球物理场等多元地学空间数据在统一的三维空间数据场构架下有效集成,实现了三维空间信息的综合研究和地学多专业的有机结合。其次,基于三维地质空间相关场分析,为三维定量预测提取定量指标集和建立预测模型。最后,使用三维定量预测模型对红透山矿外围的矿化位置与分布规律进行预测和评价,圈定找矿靶区。三维地质建模与可视化及三维地质空间相关场等技术的使用,为进行红透山矿外围隐伏矿体在三维空间中的分布及形态的定量预测提供支撑。     

基于改进三帧差分法的3D打印机轨迹检测方法

针对获取运动轨迹不清晰以及轨迹不能很好地被检测的问题,提出一种基于三帧差分法的3D打印机轨迹检测改进算法。采用USB摄像头采集图像,然后用改进三帧差分方法和高斯混合模型进行轨迹的粗略判断,并使用Qt框架实现对目标中心即3D打印机喷头的运动轨迹检测和速度计算。结果表明:该算法能够完整地获取3D打印机喷头轨迹,能较大程度地减少图像处理的计算量。     

Imaging defects with reduced space inversion of magnetic flux leakage fields

Magnetic flux leakage technique is being used for detection of defects inside a magnetically permeable bar by measuring the leakage fields outside the bar. Defects in magnetically permeable bar have been modeled as localized anti-dipoles whose moments and locations have to be determined. Generalized inverse or pseudo-inverse technique has been used to image the defects using least-square minimum-norm solution. An initial estimate of the defects is obtained by utilizing the generalized inverse of the lead matrix over the entire region of the sample space using the measured magnetic field data including random noise. By defining a suitable threshold, and ignoring the defect locations where the moment inferred in the initial estimate was below the chosen threshold, the image of the defect is again obtained by repeating the calculation in this reduced space for the lead matrix. The leakage fields from both a line defect and a deeply buried defect were simulated and utilized for inversion using this approach. It has been possible to image the defects and quantify the strengths of the moments with the correlation coefficient approaching unity for low-noise case and attain significant improvement in the correlation coefficient for data with reasonable levels of noise.     

Product analysis automation for digital MRO based on intelligent 3D data acquisition

3D data acquisition technologies are increasingly used in the area of maintenance, repair and overhaul (MRO) of long-life technical systems and industrial plants. Application fields are measuring, reengineering and reproduction of disassembled parts. Fraunhofer IPK is developing a reverse engineering process for provision of 3D product models based on 3D scans of complete assemblies to save disassembly time and to support change management and reengineering tasks. This paper depicts results of IPK's data processing approaches for automated separation and identification of single parts in 3D assembly scans as well as for mapping of assembly structures in product data management systems.     

应用于反向工程的一种3D测量算法

在反向工程中，由实体获得3D测量数据是关键的一步，不同与激光点扫描及移相等方法，本文要讨论的是一种基于图像识别和立体视觉3D测量设备的算法，比较与其他方法，这种方法的精度有很大的改善，适用范围也十分广泛。本文说明了系统各参数的校正方法，说明了算法中光栅投影模块的逻辑序列问题，及相应的计算机识别过程，打到了影响投影图像数量的原因所在。并在此基础上对识别后的拟合曲线进行3D数据的计算讨论，解决了取样及数值计算的算法问题。并用完整的实例进行了阐明。     

Explicit geometric model of a radioscopic imaging system

In this paper a new explicit model of a radioscopic imaging system is presented. The model includes three parts: X-ray projection, image intensifier and CCD camera. The X-ray projection is modelled as a linear central projection. The image intensifier is modelled using a new explicit model that considers the curved input screen and the non-linear projection caused by electromagnetic fields. The CCD camera is modelled according to a general 2D projective transformation of the output screen of the image intensifier. Thus, the back-projection, required for 3D reconstruction, can be expressed in a closed-form. The model is compared to seven other known models. The presented model achieves high accuracy.     

Mechanistic force modeling of single point cutting tool in terms of grinding angles

The cutting tool angles have conventionally been presented using projective geometry in terms of the projections of cutting edges on respective planes, which makes the visualization of geometry difficult, particularly for complex tools. Modeling a cutting tool using the actual grinding angles can simplify the geometric definition of the tools and provide a comprehensive and simple definition of tools for downstream applications. The paper presents the 3D definition of the faces of a single point cutting tool (SPCT) in terms of 3D rotational grinding angles and maps the new tool nomenclature with the ASA, ORS and NRS nomenclatures. A mechanistic model is subsequently proposed to predict the forces in terms of the grinding angles, chip thickness and velocity using second degree polynomial function, unlike the conventionally used logarithmic ones. The model has been calibrated for HSS tool and Mild Steel workpiece combination for end turning of a tubular workpiece based on the regression analysis of a central composite design of the experiments. The results have been discussed and the model has been validated for a new set of experimental data. The model shows a good correlation to the observed results.     

基于3D打印与三维图像处理的服装信息提取方法研究

在形状基不定情况下,对三维服装信息提取过程存在特征关联较弱,分割区域扩大等问题.为此,提出一种基于3D打印与三维图像处理的服装信息提取方法.首先对采集的服装三维图像进行纹理特征分割,图像序列自适应块匹配方法进行信息增强处理,然后采用桌面型3D打印技术进行服装设计中的图像三维重构,进行服装三维图像表面渲染,实现服装信息提取.最后通过仿真实验进行性能测试,结果表明:采用该方法进行服装信息提取,能准确反映服装的纹理信息和三维渲染信息,服装设计的色彩均衡性较好,有效指导服装设计优化.     

Digital image correlation-based analysis of strain accumulation on a duplex γ-TiAl

This paper discusses the experimental results obtained for a duplex γ-TiAl alloy deformed at room temperature. High resolution digital image correlation was used to measure local strain fields. The characterization of the microstructure was performed using optical microscopy and a precise correlation between the strain fields and the microstructure was found. High local strains were measured along well-oriented lamellar grains, in particular for the γ-phase. Furthermore, the analysis of the two-dimensional strain tensor shows that the largest strain component is the shear strain in the plane of the lamellar grains. This study aims to provide further understanding of the deformation behavior of γ-TiAl alloys.     

Nanoscale femtosecond spectroscopy for material science and nanotechnology

The design and implementation of a novel facility to perform ultrafast spectroscopy and three-dimensional (3D) fabrication at the nanoscale is reported. Single and multiphoton femtosecond excitation coupled to a laser scanning confocal microscope and a photon counting streak camera system allows to perform photoluminescence (PL) spectroscopy with in-plane spatial resolution of the order of 100 nm and temporal resolution of ∼2 ps. The facility combines high performance imaging capabilities in 3D with high sensitivity detection system and time-resolution of the photoluminescence. Imaging and spectroscopy are performed on the same spatial position thus allowing a direct correlation of the morphological features with the spectroscopic properties. The use of a laser scanning confocal microscope gives the advantages of far-field microscopy (possible sample perturbation as in the case of near-field technique is prevented) with spatial resolution well below the diffraction limit, and fast laser scanning for fast data acquisition and lower sample photodegradation. A possible application of this optical nano-probe is in the spectroscopic investigation and imaging of the active areas of molecular electronic and optoelectronic devices, such as TFTs, LEDs and PVs cells. The morphology of active layers within working devices can be correlated to field distributions, charge flows, charge recombination and light emission. We show the potential of this novel experimental set-up for the study of organic, hybrid, biological nanostructures and nanodevices.     

Nondestructive evaluation of transparent sheets using a full-field digital gradient sensor

A full-field, non-contact, optical inspection tool for transparent materials is demonstrated. The technique is sensitive to refractive index and thickness variations caused by inhomogeneities and defects in an otherwise uniform sheet stock. The technique utilizes a 2D digital image correlation method to visualize and quantify angular deflections of light rays in two orthogonal directions to assess the uniformity. The principle of the method and its feasibility is demonstrated by visualizing the heat affected zone in a uniform borosilicate sheet sample.     

Polycrystalline diamond cutting element control using high frequency C-scan image processing

The quality control of drilling tools used in the oil industry essentially consists of testing the cutting elements distributed around the petroleum tool. This study presents a nondestructive testing (NDT) method for the detection of different kinds of defects inside polycrystalline diamond cuttine elements (PDC). This ultrasonic method, based on high frequency (100 MHz) C-scan image processing, allows the detection of three major types of defect such as diamond layer debonding from the substrate, cracks and thermal defects of the diamond layers. These defects induce a perfectly quantified behaviour to mechanical abrasion resistance and fatigue tests. Experimental results show good correlation between our ultrasonic measurements and classical abrasion resistance tests. In fact, a PDC sample exhibiting defects detected by the C-scan technique has been submitted to a mechanical fatigue process and optical microscopic analysis. These tests have shown that each kind of defect has an influence on one or more mechanical characteristics. Using C-mode scanning acoustic microscopy (with a 50 μm pixel size), allows an extremely precise and quantified level of erosion resistance of the cutting elements without systematic resort to expensive destructive tests carried out during the reception of the batch. The rejection of samples showing harmful defects will eliminate the erratic and sometimes unexplained destruction of some tools which were considered to be defect-free.     

基于CUDA的GPU加速代数迭代重建算法

CT迭代重建算法多用于投影数据不完备的情况,但迭代重建算法在普通计算机上的计算非常耗时,主要源于需要反复地进行投影与反投影计算。为此,文章提出了一种基于NVIDIA统一计算设备架构(CUDA)的联合代数重建加速方法。采用基于射线驱动和基于体素驱动的方法分别加速投影与反投影过程。试验结果显示,在不影响重建图像质量的基础上,重建时间大大减少,具有工程应用价值。     

Modal parameter recovery from temporally aliased video recordings of cutting tools

Vision-based modal analysis methods are non-contact, do not require data acquisition systems, and facilitate full-field shape analysis. Leveraging these advantages for industrial use is precluded by the need for expensive high-speed cameras. This paper presents new methods to recover modal parameters from potentially temporally aliased video recordings of cutting tools using economical medium-speed cameras. Folding properties of fractionally uncorrelated aliased signals are used together with the eigensystem realization algorithm to recover modal parameters from tool motion extracted using image processing schemes. Results agree with those from accelerations sampled properly. Methods are generalized for use with other sensors.     

Fast X-ray tomography and acoustic emission study of damage in metals during continuous tensile tests

Model AA-2124 matrix composites with two different reinforcement sizes were pulled with a strain rate of 10⁻⁵ using a dedicated tensile rig suitable for in situ tomography. Two main novelty aspects characterize the present study. First, tomography provides a new approach towards understanding the significance of AE signals, recorded simultaneously, during image acquisition on the same sample. The number of acoustic emission events is found to be in good agreement with the number of cracks as detected by image analysis and the energy of the signals is proportional to the dimension of the cracks. Secondly, fast tomography was used to perform the first continuous in situ tensile test. The continuous procedure is compared in the paper with the standard step by step procedure.     

基于GRNN的珩磨缸套表面3D粗糙度图像检测方法

活塞-缸套系统是内燃机重要的摩擦副之一，活塞-缸套的表面质量影响着活塞-缸套系统的摩擦学性能，进而直接影响整机的服役性能。针对珩磨缸套表面 2D 粗糙度参数的局限性与表面粗糙度非接触检测方法研究，提出一种基于广义回归神经网络(GRNN)的珩磨缸套表面 3D 粗糙度图像检测方法。通过运用灰度共生矩阵(GLCM)提取缸套表面图像的纹理特征参数，并分析纹理特征参数与 3D 粗糙度间的相关性。以图像纹理特征参数作为输入，分别采用 GRNN 和多元回归分析 (MRA)建立 3D 粗糙度检测模型，通过与试验检测结果对比验证了模型的准确性。GRNN 检测模型获得的可决系数 R2均值 (0.962)优于 MRA 检测模型，且均方误差 MSE 均值(0.07)更小，与试验检测结果对比可知，采用 GRNN 建立的珩磨缸套 3D 粗糙度检测模型具有更高的精度，与实测 3D 粗糙度的相对误差均值为 7.9%。所建立的 3D 粗糙度检测模型具有较高的检测精度。     

3D打印金刚石工具的研究进展

3D打印技术作为一种快速成形技术,为复杂结构金刚石工具的制备提供了便利,是未来金刚石工具一体化成形发展的方向之一.本文介绍了用于制备金刚石工具的SLS、SLM、SLA、DIW等3D打印技术的基本原理及其在金刚石工具制备方面的研究进展,分析了使用不同结合剂时3D打印金刚石工具的特点,并对未来金刚石工具的发展进行了展望.     

基于三维测量和混合建模的刀具三维磨损形态研究

刀具磨损部位的三维形态是研究刀具几何参数合理性、分析刀具磨损原因的重要依据。采用三维光学扫描测量技术获取磨损刀具的三维点云数据,利用实体模型与点模型混合处理技术获得刀具磨损区域的三维形态,基于3D模型和点云数据的对比获得磨损前后刀具变化色谱分析图以及偏差分析报告。给出车削硬质合金刀片的三维磨损形态分析步骤,验证方法的可行性和有效性。