以壁厚约束的内高压胀形件过渡圆角半径确定

考虑到管坯外壁与模具型腔之问的摩擦接触问题,建立在内部高压和两端轴向压缩联合作用下的回转体形制件内高压胀形工艺的局部自适应网格加密划分有限元数值模型.在此基础上,基于制件壁厚减薄最小同时整个制件壁厚均匀程度最高的约束,确定了胀形变形区过渡圆角半径数值.     

船用大直径厚壁管数控弯曲工艺参数对壁厚影响的显著性分析

为实现船舶管件数控弯曲精确成型,更好地研究船用大直径厚壁管壁厚变化率,提高其成型质量,需对其弯曲过程中壁厚减薄进行有效控制。基于有限元分析软件Dynaform建立船用20#管绕弯成型过程有限元模型,对其进行可靠性验证,再通过有限元分析和虚拟正交试验对弯曲段外侧最小壁厚数据进行极差分析和方差分析,研究工艺参数对于壁厚减薄影响的显著性及规律。结果表明:管件数控弯曲成形过程中工艺参数对最大壁厚减薄率影响的显著性顺序依次为:芯棒与管材摩擦系数、芯棒前伸量、芯棒与管材间隙、夹模与管材间隙;壁厚减薄率随着芯棒与管材摩擦系数、芯棒前伸量以及夹模与管件间隙的增大而增大,随着芯棒与管件间隙增大而减小。同时利用多元线性回归方法建立显著性工艺参数与最大壁厚减薄率之间的回归方程,经对比验证,对于规格为Φ140mm×4.5mm(t)×420mm(R)船用20#大直径厚壁管,此回归预测模型结果与正交试验之间的相对误差不超过5%。     

机械式胀形关键因素对桥壳壁厚分布的影响

采用有限元模拟与试验相结合的方法,以ABAQUS软件为平台,建立桥壳机械式胀形工艺有限元模型,分析不同工艺参数对桥壳壁厚分布的影响规律。模拟结果表明:沿桥壳切口边缘壁厚分布不均匀,存在明显的壁厚增厚和减薄区域。增加工艺孔长度,壁厚减薄量显著减小,分布更均匀;增加工艺孔宽度,桥壳壁厚发生严重减薄的范围缩小,壁厚增厚量、减薄量均减小,分布均匀性提高;而两端施加轴向压力对壁厚分布影响较小。开展物理实验验证,测得的桥壳壁厚分布规律与模拟结果相一致,验证了数值模拟的可靠性。     

AA5083管件颗粒介质非均匀内压温热胀形工艺性能解析

基于管件热单向拉伸试验、颗粒介质传压性能试验和外摩擦因数试验,分析了采用温热颗粒介质压力成形工艺时,在非均匀内压下AA5083管材自由胀形区的受力情况,探讨了颗粒介质与管件内壁摩擦作用对管件胀形区壁厚分布和胀形极限的影响。理论分析和工艺试验表明,温热颗粒介质压力成形工艺中颗粒介质与管坯之间存在的有益摩擦有效抑制了管件减薄,提高了管件胀形极限。     

无缝管与有缝管液压成形性比较

通过对无缝管和有缝管在不同内压下自然液压胀形过程的有限元数值模拟,分析比较了管材胀形后的轮廓形状分布、壁厚分布和最大成形高度,探讨了焊缝材料性能对上述三个成形参数的影响,结果表明:无缝管胀形后轮廓形状对称,而有缝管胀形后轮廓形状不对称,并且这种不对称性随着内压增大而加剧;无缝管胀形后壁厚沿环向分布均匀,而有缝管胀形后,距焊缝对称中心0~15°之间的壁厚沿环向分布不均匀,距焊缝对称中心15°~180°之间的壁厚基本上呈均匀分布,且壁厚值和同种材料的无缝管在相同条件下胀形的壁厚值接近;焊缝材料强度比基体材料强度高,则极限成形高度大。     

TP2管材三维自由弯曲回弹及优化研究

回弹是金属管材在弯曲成形过程中无法避免的现象，它的存在降低了管材的成形质量。以外径12mm，壁厚1.5mm的TP2管材为研究对象，采用显式分析弯曲过程，隐式分析回弹过程。结合有限元数值模拟和实验，通过单因素分析法，探究弯曲模圆角半径和管材与导向机构间隙的变化对管材弯曲回弹的影响规律，分析参数的最优取值以优化管材弯曲成形过程。结果表明：回弹角在弯曲模圆角半径为2mm，管材与导向机构间隙值为0.3mm时最小。优化后的管材回弹角均小于2°，壁厚减薄率均小于2%，模拟结果与实验结果十分接近，优化后的管材成形质量较高。     

数值模拟分析工艺参数与拉深件壁厚变化的关系

在分析板料拉深成形有限元理论的基础上建立数值模拟的分析模型,利用数值模拟技术系统地对拉深过程进行模拟。主要研究模具圆角半径、摩擦因数、压边力与模具间隙等工艺参数与拉深件壁厚最大变薄率的内在关系。     

基于有限元模拟的铝合金管液压胀形的工艺研究

在研究管材液压胀形工艺的基础上,采用理论分析和计算机数值模拟相结合的方法对铝合金管液压胀形过程进行研究。通过理论分析计算出胀形力的大小,利用有限元软件,分析比较了胀形压力、胀形速度和摩擦因数对管件胀形成形质量的影响。模拟结果表明:胀形压力与胀形速度必须相匹配;管坯与模具之间的摩擦因数在成形力允许的情况下,尽可能的大一些。     

薄壁管绕弯工艺参数对壁厚影响分析

为探究薄壁管绕弯加工中各工艺参数对管件壁厚的影响。结合正交试验设计,利用有限元软件DYNAFORM进行了管件绕弯过程仿真,对管件弯曲段外侧和内侧壁厚数据进行了极差分析和方差分析。芯棒伸出量和压模摩擦因素对管件弯曲段外侧减薄率有较大影响,其中芯棒伸出量对减薄率的影响具有显著性;防皱模与管件间隙、压模摩擦因素、压模与管件间隙、芯棒与管件间隙对弯曲段内侧增厚率影响较大,但所有工艺参数对内侧增厚率的影响均不具有显著性。优化参数后的试验表明:减小防皱模、压模、芯棒与管件的间隙及芯棒伸出量,适当增大压模及芯棒与管件的摩擦有助于薄壁管获得更高的壁厚质量。     

半滑动式液压胀形汽车桥壳的数值模拟及成形实验

对在不同加载路径下半滑动式液压胀形工艺中的管坯预胀形及终胀形过程进行了数值模拟,分析了不同加载路径下的管坯成形情况及其周向、轴向的壁厚分布,得到了预胀形管坯壁厚分布较好的加载路径以及终胀形时可确保成形合格样件的加载路径,并在普通液压机上进行了实验验证。     

手机跌落破坏仿真分析研究

国家对电工电子产品的环境试验有严格的标准规定，其中一项重要试验项目就是自由跌落。而自由跌落作为手机环境试验的一个重要试验项目，其属于实物试验，多在产品开发后期进行。采用有限元技术仿真手机环境的自由跌落响应，可在手机模型设计初始、实物样机制造出来之前进行，能够有效地发现设计缺陷。运用MSC．RATRAN／DYTRAN软件就手机自由跌落试验仿真分析过程中加强筋厚度对手机壳体强度和刚度的影响进行了模拟仿真，并对计算数据对比和分析，得出加强筋厚度设计的通用参考数据。     

AES测薄膜厚度的误差分析与修正

本文介绍了AES测薄膜厚度的原理和方法,分析了测试过程中的各种误差,并探讨了各种误差的修正方法。     

Experimental Study of Central and Minimum Elastohydrodynamic Film Thickness by Colorimetric Interferometry Technique

Recently developed colorimetric interferometry technique was used for the study of both minimum and central film thicknesses for a wide range of operating parameters. Over 300 film thickness maps were obtained for the combination of four values of the materials parameter G, five values of the load parameter W and many values of the speed parameter U. The use of a spacer layer extended the range of film thickness measurement down to 5 nm. An excellent agreement was found between experimental values and data obtained from numerical solution presented by Venner and ten Napel, especially for thin lubrication films. An increase in a speed exponent with increasing material parameter G was observed for both central and minimum film thicknesses. The minimum film thickness and, thereby, the ratio between central and minimum film thickness was confirmed to be of a stronger dependence on material and load dimensionless parameters than Hamrock and Dowson equations predict.     

On the measurement of thickness in nanoporous materials by EELS

This work discusses thickness measurements in nanoporous MgO using the log-ratio method in electron energy-loss spectroscopy (EELS). In heterogeneous nanoporous systems, the method can induce large errors if the strength of excitations at interfaces between pores and the matrix is large. In homogeneous nanoporous systems, on the other hand, the log-ratio method is still valid, but the inelastic scattering mean-free-path is no longer equal to that in the same bulk system.     

一种高精度的超声波厚度测量仪

介绍一种高精度的超声波厚度测量仪系统。论述系统的测量原理、系统构成,给出脉冲发生器、同步电路、计数器等电路的设计。总结系统的实验结果和系统特点。     

厚度式晶体管框架分离技术

探讨根据框架厚度进行框架分离的基本原理和要求。     

Viscosity-Pressure Correlation of Liquids

A single correlation was obtained to predict Newtonian viscosity-pressure coefficients of mineral oils, resin and polymer blends, pure hydrocarbons, and nonhydrocarbons. The correlation has been tested for a temperature range from 0°c (32 °F) to 135°C (275 °F). The empirical correlation makes use of atmospheric viscosity and density at the temperature of interest and viscosity-temperature property (m_o) of the fluids. When the correlation was compared with other leading correlations, it was shown to require less physical-property data, apply to n wider range of chemical compositions, cover a wider range in fluidity, and provide greater accuracy. The correlation is presented in the form of a polynominal equation.     

Architecture of Multilayer Cr/CrN Coatings for Wear Protection in Seawater: Cr/CrN Ratio and Total Thickness

Cr/CrN multilayer coatings with various Cr/CrN thickness ratios and total thicknesses were deposited on 316L stainless steel by multi-arc ion plating. The coatings were systematically characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and nanoindentation. Tribological behaviors were investigated using a ball-on-disk tribometer in artificial seawater. The results showed that the multilayer coating phases changed from Cr₂N + CrN to Cr + Cr₂N + CrN phases with an increase in Cr/CrN thickness ratio. The adhesion showed a slight difference for the coatings with different thickness ratios but significantly increased with total thickness. The hardness was also slightly improved by thickening the coatings. The friction coefficient and wear rate were lowest at a thickness ratio of about 0.3. However, there was no large difference in the friction coefficient between coatings with different thicknesses. The wear rate was lower for the thicker coatings under various loads. The load-bearing capacity was also improved by thickening the coatings.     

漏磁法智能管道壁厚检测系统的研究

基于漏磁原理 ,针对目前国内急需的对铁磁性材料管道壁厚快速检测研制成了智能式壁厚快速检测系统 ,通过标定实验进一步验证了该检测方法的可行性。突出特点是采用了电磁励磁的方法 ,避免了永磁励磁法在工作时始终吸紧管道而产生行走难、易磨损、寿命短、成本高的不利因素。通过实验证明该装置具有操作简单 ,易于实现自动检测。     

Thin thickness measurements by means of a wavelet transform-based method

A non-invasive method for thin thickness measurements of multilayer structures is presented herein. This measurement method uses the wavelet transform for the analysis and processing of the ultrasonic signal received from the structure under test. The wavelet transform also shows itself to be a powerful tool for the detection of partially overlapping echoes in a noisy environment. This paper first describes the basic idea underlying the measurement method and then a procedure, set up by the authors, and suitable for the validation of the method when a standard multilayer structure to be used as a reference is not available, is presented and discussed. Finally, measurements of the thicknesses of actual multilayer structures and, in particular, of structures in the ophthalmic and microelectronic technology field, are carried out.