交变漏磁检测中螺纹不同缺陷位置的识别方法研究

依据缺陷在螺纹区域的不同位置，将缺陷分为三类，分析了每类缺陷检测信号的特点，提出了识别判据，最后通过对膨胀螺钉上的该三类缺陷的检测，验证了识别模型的正确性。另外，对六角头螺栓结构根部缺陷的检测进行了试验研究，利用测量信号完成了缺陷的检测。     

横波检测粘接界面层多孔隙缺陷的数值分析

建立了粘接界面层多孔隙缺陷微观结构的界面数理模型，推导了横波（SH波）在“三明治”结构传播的频散方程，对最低模式的SH波在带有多孔隙缺陷界面的双层板粘接结构的传播特性进行数值计算分析。结果表明，粘接界面层的厚度及其孔隙缺陷尺寸对导波的频散曲线有明显的影响，这可为粘接界面无损检测提供了新的方法和思路。     

抽油管在线定量探伤系统的研究

开发了抽油管在线定量探伤系统；对油管缺陷定量识别技术进行了分析并提出了量化分析模型；介绍了系统的硬件结构；采用模块化结构进行软件设计并给出了结构模型。实践表明，该系统能满足一定精度的油管缺陷量化识别要求，在采油行业中有广泛的应用前景。     

基于ShuffleNetv2-plus-YOLOX算法的压铸件缺陷检测

针对压铸件缺陷检测的数据集难以收集、检测效率较低以及工作环境较差等问题,开发了基于YOLOX模型的压铸件缺陷检测软件。用自开发软件的数据增强模块对原始数据集进行增强,解决了压铸件缺陷数据集不充裕的问题;随后将YOLOX算法的Darknet53结构替换为ShuffleNetv2-plus结构,使得利用YOLOX模型检测压铸件缺陷的平均检测精度由原模型的86.51%提升至89.19%,提升了YOLOX模型识别压铸件缺陷的准确率。     

线切割直角拖动锥度结构的变锥度控制

分析了摆动杠杆式锥度结构的特点，列举了现有锥度控制方法的缺陷，提出了变锥度切割的方法，阐述了变锥度控制法的特点以及控制模型。     

基于分子动力学模拟的TiAl涂层的阻尼性能研究

利用Materials Studio软件建立了具有位错缺陷的单晶TiAl涂层模型。采用LAMMPS分子动力学软件在700、800、900 K下对含有位错缺陷的单晶TiAl涂层进行模拟,得到各温度下模型的应力-应变曲线及模型的微观结构变化。通过模型的应力-应变曲线分析了各温度下模型的阻尼性能。由微观结构变化,进一步探讨了温度对含有位错缺陷涂层阻尼性能的影响。结果表明,800 K下TiAl涂层的阻尼性能最好。     

基于图嵌图卷积神经网络的复合材料缺陷定位

针对复合材料层合板结构缺陷的快速检测定位，提出了一种基于超声导波的复合材料缺陷检测图嵌图卷积神经网络模型(G-GCN)。G-GCN通过构建导波信号相互关系的时空特征高级表征图，由局部-全局变换构建局部图，以表征单个导波信号内的相互关系信息；再基于局部图构建全局图，表征多个导波信号之间的相互关系信息；然后利用全局图输入图卷积神经网络模型训练学习，输出相应的复合材料缺陷预测，实现极少量传感器条件下的快速精准缺陷检测与定位。最后搭建了超声导波复合材料检测试验平台，验证了G-GCN的先进性和可靠性。     

多孔SiC陶瓷增强金属基复合材料的制备

采用纸质材料制成三维管状模型，经过纸质模型碳化、反应性渗硅处理获得多孔SiC陶瓷预制体，选择铸造性能好、成形缺陷小的铸铁作为金属基体，采用铸渗法制备了SiC陶瓷增强金属基复合材料，通过XRD，SEM等分析手段研究了多孔SiC陶瓷和复合材料的显微组织和界面结构。研究表明，纸质模型800℃温度碳化，反应性渗硅温度1600℃时制备的多孔SiC陶瓷预制体三维结构稳定，烧结后变形小，微观组织结合紧密；通过铸渗法制备的SiC陶瓷增强金属基复合材料界面结合良好，无明显缺陷。该方法中增强相结构可设计性好，铸渗法制备多孔陶瓷金属基复合材料质量高，为多孔陶瓷增强金属基复合材料的获得提供了试验新方法。     

基于MATLAB的铸件缺陷分析与控制

通过对铸件缺陷与影响因素间因果关系的分析 ,利用MATLAB中的NeuralNetworkToolbox仿真环境和BP模型算法建立了用于铸件缺陷分析与控制的神经网络模型 ,详细论述了模型结构的设计、数据处理、网络初始化、训练与仿真的过程。实践表明 ,基于MATLAB的铸件缺陷分析与控制模型能有效地提高效率及直观地结果显示 ,对提高铸件质量及进一步研究具有积极作用。     

基于ADAM主动衰减退火算法的钢材缺陷检测北大核心

在工业钢材缺陷检测任务中,通过引入残差结构对传统的VGG网络模型进行了改进。通过结合特征金字塔池结构,实现了多层次的图像信息表达。基于此神经网络结构,对神经网络优化方法进行了研究。采用Adam优化方法的基础上,提出了主动衰减退火算法,实验结果表明引入残差结构并结合特征金字塔池结构的网络模型更优,主动衰减退火算法与Adam等方法相比具有一定的优越性。在钢材缺陷测试集缺陷图像分类平均精度达到了97.3%的精度,对实际工业应用有一定的意义。     

Transient regimes during high-temperature deformation of a bulk metallic glass: A free volume approach

The homogeneous deformation of a zirconium-based bulk metallic glass is investigated in the glass transition range. Compression and stress-relaxation tests have been conducted. The stress–strain curves are modeled in the framework of the free volume theory, including transient phenomena (overshoot and undershoot). This approach allows several physical parameters (activation volume, flow defect creation and relaxation coefficient) to be determined from a mechanical experiment. This model is able to rationalize the dependency of stress overshoot on relaxation time. It is shown that, due to the relationship between flow defect concentration and free volume model, it is impossible to determine the equilibrium flow defect concentration. However, the relative variation of flow defect is always the same, and all the model parameters depend on the equilibrium flow defect concentration. The methodology presented in this paper should, in the future, allow the consistency of the free volume model to be assessed.     

铈掺杂对钴草酸盐结构和形貌的影响

用化学方法使体均匀掺入草酸钴中。测量了试样的FSSS粒度。用X－ray衍射仪、SEM等分析了样品的结构和形貌。结果表明：铈掺杂使草酸钴的粒度增加；流动性变好；较大的Ce掺杂量使钴草酸盐的结构由α－晶型转变为β－晶型。     

铝材冷轧润滑剂成分分析

通过对铝材冷轧润滑剂典型产品的剖析得到基础油和添加剂的组成、类和分子结构特征、并提出了铝材轧制油配方设计原则。同时还介绍了常用的润滑剂成分分析方法。上述研究有利于我国铝材轧制油技术进步与产品创新。     

风机齿轮箱轴承应力及疲劳寿命分析北大核心

针对风机齿轮箱轴承在运转中出现的外圈局部剥落缺陷及其造成的疲劳寿命问题,以5 MW风机齿轮箱输出轴轴承为研究对象,建立无缺陷轴承和不同宽度尺寸局部剥落缺陷轴承的数值模型。对模型进行显式动力学分析,分析转速及缺陷尺寸扩展对轴承各部件的应力变化;以名义应力法和损伤理论为准则,对无缺陷轴承和有缺陷轴承进行疲劳分析,得出轴承的损伤和疲劳寿命。结果表明:随着局部剥落缺陷的扩展和转速的增大,这两轴承各部件应力均上升,但寿命均下降。     

The effect of platinum on Al diffusion kinetics in β-NiAl: Implications for thermal barrier coating lifetime

First-principles density functional theory calculations are used to study Al diffusion in β-NiAl. The activation energy and diffusion constant pre-exponential factors are calculated for five previously postulated Al diffusion mechanisms: next-nearest-neighbor Al jumps, the triple defect mechanism and three variants of the six-jump cycle mechanism beginning with an Al vacancy. We predict that the triple defect mechanism has the lowest activation energy and is the mechanism by which Al diffusion occurs in NiAl. In order to elucidate why Pt has a beneficial effect on thermal barrier coating lifetime, the effect of Pt on each of these mechanisms is also examined. In all cases, Pt decreases the diffusion activation energy, which should enhance Al diffusion in the coatings.     

X-ray modeling for industrial applications

A computer package for the simulation of the X-ray imaging process in nondestructive evaluation (NDE) is presented. The components of the radiographic inspection system are considered independently, i.e. the characteristics of the source, the geometry and the material properties of objects and defects, as well as the imaging process itself. The model is based on a ray tracer technique describing the attenuation of the radiation. The scattering effect is included in terms of built-up factors. A CAD-interface provides the opportunity to arrange independent CAD objects, e.g. the component geometry or defect shapes, defining a testing scheme. Complicated defect shapes are created by a preprocessor, the built-up factors can be received from experiments or from a separate model using an efficient solution of the scattering problem based on the theory of Markovian processes with random structure.     

NUMERICAL SIMULATION OF ULTRASONIC NONDESTRUCTIVE TESTING FOR WELDS

A computer simulation technique for ultrasonic propagation is utilized for the simulation of ultrasonic nondestructive testing (NDT).In this paper,one goal of the simulation is to compute ultrasonic field radiated by arbitrary transducers into pieces under examination.The other simulates a testing experiment.The simulation approach is based on the model for the computation of the ultrasonic field in isotropic media radiated from actual NDT transducers.After the field is known, remaining to be modeled is the interaction between this field and the scatters (defect) and the echo structure. The model of beam-defect interaction is based on the Kirchhoff‘s diffraction approximations theory applied to elastodynamics.We assumed that the incident wave fronts on the defect are plane in the case of a focused immersed transducer and material is isotropic and homogeneous.The simulating results demonstrate that the model in ultrasonic NDT of welds is practical in further research and useful in optimizing testing configurations.     

The effect of platinum on defect formation energies in β-NiAl

First-principles density functional theory is used to examine the effect of Pt on point defects and defect clusters in NiAl. It is found that Pt promotes the formation of Ni and Al vacancies and Ni and Al antisite atoms. Defect clusters that are minima in postulated Ni diffusion mechanisms in NiAl are also found to be stabilized by the presence of Pt. By decreasing defect formation energies, Pt may decrease the overall activation barrier to the diffusion of Ni and Al in NiAl. The results provide clues as to how Pt enhances thermal barrier coating lifetime.     

The native point defects in C14 Mg2Ca Laves phase: A first-principles study

The native point defects in C14 Mg₂Ca Laves phase are studied from the first-principles density functional theory calculations within GGA approximation. The defect formation energies indicate that anti-site defects are energetically favored over vacancies. Under Mg-rich and even general Ca-rich condition, defect Mg_Ca of Mg anti-site on Ca sublattice is favorable owing to the lowest formation energy. The Ca_Mg2 defect of Ca anti-site on Mg2 sublattice is also likely dominant only under extreme Ca-rich environment. The present results could explain reasonably the asymmetric off-stoichiometry of Mg₂Ca. The effective point defect concentrations of Mg₂Ca as a function of composition and temperature at experimental range are also calculated from a canonical statistical model, and the derived results show a linear relationship between the logarithm of defect concentration and T⁻¹. Geometrical factor is further studied, and it is found that atomic size possesses an obvious influence on the structure of point defect in Mg₂Ca. The electronic feature is further studied to reveal underlying mechanism for formation of point defects.     

面状缺陷超声检测图像的正演合成

为了辅助焊接缺陷超声检测的逆问题分析，通过建立仿真模型，对面状缺陷的超声检测信号进行仿真预测并对检测图像进行正演合成. 首先采用多高斯声束理论对声波在楔块、界面及被检测试件中的传播过程进行描述；其次采用Kirchhoff近似理论描述声场和面状缺陷的作用结果，制作了底面开口槽作为面状人工缺陷，并进行超声检测. 同时对人工缺陷超声检测的一维信号进行仿真预测，并正演合成二维图像. 将实际检测结果和模拟仿真结果进行比较，验证仿真模型对检测结果预测的有效性. 结果表明，正演合成图像和实际检测图像具有很好的一致性，所建立的仿真模型可辅助焊接缺陷超声检测逆问题分析.