Electromagnetic and elastic wave scattering and inverse scattering applied to concrete

Electromagnetic and elastodynamic scattering and inverse scattering techniques are combined to provide a better understanding of wave propagation and obstacle imaging in concrete. In particular we propose an electromagnetic inversion algorithm for ground probing radar data to include information about the dipole moment of the antenna; a new elastodynamic inversion scheme is even capable of processing the complete pressure and shear wave information as contained in the components of the displacement vector simultaneously, where we compute the necessary synthetic data with the numerical EFIT code (Elastodynamic Finite Integration Technique) as extended to statistically inhomogeneous media in order to validate the inversion algorithm.     

弹性联轴器失效分析

针对某矿山通风机弹性联轴器在生产中频繁出现柱销轴断裂现象 ,分析了断裂原因 ,并提出了解决措施     

输电铁塔用6.8级螺栓断裂失效分析

输电铁塔用6.8级螺栓,在使用过程中发生断裂,通过断裂螺栓的断13形貌、化学成分、显微组织及硬度的分析测试,进行了螺栓的断裂失效分析.研究结果表明,螺栓断裂形式为穿晶脆性断裂;原材料化学成分及组织正常,显微硬度基本符合国标要求;螺栓头部硬度严重超标,组织变形剧烈,是螺栓发牛脆性断裂的主要原因.在冷镦成型后进行去应力退火工艺并严格控制冷镦工艺,适时检验螺栓头部硬度及组织状况使其满足标准要求,可避免螺栓在使用过程中的脆性断裂.     

Mathematical analysis of the role of recoil pressure in weld pool dynamics during laser-MIG hybrid welding

A mathematical model was established to simulate the weld pool development and dynamic process in stationary laser-MIG hybrid welding. Surface tension and buoyancy were considered to calculate liquid metal flow patter, moreover, typical phenomena of MIG welding, such as filler droplets impinging weld pool, electromagnetic force in the weld pool, and typical phenomena of laser beam welding, such as recoil pressure, Inverse Bremsstrahlung absorption, Fresnel absorption were all considered in the model. The laser beam and arc couple effect were introduced into this model by the plasma width during hybrid welding. The role of recoil pressure in the weld formation was discussed. Transient weld pool shape and complicated liquid metal velocity distribution from two kinds weld pool to an unified weld pool were calculated. The simulated weld bead geometry with consideration recoil pressure was in good agreement with experimental measurement.     

变速器中间轴断齿失效分析

对变速器中间轴的断口形貌、化学成分、硬度、显微组织、非金属夹杂等进行了分析。结果表明,断口处有大量非金属夹杂、夹渣及孔洞,破坏了材料的连续性,导致应力集中,在外力作用下形成疲劳源,造成中间轴在试验中断裂。     

An elastic analysis of growth stresses during oxidation

A quantitative analysis of oxide growth stresses is carried out for the model advanced by Rhines and Wolf in which new oxide forms along preexisting oxide grain boundaries. The mean oxide stress developed within the oxide is calculated using standard techniques from continuum dislocation theory. This analysis shows that the mean growth stress is compressive and is directed parallel to the oxide/ matrix interface. The growth stress is found to be independent of the oxide scale thickness, provided that the scale is thicker than the oxide grain size. However, in thin scales, the growth stress is very sensitive to oxide scale thickness. The compressive growth stress increases in direct proportion to the width of the new grain boundary oxide layer formed. The oxide scale is expected to either fail by buckling, or the growth mode will change to one in which additional compressive stresses are not generated.     

具有弹性连接的组合机身压力机振动分析

针对组合机身压力机的结构特点 ,采用自由界面模态综合法进行振动分析 ,为使计算模型符合由拉紧螺栓实现各组合部件间弹性连接的实际结构 ,形成了弹性连接刚度阵 ,并对相关结构的刚度阵进行了修正 ,用该模型对一新型双击式螺旋压力机进行了计算 ,计算得到的固有频率与实测值相符。     

大型多支承变截面回转窑支承系统力学行为分析

回转窑是冶金、化工、建材等行业生产中的关键设备 ,是一种重载、大扭矩、多支点、静不定运行系统。本文针对回转窑载荷和刚度分布复杂、各支承存在偏移的特点 ,建立一种支承载荷求解的力学模型。根据模型从变形方程出发 ,导出支承载荷求解的线性方程组。用该方法对中国长城铝业公司的 2 #回转窑进行计算分析 ,得出该窑支承载荷分配与支承偏差的线性公式 ,其结论为回转窑的调整提供了依据。     

SP-160伺服压力机传动系统设计分析

根据市场需求设计伺服压力机的传动系统,利用SolidWorks软件进行压力机传动系统三维建模,并进行强度和刚度分析,校核各主要零部件是否满足设计要求。     

On the study of elastic wave scattering and Rayleigh wave velocity measurement of concrete with steel bar

This paper presents results on a study of the Rayleigh wave scattering and Rayleigh wave velocity measurement in concrete with a steel bar using transient elastic waves. To study the characteristics of the scattered waves induced by a steel bar in concrete, a three-dimensional heterogeneous finite difference formulation with staggered grids was adopted. The cases for both elastic wave propagation parallel and perpendicular to the steel bar are discussed. The effect of the cover thickness and steel bar spacing on the Rayleigh wave velocity measurement was studied. To confirm the numerical investigations, a concrete specimen containing steel bar was made and the corresponding transient elastic wave experiments were conducted. The numerical results are in good accordance with those of the measured. We note that the result of this study can serve as an important reference in the Rayleigh wave velocity measurement of concrete with steel bar.     

轧机主传动安全销弹塑性有限元分析

本文针对轧机主传动系统的安全销在破坏前已产生了塑性变形,采用三维弹塑性有限元对安全销进行应力分析,模拟出材料的应力-应变非线性曲线,并运用牛顿-拉普森平衡迭代法根据模拟出的应力-应变非线性曲线对安全销进行应力计算,通过多次试算得出其能承受的最大载荷,并提出了改进意见.     

冷连轧机主传动剪式安全销的弹塑性数值分析

轧机主传动系统的安全销需要在一定过载的情况下及时断裂以保证设备安全。针对中国重型机械研究院设计成套的冷连轧机现场调试过程中安全销出现的失效问题,对其进行了三维弹塑性有限元的应力应变分析,对今后的设计提出了一些改进意见。     

汽车变速销模锻成形有限元分析及实验验证

针对汽车变速销的形状、尺寸以及材料性能等特点,选定了单工步开式模锻的成形方法。使用CAE有限元分析软件Deform-3D对初始工艺方案进行仿真研究,分析了材料成形过程中的热、力情况,否定了初始工艺方案的可行性。从坯料尺寸、坯料温度以及模具结构3个方面出发,对成形工艺进行改进,制定了3套改进方案,并通过模拟方法得到较优工艺,即:坯料尺寸为Φ17 mm×47.5 mm,坯料温度为700℃,在凹模上增加Φ60 mm×0.2 mm的飞边槽以及在凸模前端设置1个Φ12 mm×0.5 mm的凸起。采用改进后的模具及优化工艺进行实验验证,证明了该工艺的可行性。     

电弧故障信号的小波检测与分析

焊缝质量受多种因素影响,电弧的稳定性就是其中重要的因素之一。当电弧信号发生异常时,电弧能量就会发生变化,这种能量的变化将会给焊缝成形带来影响。为了分析电弧能量变化,采用小波变换技术,这种有别于传统的信号分析方法能够对信号的局部进行放大和缩小,适合于非平稳信号的分析,尤其是对信号故障点的分析,通过调节时间或频率轴的比例,可获得满意的信号分辨率。实验表明,小波分析法不仅能够判断信号质量,也为焊缝故障的诊断提供了一种新的方法。     

20CrMnMoA钢传动齿轮断裂原因分析

20CrMnMoA钢传动齿轮的注油孔处发生贯穿性开裂,采用金相显微镜和扫描电镜对断裂齿轮进行了观察和分析。结果表明,齿轮注油孔处有渗碳层,此层表面有较多的沿晶界氧化物和黑色屈氏体组织;而注油孔所在部位很容易引起应力集中,在过大应力作用下导致齿轮开裂。     

某化工厂管道输气用不锈钢法兰漏气裂纹分析

某材质为0Cr18Ni9不锈钢法兰在巡检时发现有气体泄露现象,着色探伤发现在焊接附近存在较多周向裂纹.通过宏观与微观形貌、显微组织、化学成分、硬度测试等方法,对法兰裂纹形成原因进行分析.结果表明,法兰开裂为沿晶型应力腐蚀开裂,与焊接敏化效应无明显直接相关性.裂纹形成主要原因为法兰选材以及热加工工艺不合理导致材料应力腐蚀...     

Applied multiresolution analysis to infrared images for defects detection in materials

In this paper, an advanced approach to characterize defects in homogeneous materials based on multiresolution analysis of infrared images is presented. This is mainly a non-destructive evaluation technique based on the flash method in transmission mode. An experimental device using infrared thermography was designed and realized. The equipment includes an infrared imager for following the temporal evolution of the temperature in the rear face of the tested sample. The other front face receives a flash from a halogen lamps excitation source. The thermal images generated at the rear face are segmented using a wavelet transform multiresolution analysis in order to extract all defects zones and subsequently processed to estimate their corresponding surface sizes. The experimental results on the test materials with hidden defects show the advantage of the segmentation technique applied to the response images of the system. High precision of the localization and accurate estimation of the surface sizes of the detected defects are achieved with the advanced method, involving a denoising of the images using a thresholding of wavelet coefficients. The outcome is a significantly improved detection quality, due mainly to the advanced processing, which does not depend on the type, shape and size of the defects.