Al_2O_3-Ti系梯度功能材料残余热应力的有限元分析

采用有限元方法（ＦｉｎｉｔｅＥｌｅｍｅｎｔＭｅｔｈｏｄ）对Ａｌ２Ｏ３－Ｔｉ系梯度功能材料在制备过程中产生的残余热应力进行了线弹性分析。详细讨论了梯度层数目、梯度层厚度和成分梯度指数对应力大小和分布的影响，确定了各项最佳参数。非梯度功能材料（ＮＦＧＭ）与优化后的梯度功能材料的残余热应力对比结果显示：梯度功能材料缓和热应力的效果十分显著。     

燃烧合成TiC-Al_2O_3/Fe梯度材料及其抗热震行为

采用自蔓延高温合成结合准热等静压（ＳＨＳ／ＰＨＩＰ）制备出了具有对称结构的 ＴｉＣ－Ａｌ２Ｏ３／Ｆｅ梯度材料,并对其抗热冲击及抗热疲劳行为进行了测试和分析·结果表明, ＳＨＳ／ＰＨＩＰ制备的 ＴｉＣ－Ａｌ２Ｏ３／Ｆｅ梯度材料具有预期的梯度式组成,在热冲击和热疲劳实验过程中均无梯度层间横向贯穿裂缝,克服了传统陶瓷／金属直接接合界面的热应力剥落．     

HA-Ti生物功能梯度材料微观组织及热应力缓和特性

本文用粉末冶金法制备了ＨＡ－Ｔｉ系生物ＦＧＭ,并测定了ＨＡ－Ｔｉ复合体材料的弹性模量和热膨胀系数．应用经典叠层板理论和热弹性力学理论分析了ＨＡ－Ｔｉ系ＮＦＧＮ双层板和ＨＡ－Ｔｉ系ＦＧＭ的制备残余热应力和热应变．结果表明,ＨＡ－Ｔｉ系生物ＦＧＭ呈现出宏观不均匀性与微观连续性的组织特征．ＨＡ－Ｔｉ系复合体材料的弹性模量在Ｔｉ－ＨＡ８０达到谷值,并受到气孔率的影响．其热膨胀系数随着ＨＡ含量和测试温度的升高而增大．残余热应力和残余热应变强烈依赖于组成分布,ＦＧＭ由于组成梯度化减小了成分变化幅度,其最大残余拉应力只有ＨＡ／Ｔｉ直接叠合体（ＮＦＧＭ）的１／３,具有显著缓和热应力的功能.     

TiC-Ni梯度功能材料的优化设计

对ＴｉＣ－Ｎｉ梯度功能材料在制备过程中的残余热应力进行了计算机有限元模拟,考察了梯度组成分布指数对热应力大小,最大热应力发生的位置以及纯陶瓷ＴｉＣ侧热应力状态的影响,综合分析了热应力的大小和分布,得到了缓和制备热应力的梯度组成分布指数Ｐ＝１．０的优化设计结果。     

高速切削刀具系统固有特性和动态响应分析

高速切削刀具系统是数控刻楦机主要部件,其性能的优劣直接影响到鞋楦的加工质量．构造了高速切削刀具系统的三维实体模型,建立了系统动力分析有限元模型,计算了高速切削刀具系统的固有模态,与测试结果符合较好,基于该动力分析有限元模型,分析了加工状态下刀具承受的切削力激励载荷,计算得到刀具表面的速度和位移响应,对高速刀具进行进一步噪声分析研究具有重要的意义。     

用晶须型碳化钛陶瓷制造的刀具

日本广岛大学工程系的一个研究组已研制成一种可以高速切削镍基合金的晶须型碳化钛陶瓷（AIO3／T汇）刀具。这种黑色的碳化钛晶须陶瓷在高速切削时耐磨性高于S记陶瓷。曾用SIC晶须增强陶瓷O山／SIC）刀具和TIC晶须增强陶瓷（汕O／T汇）刀具对铬镍铁合金试件进行切削磨损试验。当试件以100～200m／min的速度车削时，两种刀具的缺口磨损最大，故应比较高的速度切削。试验发现，S记陶瓷在高速切削时，S江与铁合金反应，导致刀具表面分层剥离。当切削速度更高时，由于SIC扩散到铁合金，使S记陶瓷刀具磨损更为严重。但TIC陶瓷刀具在高…     

共沉淀法制备Al_2O_3-YAG复相陶瓷及其显微结构研究

用共沉淀法制备了Ａｌ２Ｏ３－ＹＡＧ复合粉体,ＹＡＧ的结晶温度在１０００℃左右．共沉淀法 制备的Ａｌ２Ｏ３－ＹＡＧ复合粉体经１５５０℃热压烧结,获得致密烧结体,ＹＡＧ的加入量对烧结温度 的影响不大． Ａｌ２Ｏ３－５ｖｏｌ％ＹＡＧ复合材料的抗弯强度为６０４ＭＰａ,断裂韧性为５．０ＭＰａｍ１／２; Ａｌ２Ｏ３－２５ｖｏｌ％ＹＡＧ复合材料的抗弯强度为６１１ＭＰａ,断裂韧性为４５ＭＰａｍ１／２．所有这些数据 都高于单相Ａｌ２Ｏ３陶瓷的力学性能,说明ＹＡＧ的加入有利于Ａ１２Ｏ３陶瓷力学性能的提高． 通过显微结构观察发现：大的ＹＡＧ颗粒位于Ａｌ２Ｏ３晶界上,小的ＹＡＧ颗粒位于Ａｌ２Ｏ３晶粒 内．在 Ａｌ２Ｏ３－５ｖｏｌ％ＹＡＧ复合材料中,许多小的白色区域存在于 Ａｌ２Ｏ３晶粒内,这可能和较低 的Ｙ２Ｏ３含量有关．     

高速切削加工中的刀具材料研究与应用

介绍高速切削加工技术所使用的高速钢、硬质合金、陶瓷、涂层等刀具材料的性能特点及应用,探讨在高速切削时选择刀具所考虑的因素。     

铣削GH4169高温合金用刀具的磨损机理

采用肯纳KYHS10陶瓷刀具对高温合金GH4169进行了高速铣削加工试验,结合Dino显微镜和扫描电镜观察了陶瓷刀具在高速铣削加工后的磨损形貌,并分析了在不同的切削参数下的刀具磨损机理。试验结果表明:陶瓷刀具的磨损形貌主要表现为沟槽磨损、前刀面月牙洼磨损、后刀面磨损、微崩刃和剥落等,主要的磨损机理为黏结磨损、扩散磨损、磨料磨损等,并且在不同的切削参数下磨损机理不同。黏结磨损随切削速度的提高逐渐加剧,磨粒磨损随切削速度的提高而下降。     

常用高速切削刀具材料的性能分析与应用

要实现高速切削加工,刀具材料是关键,高速切削技术是随着刀具技术如刀具材料等的发展而发展起来的。本文介绍了高速切削加工中常用的聚晶金刚石、立方氮化硼、陶瓷、Ti(C,N)基金属陶瓷等材料和涂层刀具等的特性、应用范围和发展趋势,以促进高速切削技术的广泛应用。     

Effects of geometric angle and cutting speed on cutting forces and tool wear of ceramic cutting tools during peripheral up-milling of high-density fiberboard

In this paper, cutting forces and tool wear of ceramic cutting tools are investigated by up-milling high-density fiberboard under different geometric angles and cutting speeds. The results show that tangential force (F_t) and normal force (F_r) decrease with the increase of rake angle. The values of F_t and F_r at the higher speed cutting condition are lower than that at the lower speed condition. The flank wear (VB) declines with increased clearance angle and decreased cutting speed. The tool wear patterns observed on the ceramic cutting tools are pull-out of grain, cracking, tipping, and flanking. Abrasive wear and adhesive wear are the main mechanisms of the ceramic cutting tools. In all, on the premise of guaranteeing the ceramic cutting tools’ strength, the ceramic cutting tool with a bigger rake angle and clearance angle is advisable in high-density fiberboard machining, in terms of lowering the energy consumption and production cost required for machining.     

Stress Field Analyses of Functionally Gradient Ceramic Tool by FEM

The cutting properties of the functionally gradient ceramic cutting tools relate closely to the gradient distribution. A cutting model of the functionally gradient ceramic tool is firstly designed in the present paper. The optimum of gradient distribution is obtained by way of the FEM analyses.     

Analytical modelling of thermal residual stresses in exponential functionally graded material system

An analytical model is developed for prediction of thermal residual stresses, arising from the fabrication of exponential functionally graded material (simply called E-FGM) systems. The thermomechanical properties of functionally graded layers are assumed to vary exponentially through the thickness. Residual stresses were found to increase when fully ceramic and/or fully metal regions are included in the structure, adjoining the graded zone. The effects of temperature dependent elastic and thermal expansion characteristics of constituents on residual stress were found to be small.     

Thermoelastic bending analysis of functionally graded sandwich plates

The thermoelastic bending analysis of functionally graded ceramic–metal sandwich plates is studied. The governing equations of equilibrium are solved for a functionally graded sandwich plates under the effect of thermal loads. The sandwich plate faces are assumed to have isotropic, two-constituent material distribution through the thickness, and the modulus of elasticity, Poisson’s ratio of the faces, and thermal expansion coefficients are assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. Several kinds of sandwich plates are used taking into account the symmetry of the plate and the thickness of each layer. Field equations for functionally graded sandwich plates whose deformations are governed by either the shear deformation theories or the classical theory are derived. Displacement functions that identically satisfy boundary conditions are used to reduce the governing equations to a set of coupled ordinary differential equations with variable coefficients. The influences played by the transverse normal strain, shear deformation, thermal load, plate aspect ratio, side-to-thickness ratio, and volume fraction distribution are studied. Numerical results for deflections and stresses of functionally graded metal–ceramic plates are investigated.     

The effects of residual stresses and degradation on the response of viscoplastic functionally graded materials

Functionally graded materials (FGMs), having ceramic and metallic constituents, are commonly used for extreme temperature applications. Under extreme temperature changes, the mismatches in the thermo-mechanical properties of the ceramics and metallic constituents could cause pronounced thermal stresses and could lead to degradation in the properties of the constituents. High stresses in the metallic constituent lead to plastic deformations and high tensile stresses in the ceramic constituent induce cracking. An elastic–viscoplastic micromechanical model is formulated for analyzing residual stresses and strains and degradation in ceramic–metal FGMs undergoing temperature changes due to conduction of heat. A degradation parameter that depends on the temperature and strain is introduced in order to determine the level of material degradation in the ceramics and metallic constituents. The Perzyna viscoplastic model is considered for the metallic constituent while the ceramic constituent is assumed linear elastic. The material parameters in these constituents change with the degradation. The problem leads to time-dependent coupled thermal, deformation, and degradation behaviors. The micromechanical model is implemented in a displacement based finite element (FE), which is used to determine the performance of the viscoplastic functionally graded structures subject to external thermo-mechanical stimuli.     

Comparison of tool life and surface characteristics of uncoated,coated carbide and ceramic tools during machining of SiC reinforced ZA43 alloy MMC

Abstract

In the present investigation, machinability issues of zinc–aluminium (ZA43) alloy reinforced with silicon carbide particles (SiC) were evaluated. The fabrication of composite was done through liquid metallurgy technique. Metal matrix composite (MMC) was subjected to turning using conventional lathe with three grades of cutting tools, namely, uncoated carbide tool, coated carbide tool and ceramic tool. Surface roughness and tool wear were measured during the machining process. Results reveal that roughness increases with increase in the reinforcement concentration and particle size. Feed has direct influence on roughness, i.e. surface deteriorates with higher feeds. Depth of cut has very minimum effect on the surface roughness, while inverse effect of cutting speed on the roughness was observed (i.e. increase in the cutting speed leads to better finish on the specimen). Tool wear was studied during the investigation, and it was noticed that MMC with higher reinforcement concentration and particle size cause severe wear on the flank of the cutting tool. Increase in the cutting speed, feed and depth of cut also increases the flank wear on the tool. Out of all the three grades of tools, coated carbide tool outperformed uncoated carbide and ceramic tools.     

热流温度场下功能梯度板的热问题研究

功能梯度材料因其内部组分沿着空间位置连续变化,能有效缓解热应力集中等现象,在高超音速飞行器的热防护系统设计中具有良好的应用前景.以金属-陶瓷功能梯度板为研究对象,探讨在不同热环境下功能梯度板热传导、热变形和热应力的变化规律.首先,基于功能梯度材料的幂律分布模型,分析了线性温度场、正弦温度场、热流温度场和非线性温度场四种...     

Thermal shock analysis for a functionally graded plate with a surface crack

Summary The fracture behavior of a functionally graded material (FGM) plate subjected to a thermal shock is studied. A surface crack is considered. The thermomechanical properties of the FGM plate are assumed to vary along the thickness direction. By using a perturbation method, the transient temperature field is solved. Then the transient thermal stresses and the corresponding thermal stress intensity factor (TSIF) are obtained. The transient thermal stresses and TSIF in an FGM ceramic/metal (ZrO₂/Ti-6Al-4V) plate are shown in figures. Dedicated to Professor Franz Ziegler on the occasion of his 70th birthday     

Effect of machining parameters on turning of VAT32® superalloy with ceramic tool

The objective of this research was to study the machining of superalloy VAT32® using alumina-based ceramic tool without cutting fluid, applying different machining parameters to evaluate the surface finish of parts, vibration and main wear of tools. For this, a turning process with a linear trajectory of 30 mm was performed, in which were collected data vibration and surface roughness of the stretch, as well as wear and damage in the tools. The turning tests were performed utilizing cutting speeds of 270, 280 and 300 m/min, a feed of 0.10, 0.18 and 0.25 m/rev and a cutting depth of 0.50 mm. With results, it was identified that the feed influenced significantly both the vibration and the system, since the cutting speed influenced only the vibration. Being that the best results happened for the smaller feed and greater cutting speed. It concludes that the machining of superalloy VAT32® with ceramic tool introduced herself promising.     

The influence of lubrication on tribological properties of Si3iNi4/1045 steel sliding pairs

Compared with cermet cutting tools, ceramic cutting tools have much better thermal stability and higher hardness. Si₃N4-based composite ceramics have been used progressively more for machining cast iron at very high speed. However, they have been found to be unsuitable for machining steel. One of the factors influencing this difference in behaviour is thought to be serious chemical wear of the ceramic at the high temperatures reached at the cutting tools. Lubrication could reduce the friction and the high temperature of the cutting tool/workpiece contact zone. A simulation test was carried out on a pin-on-disc tribometer in order to investigate the effect of lubrication on the friction and wear of Si₃N₄/1045 steel sliding pairs; the effects of load and speed on friction and wear were also investigated. The results show that suitable lubrication could greatly reduce the friction coefficient and wear rate of Si₃N₄ ceramic. Scanning electron microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy were used for examinations of the worn surfaces. A wear mechanism of the Si₃N₄ ceramic in sliding contact with 1045 steel is proposed. This revised version was published online in November 2006 with corrections to the Cover Date.