圆锥摩擦轮传动在大型锻形筒体环缝焊接中的应用

大型锥形筒体环焊缝是在专用滚轮架上用自动埋弧焊来完成的.由于滚轮架传动的缺陷以及筒体制造上的误差,使得滚轮架的滚轮与锥形筒体之间摩擦传动产生异常,导致锥形筒体旋转不稳定,焊接质量不能满足技术要求.为提高焊接质量,分析了上述两个影响焊缝质量的因素,提出滚轮架的滚轮摆放应符合圆锥摩擦传动原理,增加了滚轮轮缘摩擦装置来弥补筒...     

变壁厚锥形件强力旋压过程有限元力学模型的建立

介绍了变壁厚锥形件旋压过程数值模拟的有限元力学模型建立的方法和步骤,以及分析了在建立力学模型时要处理的一些问题。     

基于前馈和滑模复合结构的飞行器电动舵机控制

针对飞行器电动舵机伺服系统的控制问题,提出了一种能够有效抑制传动机构非线性摩擦的控制方法,该方法由前馈补偿器、基于LQR的PID反馈控制器以及滑模控制器构成。前馈控制能够提高系统响应的快速性,PID反馈控制提高系统的抗干扰能力,针对非线性摩擦设计的滑模控制律,用来削弱非线性摩擦对舵机伺服的影响。在分析电动舵机伺服系统构成的基础上,给出了非线性摩擦的Stribeck模型;建立了系统数学模型,在此基础上分析得出前馈补偿器的结构和参数;引入参考给定量,建立基于误差的状态控制方程,设计了基于LQR的PID控制器以及抑制非线性摩擦扰动的滑模控制律。分别对含有滑模控制器和不含滑模控制器的控制方法进行了仿真实验,实验结果表明:含有滑模控制器的控制方法能够有效抑制非线性摩擦引起的速度抖动问题以及位置"平顶"现象。     

SIP-160伺服压力机多杆增力机构自锁分析与优化

如果伺服压力机多杆增力机构设计不合理,压力机滑块会在上死点附近发生杆系卡死现象,其主要原因为多杆增力自锁引起。本文对多杆增力机构进行力学分析,得出多杆增力机构自锁的原因,对现有多杆增力机构提出优化方案并仿真分析,最终确定优化方案。     

1600kN肘杆式伺服压力机自锁分析与优化

如果伺服压力机肘杆机构设计不合理时,压力机滑块会在上死点附近发生肘杆卡死现象,这主要是由于肘杆机构自锁引起的。对肘杆机构进行力学分析,得出肘杆机构自锁的原因,对现有肘杆机构提出优化方案并仿真分析,最终确定优化方案。     

搅拌摩擦焊接头“洋葱环”层状结构形成机制探索

"洋葱环"形貌是搅拌摩擦焊接头中搅拌针作用区的固有特征,基于对搅拌针三维模型的形貌提取和修正,构建了搅拌摩擦焊接头"洋葱环"层状结构模型,通过模型叠加与剖切分析,获得了搅拌摩擦焊接头沿不同方向剖切后层状结构模型,所获得的模型与实际焊接接头层状结构形貌相一致。基于层状模型分析,将搅拌摩擦焊接头"洋葱环"层状结构形成过程分为"迁移阶段"和"回填阶段"两部分。基于三维模型分析,深入揭示了搅拌摩擦焊接头搅拌针作用区"洋葱环"层状结构的形成机制,为深入理解搅拌摩擦焊接头形成过程提供了理论基础。     

水平式扭力杆机构的研究

本文对水平式扭力杆机构的扭转进行了分析研究,建立了该机构的运动方程和力学模型。分析了转炉在倾动过程中扭力杆机构的受力,并给出了球面滑动轴承的摩擦圆计算公式,对设计该机构具有较大的参考价值。     

受限颗粒体引发混合摩擦非线性的研究现状与展望

机械摩擦界面中多多少少存在一些受限颗粒体,这些受限颗粒体和复杂的微凸体接触,并与局部液体润滑膜共同形成了具有明显非线性的混合摩擦状态。受限颗粒体在机械副中的行为往往处于介观尺度,并且形式多样、机理复杂。首先阐述了摩擦非线性在机械摩擦副中的体现以及受限颗粒体在此问题中的机理,并概括了受限颗粒体在不同界面条件下可能起到的减摩、增摩、诱发噪声或摩擦力不稳定性等作用。针对混合摩擦状态下的受限颗粒体引发的摩擦非线性问题,对不同应用背景的含受限颗粒体的摩擦界面的实验研究,包括颗粒Couette流剪切实验、粉末层SEM观察实验、外来颗粒以及磨损颗粒实验,进行了归纳,并对摩擦界面内受限颗粒体实验研究的空白和难点进行了总结。针对受限颗粒体在摩擦界面中的行为的建模研究,包括FEM、DEM以及动力学建模,分析了各种建模方法的优劣,并提出了未来建模工作的趋势。最后,对受限颗粒体诱发的机械副的黏滑和爬行现象的机理进行了分析,并阐述了其研究意义。     

WC-Co硬质合金微观结构的自适应参数化模型

为了研究材料微观结构对材料性能的影响以及缩短材料开发周期,基于WCCo硬质合金本真微观结构,提出了"自适应"建立二维微观结构参数化模型的方法 ,统计了真实测微观结构的WC平均晶粒尺寸及其分布、WC晶粒长短径、形心位置、取向角、Co含量等参数值,其中晶粒长短径则根据提出的"椭圆等效"法进行统计;然后基于Auto CAD的二次开发将统计的实验测量值输入到参数化模型中并投放WC颗粒,利用自适应算法自动调整每次新投放的WC颗粒,从而建立了反映真实微观组织的参数化模型。结果表明:WC-Co硬质合金微观结构参数化模型的参数设计值与实验测得值基本吻合,反映了参数化模型的可靠性。     

测量黏弹性材料力学特性的微型液压驱动机构

针对生物工程领域中传统力传感器无法实现机器人精确触觉感知的问题,提出一种可测量黏弹性材料力学特性的微型液压驱动机构。该机构通过直接接触目标对象来测量反作用力和位移,其末端执行器的尖端由微型气缸构成,并使用帕斯卡原理进行放大处理。对微型气缸的最佳尺寸进行分析,并给出微型液压驱动机构的供液系统。采用内径为1.6 mm的微型气缸对不同硬度的黏弹性材料进行蠕变实验和测量实验。根据离散的位移和载荷数据,分别通过开尔文模型和标准线性体模型计算接触物体的刚度和黏性系数。结果表明:相比标准线性体模型,采用开尔文模型的微型液压驱动机构识别出的刚度和黏性系数最接近真实值,能够满足机器人触诊系统中高精度力学特性测量的需求。     

Parametric optimization of power in hydrostatic extrusion

The process of hydrostatic extrusion has gained great popularity in recent years because of its simplicity and low cost. The material to be extruded is in contact with the die only, whilst in conventional extrusion the material is in contact with three components, the ram, the chamber, and the die. Therefore, the power required to extrude the product is less in hydrostatic extrusion. Added to this, the frictional losses are kept to a minimum because of the hydrodynamic lubrication that takes effect at relatively high extrusion speeds, which prevents the product from coming into contact with the die.

In this study, an analytical model for studying hydrostatic extrusion is introduced. The model is used to investigate various parameters affecting extrusion, these parameters being: the die cone angle, the reduction ratio (the ratio of the billet diameter to the product diameter), the friction coefficient, the extrusion and back-pressure ratio, and the die shape. The model is extended to optimize the aforementioned parameters for securing a better product, and effecting minimum power requirement and small frictional losses. In order for it to gain recognition, the model was substantiated experimentally employing three commonly used engineering materials, the analytical and the experimental results being found to be in good agreement.     

Comparison of spherical and truncated cone geometries for single abrasive-grain cutting

The purpose of the present work was to compare the cutting action of two different abrasive-grain geometries using experimental observations and a validated finite element model. A spherical tool was used to approximate a dull abrasive grain while a truncated cone tool was used to approximate an abrasive grain with a well defined cutting edge. The selected geometries were chosen to represent extreme cases in order to bracket the cutting action of a range of cutting geometries. The results showed that both tools produced similar normal and tangential forces per unit width up to a depth of cut of approximately 3 μm. The improved cutting geometry of the truncated cone tool caused the normal force per unit width to decrease and the tangential force per unit width to increase in relation to the spherical tool. The truncated cone tool was shown to experimentally and numerically be more efficient based on the reduced pile-up heights and improved stress distributions. It was also shown that both geometries converged towards the same specific energy to displace material at suitably large depths of cut, which suggests that there is a minimum specific energy obtainable for a given workpiece material that is independent of the grain geometry. However, specific energies to remove material were higher for the spherical tool as compared to the truncated cone tool. Analysis of the energy components of the finite element model showed that frictional energy contributions were high with the spherical tool and low with the truncated cone tool. Finally, it was found that both tools required approximately the same energy to shear a chip from a workpiece when friction was subtracted from the specific energy for material removal.     

Flexible diamond-like carbon films on rubber: Friction and the effect of viscoelastic deformation of rubber substrates

This paper focuses on the frictional behavior of flexible diamond-like carbon (DLC) film-coated hydrogenated nitrile butadiene rubber. By making use of the substantial thermal mismatch between DLC film and rubber substrate, a dense network of cracks forms in the DLC films and contributes to flexibility. The influence of the size of DLC film microsegments on the frictional performance is studied. The effect of viscoelasticity of the rubber substrate on the frictional behavior of the DLC film-coated system is scrutinized by tribo-tests and theoretical analysis. The importance of adhesive and hysteresis contributions to friction is revealed, and an overarching model is presented.     

基于CFD-DEM仿真的喷丸工艺参数优选

目的综合考虑喷丸过程的能量效率,以最少喷打时间和最小比能为目标进行喷丸工艺参数优选。方法通过分析弹丸群以单对称单元模型喷打的弹痕排布方式,以及满足一定覆盖率时平均每个弹丸形成的弹坑面积,得到随机喷打时的材料去除体积,进而得到能量利用效率。以喷丸入口压强、弹丸直径和弹丸流量三个工艺参数为变量,以一定覆盖率下的最小喷丸时间和最大能量利用率为目标,建立喷丸工艺参数优化模型。通过建立CFD-DEM气固两相耦合的喷丸仿真模型,进行仿真实验,得到出口弹丸速度与工艺参数的关系,进而得到每组实验的喷丸时间和能量利用率。结果通过16组仿真实验,得到第4组工艺参数为最优喷丸工艺参数组合,即入口压强为0.5 MPa,弹丸直径为1.0 mm,弹丸流量为0.6 kg/s。结论CFD-DEM仿真模型能够得到出口弹丸速度与其他工艺参数的关系,喷丸工艺参数优化模型能够兼顾效率和能量利用率,并筛选出最优工艺参数组合,为喷丸工艺参数决策提供指导。     

工艺参数对减径挤压的影响

影响减径挤压的工艺参数主要包括凹模锥角、定径带长度、摩擦系数、高径比等。采用有限元模拟技术模拟了不同工艺参数条件下的减径挤压变形过程。以内缩量为评价标准,分析了这些工艺参数对减径挤压的影响规律。     

摩擦片非线性损伤累积计算与寿命预测

摩擦片是车辆传动系统的重要部件,持续性的制动或者离合使得摩擦片承受较大范围的冲击载荷,需要对该工作环境摩擦片进行寿命预测.提出了一种基于冲击非线性损伤累积的摩擦片损伤计算方法,即:设定应力门槛值,对超过应力门槛值的冲击衰减应力曲线积分,进行非线性损伤计算.理论计算与试验结果对比表明:该方法可用于摩擦片损伤计算和寿命预测,效果良好.     

A phenomenological model for frictional contact of coated steel sheets

A simple phenomenological model for frictional contact with hardening is proposed. The objective is to simulate the frictional behaviour of coated steel sheets subjected to large sliding distances. Within the context of thermodynamics with internal variables, the friction coefficient is assumed to be a function of the frictional work resulting in a theory analogous to classical work-hardening elastoplasticity. The technique for experimental identification of the proposed model is described briefly and the material parameters obtained for Electrogalvanised steel sheet and BAF Al-killed steel sheet are presented. Within the computational scheme, a robust algorithm based on an operator split method (elastic predictor-frictional sliding corrector) is used for numerical integration of the friction constitutive equations. The finite-element simulation of a series of sliding tests is carried out and the results are compared with experiments.     

基于SolidWorks直齿圆锥齿轮参数化设计及有限元分析

论述利用三维软件SolidWorks进行直齿圆锥齿轮参数化建模的具体方法,用该方法开发出直齿圆锥齿轮参数化程序;通过运行程序生成直齿圆锥齿轮三维模型,对模型在载荷作用下的应力状态应用COSMOS/Works做了有限元仿真分析,整个研究过程对齿轮模型库开发、改进和优化齿轮设计参数等都有一定参考价值,同时为综合利用三维软件的各种功能提供借鉴。     

Themo-elasto-viscoplastic modelling of friction stir welding

Abstract

A coupled two-dimensional Eulerian thermo-elasto-viscoplastic model has been developed for modelling the friction stir welding process. First, a coupled thermo-viscoplastic analysis is performed to determine the temperature distribution in the full domain and the incompressible material flow around the spinning tool. Next, an elasto-viscoplastic analysis is performed outside the viscoplastic region to compute the residual stress. Both frictional heat and plastic deformation heat generation are considered in the model. Furthermore, this is the only known model computing residual stress accounting for plasticity caused by both thermal expansion and mechanical deformation due to material spinning. The computed residual stress is verified by comparing to experimentally measured data.