磨具弯曲成形法非球面研磨的研磨模型

磨具弯曲成形法是加工光学非球面零件的新方法,是线接触研磨过程.给出了弯曲成形法研磨的原理,基于Preston方程,限定磨具弯曲成形法特定研磨条件,分析了加工面上的任意一点的压力函数和相对速度函数,推导了磨具弯曲成形法研磨材料去除量函数表达式,推导了研磨作用时间函数.该研磨模型为磨具弯曲成形法研磨实践提供了理论依据.     

黄麻纤维毡吸声模型构建与试验验证

为更好地指导黄麻纤维毡的产品设计与应用,开展基于JCA吸声模型的黄麻纤维毡声学有限元模型构建与验证研究.利用阻抗管测取黄麻纤维毡吸声系数,并辨识出用JCA吸声模型表征的黄麻纤维毡相关物理特征参数,基于所建立黄麻纤维毡声学有限元模型获取其吸声系数和声压、声能分布.研究表明,黄麻纤维毡在高频率范围内具有较好吸声性能,其在中...     

氧化锌透明陶瓷光学透过模型构建与实验验证

本研究以ZnO透明陶瓷为研究对象, 基于Mie理论及Rayleigh-Debye近似散射理论, 建立了单轴六方晶系透明陶瓷的双折射散射与其直线光学透过率之间关联的理论模型, 阐明了ZnO透明陶瓷光学直线透过率随晶粒尺寸减小、陶瓷织构度的提升而增大的关系。采用强磁场下的注浆成型工艺结合优化放电等离子体烧结参数, 实现了ZnO透明陶瓷显微结构的有效调控, 使得制备的ZnO透明陶瓷符合模型要求。实验结果表明: 当ZnO陶瓷平均晶粒尺寸从1.72 μm减小至0.66 μm时, 其600 nm处的直线透过率从5.1%提高到12.9%; 对于亚微米级ZnO陶瓷(平均晶粒尺寸0.35 μm), 当陶瓷织构度从4.0%提高到24.7%时(XRD计算), 样品光学直线透过率从21.6%提升到36.6%。所获得实验结果与构建的理论模型计算结果吻合, 证实了所构建的模型。     

阀盖模锻成形模拟分析与试验验证

目的 某型号不锈钢阀盖是一种典型的长肋条内空型零件,在模锻制造过程中,阀盖锻件容易出现不同程度的折叠和裂纹缺陷,亟需改进成形工艺以提升合格率.方法 采用有限元方法分析坯料在制坯/预锻/终锻全流程的金属流动规律和终锻件成形质量,得到最佳成形工艺方案.结果 方坯在后续成形时易产生横向流动,且局部充型不饱满;六边型坯在预成形和终成形时流动均匀、横向流动小,且有效抑制了充型不饱满缺陷;预制坯在过渡区长度过短,产生了折叠缺陷;采用六边形坯料和增加过渡区长度可以获得无缺陷阀体锻件.结论 采用新工艺制备的阀盖锻件合格率达到了100％,通过全流程工艺分析,能够得到金属流线规律,进而优化模锻成形方案,改善成形质量.     

金刚石刀具机械研磨过程中材料的去除机理

从原子量级揭示了金刚石刀具机械研磨过程中材料的去除机理——研磨过程中,研磨区域原子的相变是材料去除的主要原因．使用分子动力学方法建立了金刚石刀具和刚性金刚石磨粒的三维模型．采用Tersoff势函数计算了所有原子之间的作用力,并以1．5个晶格的切深进行了研磨过程模拟．通过观测模型内部原子位置的变化发现,研磨区域刀具原子的晶胞在研磨过程中被压扁,发生了从金刚石体心立方结构向无定形碳结构的转变．计算了研磨区域原子研磨前后的径向分布函数,进一步验证了该相变过程．同时,使用X射线衍射方法分析了研磨实验过程中产生的碎屑．分析结果表明研磨过程中确实有相变发生．     

压制模型腔的等温成形与超塑性成形研究

模具型腔的等温成形与超塑性成形是一种新的制模工艺,这一工艺所具有的优点使之成为模具型腔制造的一种有力手段。本文重点介绍了热固性塑料压制模型腔的等温成形与超塑性成形工艺,介绍了有关的工艺参数、工装设计,并阐述了该工艺的应用实例。     

发电机碳刷故障的分析与处理

碳刷是发电机进行正常发电和传导电流的重要部件之一。因碳刷选取不当或是发电机在运行过程中缺乏对碳刷的维护,导致发电机出现的滑环和停机的现象会给企业造成重大的经济损失,所以说碳刷在发电机中能否良好正常的运行,直接影响着发电机运营的安全。本文中,笔者分析了引起发电机碳刷故障的几种类型,并探讨了发电机碳刷故障的解决对策和方法。     

弯曲成形法非球面研磨中磨具等距线误差分析

弯曲成形法研磨非球面零件中,磨具的等距线误差是影响弯曲成形精度的关键因素,直接影响加工工件的精度。用三点法求出理论曲线的最小平移距离,再用两点距离法建立磨具加工面上各点误差的数学模型,该模型适合各类二次曲线磨具等距线误差的计算。应用误差模型对一个椭圆磨具的等距线误差进行了计算,结果表明,磨具等距线误差变化范围为0~0.7μm,成形精度能满足大多数工件的面形精度要求,且磨具两端的误差较大,最大误差为0.62414μm;同时,磨具弯曲成形的曲线陡度越大等距线误差越大。这种方法加工小陡度的零件更具有优越性。     

AA5052铝合金管件电液成形数值模拟与试验验证

目的 建立AA5052铝合金管件电液成形数值模型,分析其成形过程.方法 应用Johnson-Cook本构方程,基于LS-DYNA平台对成形过程进行数值模拟分析,然后开展工艺试验,验证数值模拟模型的可靠性.结果 在管件电液自由胀形过程中,冲击波波阵面波头压力最高,管壁所受冲击波传递压力的分布关于金属丝几何中心始终是对称的...     

汽车钢板胀形区成形极限图的预测与验证

通过对胀形区成形极限图的理论分析和经验修正,建立了胀形区成形极限图的计算公式,经试验验证,在不同钢种、不同退火工艺、不同镀锌方式、不同表面处理方式下,按此公式计算的结果都能很好地符合试验结果.     

Templated assembly by selective removal: simultaneous, selective assembly and model verification

The use of templated assembly by selective removal to simultaneously and selectively assemble silica microspheres of two different diameters into designated sites on a surface was demonstrated. Microspheres with diameters of 636?nm and 2?μm were assembled from fluid onto templates patterned to contain holes that matched the shapes and sizes of the spherical components. The assembly experiments were carried out for a range of experimental conditions, including different fluid compositions and different intensities for the fluid excitation. A comparison of the measured assembly yield with the yield predicted using a model based on the work of Jung and co-workers (Jung et al 2005 Nano Lett.?5 2188-94) shows excellent agreement, indicating the applicability of the model over a broad range of experimental conditions. High yield is both expected and observed when the ratio of the moment that retains components in their locations to the moment that removes components from their locations is greater than 1, as long as stirring of the fluid medium is sufficient.     

Computer thermal model for hardening grinding

A mathematical model of heat transfer in steel parts under force grinding is considered that allows one to determine the grinding parameters at which a steel layer of prescribed thickness is heated up to hardening temperatures. Results of numerical simulation of the process of hardening grinding are compared with experimental data. The internal structure of the material after hardening grinding is analyzed. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 2, pp. 430–438, March–April, 2000.     

Material model calibration for superplastic forming

Superplastic forming is a slow forming process. The forming time can be minimized by optimizing the pressure profile applied to the forming sheet. The optimization of the superplastic forming pressure is usually done such that a target strain rate at a high strain rate sensitivity is maintained. Careful consideration of the strain rate is required, since localized thinning can occur when the material is strained too quickly. This paper demonstrates that it is essential to explicitly include strain rate sensitivity data, obtained from strain rate jump tests, during the calibration of material model used for superplastic forming simulations. Conventional calibration methods only consider stress–strain data at different strain rates. Such an approach implicitly assumes that a material model that matches the stress–strain data at the different strain rates, will automatically match strain rate sensitivity data. However, by explicitly including the strain rate sensitivity data, the selected material model is more susceptible to localized thinning as the applied strain rate is increased. It is essential for the selected material model to exhibit this behaviour to prevent superplastic forming simulations at high strain rates from predicting stable deformation, when in fact localized thinning will occur.     

齿轮成型磨削的分度补偿技术研究

文章以分度理论为基础,分析了齿轮成型磨削时,分度机构的工作原理和分度误差产生的机理,找出了影响分度机构传动精度的主要误差源,确立了完整的在机分度误差补偿方案,进行了控制系统的设计和控制程序的编制,通过试验验证了分度误差理论分析的正确性和整个误差补偿系统的实用性。     

2D-C/SiC高速深磨磨削特性及去除机制

采用树脂结合剂金刚石砂轮, 通过对2D-C/SiC复合材料高速深磨磨削加工, 并对磨削表面形貌和亚表面损伤进行了观察。提出了2D-C/SiC摩擦层(表面)的磨削力理论公式, 讨论了磨削加工用量对磨削力和磨削力比的影响。实验结果表明, 2D-C/SiC复合材料的高速深磨材料去除机制与其自身的微观结构相关, 既不同于塑性材料, 也不同于普通脆性材料, 而是以脆性断裂去除为主。     

总有机碳分析仪检定规程的适用性

以检定规程规定的标准物质与《中国药典》2010年版中规定的参考物质,对三种不同工作原理的总有机碳分析仪进行示值误差和重复性试验,由试验结果结合仪器工作原理分析了三种总有机碳分析仪检定规程的适用性,采用薄膜-电导检测技术的总有机碳分析仪不适用于JJG821-2005《总有机碳分析仪》;高温催化燃烧氧化法的仪器量程范围内低端部分也不一定能满足规程的技术要求。     

磁流变阻尼器的双sigmoid模型及试验验证

在对MRD进行力学性能试验研究的基础上，提出一个新的力学模型—双sigmoid模型。该模型的突出优点是考虑了施加电流、激励性质等因素的影响，且参数识别容易、物理概念清晰。在不同激励性质和电流下，该模型与试验结果相比均能较准确地描述MRD低速区的滞回非线性及在高速区的饱和特性。     

影响超精密环抛相对磨削量因素的计算模拟

利用Preston方程,考虑了超精密环抛中的诸因素,如工件和磨盘转速比、偏心距以及压强,计算模拟了它们对磨削效果的影响。模拟表明,当转速比越接近1或偏心距越大时,磨削越均匀;均匀分布的压强越大,磨削越不均匀。在这三个影响因素中,转速比的作用最为显著。实现均匀磨削所需的压强应为二次型分布。这些为超精密环抛提供了指导,有助于实现主动控制。     

Measuring,monitoring, and verification of carbon benefits for forest-based projects

Worldwide, there are many pilot forestry projects that are under some stage of implementation, and much experience has been gained from them with respect to measuring, monitoring, and accounting for their carbon benefits. Forestry projects have been shown to be easier to quantify and monitor than national inventories, partly because not all pools need measuring: a selective accounting system can be used that must include all pools expected to decrease and a choice of pools expected to increase as a result of the project. Only pools that are based on field measurements should be incorporated into the calculation of carbon benefits. Such a system allows for trade-offs between expected carbon benefits, costs, and desired precision, while maintaining the integrity of the net carbon benefits. Techniques and methods for accurately and precisely measuring individual carbon pools in forestry projects exist, are based on peer reviewed principles of forest inventory, soil sampling, and ecological surveys, and have been well tested in many part of the world. Experience with several forestry projects in tropical countries has shown that with the use of these techniques carbon stocks can readily be estimated to be within less than +/-10% of the mean. To date, there is little experience with measuring the changes in carbon stocks over time but, using the correct design and sufficient numbers of permanent plots, it is expected that precision levels will be maintained at less than +/-10% of the mean. Internal verification can be accomplished through use of quality assurance/quality control plans. External or third-party verification is still in its infancy, and would greatly benefit from international agreements in relation to protocols used for all aspects of project design and implementation.