5083铝合金大规格扁锭熔铸工艺研究

分析了5083铝合金440 mm×1 500 mm规格扁锭的熔铸工艺特点,试验了不同铸造工艺参数对铸造性能的影响。重点分析了铸锭裂纹倾向及预防措施。     

高压汽轮机汽缸调门座裂纹的挖补处理

崇明电力公司16号汽轮机调门座发生裂纹后，通过对该阀门座合金钢材料焊接性、再热裂纹敏感性的理论分析，为现场焊补工艺提供了预热湿度和焊后热处理的工艺依据。论文叙述了在现场施焊工艺中选择了与母材化学成分基本相同的超低氢电焊条和其它严格的焊接的工艺措施，确保了优质焊接质量。实践证明，采用此种焊接工艺方法是现实和可行的。     

Weep hole inspection by circumferential creeping waves

This paper reports the development of a novel ultrasonic inspection technique that detects radial fatigue cracks on the far side of thin airframe stiffener ‘weep’ holes. These cracks are located on the upper part of the weep hole (12 o'clock position), away from the lower skin of the wing. Cracks in this position are not readily detectable by conventional ultrasonic inspection techniques, particularly for short cracks. A special technique using circumferential creeping waves was adapted to inspect for these cracks. The conventional creeping wave technique experiences a strong specular reflection from the near surface of the hole that masks the creeping wave signal that arrives later in time. In order to overcome this difficulty, a split-aperture (two-element) transducer was used that resulted in the specular and creeping wave echoes being approximately equal in magnitude. The two separate transducers allowed us to alternate between pulse-echo and pitch-catch modes of operation with a resulting improvement in detection sensitivity. In the case of 0.25-inch-diameter weep holes, optimum sensitivity was calculated to be around 5 MHz. The detection threshold was found to be approximately 0.003 inches and the signal saturated at crack lengths in excess of 0.020 inches. The original paint and surface finish had no substantial adverse effects on the technique's sensitivity. Similarly, changing the weep hole diameter or chamfer conditions did not significantly affect the technique's performance. These results were obtained using specimens with both machined notches and real fatigue cracks.     

某混凝土重力坝裂缝分类及 产生原因综述

某水利枢纽工程碾压混凝土重力坝大坝混凝土在施工期产生一些裂缝,本文对混凝土裂缝进 行了分类,并对裂缝产生的原因进行了初步分析,供其他类似工程借鉴。     

基于改进对比学习的道路裂缝图像分类

道路裂缝是路面破损的重要组成部分,而道路裂缝分类可以对道路养护策略的制定进行针对性的安排.针对人工标注分类耗时长,效率低等问题,本文提出了一个基于对比学习的道路裂缝图像分类方法,在传统的对比学习框架中,对特征提取部分进行改进,使得模型对细小裂缝的特征更敏感.首先对进行数据增强,其次在特征提取部分对ResNet50的部分进行改进,使用多尺度的方法提取特征;再使用多层感知机(MLP)对提取到的特征进行降维处理,并投影到向量空间;最后使用余弦相似度与用归一化温度标度的交叉熵损失对模型进行优化.实验结果表明,改进后的模型比原模型在裂缝图像上的分类效果提高了0.22%,达到了92.1%,对裂缝图像分类有较好的效果.     

Isogeometric analysis of fluid‐saturated porous media including flow in the cracks

An isogeometric model is developed for the analysis of fluid transport in pre‐existing faults or cracks that are embedded in a fluid‐saturated deformable porous medium. Flow of the interstitial fluid in the porous medium and fluid transport in the discontinuities are accounted for and are coupled. The modelling of a fluid‐saturated porous medium in general requires the interpolation of the displacements of the solid to be one order higher than that of the pressure of the interstitial fluid. Using order elevation and Bézier projection, a consistent procedure has been developed to accomplish this in an isogeometric framework. Particular attention has also been given to the spatial integration along the isogeometric interface element in order to suppress traction oscillations that can arise for certain integration rules when a relatively high dummy stiffness is used in a poromechanical model. © 2016 The Authors. International Journal for Numerical Methods in Engineering Published by John Wiley & Sons Ltd.     

基于阵列涡流技术的裂纹特征量研究

阵列涡流传感器能够实现导电材料的大面积高速扫描。不同走向的裂纹对线圈间互感的影响是不同的,因此,测量线圈间的互感能够获得更多的缺陷信息。利用ANSYS软件对横向和纵向裂纹进行了三维有限元仿真,得到了相应的阵列涡流敏感线圈感应电动势幅值变化曲线。仿真结果表明:通过测量线圈间的互感,可以实现对裂纹长度和方向等特征量的检测。     

A Neural Network Approach to the Frictionless Grasping Problem

This article presents a heuristic technique used for solving linear complementarity problems(LCP). Determination of minimum forces needed to firmly grasp an object by a multifingered robot gripper for different external force and finger positions is our proposed application. The contact type is assumed to be frictionless. The interaction in the gripper–object system is formulated as an LCP. A numerical algorithm (Lemke) is used to solve the problem [3]. Lemke is a direct deterministic method that finds exact solutions under some constraints. Our proposed neural network technique finds almost exact solutions in solvable positions, and very good solutions for positions that Lemke fails to find solutions. A new adaptive technique is used for training the neural network and it is compared with the standard technique. Mathematical analysis for the convergence of the proposed technique is presented.     

Defect identification and sizing by the ultrasonic satellite-pulse technique

Shape and size are the most important defect characteristics that need to be determined for the reliable prediction of the remaining service lifetime of a defective structure or part. The analytical and supporting experimental results presented in this paper concern a general, pattern recognition-based, ultrasonic defect identification and sizing method. The satellite-pulse technique (SPT) is based on the interpretation, in terms of defect types (shapes) and dimensions, of the separation in time of arrival between the readily detected specularly reflected pulse and its generally ignored tip-diffracted or tangentially scattered satellite contained in the received waveform. Calibration procedures were also developed that enable the ultrasonic examiner to read the time scale of the oscilloscope for equivalent crack depth or void diameter as appropriate.     

Fatigue lifetime prediction with the aid of SAW NDE

The present studies concentrated on predicting the remaining fatigue life for single fatigue cracks in the Paris regime of macrocrack propagation. Acoustic surface waves were used to interrogate the crack during cyclic fatigue. The inversion of the obtained scattering data provided crack depth and crack length as a function of the number of cycles applied in tension-tension fatigue. Auxiliary experiments were conducted to study the acoustic response of the crack to tensile and compressive loads, thought to open and close the crack. The technique may allow for new insights into the physics of the crack closure effect.