Research on Eddy Current Testing System of the Carburized Layer Depth of 20CrMnTi Steel

In this paper the carbon distribution in the carburized layer of 20CrMnTi steel was studied. The relationship between the depth of a carburized layer and the surface carbon distribution was established. Eddy current testing system of the case depth of this carburized steel was built by using ANSYS software as second development platform.

Parametric study on single shot peening by dimensional analysis method incorporated with finite element method

Shot peening is a widely used surface treatment method by generating compressive residual stress near the surface of metallic materials to increase fatigue life and re- sistance to corrosion fatigue, cracking, etc. Compressive re- sidual stress and dent profile are important factors to eval- uate the effectiveness of shot peening process. In this pa- per, the influence of dimensionless parameters on maximum compressive residual stress and maximum depth of the dent were investigated. Firstly, dimensionless relations of pro- cessing parameters that affect the maximum compressive residual stress and the maximum depth of the dent were de- duced by dimensional analysis method. Secondly, the in- fluence of each dimensionless parameter on dimensionless variables was investigated by the finite element method. Fur- thermore, related empirical formulas were given for each di- mensionless parameter based on the simulation results. Fi- nally, comparison was made and good agreement was found between the simulation results and the empirical formula, which shows that a useful approach is provided in this pa- per for analyzing the influence of each individual parameter.

Effects of Surface-Active Elements Sulfur on Flow Patterns of Welding Pool

A 3D mathematical model is developed to calculate the temperature and velocity distributions in a moving gas tungsten arc (GTA) welding pool with different sulfur concentrations. It has been shown that, the weld penetration increases sharply with increasing sulfur content. When sulfur content increases beyond 80 × 10-6, the increase in sulfur content does not have an appreciable difference on the welding pool size and shape, and the depth/width remains constant. Sulfur changes the temperature dependence of surface tension coefficient from a negative value to a positive value and causes significant changes on flow patterns. The increase in soluble sulfur content and the decrease at free surface temperature can extend the region of positive surface tension coefficient. As sulfur content exceeds 125×10-6, the sign of surface tension coefficient is positive. Depending upon the sulfur concentrations, three, one or two vortexes that have different positions, strength and directions may be found in the welding pool. The contrary vortexes can efficiently transfer the thermal energy from the arc, creating a deep welding pool. An optimum range of sulfur content is 20-150×10-6.

The Effect of the Trace Elements Concentrations on the Cancerous and Healthy Tissues in Radiotherapy

The study is aimed to investigate the effect of the trace element concentrations in healthy and cancerous prostate tissues on dose distributions in radiotherapy. In this work, the trace element compounds completely soluble in the water were used and their concentrations given in the literature were mixed homogeneously with pure water. This is the first time study in literature as far as we know. The percent depth dose (PDD) measurements were performed using Elekta Synergy Platform Linac device for 6 and 18 MV photon energies. We also obtained the PDDs results by choosing higher trace element concentrations than given in literature in cancerous prostate tissue to see the effect on radiotherapy. The experimental measurements were compared with the results obtained from the GATE simulation code. The TPR20/10 was calculated for 10 × 10 cm2 field size at 6/18 MV energies photons and compared with simulation results. The differences between simulation and measurement for 6 MV and 18 MV photons are 1.75% and 1.82% respectively. The experimental results and simulations were presented an uncertainty lower than 3%. Simulated dose values are in good agreement with less than 2% differences with the experimental results. We see that the trace element concentrations of healthy and cancerous tissues did not affect the dose distribution at high-energy photons. This is expected and well known result. We believe that this in vitro study is important for proving the reliability of the dose given in radiotherapy treatment once again.

输水工程中淡水壳菜侵蚀混凝土的机理研究

淡水壳菜附着在输水建筑物内壁会导致混凝土性能劣化,研究淡水壳菜附着规律与侵蚀混凝土的微观机理对建筑物防护对策的制定具有重要价值。本文研究了淡水壳菜在输水建筑物内部附着规律、足丝入侵机制、体长空间差异性;通过原位混凝土硬度、侵蚀深度测试,分析了淡水壳菜对混凝土物理性质的影响;基于侵蚀前后混凝土微观形貌、化学元素变化及XRD衍射图谱,解析了淡水壳菜对混凝土侵蚀的微观机理,提出了侵蚀后混凝土的物相转化机制。结果表明:淡水壳菜附着密度在渡槽内部自入口到出口呈现出衰减规律;在倒虹吸内部附着密度呈现出沿程波动特点,但总体稳定。淡水壳菜平均垂向分离力与体长呈正相关关系;淡水壳菜体长在大尺度空间上表现为“南方长,北方短”特点,相差10 mm,体长分布形式符合高斯分布。淡水壳菜长期附着下,混凝土硬度降低、侵蚀深度有所增加;微观形貌疏松多孔,Ca、Fe等元素流失;混凝土的侵蚀产物主要为二氧化硅。

鄂尔多斯盆地东南部晚石炭世—中二叠世沉积环境及演化

通过对鄂尔多斯盆地东南部上古生界泥岩样品微量元素的分析测试,并结合岩石沉积学特征、地球物理测井等多种方法,定性、半定量及定量地分析整个研究区晚石炭世本溪组至中二叠世下石盒子组盒8段的沉积水体环境和古气候等特征,并在此基础上探讨沉积环境的演化特征。结果表明,砂岩中多以反应牵引流水动力条件的沉积构造为主,沉积期水动力较强;Sr/Ba值指示研究区处于混合水-淡水环境;岩性组合、典型自生矿物、V/Cr、Ni/Co、V/(V+Ni)、δU及自然伽马能谱测井资料定性及半定量判别表明,研究区主体为富氧浅水环境;结合La-Co法定量判别认为研究区古水体深度多小于25 m,但古水深频繁变化;Sr/Cu值指示研究区属温湿的古气候。由本溪组至下石盒子组盒8段,水体盐度逐步降低,水体深度稳步下降,古气候由湿润趋于干燥,亦揭示出鄂尔多斯盆地东南部上古生界经历了由近海湖盆至内陆湖盆的沉积演化过程。

Hydrogeochemistry of karst underground waters at shallow depth in Guiyang City, Guizhou Province

The aim of this study is to shed light on the hydrogeochemical characteristics of karst underground waters at shallow depth in Guiyang City, Guizhou Province with an emphasis on the geochemistry of major elements. Guiyang City bears abundant underground waters and it is also an important representative of the karst areas throughout the world. Ca+{2+} and Mg+{2+} are the dominant cations, accounting for 81%-{99.7%} of the total, and HCO+--3 and SO+{2-}-4 are the dominant anions. Weathering of limestones and dolostones is the most important factor controlling the hydrogeochemistry of underground waters, and weathering of sulfate and evaporite rocks is less important. Moreover, the precipitation and human activities also have a definite influence on the hydrogeochemistry of underground waters in the region studied.

An Efficient Model for Transient Surface Waves in Both Finite and Infinite Water Depths

A numerical model is developed to simulate fully nonlinear extreme waves in finite and infinite water-depth wave tanks. A semi-mixed Enlerian-Lagrangian formulation is adopted and a higher-order boundary element method in conjunction with an image Green function is used for the fluid domain. The botmdary values on the free surface are updated at each time step by a fourth-order Runga-Kutta time-marching scheme at each time step. Input wave characteristics are specified at the upstream boundary by an appropriate wave theory. At the downstream boundary, an artificial damping zone is used to prevent wave reflection back into the computational domain. Using the image Green function in the whole fluid domain, the integrations on the two lateral walls and bottom are excluded. The simulation results on extreme wave elevations in finite and infinite water-depths are compared with experimental results and second-order analytical solutions respectively. The wave kinematics is also discussed in the present study.

基于深度域适应迁移学习的滚动轴承故障诊断方法研究

在实际工业生产中,滚动轴承故障数据稀疏,构建的小样本数据集易导致模型过拟合,需要进行数据增强构成训练域。由于机械设备在运行中存在工况时变性,导致训练数据和测试数据之间存在差异,进而造成轴承故障诊断准确率不高,故提出一种基于生成对抗网络和多核最大均值差异(MK-MMD)的深度域适应迁移学习方法。文中通过有限元模拟获得大量带有标签的仿真故障数据,在此基础上构建深度域适应迁移学习的故障诊断模型,并利用凯斯西储大学的轴承数据集对轴承故障诊断模型进行测试。此外,通过与卷积神经网络(CNN)、深度适配网络(DAN)和深度域自适应网络(DANN)的故障诊断结果对比,证明基于有限元模拟的数据增强和迁移学习的轴承故障诊断方法可有效提高轴承故障诊断的准确度。

方拱形波纹钢管廊弯矩解析解及断面参数研究

方拱形结构因空间利用率较高而广泛应用于我国地下综合管廊的建设中,但其结构承载特征、力学机制及相关设计方法研究尚少。为研究方拱形波纹钢管廊结构弯矩的解析计算理论以及合理的断面形式,利用结构力学、土力学基本理论和相关规范,推导方拱形波纹钢综合管廊的弯矩解析解,并用二维平面应变模型对弯矩解析式的正确性进行验证,同时建立不同管顶覆土深度的方拱形波纹钢管廊三维地层-结构有限元数值模型,将数值分析结果与弯矩解析式计算的弯曲应力进行对比,分析弯矩表达式的适用覆土深度,基于弯矩解析表达式对管廊断面参数进行优化分析,并给出推荐断面参数范围。研究表明:1)方拱形波纹钢综合管廊的弯矩解析解与数值解相吻合,理论计算的弯矩与数值解的最大误差为5.79%;2)弯矩解析表达式的适用覆土深度为H≤10 m;3)针对依托工程,计算结果表明管廊断面矢跨比、顶板和侧板跨度比均处于0.6~0.8,管廊结构弯矩分布较合理,有利于保障结构安全。

Ⅲ类骨质中种植体长度及植入深度对周围骨应力的影响

目的:应用三维有限元分析法分析Ⅲ类骨质中种植体长度及植入深度对周围骨组织生物力学的影响。方法:利用建模软件Mimics等建立直径为5 mm、长度分别为8和10 mm的平台转移型种植体,并将种植体颈部平台置于平牙槽嵴顶、牙槽嵴顶下1 mm和牙槽嵴顶下2 mm的颌骨中,共包含6组三维模型。分别对每个模型给予垂直225 N及斜向200 N的载荷,研究种植体周围骨组织Von Mises应力/应变峰值及分布特征。结果:应力云图显示应力/应变主要集中在种植体颈部平台周围的骨质中,当种植体颈部平台位于牙槽嵴顶下1 mm时,皮质骨顶端区域应力/应变分布范围最小。在同一种植体长度下,随着种植体颈部平台下移,皮质骨应力/应变峰值先增大后减小,松质骨的应力/应变峰值逐渐增大,牙槽嵴顶端应力均逐渐减小。当种植体颈部平台位于牙槽嵴顶下2 mm时,松质骨所受应力/应变峰值超过松质骨生理强度安全范围上限。种植体长度增加,种植体周围骨组织应力/应变减小。种植体颈部平台植入深度比种植体长度对周围骨应力的影响更大。同等条件下,斜向加载Von Mises应力/应变峰值均大于垂直加载。结论:两种长度种植体的力学结果相似,植入深度对种植体-骨界面的影响大于种植体长度。颌骨可用高度一定时,长度8 mm、植入深度1 mm的种植体更有利于种植体周围骨组织及软组织保存。

短冠磨牙远中邻牙合缺损髓腔固位冠修复的三维有限元分析

背景:对于牙冠高度正常的牙齿,不同髓腔固位深度及不同修复材料的髓腔固位冠修复对牙体组织应力大小及抗折性有影响,对于短冠磨牙缺损利用髓腔修复的研究多集中在临床观察及体外抗折性实验。目的:建立根管治疗后短冠磨牙髓腔固位冠修复的三维有限元模型,分析不同髓腔固位深度及修复材料的修复体对牙本质等效应力分布及大小的影响。方法:在建立完整短冠下颌第一磨牙模型的基础上,建立不同髓腔固位深度(h=2,3,4 mm)、不同修复材料(氧化锆、二硅酸锂)的髓腔固位冠修复短冠磨牙远中邻牙合缺损的三维有限元模型,采用斜向加载,观察等效应力分布情况,计算牙本质等效应力峰值及近中髓室壁近髓室底等效应力平均值。结果与结论:①等效应力集中部位:完整短冠磨牙及修复后各模型应力主要集中在近中根近中颈部及近中根舌侧颈部,修复后各模型垫底层对应的近中髓室壁近髓室底处均有应力集中区,其中以髓腔固位深度4 mm组应力集中明显;②在相同修复材料下,修复后各模型牙本质等效应力峰值均以髓腔固位深度3 mm组最小,近中髓室壁近髓室底处牙本质等效应力平均值均为髓腔固位深度3 mm组最小;③在相同固位深度下,氧化锆组及二硅酸锂组牙本质等效应力峰值及近中髓室壁近髓室底处牙本质等效应力平均值均相差不大;④结果表明,在此次实验条件下,短冠磨牙缺损采用髓腔固位冠修复时固位深度为3 mm更有利于保护剩余牙体组织,修复材料选择氧化锆或二硅酸锂对牙本质应力影响区别不大。

钢梁腐蚀相关性对钢-混组合梁桥体系可靠度的影响

服役环境中钢主梁的腐蚀本质上是一个随机过程,腐蚀深度随机变量既有时变性亦有空间性。现有测量方法只能获得单根钢梁腐蚀深度数据,尚不能明确结构体系腐蚀深度变量的联合分布模式,可能导致腐蚀结构体系可靠度计算模型失真。以某钢-混凝土组合梁桥为研究对象,首先建立了钢主梁腐蚀深度增长Gamma随机过程模型,并利用钢梁腐蚀深度实测数据对模型进行了验证;然后采用Kendall秩相关系数量化表征主梁腐蚀深度相关性,推导了腐蚀钢梁的时变抗力计算公式;最后基于Copula函数提出了考虑主梁腐蚀相关性的梁桥体系失效概率计算方法,对比研究了钢梁腐蚀相关性对钢-混组合简支梁桥体系可靠度的影响。研究结果表明:桥梁运营前期腐蚀相关性对梁桥受力性能影响较小,在运营中后期,中高程度的腐蚀相关性将会对梁桥体系的可靠度影响较大。研究提出了钢梁腐蚀空间相关性量化方法,获得了更精确的钢-混组合梁桥体系可靠度计算方法,可为组合梁桥体系的时变可靠度评定提供参考。

聚合物微针阵列热压印成型仿真与试验研究

【目的】针对聚合物微针阵列热压印成型过程中充型不完整、脱模后继续变形和应力集中等问题,将成型仿真与试验相结合,探究热压印成型参数对残余应力与平均填充深度的影响,以满足高精度批量制造聚合物微针阵列的需求。【方法】在聚合物材料热-机械性能研究的基础上,建立微针阵列的有限元模型,分析热压印温度、热压印速率和下压量等成型参数对残余应力及其分布的影响,进行热压印成型试验,探讨相关成型参数对微针成型的影响,对比分析了平均填充深度仿真与试验值。【结果】随热压印温度的升高,最大成型应力呈先降后升的趋势;随热压印速率与下压量的增加,最大成型应力均呈增大的趋势;除热压印温度高于125℃之外,平均填充深度的仿真值与试验值变化趋势一致,且仿真值均高于试验值。此外,还获得了适用于聚苯乙烯微针阵列的最佳热压印参数,即热压印温度125℃、热压印速率10μm/s、下压量2.6 mm。【结论】在一定温度范围内,该数值仿真结果具有较高的指导意义,聚苯乙烯微针阵列结构的残余应力与平均填充深度具有较为敏感的温度与时间相关性。

基于变波长矩阵结构的平面叉指电容传感器设计

针对平面叉指电容传感器在陶瓷材料介电常数测量时存在的穿透深度有限、测量准确度不高的问题,提出了一种改进方案。新型传感器采用电极矩阵结构,融入波长渐变设计。通过COMSOL Multiphysics有限元仿真软件,分析了传感器矩阵的静电场分布,比较了不同电极组合下的信号变化趋势,优化了电极矩阵结构。实验结果表明,改进后的叉指电容传感器对陶瓷材料的穿透能力超过了4 mm,相较于传统结构传感器,其探测能力提高了两倍以上。

青藏高原积雪深度变化及其影响因素分析

基于青藏高原逐日积雪深度和地表太阳辐射、逐月气温和降水量资料,利用多种统计方法,分析了该地区近几十年雪深变化特征及其与气象因素的关系。结果表明:高原积雪深度在1970s和1980s总体呈现显著增加的趋势,1990s中期之后开始减少,2000年后高原雪深仍然以减少为主,显著减少区域位于羌塘高原,显著增加区域位于喜马拉雅山脉、喀喇昆仑山以及高原中东部高海拔地区。雪深由少雪期到多雪期的突变时间主要处于1960s中期至1970s初,由多雪期到少雪期突变时间主要处于1990s末期至2000s初。青藏高原西部地区雪深存在13~17 a左右的周期变化,而东部地区存在3~7 a左右的周期变化。地表太阳辐射的减少是高原1970s和1980s积雪增加的主要因素,两者呈现较为显著的负相关,1990s中后期气温的显著增加是积雪减少的主要因素,两者呈负相关性,降水量与积雪整体呈正相关性,在温度相对较低,地表太阳辐射较低的情况下,降水量的增减对积雪的影响更明显。

有限元仿真研究不同栽桩深度下AG螺纹受力分析

为解决螺栓预紧力退化的难题,采用有限元仿真的方法,探究螺纹结合面间的微观接触运动,对不同栽桩深度下AG系列螺纹进行受力分析。结果显示:当栽桩深度为5P、6P、7P、8P时,计算得到的转矩结果符合使用标准,AG6×1螺纹副实现过盈螺桩连接功能。根据研究结果,AG6×1栽桩深度建议为6 mm。

机器人自动磨抛飞机蒙皮切边去除深度工艺

根据Preston理论建立蒙皮切边材料去除深度摸型,确定影响材料去除深度工艺参数,获得工艺参数对材料去除深度的影响规律。采用单因素实验法通过Ansys有限元软件仿真和机器人磨抛实验验证模型的正确性,设计正交试验对工艺参数进行优化使达到预期去除深度。研究结果表明,工艺参数对材料去除深度的影响程度从大到小依次为接触力、百页轮转速、进给速度,经验证优化的参数组合去除材料深度达到预期要求,证明该模型的正确性。

铣削工艺参数对AZ31B已加工表面残余应力的影响

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