Al2O3f+Cf/ZL109干摩擦磨损行为及其人工神经网络分析

采用挤压铸造法制备了氧化铝及碳短纤维混杂增强ZL109合金复合材料,考察了该复合材料的干摩擦磨损行为.结果表明该复合材料的摩擦磨损性能随纤维总体积分数的增加而降低;当纤维总体积分数一定时,随碳纤维含量的增加复合材料摩擦磨损性能降低.采用人工神经网络技术对该复合材料的干摩擦磨损试验结果进行了综合分析,其结果与试验值吻合较好.分析表明纤维总体积分数较小时,碳纤维含量对复合材料耐磨性的影响较大,随纤维总体积分数的增大其影响减弱;无论纤维总体积分数如何变化,碳纤维含量对复合材料摩擦系数均有较大影响,这是其自润滑作用的结果;载荷较小时,该复合材料摩擦磨损的跑合时间较长;随载荷的增大摩擦系数减小;磨损达到稳态后载荷对复合材料摩擦系数的影响不大.     

AI2O3＋Cf／ZL109干摩擦磨损行为及其人工神经网络分析

采用挤压铸造法制备了氧化铝及碳短纤维混杂增强ＺＬ１０９合金复合材料,考察了复合材料的干擦磨损行为。结果表明：该复合材料的摩擦磨损性能随纤维总体积分数的增加而降低;当纤维总体积分数一定时,随碳纤维含量的增加复合材料摩控磨损性能降低,采用人复合材料的干摩控磨损试验结果进行了综合分析,其结果与试验值吻合较好,分析表明：纤维总全积分数如何变化,碳纤维含量对复合材料摩擦系数均有较大的影响,「这是其自润滑作用     

碳黑填充超高分子量聚乙烯复合材料摩擦磨损性能研究

采用MM-200型摩擦磨损试验机考察了载荷及偶件表面粗糙度对碳黑填充超高分子量聚乙烯(UHMWPE)复合材料摩擦磨损性能的影响；利用扫描电子显微镜观察复合材料磨损表面形貌并分析了其磨损机理．结果表明：同UHMWPE相比，碳黑填充UHMWPE的磨损质量损失随载荷增加而增大的幅度较小；偶件表面粗糙度对碳黑填充UHMWPE复合材料的摩擦磨损性能影响较大，随着偶件表面粗糙度的增大，摩擦系数和复合材料的磨损质量损失均显著增大．UHMWPE及其碳黑填充复合材料在干摩擦条件下同45“钢及SiC喷涂层涂覆45“钢对摩时主要呈现犁削和塑性变形特征，犁削和塑性变形程度随载荷和偶件表面粗糙度增加而加剧。     

碳纤维增强聚醚砜复合材料的摩擦磨损性能研究

利用销－盘磨擦磨损试验机考察了聚醚砜及其复合材料在干滑动摩擦条件下的摩擦磨损性能。结果表明：碳纤维使聚醚砜的摩擦磨损性能得到明显的改善,春改善程度同碳纤维的长度和体积分数相关;当碳纤维的体积分数约为１５％时,聚醚砜复合材料的摩擦系数及比磨损率最低;添加固体润滑剂可以使复合材料的摩擦磨损性能得到进一步改善;随着温度及外载荷的变化,摩擦系数及比磨损率表现出不同的变化趋势。     

PTFE基复合材料在干摩擦和液氮介质中的摩擦磨损性能研究

对比考察了聚苯酯(Ekonol)和PAB纤维增强PTFE复合材料在干摩擦和液氮介质中的摩擦磨损性能,利用扫描电子显微镜观察分析在干摩擦和液氮条件下Ekonol/PAB纤维增强PTFE复合材料的磨损表面形貌及其磨损机理,同时还考察了温度对复合材料冲击韧性的影响.结果表明:在液氮条件下,PTFE的抗犁削能力增强,Ekonol/PAB/PTFE复合材料的磨损量明显比干摩擦下低,复合材料的摩擦系数比干摩擦下大,载荷对复合材料的磨损量影响较小,复合材料的摩擦系数和磨损量随着滑动速度增加基本保持不变,材料的磨损机理主要为轻微犁削和脆性断裂;而在干摩擦条件下,载荷对复合材料的磨损量影响显著,随着滑动速度增加,复合材料的摩擦系数先增后减,磨损量逐渐增大,材料的磨损机理主要以犁削、粘着磨损及疲劳磨损为主.在2种试验条件下复合材料的摩擦系数均随载荷增加而减小;低温时材料的冲击韧性约为常温时的1/2.     

超高分子量聚乙烯及其纳米Al2O3填充复合材料摩擦磨损性能研究

采用MM - 2 0 0型摩擦磨损试验机考察了载荷及对摩偶件表面SiC粒度对超高分子量聚乙烯及其纳米Al2 O3填充复合材料摩擦磨损性能的影响 ,利用扫描电子显微镜观察磨损表面形貌并分析了其磨损机理 .结果表明 :纳米Al2 O3 可以提高超高分子量聚乙烯的硬度及抗磨粒磨损性能 ;随着载荷的增大 ,超高分子量聚乙烯及纳米填充复合材料的磨损加剧 ;纳米Al2 O3 填充超高分子量聚乙烯复合材料的摩擦系数较超高分子量聚乙烯的略有增大 ;纳米Al2 O3 含量的增加有利于超高分子量聚乙烯复合材料抗磨粒磨损性能的提高 ;偶件表面喷涂SiC粒度的大小对超高分子量聚乙烯及其纳米Al2 O3 填充复合材料的磨损影响较大     

Cu—纳米TiB2原位复合材料的摩擦磨损性能

采用销-盘式摩擦磨损试验机考察了Cu-纳米TiB2原位复合材料在滑动干摩擦条件下的磨损行为.结果表明:载荷和滑动速度对纳米TiB2颗粒原位增强Cu基复合材料的摩擦磨损性能有重要影响;随着载荷的增加,Cu-纳米TiB2原位复合材料的磨损率和摩擦系数增大;由于在较高载荷下发生表面开裂,TiB2增强相含量较高的原位复合材料的磨损由轻度磨损向严重磨损转化;在中等载荷下,表面保护性氧化膜和基体中纳米TiB2相使复合材料具有良好的抗软化能力,Cu-纳米TiB2原位复合材料的磨损率和摩擦系数随着滑动速度的增加而降低;在较高滑动速度下,复合材料的主要磨损机制为塑性流变和氧化磨损.     

干摩擦和水润滑条件下芳纶浆粕/环氧树脂复合材料摩擦磨损性能研究

研究了芳纶浆粕纤维增强环氧复合材料在干摩擦和水润滑条件下的摩擦磨损性能,探讨了纤维含量对复合材料摩擦磨损性能的影响,并分析了复合材料的磨损机理.结果表明:芳纶浆粕纤维能够大幅度提高环氧树脂的摩擦磨损性能;当纤维体积分数为40%时,复合材料的比磨损率最小;在水润滑条件下,复合材料的摩擦系数和磨损率均比干摩擦下的明显降低,这是由于水起到了润滑和冷却作用;干摩擦时的磨损机理为粘着磨损和塑性变形,水润滑时主要为犁削和轻微的磨粒磨损.     

增强纤维含量对汽车摩擦材料性能的影响

研究了混杂纤维增强材料对汽车摩擦材料的机械性能及摩擦磨损性能的影响．结果表明：摩擦材料的冲击强度、三点弯曲断裂强度及硬度随纤维含量的增加而提高,并均达到使用要求;纤维含量对摩擦系数和磨损率影响较大,含体积分数１０％ 混杂纤维的材料具有较高的摩擦系数和较低的磨损率;ＳＥＭ 及ＥＤＡＸ分析表明,其磨损机理亦与增强纤维含量密切相关．     

粉末冶金Cu-Fe复合材料的摩擦磨损行为

研究了 Ｆｅ 含量、施加载荷和滑动速度对粉末冶金 Ｃｕ Ｆｅ 复合材料摩擦磨损性能的影响,并用电子显微镜和 Ｘ 射线能谱分析了 Ｃｕ Ｆｅ 复合材料的磨损机理．结果表明：载荷和滑动速度对摩擦系数影响不大, Ｃｕ Ｆｅ 复合材料的摩擦系数随 Ｆｅ 含量的增加略有增加;在低载荷下,随 Ｆｅ 含量的增加, Ｃｕ Ｆｅ 复合材料的耐磨性提高;当载荷大于 ２００ Ｎ 时,含 Ｆｅ 量高的复合材料的耐磨性反而降低;在低载荷高速滑动条件下,随滑动速度的增加, Ｃｕ Ｆｅ 复合材料磨损率下降     

Adaptive wall functions for the v2‐f turbulence model

Adaptive wall functions for the v²‐f turbulence model have been derived for the flow over a flat plate at zero pressure gradient. These wall functions were implemented via tables for the turbulence quantities and the friction velocity u_τ. A special treatment for the ε and f boundary conditions is proposed. On fine grids (y⁺<1) this approach yields results consistent with the wall integration solution. Detailed numerical results are presented for a zero pressure gradient boundary layer and separated flow over a ramp. Copyright © 2006 John Wiley & Sons, Ltd.     

短纤维取向对Al_2O_(3f) C_f/ZL109复合材料干滑动摩擦磨损性能的影响

利用挤压铸造法制备了 Al2 O3 f Cf/ZL10 9短纤维混杂金属基复合材料 ,并利用统计学方法对比研究了在滑动速度 0 .837m/s、载荷 196 N条件下纤维取向对该混杂复合材料干滑动摩擦磨损性能的影响 .结果表明 :在纤维平行取向和垂直取向时 ,该混杂复合材料的磨损率和摩擦系数均服从正态分布 ;平行取向情况下磨损率均值大于垂直取向下的磨损率 ,而摩擦系数均值小于垂直取向 ;纤维垂直取向有利于复合材料耐磨性能的提高 ,2种取向下复合材料的主要磨损机制均为犁沟磨损     

Phragmen-Lindelöf alternative results for the initial boundary problem of stokes equation

In this paper we prove Phragmén-Lindelöf type alternative for the initial boundary problem of Stokes equation, i. e. we show that the energy expression for the solution of the initial boundary problem must either grow exponentially or decay exponentially with axial distance from the end of a semi-infinite strip. For the case of decay, we also establish the pointwise estimate for the maximum module of the Stokes flow and present a method for obtaining explicit bounds for the total energy.Project supported by the National Natural Science Foundation of China and Zhongshan University Science Foundation     

Calculation of complex near-wall turbulent flows with a low-Reynolds-number k-ϵ model

An improved low-Reynolds-number k-? model has been formulated and tested against a range of DNS (direct numerical simulation) and experimental data for channel and complex shear layer flows. The model utilizes a new form of damping function adopted to account for both wall proximity effects and viscosity influences and a more flexible damping argument based on the gradient of the turbulent kinetic energy on the wall. Additionally, the extra production of the inhomogeneous part of the viscous dissipation near a wall has been added to the dissipation equation with significantly improved results. The proposed model was successfully applied to the calculation of a range of wall shear layers in zero, adverse and favourable pressure gradients as well as backward-facing-step separated flows.     

A simplified v2–f model for near‐wall turbulence

A simplified version of the v²–f model is proposed that accounts for the distinct effects of low‐Reynolds number and near‐wall turbulence. It incorporates modified C_ε(1,2) coefficients to amplify the level of dissipation in non‐equilibrium flow regions, thus reducing the kinetic energy and length scale magnitudes to improve prediction of adverse pressure gradient flows, involving flow separation and reattachment. Unlike the conventional v²–f, it requires one additional equation (i.e. the elliptic equation for the elliptic relaxation parameter f_µ) to be solved in conjunction with the k–ε model. The scaling is evaluated from k in collaboration with an anisotropic coefficient C_v and f_µ. Consequently, the model needs no boundary condition on and avoids free stream sensitivity. The model is validated against a few flow cases, yielding predictions in good agreement with the direct numerical simulation (DNS) and experimental data. Copyright © 2007 John Wiley & Sons, Ltd.     

An extended κ–ϵ finite element model

An extended κ–? model (to include low-Reynolds-number regions) employing weighting functions is presented. Wall functions for the near-wall zones are developed giving correct boundary values for the Shear stress and κ–?. A finite element model using a penalty formulation for incompressible turbulent flow is applied to Solve a flow between two plates. Results with mesh boundaries situated in the near-wall region and a: the wall are compared with measured values.     

加工Al2O3f+Cf/ZL109混杂增强复合材料的刀具磨损性能研究

利用挤压铸造法制备了炭短纤维(Cf)和Al2O3f短纤维增强以及混杂增强ZL109复合材料,研究了切削加工Al2O3f Cf/ZL109混杂复合材料过程中,Cf短纤维和Al2O3f短纤维含量以及切削速度对刀具磨损性能的影响.结果表明,刀具后刀面的磨损量随着纤维含量的增加而增加,Al2O3f短纤维对刀具磨损性能的影响程度大于Cf短纤维;2种短纤维混杂增强较单一Cf或Al2O3f增强时刀具后刀面的磨损将进一步加剧,但2种纤维对刀具磨损的交互作用并不显著;随着切削速度的增加,刀具后刀面的磨损量明显增大.高硬度PCD刀具和CBN刀具适用于加工Al2O3f Cf/ZL109混杂复合材料.     

Assessment of the finite volume method applied to the v2 − f model

The objective of this paper is to assess the accuracy of low‐order finite volume (FV) methods applied to the v² ? f turbulence model of Durbin (Theoret. Comput. Fluid Dyn. 1991; 3 :1–13) in the near vicinity of solid walls. We are not (like many others) concerned with the stability of solvers ‐ the topic at hand is simply whether the mathematical properties of the v² ? f model can be captured by the given, widespread, numerical method. The v² ? f model is integrated all the way up to solid walls, where steep gradients in turbulence parameters are observed. The full resolution of wall gradients imposes quite high demands on the numerical schemes and it is not evident that common (second order) FV codes can fully cope with such demands. The v² ? f model is studied in a statistically one‐dimensional, fully developed channel flow where we compare FV schemes with a highly accurate spectral element reference implementation. For the FV method a higher‐order face interpolation scheme, using Lagrange interpolation polynomials up to arbitrary order, is described. It is concluded that a regular second‐order FV scheme cannot give an accurate representation of all model parameters, independent of mesh density. To match the spectral element solution an extended source treatment (we use three‐point Gauss–Lobatto quadrature), as well as a higher‐order discretization of diffusion is required. Furthermore, it is found that the location of the first internal node need to be well within y⁺=1. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessment of variants of the k–ϵ turbulence model for engine flow applications

This paper is concerned with simulation of the mean flow and turbulence evolution in a model engine and comparison of the behaviour of certain important turbulence parameters, namely the intensity, length scale and dissipation time scale, as predicted by three variants of the k–? model developed for application to strongly compressible flows. The predictions pertain to the axisymmetric, disc-chamber, four-stroke, Imperial College model engine operating at 200 rpm and compression ratios of 3·5 and 6·7. The paper analyses the predicted variations of these parameters during the induction, compression and expansion strokes and identifies the versions that produce the most consistent and physically plausible variations. The significance, to the turbulence evolution, of the ratio of the turbulence dissipation time scale to the time scale of compression/expansion is also discussed. It is concluded that on these grounds the Morel–Mansour and El Tahry versions are, and the Watkins version is not, suitable for engine applications.